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Leisure Battery Charging system

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  • 01-04-2017 9:05pm
    #1
    jace_da_face
    Registered Users Posts: 480 ✭✭


    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?


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    #2
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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. :)


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    #3
    crabbypaddy
    Closed Accounts Posts: 1,040 ✭✭✭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.


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    #4
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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!!


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    #5
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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    #6
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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. :D

    389194.jpg

    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.


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    #7
    jace_da_face
    Registered Users Posts: 480 ✭✭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?


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    #8
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #9
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    414073.jpg

    10A Max Load


    414074.jpg

    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.

    403293.jpg

    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.


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    #10
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #11
    jace_da_face
    Registered Users Posts: 480 ✭✭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?


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    #12
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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. whistling.gif

    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.


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    #13
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


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

    406942.JPG

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

    51svLIH9a0L._SX425_.jpg

    Here's the results:

    414051.jpg

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


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    #14
    jace_da_face
    Registered Users Posts: 480 ✭✭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?


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    #15
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #16
    jace_da_face
    Registered Users Posts: 480 ✭✭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?


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    #17
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.

    414091.jpg

    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.


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    #18
    jace_da_face
    Registered Users Posts: 480 ✭✭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


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    #19
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #20
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #21
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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    #22
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


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

    12VDC%20Local%20Service_zpsmtv74byp.jpg

    DSC_1998_zpsmnskk2rs.jpg


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    #23
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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    #24
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


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

    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%.


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    #25
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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    #26
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.


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    #27
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.

    touchwheel5.jpg

    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


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    #28
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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    #29
    jace_da_face
    Registered Users Posts: 480 ✭✭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?


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    #30
    [Deleted User]
    Posts: 5,238 ✭✭✭ [Deleted User]


    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.

    421499.jpg


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    #31
    jace_da_face
    Registered Users Posts: 480 ✭✭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.


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