12V Three Way Fridge Problem

[Gareth]

Hello, new boy here again. I am trying to work out how to get the fridge to run off the leisure battery. While it is not a good idea, I need to to know how it works. I have it running with no problems off the gas, but when I turn that off and flick the 12V on, nothing, no little red light! Now either my fridge is busted, or there is a pesky fuse somewere that I dont know about. I have a Hymer S660 and just cant find a fuse for it, anyone out there with a S660 who knows were I can find it? Thanks, Gareth

[trigrem]

Hi Gareth The 12 volt feed to the fridge only works via a relay when the engine is running, so you should see a indicator light when swithrd to 12 volt position and engine is running.If not then look at fuse and or relay. Doug.

[Guest peter]

They are not wired to run off 12V unless the engine is running, as it will flatten your domestic battery in no time. Try it with the engine running, if it still does not work there is a problem with the split charging relay or wiring/fuse.

[Clive]

Normally Hymers have a part potted lump of electronics under the drivers seat which includes the split charge relay and the fridge relay. For a simple circuit to help understanding have a look at http://www.motts.dsl.pipex.com/SPLIT%20CHARGING%20SYSTEM.htm Good luck C.

[Gareth]

I have tried to turn on the fridge while the engine is running and nothing happened! I wonder if the fridge gas starter is wired somewere else, while the electric running side is connceted to the battery relay as described earlier but I just cant find a fuse or relay marked fridge? :'(

[Burstner620]

[QUOTE]Gareth - 2006-07-10 11:48 AM I have tried to turn on the fridge while the engine is running and nothing happened! :'([/QUOTE] It won't work at engine idle speed !!!

[Guest peter]

Mine does.

[Derek Uzzell]

Gareth: I don't know if you've got a handbook for your fridge. If not (and it's an Electrolux model), then you may be able to download a manual from the Dometic website. A 12V gas-igniter normally receives its power from the motorhome's leisure-battery (see diagram in The Motorcaravan Manual), so a functioning 12V gas-igniter should have no bearing on whether or not a fridge will work on 12V delivered via the 'motor battery'. Unfortunately, there appears to be little standardisation in the way motorhome manufacturers install electrical systems/appliances in their vehicles. And, as for labelling fuses according to their function, dream on! Hymer (and other Continental motorhome converters) don't necessarily follow UK practice regarding vehicle wiring, often employing a 'black box' approach where many of the discrete elements of a UK-norm 12V system (split-charger, fridge relay, etc.) are integrated into a single unit that may (or may not) carry the related fuses. (Have you done as Clive suggested earlier and looked for an electronics-box beneath a cab-seat?) It's clear you are taking a live-in-hope approach and assuming fuse/relay failure is the cause of your fridge's 12V-operation switch not illuminating. This is just one possibility among several - it could be a loose or broken electrical connection between battery and fridge, a fuse or relay fault, a faulty earth connection, a faulty fridge, or perhaps just the switch itself. (Have you confirmed that the bulb in the switch is OK and that the switch's ON/OFF function works?) If you can't find a no-brainer cure (like a dead fuse, duff switch or dead bulb) then (having confirmed that there is indeed no 12V power at the fridge when your Hymer's motor is running) you'll have to work backwards from the fridge to the battery to try to detect where the power-supply interruption is. If all else fails then you'll need to seek professional assistance, preferably from a company with Hymer expertise. (I suppose it's worth mentioning too that a lit-up ON/OFF switch does not guarantee that a fridge will actually cool on 12V, but at least it's a step in the right direction.)

[Brian Kirby]

[QUOTE]trigrem - 2006-07-09 10:34 PM Hi Gareth The 12 volt feed to the fridge only works via a relay when the engine is running, so you should see a indicator light when swithrd to 12 volt position and engine is running.If not then look at fuse and or relay. Doug.[/QUOTE]

Gareth, just to be clear, the fridge never runs off the habitation battery, not does it run from the starter battery.  When on 12V, the fridge runs from the alternator only.  Unless the engine is actually running, the 12V feed to cool the fridge will be dead.  However, do not confuse this with the 12V gas igniter circuit, which is not so controlled and should be available at all times.

You do need to find the famous Hymer electrical control box.  You should have a master switch for the 12V circuits on your main control panel.  With the 'van parked and the engine off, so it's nice and quiet, try switching this off and then, after a pause, on.  There should be an audible click from somewhere, a second or two after the switch is turned off.  Trace the click, and you'll find the control box. 

You'll probably need a Hymer handbook, try contacting them to see if they can come up with one.  However, if your box is labelled ELEKTROBLOCK EBL99, look for connector "Block 1", which carries the fridge supplies, and check it's plug is properly pushed home.

Since this is a common item on several Hymer group motorhomes, my Burstner has one.  The only 12V fridge fault checks quoted are a 50A jumbo flat fuse mounted on the starter battery, a 20A flat fuse mounted ditto, the relay (which is inside the EBL99 box - not customer serviceable) or too low an operating voltage.  Assuming your Hymer may be similar, see if these fuses can be located and check they are sound.  Mine are easy to see, they're on the starter battery positive terminal.  If all that fails to produce a result you'll need to visit someone who knows their way around the Hymer 12V electrics.

Hope this is of some help.

[Derek Uzzell]

Brian: If a fridge operating on 12V gets its power direct from the altenator rather than via a battery, why do motorhome converters bother to fit a relay to ensure that the fridge can only operate on 12V when the vehicle's engine is running?

[Brian Kirby]

[QUOTE]Derek Uzzell - 2006-07-17 7:09 PM Brian: If a fridge operating on 12V gets its power direct from the altenator rather than via a battery, why do motorhome converters bother to fit a relay to ensure that the fridge can only operate on 12V when the vehicle's engine is running?[/QUOTE]

Derek

It may be my way of understanding this, or possibly my terminology but, since the fridge 12V supply only livens when the engine is actually running, and not just when the ignition is turned on (at least, mine doesn't!), I reason, correctly or otherwise, that the work is actually being done by the alternator, and not by the battery.

I know the main 12V feed is from the battery "+" terminal but, once the engine is running, the alternator output voltage is higher than the battery voltage.  The true position then, surely, is that the alternator is actually supplying both the starter battery (and of course the habitation battery) and the fridge?

The relay, as I understand it, is there to connect the 12V fridge supply when the alternator begins generating, and to disconnect it again when the alternator ceases generating.  This suggests to me that the starter battery has no actual role in suplying the fridge.  This feature of the wiring seems mainly designed to ensure that, even if the ignition is left "on" without the engine running - listening to the radio, for example - the fridge will not run the starter battery flat.

However, I'm sure Clive can quote chapter and verse!

[Derek Uzzell]

Brian: That's one way of looking at it I suppose! But, based on the sample wiring-diagrams shown in The Motorcaravan Manual (and all the diagrams I've seen in motorhome handbooks) I think most people would agree that a 3-way fridge gets its 'cooling' 12V power-supply from a battery and that the vehicle's alternator merely tops up that battery's charge-state. Traditionally, this battery would have been the vehicle-battery; nowadays the habitation battery may be used instead. As 3-way fridges have a high 12V current-demand a relay is fitted to prevent 12V power being supplied to the fridge by the battery unless the alternator is providing charge (though the fridge-relay on my Herald operated as soon as the vehicle's ignition-light illuminated). If the relay fails in the 'closed' position and the alternator is not providing charge, then selecting a fridge's 12V option will soon flatten the battery that is supplying it with power. I don't know what electrical arrangement your motorhome has, but the CBE-made PC-100 system fitted to my Hobby is very widely used in motor caravans. The PC-100 12V distribution box has connections to the vehicle and habitation batteries and there is also a "simulated output D+ alternator" connection that's there to trigger the fridge-relay, electric-step operation, etc. However, there's little doubt where the fridge obtains its 12V 'cooling' power from and, with the CBE system, it's via the connection to the habitation battery. If you are going to claim that, because my motorhome's alternator offsets the current-drain placed on the habitation battery by the fridge operating in 12V mode, it's REALLY the alternator that's powering the fridge rather than the battery doing the work, then that seems a peculiarly convoluted argument to me.

[Brian Kirby]

Derek

I have to say that, to me, how you see and understand the 12V power supply to the fridge, and how I see and understand it, do look somewhat similar.  Bit close to debating the number of angels dancing on the proverbial pin head! 

The main point I was trying to convey to Gareth, was that unless his engine is actually running, and his alternator actually generating, his fridge is unlikely to be getting any 12V power. 

That was postulated on his Hymer electrics using an EBL 99 controller working in a similar way to that in my (Hymer group) Burstner.  Other 'vans may, indeed, energise the fridge supply via the ignition.  However, I believe the Hymers use the alternator output to control the fridge relay.  That information, I thought, might be of some use to Gareth.

Whether the physics says that the power emanates primarily from the battery, with the alternator topping it up as it goes, or from the alternator, which is simultaneously re-charging the battery after it has started the engine, doesen't seem to matter a great deal if the fridge isn't getting any power in the first place!

Regards :-)

[David Dwight]

Hi Guys, Now for my twopenneth, we have just come back from two week in scortching France. We stayed on Aires several nights and used the 12volt for the Fridge and it worked OK. Obviously not as good as on 240v or Gas but kept things cool. David

[Derek Uzzell]

David: Presumably you're not saying that you ran your fridge on 12V while you were overnighting!? Current model Dometic fridges now have thermostatic control over 12V operation and, as far as my own fridge is concerned, cooling is fine in any of the 3 modes of operation.

[David Dwight]

Derek, Yes the first night was when we came off the Ferry, just switched over to leisure battery, could'nt be bothered to get out and turn the gas on, if it would have worked after travelling, any way at 1-30 am I wanted my bed, as we had both been at work from 7am that morning. The second occasion I tried to light the fridge on gas again after travelling, and then forgot so it stayed on leisure battery again all night. David

[peter.maniac]

Whilst i don't know about Hymers my experience is that when you switch to 12v on the fridge there is always a delay of a minute or two after the engine starts before the light comes on - i always imaged that this was the relay tripping in once power from alternator had started charging the battery. Peter

[Derek Uzzell]

David: I've never come across a 3-way fridge installation that would permit the fridge to cool on 12V without the motorhome's motor running (that's assuming the fridge-relay is working properly!) Fridges can, of course, be switched to 12V with the vehicle's motor stopped, they just don't cool. More details of what you did would be helpful (also what motorhome you own).

[Brian Kirby]

[QUOTE]David Dwight - 2006-07-19 11:06 PM Derek, Yes the first night was when we came off the Ferry, just switched over to leisure battery, could'nt be bothered to get out and turn the gas on, if it would have worked after travelling, any way at 1-30 am I wanted my bed, as we had both been at work from 7am that morning. The second occasion I tried to light the fridge on gas again after travelling, and then forgot so it stayed on leisure battery again all night. David[/QUOTE]

Assuming a Dometic fridge, if this was working from your starter or leisure battery, as you say, then, unless you have huge battery capacity, you should have had:

a) a warm fridge by morning, or

b) a completely flat battery, or

c) both!

These draw in the region of 8-10A.  (I used to run a small, 8A, caravan fridge from a leisure battery during a 4 hour channel crossing.  It worked, but a 75Ah battery was just about dead after even that time.)  Are you sure the fridge was, actually, working?  Or is yours an AES fridge, that simply switched itself over to gas when you were'nt looking?

Very puzzling!

[Derek Uzzell]

The data for my Dometic RM 7651(L) fridge show a 12V consumption of 170W (that's over 14 Amps), so my 80A/h battery wouldn't last long if asked to provide that. I notice that the latest Dometic AES fridges can select their 12V supply from a solar-panel system, but I would think few motorcaravanners would have a system powerful enough to cope with the current-demand required.

[David Dwight]

Brian and Derek, Yes as you say puzzelling. I have re-read the manual for my M/home. It states that the 12v fridge will not work unless the ignition is switched on. It definately works when ignition swithced off, I tried it when I came home from work this pm ambient temp 32c the fridge was working, I could feel the heat coming from the vent, and the fridge was beginning to cool. Now I did have a problem last year with a flat battery due to the vehicle battery failing. I quiried this at the time with the dealer, and said I thought that there was a fault with the electrical system. Oh no says they, we have checked everything over and it is all OK. Well it aint is it. I dont mind the fridge working on 12v as long as I remeber to have it on leisure battery. Just checked again and the fridge is cool. Well my son is a sparks so he can have a poke around. A friend of mine had a problem with the 12v fridge in his Caravan, dealer says no problem, it went back to the Manufacturer to have a new side wall due to water ingress, they checked the fridge no problem. There friendly guy who services their caravan folund the problem a loose wire. So can we realy trust the dealers.. Oh by the way my M/home is an Ace Milano. Thanks for all the interest. David

[Derek Uzzell]

David: With current Dometic "Powerfridges" there is a set of LEDs by the selector-switch to indicate gas, 230V or 12V cooling is in operation. Unlike Electrolux 'Old Faithful' fridge designs that had whopping great illuminated switches these LEDs are pretty dim. Nevertheless, if the switch is turned to select 12V operation and the LED illuminates it's reasonable to assume the fridge is cooling via 12V (and vice versa if the relevant LED doesn't light up). However, I'm pretty sure that Dometic went through a 'no tell-tales' design phase prior to the introduction of the present Powerfridge, where the position of the selector-switch was the only visual clue to whether or not 12V operation had been chosen. If you've got one of these then I can understand you needing to confirm 12V fridge cooling by heat coming from the ventilation grilles, otherwise I would expect you to have said "It's definitely working on 12V because the 12V indicator-light is on." What does concern me somewhat is your 'flat battery' comment, as many (most?) UK-built motorhomes traditionally take the fridge's 12V power-supply from the vehicle-battery rather than the leisure-battery. (I've been unable to find a photo of the control-panel used in Milano so I can't make even an educated guess about this in your case.) Your fridge's capability of operating on 12V without your motorhome's engine running definitely indicates something cock-eyed about your 'van's electrical system. (It's possibly something as simple as the cables being connected to the fridge-relay in the wrong order.) If you forget that you've left the fridge on 12V and its power-source is the leisure-battery then a flattened leisure-battery ain't so bad, but a flattened vehicle-battery is a different proposition altogether.

[Brian Kirby]

David and Derek

Swift's website gives access to p.d.f downloadable user manuals, so I had a peek.  The draw from the fridge is indicated as 10-14 A.  I think almost any battery would be flattened by that after just a few hours.  Therefore, I can only understand (limited faculties whirring furiously) this in terms of more than one battery being connected.

A thought occurred: I wonder if David’s van has a wiring/relay fault allowing both batteries to be used simultaneously?  That might explain why the battery isn’t generally flat after an overnight stop, but also David’s unexpected flat starter battery incident.  The leisure battery would presumably be bigger, and so better able to cope with the extended discharge time.

Might this condition arise if the contacts for the fridge relay had welded themselves closed so that, with the engine off, there is a permanent supply to the fridge from the starter battery, instead of this being disconnected?

The current model control panel shown has a three-position battery selector rocker-switch.  This is set up for the leisure battery, down for the starter battery (with a warning about not using this for long!) and the mid point for neither.  Thought two: that switch is incorrectly wired, so that when the leisure battery position is selected the starter battery remains in circuit.

Oh, and one last thing.  The manual warns against using the fridge on the 12V supply when stationary, advising that 240V mains or gas should be selected.  (Naughty David!)  This seems to imply that the wiring may permit this option, though why this should be enabled if it is then stated undesirable escapes me!  Perhaps Swift should be asked for an explanation?

Any help?

[David Dwight]

Hi Brian, Thanks for your input, it would'nt surprise me if the switch was at fault, seeing that some of the other switches were put in upside down, ie the step switch worked press the up for down and visa versa. David

[Derek Uzzell]

Brian: I believe there is nothing 'clever' about the electrical system used in Swift Group motorhomes, but there is plenty of opportunity for incorrect installation or faults to develop. Current Dometic Powerfridge manuals say "The refrigerator should only be used while the motor is running, otherwise the on-board battery would be discharged within a few hours!" I think they've always said this even though, with an operative fridge-relay in the circuitry, the leisure-vehicle owner should not have the choice of 'motor off/fridge on 12V' operation. Presumably the caveat is there for DIY fridge installers who don't fit a fridge-relay. In fact, with present Powerfridges, if the motorhome is 'stored' for any length of time, it's important to switch the fridge fully OFF as leaving the selector-switch on 12V (as people, including myself, used to be fond of doing with earlier Electrolux fridges) allows the fridge's electronics to continue to draw current and, eventually, to flatten whichever battery the fridge is connected to. I read somewhere that, when current-model Powerfridges were first introduced, they had been fitted to a batch of Swift Group motorhomes with the fridge-electronics connected to the vehicle-battery. The owners drove home with the fridges on 12V, left the selector-switch in the 12V position and, when the time came to start their vehicles the batteries had become discharged.