Leisure Battery Charging system

jace_da_face

Is it a good idea to connect multiple charging sources to a leisure battery simultaneously? I'm new to camper electrics so just trying to get up to speed. I've just managed to sketch out a schematic of the electrical system in a newly purchased camper.

Basically a split charge relay allows for alternator charging and a Zig battery charger provides charging on hook up. I've wondered what might happen if the engine was running while still connected to campsite power. Paralleling voltage supplies rarely seems to be a good idea. I wouldn't want alternator current flowing into the Zig. Perhaps the Zig would see the high Alternator voltage and figure the battery doesn't need charging and all will be fine. As I'm really not sure I would just not do it.

But it gets more complicated if I wanted to add solar power. Now I could potentially have a MPPT and Zig charger battling or complementing each other, I'm really not sure which, or indeed the MPPT and Alternator, for that matter.

If it was a good idea to keep charging sources isolated, I could just install a selector switch to provide one source at a time. Any ideas on this?

Well the greatest danger is driving away with the hook-up still plugged in to be honest.

Paralleling DC is a lot easier than AC.

In answer to the question it's not ideal but there are exceptions. The chargers will oppose voltages so in most cases they keep their magic smoke inside.
The alternator works with solar pretty well given practical use, alternator runs a few hours at most in bulk and solar assists or throttles then takes over when the engine is off.
The problem comes with mains chargers and solar as the mains charger is trying to regulate charge to the battery voltage but reads the solar voltage instead and they both stop charging a partially discharged battery.
Most chargers calculate absorption time proportional to bulk charge time so this confuses the bejaysus outtov them.
If you want mains and solar to work together you'll need one of my patent pending solar controller hybrid chargersᵀᴹ. Where you use a diode protected constant current 16VDC PSU on the solar controller input in parallel to the PV.
Short of that yes best isolate them...you can use a relay or a switch.

Good hunting.

crabbypaddy

MPPT, ZIG and alternator will all have diodes at the output so there should be no magic smoke.

The zig units I've seen are primitive and conservative so most likely the alternator would have a higher voltage than the ZIG so the zig would output nothing when the engine was started.

If the mppt is on boost or equalisation when the van started it may have a higher voltage and contunue to output something to the battery.

Yurp them zigs are chocy teapots alright, most factory fitment chargers are, and they have the cheek to charge more than a good charger fit for purpose.

If you want to know the true nominal output divide what's written on the box by 2.

CC PSUs and PV for everybody!!

jace_da_face

So not much respect for the zig brand I take it? It's what I'm stuck with for now I suppose. Anyway, my reservations about paralleling charging sources are not unfounded. So an isolating switch is probably a good call (although I'm curious about Liam's patent pending device, details please).

I wonder if a good solar rig could rule out relying on the alternator entirely? At least for half the year anyway. Minimising engine current would surely improve fuel economy, engine wear etc.

jace_da_face

jace_da_face wrote: »

So not much respect for the zig brand I take it?

Yeah..sorry. You'll understand why if you fit a battery monitor.
If it's any comfort I've never met a mains charger worth it's salt.

jace_da_face wrote: »

Anyway, my reservations about paralleling charging sources are not unfounded. So an isolating switch is probably a good call

Well you could just use the PV panel fuse, ideally you'd fit a PV service isolator as a matter of course. I use a relay triggered by the charger output, it automates the isolation I'd swap it for a diode if I could be bothered. I may be upgrading my PSU anyways since I went mad and installed 150W of lighting. :rolleyes:

I wouldn't worry about isolating the alternator from aught.

jace_da_face wrote: »

(although I'm curious about Liam's patent pending device, details please).

Here's a version I made earlier...perhaps a mite over-engineered for your purposes; it does isolation/combination & solo-ing.
I'll put you on rotation for a simpler schematic.



you just need a CC fake solar panel and a shottky diode for PV parallel or a SPDT changeover relay for switched inputs and a solar controller to handle max load. I've only tried it with PWM controllers though, MPPT may be difficult.

jace_da_face wrote: »

I wonder if a good solar rig could rule out relying on the alternator entirely? At least for half the year anyway. Minimising engine current would surely improve fuel economy, engine wear etc.

It can except for normal auto-electric loads, lights etc..
The alternator is self regulating if it's not needed it lowers it's magnetic field and doesn't load the engine....alternators are great when they're wired properly and they generally only use half a horse power maybe 1.25hp onna bad day.

jace_da_face

Wow, 1.75 kw PV. I was thinking more like 100w lol. I did think about diodes but wouldn't the inevitable voltage drop mislead the charging somewhat? That said, Schottky performance much better, but even still.

PWM vs MPPT? Does it matter? BTW, What drawing package do you use Liam?

Ralph: Bogart Engineering

It's from an if money wasn't an object live-aboard system I designed one slow week.

The shottky protects the PSU from the PV. You can compensate for the drop at the PSU. It's upstream of the solar controller so the controller can regulate as normal.

I go PWM unless I get MPPT for the same price.
Yes it matters. Especially when (theoretically) it's MPPT sweeping a power supply expecting it to be a string of silicon wafers.

Ralph: Bogart Engineering wrote:

A very good question! They BOTH have good and bad. Plenty of hype has been written already. Here's my (Ralph's) view:

The "good" for PWM: It is simpler and lower cost technology. Under some common circumstances–it can actually deliver more amps to the battery. That could be when:

(1)days are moderate or warm, with few clouds.

(2) batteries are charging at over 13 volts, (in a 12 battery system) which they almost always are when actually CHARGING.

(3) Panel voltage is properly matched to the battery voltage, for example "12V" panels are being used with a 12V system.

PWM is actually more "power efficient" than MPPT–which means less total power loss in the controller itself. So heat sinks in the design can be smaller (and less expensive). Missing in most analysis of MPPT is that there is always a conversion loss with MPPT, which tends to be higher the greater the voltage difference between battery and panels. That's why PWM can actually beat MPPT under circumstances described above.

Some places that analyze MPPT assume that panels with 30V open circuit voltage are being used in a 12V system. Any good MPPT system will easily provide better performance in that case. They also may assume batteries are charging at 12 or even 11 volts, which is unrealistic. Lead acid batteries are typically below 13 volts only when discharging, or perhaps charging with very little charging current–meaning the actual potential gain in amps is not great.

The benefit for MPPT becomes apparent if you use panels not voltage matched for the battery. If they are not, MPPT will utilize more of the potential energy of the panels. For example, if you use 24 volt panels to charge a 12 volt battery system you must use MPPT, otherwise you would be using your panels very inefficiently. If you are trying to use PWM in that case, you are misusing the PWM technology.

Another potential benefit with MPPT is that if distance between panels and batteries is far, smaller wire can be utilized by running panels at higher voltage to the batteries. Running at twice the voltage reduces wire size to 1/4, which for a long run can be a significant saving in copper wire.

If temperatures are low enough, the slightly less power efficiency of MPPT will be compensated by the higher panel voltages, which will result in a little more battery current. But in actual measurements we made using a commonly sold MPPT solar controller, this would occur at temperatures less than 55 F degrees (in full sun, when charging at more than 13 volts), where there is a slight advantage to MPPT in my location (Boulder Creek, near the California coast). As temperature drops below that (in full sun) MPPT will get some advantage, such as could occur at high elevations in Colorado in the winter. Potentially this would be maximum about a 2.5% improvement in amps output for every 10 degrees F lower in temperature (or 4.6% per 10 degrees C colder. I'm using data from Kyocera KD-140 panels.)

There can be theoretically optimal situations (that I don't personally experience where I live) where MPPT could give some advantage: that is when solar current is present, but the batteries are quite low in charge–but because loads are high and even greater than the solar current the batteries are still discharging despite the solar current. Under these conditions the voltage COULD be at 12.5 volts, or even lower. Again, using data from Kyocera panels, ("Normal Operating Conditions") there is a theoretical maximum gain over PWM of 20% current assuming NO MPPT conversion loss and no voltage drop in the wires to the panels, at 20C (68F). With PWM, the voltage drop in the wires in this case would not affect the charging current. Now if in addition you lower the temperature to below freezing at 28 degrees F (while sun is shining) you might actually get up to a THEORETICAL nearly 30% gain while the batteries are discharging.

The only REALLY BAD part of MPPT, is all the hype surrounding it–for example one manufacturer advertises "UP TO 30% OR MORE" power harvested from you panels. If you are using solar panels properly matched to the batteries, 30% ain't gonna happen unless it's EXTREMELY cold. And your batteries have to be abnormally low in charging voltage–which tends not to happen when it's cold (unless you assume the battery is still discharging while solar is happening). Virtually all the analyses I've seen touting MPPT on the Internet ignore the conversion loss, assume really cold temperatures, assume unreasonably low charging voltages, assume no voltage drop in the wires from panels to batteries, use STC conditions for the panels (that the marketing types prefer) rather than more realistic NOCT conditions, and in some cases assume panels not voltage matched to the batteries.

The other thing that is misleading about MPPT, is that some manufacturers make meters that show both the solar current and the battery current. In almost all cases for a well designed MPPT type the battery current will be greater. The engineers making these know better, but it is implied (by marketing types?) that if you were NOT using MPPT you would be charging your batteries with only the SOLAR current that you read on their meters. That's not true, because the PWM BATTERY current should always be higher than the MPPT SOLAR current. It is the nature of the MPPT that maximum power occurs when the current is lower than the maximum, so they must operate there to get the maximum power. So to properly compare the two you need to compare MPPT with an actual PWM controller in the same circumstances.

Finally, the reason we went to PWM is that I was anticipating that panel prices were going to drop (which they certainly have over the last 5-10 years!) and that the small advantage of MPPT (under conditions where the correct panels are used for the batteries) would not justify their additional cost and complexity. So my thinking, for more total benefit per $, put your money in an extra panel rather than a more expensive and complex technology.

10A Max Load




20A Max Load

The two above examples are for occasional use systems. If you want a true performance powerhouse that can't be beat on price & features then a 45A TriStar is the one to get.

12V/24V & 48V Fully programmable.
500W Charge capability @ 12V
Load & Temp Compensating
Data Logging

Solar Control or Diversion Control
Passive Cooling

You won't find anything in the same league price-wise even with the extra expense of a PSU....and you get a free state of the art solar controller.

As an aside I've recently found some proper DIN Rail DC rated Switch Disconnects for PV isolators.

In case anyone is wondering why I keep recommending MorningStar it's not through any affiliation it's because I can vouch for their device performance. They are the only charger I've come across that can get my flooded batteries to 100% charge or Specific Gravity 1.280. Most I find stop at 1.260 and a Sterling PCU got 1.265. That's enough of a discrepancy to slowly sulphate my lead with repeated undercharge and start a cycle of diminishing returns. I stopped looking for anything else to hold a candle to them after Sterling, Aldi, Halfords, MasterVolt & Victron had all tried and failed to cut mustard.



After wasting a whole lot of spondulix on "proper" mains chargers and retiring them the week of purchase I now almost exclusively use MS for charging.

I should probably mention PWM switching noise can be very tedious (much worse from a PSU than a PV module), so I recommend using a voltage adjustable PSU; the closer the input voltage is to the regulation voltage the more silent it is. Fairly easy completely tune it out this way.
Much as I like that PSU I linked to and it's served me well for the past 2.5 years of light use I've given it. Probably only fair to mention also it's filled with shoddy CapXon Electrolytic Caps.

jace_da_face

Both options above look good Liam. Well done. I like the automatic behaviour and lack of needing to throw a switch. Either solution above requires the addition of a PSU and decommissioning of my Zig charger. From a cost perspective I would probably opt for the Zig charger/ Solar charger combo, for the moment anyway, using the relay to switch between the two.

Any word of advice on charging current? How much would a 110 Ah battery accept? As much as the charger supplies? Or is there an upper limit that depends on the particular battery?

jace_da_face

jace_da_face wrote: »

Both options above look good Liam.

I amended the schematic for the switching controller. Added a relay coil snubber to improve latching against PWM.

Depends on what you want. All the small controllers are regulated as a fire and forget variety, they max out at 14.4V regulation + temp compensation. I believe the reason for it is for little used systems to reduce gassing and hence maintenance. It means much longer charge times though and if it's a daily it'll get a bit sulphatey.
Hence I went for a programmable charger so I could set the absorption to 14.8V + temp. comp.

jace_da_face wrote: »

From a cost perspective I would probably opt for the Zig charger/ Solar charger combo, for the moment anyway, using the relay to switch between the two.

I don't consider Zigs to be chargers, they're more float maintainers. It'd be worth investing in a hydrometer and assessing if it's helping more than not before considering how useful or otherwise it is to you.

jace_da_face wrote: »

Any word of advice on charging current? How much would a 110 Ah battery accept? As much as the charger supplies? Or is there an upper limit that depends on the particular battery?

The slower & longer the better. Most charger sellers will tell you 10% capacity rating (usually a sign they are just regurgitating the sell sheet).
I'd consider 30% an upper limit and aggressive. You can go much higher with flooded but you're into fast charging and all that entails then.
I use 2.5% from mains because I don't generally discharge very deeply and I've quite a good alternator/PV setup.
On the other hand if you are using the charger to power loads in the vehicle while charging you have to offset this demand against the charge current so say you have a 20A charger and you are running 10A of lighting and youtoobs from it while docked then your charge current is 10A.

Sterling PCU (also populated with CapXon)...given the choice get a ProNautic....same thing with better build quality...allows for 25%,50% 75% or 100% duty setting.

My pat pending hybrid solar charger controllersᵀᴹ allow for fully adjustable current input down to 0.01A accuracy.

I have other pat pending designs to load share the 12volt system via switch mode supplies instead of relying on the charger for everything because big chargers are more expensive than bog standard PSUs and they're equally fit for purpose. Given the same installation expense I usually go for two systems instead of one...better redundancy.

I just did a routine health check of my drill battery.



I left it on a ProStar 30 for 3 weeks undisturbed set to 14.0V Absorption.



Here's the results:



They've a new Gen. 3 model just released, fully programmable with datalogging.

jace_da_face

So I've had a very lucky encounter today. Possibly anyway. I might just be able to get my hands on a 260W 36v PV. Maybe. I'll say no more unless it transpires. I'd imagine the Morningstar Sunsaver would handle this?

Voc 36V.
Not really that's a 24V panel.

Using a PWM controller with that will throttle it to ~110Wp
MPPT can handle it.

You can hack the module to give you Voc 18V...depends on what your time and effort is worth and how good a deal it is.

jace_da_face

Yeah it's actually 37.8 v open circuit. That's what the label says. And I tested it myself on load. I had to test it because it is actually damaged. Glass shattered. I know I can hear some people shriek at the thought of pursuing with a shattered panel but I reckon I can seal it. I've seen it done on YouTube with some adhesive laminate.

So must be MPPT to harness all the juice?

Run a mile.
You need to load test it under the circumstances.

The cost of an MPPT controller will cancel any "savings" you may have made.

If it's free and already hooped then I'd hack it and go PWM. I wouldn't stick it to anything in a permanent sortov way all the same.



You need a new backing box, cut through the tabbing wire on the bottom of the module from the rearside and split the series string into two parallel. Delete the diodes and install reconfigured bigger ones or live without. Presto 18VOC.

jace_da_face

Well I could lay the panel up in a temporary configuration whilst charging the camper. But as for real on the road testing, I don't see how it could be mounted other than to be permanently glued in place.

Here's an inexpensive charger that accepts PV 40 volts

https://www.amazon.co.uk/Esky-Intelligent-Regulator-Controller-Environment/dp/B013UDSDIO/ref=cm_cr_arp_d_product_top?ie=UTF8#Ask

My concern would be unpermanentifying it when it fails.

I never understand the economy of cheap charge controllers. That's where the rubber meets the road.

PWM only passes current by the way (it will not make more than the panel can produce unlike MPPT) so it limits the panel to whatever the battery voltage is x Imp Isc = max watts.

You need to match the panel to the battery to get the most outtov PWM.

jace_da_face

Sir Liamalot wrote: »

PWM only passes current by the way (it will not make more than the panel can produce unlike MPPT) so it limits the panel to whatever the battery voltage is x Imp Isc = max watts.

You need to match the panel to the battery to get the most outtov PWM.

Yes indeed. No point in wasting watts.

I don't think the 260 watt panel is a runner. I'm restricted by skylights and after doing measurements I now realise it would protrude from the front by a couple of inches. It wouldn't look great and would catch more wind. Not worth the trouble.

Think I'll start with a 100 watt. If I feel the need, or budget permits, I could always add a second one at a later stage.

I've been tidying up my mad-scientist-lab 12v system.

jace_da_face

Nice work Sir Liam! Looks tidy.

By the way, I got my hands on some 24V strip LED lighting. I don't suppose the Morningstar controllers have an option for outputting a 24V rail for convenience? Otherwise i'lll just source a DC-DC converter somewhere.

jace_da_face

Cheers still a lottov tidying to do.
Possibly a mite overspec-ed.

I'm onto the 250Ah @ 48V beside it soon...and there's a little grid tied rig around the corner for good measure.

jace_da_face wrote: »

I don't suppose the Morningstar controllers have an option for outputting a 24V rail for convenience? Otherwise i'lll just source a DC-DC converter somewhere.

Not unless you want to run a 24v habitation battery which makes a lot of sense to be fair.
Yeah switching converter or less lossy 12V strip. Very little in the difference in cost. DC-DC converters aren't bad...95%ish efficient (real world) if an inverter says 95% though it usually means ~80%.

jace_da_face

Nothing wrong with overspec-ed IMO. So the 24V strip has RGB mixing functionality. I thought a sequencer running LEDs would be cool!

Just witnessed a 60kW solar rig being commissioned today. A beautiful thing. Same guys I rubbed shoulders with regarding smashed PV panel, but not to be. My background is not solar, but good to work them and educate myself.

It'd be a more beautiful thing if Joe Public was offered a feed in tarriff for his home rig

You can get those leds in 12v too but I think static and natural colour mixing works best.

jace_da_face

jace_da_face wrote: »

I thought a sequencer running LEDs would be cool!

I bought one of these controllers and I'm very impressed for the price.



Very low noise. Fits a standard Pattress back box (screws not included).
7W a day parasitic load (put a switch on it and use that instead of the soft touchy "off" pad.
It does disco mode too but I haven't tried it.
Colour mixing with Master intensity control.

This is the strip to go for RGBcW 12v IP65

jace_da_face

That is a good price.

I bought one of these chargers.

Not in the same price bracket as a CTEK but let's see how it performs.

jace_da_face

I have my 100W solar panel installed and it seems to be doing the biz. I had the camper on a three day tour without any need for E.H.U. Now I'm wondering if I should disable the alternator charging of the leisure system altogether (leaving the fridge 12V system connected).

I guess I have lots of questions in terms of trying to understand the implications of leaving the alternator charging in place.

Would disconnecting the alternator actually produce a saving in starter battery/ alternator lifetime and fuel efficiency?

Would leaving the alternator charging in place possibly cause the leisure battery to over charge?

Or would a reasonably charged leisure battery not 'ask' for too much current before a journey begins anyway?

Or do I take it for granted that the leisure battery will be receiving additional amounts of high charging amps whether it is good for the battery or not?

jace_da_face

jace_da_face wrote: »

I have my 100W solar panel installed and it seems to be doing the biz.

based on voltage readings or SOC calculations?

jace_da_face wrote: »

...if I should disable the alternator charging of the leisure system altogether).

Nope it's self regulating if it's not needed it self idles.
PV doesn't work from November to February.

jace_da_face wrote: »

Would disconnecting the alternator actually produce a saving in starter battery

Nope.
Connecting the pv to parallel charge the starter battery will though.

jace_da_face wrote: »

Would disconnecting the alternator actually produce a saving in alternator lifetime and fuel efficiency?

Yes but negligible.

jace_da_face wrote: »

Would leaving the alternator charging in place possibly cause the leisure battery to over charge?

Nope.

jace_da_face wrote: »

Or would a reasonably charged leisure battery not 'ask' for too much current before a journey begins anyway?

In well designed and executed system this would be true. In the real world of factory fitment and DIY legacy overcharge is an impossibility; charge starvation and degenerative cycling is the norm.

jace_da_face wrote: »

Or do I take it for granted that the leisure battery will be receiving additional amounts of high charging amps whether it is good for the battery or not?

If you want to overcharge a deep cycled battery with an alternator you'd have to run the engine for >80 hours if it was wired to charge the service battery at 14.8V.

jace_da_face

No SOC estimating, just basing it on anecdotal observations and occasional spot check voltage measurements.

On a three night trip, with moderate usage of water pumps and a couple of showers thrown in, low powered LED lighting use and extended stereo use, the solar charger would indicate a fully charged battery each morning. Night time voltage readings would be about 13V. With the vehicle parked up since, the battery sits fully charged with no need for additional charging needed.

Any spot check voltage measurements I take with the vehicle sitting idle for days are in the region of 14V during daylight. The manufacturer of the charger specify a float voltage of 13.7V. I'm not sure why I'm seeing higher. My Fluke meter hasn't been calibrated in years but I don't think it's too wrong. I'm not overly concerned. The controller can charge a second battery so I might use it to charger the starter too.

There is a remote RJ-45 panel available for the charger which will indicate charge. Would be nice to have but a bit pricey.

jace_da_face

My battery will hold 12.6V for hours at nominal load @ 80% SOC. Voltage is a very poor indicator when you add solar because you are often seeing a charging voltage not a resting voltage...the system is never resting with PV.

You're probably fine, I'm just being dramatic to demonstrate a point.

jace_da_face wrote: »

the solar charger would indicate a fully charged battery each morning.

Well that can't be true if you used any lecky the night before.

jace_da_face wrote: »

Any spot check voltage measurements I take with the vehicle sitting idle for days are in the region of 14V during daylight.

When mine says 14.9V I know I'm on the home stretch. Mine is PWM so it starts to buzz when the battery is >95%

jace_da_face wrote: »

The manufacturer of the charger specify a float voltage of 13.7V. I'm not sure why I'm seeing higher.

It absorbs >14V before it floats.



Your charger ought to be doing what your battery manufacturer dictates by the way.

jace_da_face wrote: »

My Fluke meter hasn't been calibrated in years but I don't think it's too wrong.

I buy meters instead of calibrations, my 3rd hand 87V on it's umpteenth HRC and factory cal is still agreeing with other meters of it's calibre.

jace_da_face wrote: »

I might use it to charger the starter too.

It'll add years of service

jace_da_face wrote: »

There is a remote RJ-45 panel available for the charger which will indicate charge.

Solar controller meters are not so useful. Get a battery monitor if you get anything then you see the whole picture. Everything in and out of the battery.

Controller meters only show you the in from one source.

jace_da_face

Interesting links to Bob' blog. I hear you on the "Voltage is a very poor indicator " compounded by the fact that the solar charger is raising the terminal voltage. I would generally only be inclined to take the night time voltage readings as a better indicator of battery voltage. An so far the voltage measured intermittently at night and under load, has always remained above 12.7V.

And though I can't infer SOC from this knowledge, it does inspire some confidence. I can however judge SOC the following day from a couple of parameters, however inaccurate.

(1) The solar controller indicates a fully charged battery.
(2) The battery's charge indicator, visible through a small window, is green indicating 'charged'.

On point 1 above, I should point out that any morning checks are well ... not too early in the morning! And so several hours of sunlight have passed.

On point 2, I have no idea what tolerance the battery indicator operates within. The green indicator is simply showing a specific gravity indication for a single cell. Without a data sheet for the Halfords 115Ah, I have no idea what that range is. This indicator would be more useful for telling you something is really wrong.

If the solar charger's optional remote panel could indicate an accurate SOC, it would be worth having. It would connect in a non-invasive manner over ethernet and not disturb the current path, such as with shunts and the like. But since it only knows battery voltage and how many Ah it has put in, how could it be reliable? It surely would need to know the total charge and discharge currents wouldn't it?

Maybe I'll get a battery monitor down the line but in the meantime I might just grab a hydrometer for intermittent checking.

jace_da_face

jace_da_face wrote: »

Interesting links to Bob' blog.

Yeah Bob's a legend and an almighty grump. The RV charging puzzle is the meat and potatos of the blog.
I sent him a donation a long while back in thanks for his advice which is some of the best around. Himself and Gibbo of SmartGauge fame are elusive gurus of esoteric battery phenomenon.

jace_da_face wrote: »

I hear you on the "Voltage is a very poor indicator " compounded by the fact that the solar charger is raising the terminal voltage. I would generally only be inclined to take the night time voltage readings as a better indicator of battery voltage.

It is possible to measure capacity by observing voltage and charger behaviour if the way of the electron is strong with you.
Having an ammeter is a powerful diagnostic tool worth bringing to the party.
Say I deplete my battery to 60% SOC resting voltage 12.3V, 90Ah discharged. Then I drive for 2 hours with a nominal charge current of 20A (over 90mm² cable, from an 80A Alternator) I have returned 40Ah. Battery reads 12.7 under load for two hours. Great. Battery charged? Not at all it's 80%.

jace_da_face wrote: »

An so far the voltage measured intermittently at night and under load, has always remained above 12.7V.

Healthy happy battery so. PV rocks.

jace_da_face wrote: »

And though I can't infer SOC from this knowledge, it does inspire some confidence. I can however judge SOC the following day from a couple of parameters, however inaccurate.

(1) The solar controller indicates a fully charged battery.

Biased Witness.
Never trust a charger unless the hydrometer reads battery acid of specific gravity 1.275 on all 6 cells.

jace_da_face wrote: »

(2) The battery's charge indicator, visible through a small window, is green indicating 'charged'.

The only reason they put that there is because it costs the manufacturer next to nothing to add a feature. If it ever changes colour which is unlikely it means that particular cell has expired.

jace_da_face wrote: »

On point 1 above, I should point out that any morning checks are well ... not too early in the morning! And so several hours of sunlight have passed.

I use about 25Ah a night. My battery still takes 8 hours to recharge.
"They" say lead acid chemistry is 80% efficient.
The reality is it's proportional to the level of discharge.
@ 50% SOC it's unity give or take.
@ 80% SOC it's 98% efficient
@ 90% it's ~90%
@ 95% it's ~50%
@ 98% it's ~5%

Hence for me to charge my battery it takes 80hours on mains or 3 weeks on solar from a ~7 day deep cycle.
I've never seen a charger that charges a battery like a solar controller.
I think they'd be embarrassed to spend 3 days to charge a battery for the last 3% charge. The average I've seen from mains chargers is 93% SOC. I'm refering to good mains chargers now...not ziggybloks

This is curious to me when the industry insists that not having a weekly full charge causes a battery to deteriorate, yet every charger on the market I have tested doesn't fully charge a battery.

So low and behold I have my Mk..who's counting?.....let's say Mk-11 charge system that can charge a battery and deep cycle for 3 weeks with no apparent or calculable deterioration.

The simple truth of the matter is the charger's opinion is only admissible if it's corroborated by a hydrometer reading.

jace_da_face wrote: »

On point 2, I have no idea what tolerance the battery indicator operates within. The green indicator is simply showing a specific gravity indication for a single cell. Without a data sheet for the Halfords 115Ah, I have no idea what that range is. This indicator would be more useful for telling you something is really wrong.

It's just art and a child of marketing. Don't worry about it.

jace_da_face wrote: »

If the solar charger's optional remote panel could indicate an accurate SOC, it would be worth having. It would connect in a non-invasive manner over ethernet and not disturb the current path, such as with shunts and the like.

I prefer independent metering. Even chargers I trust have meters that lie.



Disturb the current path? I use 500A 50mV shunts that have a lug contact resistance of 800µΩ and dissipate 6mW at my nominal load. I've sacrificed this for 0.25W accuracy.

My crimper does tend to weld copper under compressive load though so contact resistance is mitigated.



The controller probably has an internal shunt anyways.

jace_da_face wrote: »

But since it only knows battery voltage and how many Ah it has put in, how could it be reliable?

Great question. Glad you asked.
It's a voltmeter in disguise usually.

jace_da_face wrote: »

It surely would need to know the total charge and discharge currents wouldn't it?

Correct.

jace_da_face wrote: »

Maybe I'll get a battery monitor down the line but in the meantime I might just grab a hydrometer for intermittent checking.

It's like any good tool it only hurts the day you buy it. Then you appreciate it the rest of it's life.

The more battery monitors I test the more I appreciate my TriMetric.
I've a Master an ApprenticeVolt job on trial at home...meh...not impressed...s'ok. Cost doesn't represent the hardware and certainly not the interface design. Can't read it across a room? QC Fail!

jace_da_face

Great analysis Sir Liam. Plenty of food for thought as usual.

jace_da_face

So my latest conundrum centers around my 3-way fridge on 12V operation and my Smartcom RCT460 Split Charge relay. Quite a few months ago I noticed that when the fridge was switched to 12 volt operation with engine running, after about twenty minutes or so the fridge's 12V neon switch light would flash on and off. It would do this quite periodically about once every two seconds, that it looked like a deliberate fault warning designed into the fridge. Perhaps it didn't like the voltage supplied or there was an internal fault.

It then occurred to me to go to back of van and listen to what the split charge relay was doing when the fridge power switch was flashing, and low and behold the relay was clicking on and off. I wondered was this an Alternator or starter battery problem but then took a closer look at the wire feeding the split charge relay from the battery. Far too underated. Couldn't tell you what the gauge was but way to light. The cable had stiffened at the relay end and PVC insulation was discoloured. I measured about 1.4V drop across the cable.!!So I replaced the cable thinking that's the culprit for sure. I ran much thicker wire and the voltage drop was now about 0.2V. To my surprise the same thing happened after running the fridge for about 20 minutes.

Initially I thought it must be a case of now replacing the wire running from the relay to the fridge as that is probably underrated too. But then I figured no that's irrelevant. That might be true if the fridge's power was cutting out and the relay was staying switched on. The relay is still clicking on and off. So even if the wire feeding the fridge is underrated, it could not cause the relay to cut out. The relay is switching in and out because it's supply is dipping in response to the fridge load on the starter battery. So I would suspect the starter battery is not up to the job. Possibly even an alternator fault but I would start with the battery.

So clearly current is being drawn by the fridge from the starter battery/ alternator and resulting in a voltage dip that causes the relay to switch out. The battery voltage then recovers under a no-load condition causing the relay to switch back on, etc. etc. in an endless cycle.

Now my question is this. To anyone with knowledge of the Smartcom Split charge Relay, does this relay restrict the direction of current from starter battery/ alternator to leisure battery? I can see a couple of ways this could be important.

(1) In my situation described above, could the leisure battery also be forced to supply current to the fridge when the starter battery dips below the leisure battery voltage? If the two batteries were simply connected as one through a simple relay with no intelligent current routing this could be a problem.

(2) In normal operation, when the vehicle engine is switched off, but the starter battery voltage is still high enough to keep the relay closed. Then restarting the vehicle could cause cranking amps to be supplied from leisure battery if no circuitry prevented current coming back from the leisure battery. In this scenario both batteries appear as one and provide cranking current. This is unlikely to be what you would want.

Without a circuit diagram of the Smartcom split charger, I can't tell. Any thoughts?

jace_da_face

Heavy Duty
30 Amp
Charge Relay.

Sorry Jace the problem is you've been lied to.
That's a 5amp unit. The manual recommends you install on a 15A fuse, on 1 amp cable and I doubt very much you can get more than 10amp cable inside.

That unit and many like it are not fit for purpose and don't work.




Those look to me like Omron 5A DPDT PCB mount relays, probably with parallel switch loading. So ~8A rating. One relay for the fridge and one for the "charge".

The symtoms you describe are your fridge, battery system and alternator are underwired. Your fridge is discharging your service battery while the engine is running. This means you cannot charge your service battery while driving and running a fridge. The service battery might recieve charge while driving when the fridge is off but it's not much.

How can we fix this
Bin that Stoopidcon outtov the gates it's making matters worse.
Get a contactor fit to task. Put it on a new ~35mm² line from the Alternator B+ directly as true as you can to the service battery on a fuse 20% bigger than your alternator peak rating through the contactor load terminals.
Wire in a new fuse on the engine battery, on 6mm² to your fridge through a 9.5mm spaded bosch type make and break relay with an ignition switched coil and power the fridge 12volt side from this. Do not wire absorption fridges onto service batteries. I don't care what the manual says the person who wrote it does not use it like we do.
Install a shunted battery monitor and next time you find a snake oil product you'll know straight away.

All bets are off if you have alternator regen braking. For that we need more sophisticated things than copper or more alternators.

jace_da_face wrote: »

Now my question is this. To anyone with knowledge of the Smartcom Split charge Relay, does this relay restrict the direction of current from starter battery/ alternator to leisure battery?

The StoopidCon is a teeny tiny switch. I don't think you can actually get smaller electro-mechanical relays. :rolleyes: Heavy Duty? Spare me!

This is heavy duty.




It definitely restricts. Like diverting hydro power through a drinking straw.

jace_da_face wrote: »

(1) In my situation described above, could the leisure battery also be forced to supply current to the fridge when the starter battery dips below the leisure battery voltage?

Could?
It is partially running your fridge only assisted by the alternator.

jace_da_face wrote: »

If the two batteries were simply connected as one through a simple relay with no intelligent current routing this could be a problem.

You'd drain both batteries equally, half as fast.
If you up-spec the wiring and you don't have alternator regen. braking then you can charge all batteries proportional to discharge level while powering all loads up to about 60% of your alternator's rated capability.

jace_da_face wrote: »

(2) In normal operation, when the vehicle engine is switched off, but the starter battery voltage is still high enough to keep the relay closed. Then restarting the vehicle could cause cranking amps to be supplied from leisure battery if no circuitry prevented current coming back from the leisure battery. In this scenario both batteries appear as one and provide cranking current. This is unlikely to be what you would want.

The voltage sensing relay will open with the glow plug induced sag.

My 235Ah semi-traction service battery can supply 70A to my 85Ah starter battery's 700A. I can do this the chemistry forbids I do it evenly. It's bad practice. I want the ability to do it selectively.

If you buy a "leisure" battey. Chances are you are buying a starter battery with a leisure battery sticker. In this case it doesn't matter at all but you may not want to discharge both together.

jace_da_face

Well I took the van for a spin today and tested voltages once the split charge relay started flip-flopping again. Even though the wiring around the split charging is underrated, I was still expecting to see an alternator voltage varying by a couple of volts as the relay clicked back and fort. But no, the alternator voltage was pretty stiff I would have to say, varying only between 14.4 and 14.2 volts. Loading the battery by 20 mV should not cause the VSR to cut out.

So you are quite correct Liam, this is inadequate cabling, as well as a relay not fit for purpose as you point out. Even when I had more than doubled up on the wiring from battery to split charge relay, and was initially seeing a very small voltage drop across the wire when the ignition was first started, once things warmed up the cable resistance increased and so too the voltage drop.

So I plan to replace what's there with 4mm wiring. I have plenty of solar cabling left over so I can put it to good use. I don’t think I can get to the alternator B+ post so will have to run to starter battery as before but I do plan to change to a heftier relay/ contactor. I still need ignition switching so I might just utilize the Smartcom VSR for that, so that it is now just triggering a bigger relay to supply the leisure battery and fridge.

I have a second battery charging output on my solar controller. It would be nice to have this run back to the starter battery but this will result in triggering the VSR, hence closing the (new) split charge relay with engine not even runnng. I could put in a manual override switch but that is just one more thing to think of. Having a switched ignition signal would be handy for triggering the relay instead of relying on a VSR but I am not sure I can access one. I could probably solve a lot with a Ctek b2b charger. This would also control charging paths and restrict the leisure battery supplying current to where it should not be going. But budget does not permit.

Cheers again

jace_da_face

jace_da_face wrote: »

Well I took the van for a spin today and tested voltages once the split charge relay started flip-flopping again.

Might be the adjust pot track is worn out on the VSR. Try tweaking it clockwise or anti-clockwise 5°

VSR hysteresis is a sign or poor wiring.

jace_da_face wrote: »

Even though the wiring around the split charging is underrated, I was still expecting to see an alternator voltage varying by a couple of volts as the relay clicked back and fort. But no, the alternator voltage was pretty stiff I would have to say, varying only between 14.4 and 14.2 volts. Loading the battery by 20 mV should not cause the VSR to cut out.

Measure at the relay terminals.
Either the relay is squiffy or the fridge is providing more load than the alternator can supply in it's current configuration....
...oooor.....and/or....yer service battery is weak
If yer service battery is weak I'd fix the charger before replacing the battery.

jace_da_face wrote: »

Even when I had more than doubled up on the wiring from battery to split charge relay, and was initially seeing a very small voltage drop across the wire when the ignition was first started, once things warmed up the cable resistance increased and so too the voltage drop.

Doubling it isn't enough. Going from 1.5mm² to 35mm² is a twentyfold increase.
16mm² is what I'd regard min spec.

jace_da_face wrote: »

So I plan to replace what's there with 4mm wiring. I have plenty of solar cabling left over so I can put it to good use. I don’t think I can get to the alternator B+ post so will have to run to starter battery as before but I do plan to change to a heftier relay/ contactor. I still need ignition switching so I might just utilize the Smartcom VSR for that, so that it is now just triggering a bigger relay to supply the leisure battery and fridge.

Two relays...
One Contactor for Alternator to Service Battery
One Relay for Engine Battery to Fridge.

4mm²'s too light for the fridge and it's definately too light for battery charging and starting currents.
6mm² for the fridge, the less cable resistance the better it works because it's a linear load. I'd use 6mm² for a compressor fridge too. Motors don't like undervoltage.

You need a continuous line from the alternator so you have to get to the B+ anyway. Stock alternator cables are usually pretty anemic in high spec insulation.

You can go manual switching.
The VSR triggering a relay would be better use I think. I use a SmartBank you can find them used for not a lot they are a better solution again. It can drive contactor relay coils at reduced duty using PWM so that it consumes only half the coil power ...I always think that's great...sounds broken and disable it. Good option if you can mount it outtov ear-shot though. It's a lot more intelligent than most.

jace_da_face wrote: »

I have a second battery charging output on my solar controller. It would be nice to have this run back to the starter battery but this will result in triggering the VSR, hence closing the (new) split charge relay with engine not even runnng. I could put in a manual override switch but that is just one more thing to think of

Turning on your atmospheric heater fridge too.!
The second output has already linked the batteries at that point the VSR is just a parallel path.

jace_da_face wrote: »

Having a switched ignition signal would be handy for triggering the relay instead of relying on a VSR but I am not sure I can access one.

Seat Selt Switches.
Seat Belt Seat Sensors.
Hazard Switch.
Dash Illumination
Indicator Switch
Wiper Switch
Demister Switch
Switched Cigarette Lighter Sockets
D+ Alternator
Battery Light Dash (D+)
Electric Windows?
Gauge Power

jace_da_face wrote: »

I could probably solve a lot with a Ctek b2b charger.

It's an expensive way to limit yourself to a consistent 20amps. Enough good copper alone can do 30A on a mediocre day. I find it more reliable and has a better resale value.

jace_da_face

Sir Liamalot wrote: »

Measure at the relay terminals.

Yes I have measured at the starter battery terminals and at the relay terminals. A quick subtraction of the two shows the cable voltage drop is too big. The battery/ alternator voltage is good so I do not suspect a problem here.

Sir Liamalot wrote: »

4mm²'s too light for the fridge and it's definately too light for battery charging and starting currents.

I am actually proposing 4mm diameter cable, not 4mm². I think that's about 12mm². Not quite the 16mm² you recommend but should be a big improvement.

Sir Liamalot wrote: »

You need a continuous line from the alternator so you have to get to the B+ anyway.

Yeah I can't get to the alternator too easy so the starter battery + terminal will have to do. This battery is located under the cab floor. Obviously this ties back to the B+ terminal.

All the points you mention for getting a switched ignition signal, while all good, are just a little tricky for me to get at. The ideal point for me to tie in would be at the main fuse panel, but I would really need to remove some casings and trim on the dash. Anytime I've ever disturbed the trims on a dash, I have never been able to put things back right. But I'll have another look. Besides, I need to get 12V to my rear reversing camera monitor at some stage anyway so could be a good opportunity.

Regarding the current draw through my atmospheric heater fridge, I measured this at 8 amps before. Once I get all the new wiring in I'll check again.

jace_da_face

jace_da_face wrote: »

Yes I have measured at the starter battery terminals and at the relay terminals. A quick subtraction of the two shows the cable voltage drop is too big. The battery/ alternator voltage is good so I do not suspect a problem here.

You have to compensate for load when taking these readings.

jace_da_face wrote: »

I am actually proposing 4mm diameter cable, not 4mm². I think that's about 12mm². Not quite the 16mm² you recommend but should be a big improvement.

Probably in the region of double.


I'm on Mk-12 and have so far got a tenfold increase on Mk-1

jace_da_face wrote: »

Yeah I can't get to the alternator too easy so the starter battery + terminal will have to do.

It'll do about half with a downstream service battery than vice versa.

jace_da_face wrote: »

This battery is located under the cab floor. Obviously this ties back to the B+ terminal.

It does but it's compounding all the failings of the circuit. Cable distance, cable gauge and regulation to battery delta voltage.

jace_da_face wrote: »

Regarding the current draw through my atmospheric heater fridge, I measured this at 8 amps before. Once I get all the new wiring in I'll check again.

Sounds low. Is it rated 10A? Dare I say it sounds under-wired.

jace_da_face

Sir Liamalot wrote: »

You have to compensate for load when taking these readings.

Absolutely. Measurements meaningless otherwise. I am seeing the supply voltage to fridge and leisure battery pulled low when the split charge relay closes and the fridge draws current.

I have now finished my re-wiring and have installed two new relays. One to supply the fridge and one to supply the leisure battery. Each relay runs on a separate 12mm2 wire back to the starter battery. The Smartcom VSR is now only used to fire the two supply relays, so it will no longer pass supply current.

I ran 2.5mm2 wiring from the fridge supply relay to the fridge. This is a big improvement on what was there. Electrolux specifies 2.5mm2 if cable length exceeds 9 meters. My run is under that.

So with engine idling and fridge switched on, I still loose about a half a volt over the improved wiring supplying the fridge. However, the leisure battery is now on a separate feed and is within acceptable range of the alternator supply.

jace_da_face

jace_da_face wrote: »

The Smartcom VSR is now only used to fire the two supply relays, so it will no longer pass supply current.

So it turns on the fridge when it sees solar charging?
This is less than ideal.

Your Split Charge Relay is far too small. Any of those bosch types take the plated rating and divide by 2 for the true rating. I spec them to voltage drop and contact resistance though not ampacity because any losses in that circuit exponentially reduces the output.
How did you fit 12mm² cable in a terminal rated for 1.5mm² > 2.5mm² cable? Those blue push-ons are 15A rated & I'm just going to pretend I can't see the solder joints..
Splash out on some cable stress relief in the name of reliability...or go all out and use a relay holder you can disconnect and reconnect without head scratching...my €0.02

jace_da_face wrote: »

I ran 2.5mm2 wiring from the fridge supply relay to the fridge. This is a big improvement on what was there. Electrolux specifies 2.5mm2 if cable length exceeds 9 meters. My run is under that.

From the people who brought you the world's most overpriced, inefficient, under-featured (mostly) thermostatless fridges on the market. Sorry they have zero credibility in my book but call me a cynic and feel free to take their advise.
If it runs at the rated amps then you're all good.

I said 6mm² because that will cover most distances onboard and people prefer resolute answers rather than if thens, if it's under 5m cable distance 4mm² is adequate.

jace_da_face wrote: »

So with engine idling and fridge switched on, I still loose about a half a volt over the improved wiring supplying the fridge.

Measure the current J. The Voltage is just pressure not flow. If your 120W fridge runs at 10A, wiring = ok. If your 120W fridge runs at 13.5volt we know very little more than before measuring.

jace_da_face wrote: »

However, the leisure battery is now on a separate feed and is within acceptable range of the alternator supply.

Can you quantify acceptable?
Supplying what current at 25% DOD?
Min spec I'd advise a 10% battery capacity charge rate at 80% SOC while running full load with a terminal voltage no lower than 13.6V at the final battery.
From factory they generally net zero after refrigeration.

Any fuses? Split charge needs one either side of the relay switch at the battery terminals.
Fridge also requires one at power source. If you use a 10A fuse on a 10 amp circuit it won't blow but it will melt. Try 15A.

jace_da_face

Liam, I think you are misunderstanding. The VSR is not supplying power. It doesn’t take 12mm2 cable. It is now only used to sense alternator voltage and turn on the two new relays. It need only uses small gauge wires now. The two new relays handle all the power distribution and they are rated for 30 amps. And no, the solar charging will not trigger the VSR as the solar circuit is not connected to the starter battery.

The voltage appearing at the fridge terminals is an important indicator of how the cabling performs once the fridge draws the normal operating current. The fridge draws about 7 or 8 amps under 12 volt operation.

Acceptable feed to the leisure battery?. Well it's now getting a dedicated 12mm2 wire from the starter battery via it's own 30 amp rated relay. 14.4 volts measured at alternator, 14.2 volts measured at leisure battery. This is a vast improvement to when it was runnng through the split charge relay, along with fridge and through underrated cabling and all that that entailed with excessive voltage drop and cable stiffening at the relay terminals.

Hey, go easy on my wiring job. It is just a temporary layout at present for testing. It will all get tidied eventually. The soldering was temporary, ran out of spades. And yes, everything is fused. 15 amp fuse to fridge and 20 amp to leisure battery .

The two power relays have PV cable terminated on blue push-on crimp terminals with an aperture of 2.5mm²!

Rated 30A? Ok take one, put 30A through it for 6 hours then take a photo of what's left. After one hour measure the voltage drop between terminal 85 and 30.

What is the fridges rated draw? If it is 8A the cable is adequate if the fridge is rated 10A the fridge is underperforming by 20% due to wiring losses.

What I'm trying to say about acceptable charge is how much current? This is what charge is. Voltage cannot tell you how well it performs just that it is operating.

Sorry Jace I'm not slating the job it's better than my 3rd attempt. Just offering advise in my natural "this whole leisure market electrics industry is rife with snake oil and advise that's simply not fit for purpose".
In case you hadn't noticed most all of my charge system is constituting elements from telecoms, off-grid & industry because the camper stuff is just woefully bad, I've tried and tested it. This is something I have learned from experience...I think most members can and do use their Liamalot filter when asking the question how good is good enough.
My rule of thumb is if it says camper on it then it's inappropriate for a camper.

Fair play. It's a definite improvement.

Ermm..so the 2.5mm² relay outs are they flexible cable or solid core domestic mains?

Of course, it all depends on how you use the motor. Having a go-anywhere vehicle that needs a tether is a failure of design in my opinion. If campsite to campsite is the order of the day factory fitment is passable.

jace_da_face

jace_da_face wrote: »

the solar charging will not trigger the VSR as the solar circuit is not connected to the starter battery.

but it is across the relays which are closed when a voltage of 13.6V is seen at either battery.

[Edit]: Actually, maybe it doesn't the manual is unclear. You can see if the fridge turns on by sticking a mains charger on the service battery.

I understand it's difficult to believe I might be right, some lad on tinternet and the auto-electric industry as a whole is pretty farcical and the camping electrics as an addendum is moreso.

Here's a good example, as good as I'm willing to spend time on. Feel free to do you own research and when load testing relays make sure you disconnect them every few minutes just to be sure to be sure.

Why do you think that lighting wiring kits for 9.5A fixture combined load come with 30A relays and 15A fuses if the relays were up to task?

I know Ebay is not a reputable source of data but it's pretty hard find a listing that specifies the relay rating.

jace_da_face

Sir Liamalot wrote: »

The two power relays have PV cable terminated on blue push-on crimp terminals with an aperture of 2.5mm²!

Well there are no flies on you Liam! That is nearly true. The relay on the right does indeed have a 15 amp, 2.5mm² terminal crimped on to 4mm solar cable. That is true. Just as I will be going out to buy new crimp connectors tomorrow and unsoldering and crimping the relay grounds, I will also be buying bigger spades to re-terminate the 4mm cable you see on the right. It's all temporary proof of concept stuff just now and will get tidied.

However, the 4mm cable feeding the left relay is actually terminated on a spade that handles the wire gauge. It's not obvious but if you take a look at the picture again you might notice a glimpse of yellow spade terminal behind the blue spade. The blue spade actually sits on the yellow spade which is a piggy back type. The blue spade is just for tapping off the supply from starter battery to provide the sensing voltage to the Smartcom. The left relay supplies current to the leisure battery and this is the solid 14.2 volts, not influenced by the fridge loading, which is supplied on the right relay. See pic. attached for clearer view.

I take your word on the ratings on those relays. I think I have given myself plenty of head room though. And the system is fused well below 30A. From what I gather 7 or 8 amps is normal enough for these fridges on 12 volts as they do not provide the same level of cooling as when on mains or gas.

Sir Liamalot wrote: »

but it [Solar] is across the relays which are closed when a voltage of 13.6V is seen at either battery.

Nope, the solar will not trigger the VSR. The VSR is connected to the starter battery. The solar only charges the leisure battery. I wouldn't mind wiring a switched ignition source at some point to switch the relays and do away with the VSR, just so I could also solar charge the starter battery.

Sir Liamalot wrote: »

Ermm..so the 2.5mm² relay outs are they flexible cable or solid core domestic mains?

They are stranded, 30 cores I think??

jace_da_face

Liam filter ... lol

jace_da_face

Hmmm, thinking about the solar thing again. With the engine off and VSR open, the vehicle and leisure battery are not connected. Only an engine start can close the VSR. The engine starts and closes the VSR. Both batteries now connected. The engine turns off, but the solar charger keeps a high voltage on the starter battery? Maybe. It didn't today during testing, but the solar charger was only outputting 13.3 volts and the VSR is adjusted for about 13.8 volts to switch on and about 13.6 switch off (hysteresis thingy).

I think the fridge would probably discharge to below 13.5 volts quickly enough (if switched on), but who knows on a sunny day. I will keep an eye on this. I could always put a NC relay on the solar circuit to prevent any solar charging when engine running, if needs be, or just get an ignition switched source and do away with the VSR.

Hrmm ok well yellow push-ons (the spades are the males) have an apperature of 6mm² so that makes me think your solar flex is standard 4mm² not 12mm².

There's no way you can attach 12mm² to that relay you won't find a terminal suitable because the relay isn't suitable. You need a stud type for this and copper lugs.

Those piggy backs are a liability because you can't insulate them very well. I only use insulated push-ons and rings. The forks are junk too they are designed for ease of install and fall out with vibration. Butt crimps there's no good reason for, I use them for prototyping and under duress but a continuous line or terminal strip is the correct way.


Do not use this tool, also rubbish (swear to gawd I sound negative but it's true).



Your crimps will fail if you do.
Use a ratcheting double crimp type that has a set compression every time.



Those crimp terminals are €10 for 100 get them in an electrical wholesalers because you'll get robbed in a motor factors.

I'd get relay holders instead, they are more secure and a better for servicing.

Solder makes wire hard and it breaks under vibration so I'd try to avoid it. It also takes ages so it's really not worth the effort.

Heat shrink the hairies.

The available charge will be reduced by load I guarantee you. You'll see it on your meter when you engage the fridge.

Plenty of head room? A what amp alternator on a 30A 15A relay? You are relying on a current limiting installation to not blow fuses (standard practice).

Most VSRs monitor both batteries because you can have chargers on either...it's best to check.

I never bother with 12V fridge operation, except in conjunction with mains for turbo. I manually run mine from an inverter when driving because the mains side has a thermostat. The 12volt side Dometic in their Wisdom decided was so useless nobody would practically use it and a thermostat wasn't necessary. :rolleyes:

Stranded cable is recommended, solid and semi-solid core work hardens and breaks with vibration. Thin wall cable is what you really want.

Nothing wrong with solar charging while driving they work in harmony one will play second fiddle to thuther.

The fridge will drop yer battery below 12.5v in short order without a large charge source so this is kindov ok, as long as the VSR isn't sensing the service battery it will work fine, if it is it will pull down the solar and prevent it from working.