Frustrating battery discharge problem - fridge-related

CelticRambler · 09-04-2017 1:57pm #1

Long standing problem that's taken ages to narrow down, but now I know that my three-way Dometic fridge appears to be drawing every last amp out of my leisure batteries while I'm driving, and I can't figure out where exactly the fault is. Googling suggests this is a relatively common problem, but none of the discussion seems to relate to my situation.

I'm in a 2013 Benimar, still using the factory-fitted alternator/45W solar panel/regulator/etc. I have two 90aH sealed car batteries as "leisure" batteries, replaced two years ago. Everything seemed to be fine until Jan/Feb last year when I noticed that I'd arrive at my destination after a day's drive with only 70% leisure battery. Turning the fridge off "fixes" the discharge problem. Last week though, in just the time it took me to manoeuvre into a tight alley I'd left the fridge on and according to the display panel, the charge dropped from 95% to 65%. :eek:

When not driving, everything's fine. Even with only a single 45W solar panel, I have all the power I need for pumps, motors, gadget batteries, two laptops, etc. For now, I'm getting by by throwing a load of ice-blocks in the turned-off fridge while I'm moving between hook-ups; but later in the year, I'm hoping to go "off grid" for several weeks and need to be able to rely on the engine to do it's share of the work!

I've had the control panel out and can't see any burnt out components, nor any damaged wiring. Any suggestions as to where and what I look at and test next?

crabbypaddy · 09-04-2017 4:44pm

The display panel capacity meter is a guestimation and is only relevant on fully rested battery its completely meaningless on a battery underload or recently loaded. Fridge is probably 8-10A on 12v if you only use 12v while driving and its flattening the battery then the alternator is not charging the leisure battery.

CelticRambler · 09-04-2017 4:59pm

The thing is, the alternator is charging the leisure battery, as long as the fridge is not on. Say I forget to turn the fridge off during a long day-time drive, when I stop, the panel is warning me that the leisure batteries are flat, and any 12V devices will struggle to work (lights ok, but very dim, water pump no, cooker piezo very slow to click, etc).

On the other hand, say I'm parked up for a week in cloudy conditions so there's hardly any charge coming down from the solar panel, then drive through the night, as long as I've turned the fridge off, when I get to my destination, I can get a week's worth of not-too-sparing use out of the leisure batteries based on only that charge.

When the engine's running, the control panel shows that it thinks there's 14.4V going to/coming from the leisure batteries, dropping to around 13.7V if I have e.g. a laptop on charge (12V -> 19V adaptor)

09-04-2017 9:04pm

Problems like this is why my first response is usually install an ammeter!
It sounds like your battery charge circuit is so under-wired it's running at discharge under load while alternator "charging".

0.7V drop to run a laptop is huge. Mine is 0.1V with an 80W load on (225Ah).

Unless your meter is a SmartGauge or amp hour counting I'd consider it's synopsis as art not science.

CelticRambler · 09-04-2017 9:45pm

I'm happy to accept that - but what would have changed last year, after twelve years of trouble-free performance?

Has the fridge always been drawing its current from the leisure batteries while driving? I'd assumed it was being fed directly from the one of the many connections to the engine battery, or from the alternator ...

09-04-2017 10:03pm

It should be running from the alternator. That's the power source, a lot of people think the battery runs things, in truth power comes from the alternator and passes the battery posts then goes onto the fridge.

Two possibilities spring to mind. It never worked but because you've flattened the batteries so much now they have a much diminished capacity it's more noticeable.
The other is the old "I haven't got 4mm² cable" said the installer "so I'll just use 2 x 2.5mm² instead" chestnut and one of the lines has dropped out.

Might be worth replacing the cable altogether for a more direct route & much heavier gauge and disconnecting the stock fridge and split charge circuits. You could probably decommission the stock setup by pulling 2 fuses.

Still though diagnosis is your best starting point. Try to get your hands on a DC clamp meter to troubleshoot it.

spaceHopper · 10-04-2017 10:53am

Check the alternator belt maybe it's slipping a little bit and can only manage to charge the battery when it's not loaded. Also is there a relay between the fridge and battery maybe the contacts are pitted and you are losing voltage there when charging.

CelticRambler · 27-11-2017 5:31pm

Well, I think I've got to the root of this problem, and (unless there's another one lurking elsewhere in the circuitry) it seems it was a "simple" one: a temperature-sensitive crack in the solder of the separator relay. The fridge is wired directly to the leisure battery (as per the Dometic instructions) with a signal cable running to/from the alternator. On the road, with the alternator operating as normal, the fridge was being told that it had 14.5V to play with, but in fact little or none of this was getting through to the leisure battery.

After a quick bodge-it fix on the road, I rigged up a voltmeter so that I could see what was happening while driving. At an altitude of over 1500m and/or a temperature of under 10°C the relay worked as expected; below 1000m and above 15°C it would close/open/close/open at irregular intervals, provinding enough intermittent current to make the batteries look like they were charged each time I stopped and checked, but not enough to also supply the 14.5A drawn by the fridge while running on 12V.

Now what? I've re-soldered the relay, subjected it to alternate freezing and cooling, and so far it seems to be performing as it should. However, I only re-fitted it to the camper yesterday, and haven't tested it under real working conditions yet. The exact part is readily available to buy online, but I'm wondering if I would be better off upgrading this section entirely. Everything is contained within this box, attached to the chassis:

A 10mm² cable comes from the alternator (120A) to "relay E-772" on the left, 10mm² blue cable carries the current from there to the first of two leisure batteries. An accessory relay receives the brown signal cable from the alternator, and passes it on to the fridge via the violet cable seen on the right.

It seems strange to me to have the fridge deciding that it's OK to use the 12V supply, based on a signal carried over a separate circuit to the one supplying the necessary volts, but Benimar provided the original wiring diagram for this model, and it looks like that's exactly how it was meant to be.

29-11-2017 1:42pm

Voltmeters are only a vague idea of what is going on a clamp on ammeter is much better for taking these readings.

14.5A fridge :eek:
That'll put a big dent in available charge current.

CelticRambler wrote: »

I'm wondering if I would be better off upgrading this section entirely.

You can do a lot better. I'd say by the looks of things your fridge could be draining your battery faster than your alternator can charge it.

That relay is too small for the job. Better have a relaysocket/holder for the fridge connection rather than individual push ons that are confusuing when you disconnect them.

This is a 100A Contactor

I'd run 35mm² from the alternator to one side of a split charge contactor and 35mm² continuing to service battery fused at both ends.

I'd take the input from the fridge power terminal (should be 30) and feed it from the starting battery. In contravention to Dometic instruction because that fridge will pull down the charge system, better to tie it in with auto-electrics than fighting voltage drop of a huge load downstream a downstream battery.

That should help give you a steady 15A charge with a running fridge.
Use 6mm² or 10mm² for the fridge power.

CelticRambler wrote: »

It seems strange to me to have the fridge deciding that it's OK to use the 12V supply, based on a signal carried over a separate circuit to the one supplying the necessary volts

It's one circuit. The fridge is told to switch on from the D+ which is the alternator excitation field. The Alternator Output B+ powers the fridge. The problem you are facing is removing all the poor conducting material in the middle that is standard practice to fit.

CelticRambler · 29-11-2017 10:59pm

Thanks for the comments. A lot to think about, which I'll do when I get back from my first-in-a-long-time non-camper short break. (Packing a suitcase is really hard when you're used to taking a whole wardrobe ... literally! :pac: )

CelticRambler · 10-01-2019 11:48pm

Some time later ... :eek:

@ SirLiamalot, circumstances dictate that I can't follow all of your instructions re the above, notably re-routing all the cables, but I have acquired a heavy-duty relay (either an original SW180 or a Chinese knock-off) and a waterproof box twice the size of the previous one in which to install it! Alas, I can't install the full SmartGuage suite at this time, so I've got to work with the on-board box of tricks and associated cabling for now.

Before I go any further, though ... what wire goes where? :cool:

Or rather, can you offer a second opinion, cos a friend who knows about auto electrics has said I need to add an extra red wire ...

Here's the original set-up, now fully disconnected:
(factory-installed, apart from the renewed ground connection lower left)

The manufacturer's wiring diagram:
(violet 12V to the fridge is the control wire; 12V to the fridge comes directly from the leisure battery)

Out with the old; in with the new ... which has three extra blades!

What the original looked like before it was manhandled by a posse of burly French mechanics :pac:

My specific question is this: pic 1 shows the original configuration with a red 2.5mm running from the splitter's input terminal to the small relay. My "man who knows" says I should replicate that (as per wiring diagram), but also add a connection from one of the SW180's two +ve blades to the M8 output terminal, where none is indicated in the schema.

Should I?

Supplementary question: I haven't been able to find a spec sheet for the SW180 that gives info regarding cut-in/cut-out voltages as displayed on the E772. Is this likely to be built-in or usually outsourced to the control panel; and in which case, is E772 smarter than it looks, and could I run into problems with the control panel not controlling which electrons go where?

11-01-2019 1:26am

CelticRambler wrote: »

Some time later ...
(either an original SW180 or a Chinese knock-off)

That'd be a Chinese knock off. I doubt very much it's got silver alloy contacts.

CelticRambler wrote: »

Alas, I can't install the full SmartGuage suite at this time,

Shucks, Clicky.

CelticRambler wrote: »

Before I go any further, though ... what wire goes where? :cool:

Big contactor terminal to +ive Battery A, thuther big terminal to Battery B +ive, one side of coil to 12V trigger, thuther side of coil to ground.

CelticRambler wrote: »

Or rather, can you offer a second opinion, cos a friend who knows about auto electrics has said I need to add an extra red wire ...

Well I wouldn't be using the stock cable it's too feeble.

CelticRambler wrote: »

Here's the original set-up, now fully disconnected:

Always a good start.

CelticRambler wrote: »

(factory-installed, apart from the renewed ground connection lower left)

didja clean the chassis metal?

CelticRambler wrote: »

The manufacturer's wiring diagram:
(violet 12V to the fridge is the control wire; 12V to the fridge comes directly from the leisure battery)

Hrm not quite, but, don't assume they did it right either....

CelticRambler wrote: »

Out with the old; in with the new ... which has three extra blades!

The lower two are parallel and the upper two are parallel. So 4 blades for 2 coil contacts.

CelticRambler wrote: »

What the original looked like before it was manhandled by a posse of burly French mechanics :pac:

Bon courage!

Contactor on the left is rated to 200A relay on the right is rated 150A..canya guess who's lying?

CelticRambler wrote: »

My specific question is this: pic 1 shows the original configuration with a red 2.5mm running from the splitter's input terminal to the small relay. My "man who knows" says I should replicate that (as per wiring diagram), but also add a connection from one of the SW180's two +ve blades to the M8 output terminal, where none is indicated in the schema.

Your man who knows thinks 2.5mm² (20A) cable is suitable for a 200A contactor does he? No mention of a fuse stepping down from a ~100A alternator cable to a 1A coil control cable?
I'd uprate it at least 5 times that gauge.

CelticRambler wrote: »

Should I?

I dunno what is it you're attempting to do?
I require a mission statement.

CelticRambler wrote: »

Supplementary question: I haven't been able to find a spec sheet for the SW180 that gives info regarding cut-in/cut-out voltages as displayed on the E772.
Is this likely to be built-in or usually outsourced to the control panel; and in which case, is E772 smarter than it looks, and could I run into problems with the control panel not controlling which electrons go where?

It's primitive, it's just on or of, you have to be smarter than it and figure out how you want it controlled.
They're actually DC motor contactors originally.
Datasheet clicky

The E772 is about as dumb as it looks, it's a Nagares clone...cheap Durshyte knock off. Like copying homework off the likable dunce....

You can drive the SW180 with the "clever" relay but I'd still upgrade the charge conductors and I think the voltage thresholds are pretty poorly selected. Or you could go manual (recommended as a lazy soft start) I don'tdrop a 100A load on my alternator with a cold engine corz the belt starts screaming.
Or you could go D+ switched. Either way off to the cable merchants.

Repeat after me "I will not settle for blue and brown cable when I want red and black cable!":)

CelticRambler wrote: »

and could I run into problems with the control panel not controlling which electrons go where?

AKA upgrading.

...problems like 3 times Morah Powah from shorter fatter cables?

You know that thing has a 15W coil?
That's like a running laptop. 200A is a mite big.

CelticRambler · 11-01-2019 11:02pm

"I will not settle for blue and brown cable when I want red and black cable!"

"I will not settle for blue and brown cable when I want red and black cable!"

"I will not settle for blue and brown cable when I want red and black cable!"

But much and all as I want only red and black cables, and of a hefty diameter, I'm very limited in what I can actually do as all these changes/repairs are (literally) done on the roadside, with very hit-and-miss access to supplies (the joys of living and working in France ... :rolleyes: )

Therefore:

Sir Liamalot wrote: »

I dunno what is it you're attempting to do?
I require a mission statement.

To replace the faulty E772 with something that will work in the same way and charge my leisure batteries, without discharging them while the fridge is on, and charge the engine battery from mains/solar while parked up (i.e. do what E772 did till it stopped doing it)

Sir Liamalot wrote: »

You can drive the SW180 with the "clever" relay but I'd still upgrade the charge conductors and I think the voltage thresholds are pretty poorly selected. Or you could go manual (recommended as a lazy soft start) I don'tdrop a 100A load on my alternator with a cold engine corz the belt starts screaming.
Or you could go D+ switched.

Is it not already D+ switched (brown wire to small "yellow connectors" relay? Or was it only telling the fridge that there was alternator power available?

Sir Liamalot wrote: »

didja clean the chassis metal?

I did - and used a shiny new self-tapping bolt for extra points.

Sir Liamalot wrote: »

Your man who knows thinks 2.5mm² (20A) cable is suitable for a 200A contactor does he? No mention of a fuse stepping down from a ~100A alternator cable to a 1A coil control cable?

Yeahhhh ...That's why I thought I'd get a second opinion. :pac:

Sir Liamalot wrote: »

The E772 is about as dumb as it looks, it's a Nagares clone...cheap Durshyte knock off. Like copying homework off the likable dunce....

I follow the logic re amps and contact size when comparing these mini-things to the SW180 - but any Nagares I've seen is about a third of the price of the E772, and the Chinese clones half that again. What does the extra 40-60€ pay for in an E772?

In any case, my roadside workshop has evolved from zero degrees and dry to +5°C and raining, so I won't be lying on the ground looking up at a junction box for another while. Time to revisit the routing of the fridge's 12V supply cable instead, I think.

13-01-2019 7:28pm

CelticRambler wrote: »

Therefore:

To replace the faulty E772 with something that will work in the same way and charge my leisure batteries, without discharging them while the fridge is on, and charge the engine battery from mains/solar while parked up (i.e. do what E772 did till it stopped doing it)

Any 12V VSR, AVR will do, the generic ones are good for 50A ignoring the rating.
I like
Connect @ 14.0V
Disconnect @ 13.4V

Adding the SW180 won't gain you any significant current gains without the cable to accommodate it. So if you fuse your 200A contactor at 20A all you are gaining is a 1A coil consumption parasitic.

CelticRambler wrote: »

Is it not already D+ switched (brown wire to small "yellow connectors" relay?

[Gets out spectacles]

Aye tis. You can trigger yer SW180 with that. (Fridge Relay 86 terminal (maroon))
Or make it manual and put a switch somewhere easy to get to.
Or get another as clever replacement.

CelticRambler wrote: »

Yeahhhh ...That's why I thought I'd get a second opinion. :pac:

He's not exactly wrong if the upstream fuse is adequate for all cabling.
But I have a 150A charge cable and 10A control cable so....

CelticRambler wrote: »

What does the extra 40-60€ pay for in an E772?

Affiliation pricing

CelticRambler wrote: »

Time to revisit the routing of the fridge's 12V supply cable instead, I think.

.Aarah stop messin', put her out to pasture and go electric. I've had hassle refrigeration free since installation. :cool: ...best fix that freezer door thing...

CelticRambler · 13-01-2019 7:57pm

Sir Liamalot wrote: »

Aarah stop messin', put her out to pasture and go electric. I've had hassle refrigeration free since installation. :cool: ...best fix that freezer door thing...

Well as it happens ...

You posted a cost-benefit analysis for someone else a while ago which coincided with the installation of a shiny new Linky meter on my domestic supply, that gives me a half-hourly record of my global electricty consumption. Guess which camper appliance causes a huuuuge spike when I plug into the house mains on my return to base. :rolleyes:

I've found a fridge-freezer I'd like to use ... but of course it's annoyingly wider than the Dometic-sized space available without launching into a major refurb of the interior.

Still thinking about it, though. There's a pretty useless void in the cabinet next door that'd be just right for two dedicated batteries and an inverter.

13-01-2019 11:00pm

You can buy the compressor gubbins stand alone and make the rest of the fridge with a foam cutter. Popular thing on boats.

Frustrating battery discharge problem - fridge-related

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