12v LC Fridge Supply problem

[Cavingaz]

Hello,
my first post so please be gentle.
Looking for advise on fitting a new Thetford fridge!
We have bought a new Thetford N4090 fridge for our 2011 Solaris. We have successfully wired the 240v and piped the gas and both working fine. However, when trying to get it to run on the engine (via the leisure battery I believe), the 2 LC wires that feed the electronic fridge controls switch off when the engine starts, so fridge turns off.
The LC feed (to the fridge) is activated from the control panel in the van, switching on the main switch on the control panel activates the 12v lights, water pump and fridge). As mentioned above once the engine is running the 12v feed goes off. This can be also confirmed at the control panel as the main switch remains in the on position (with a green light still illuminated) but the rear interior lights go out and the water pump no longer operates. Lastly when this all happens the "G" lights up on the control panel display indicating the leisure battery is charging from the alternator.
We are running a DS-300UK distribution box and having read the manuals it suggests a couple of options that we have tried.
1. Remove the 3A fuse in position 6 which "gives power to the cutting out device of all 12v mains during the trip, except the 12v refrigerator"
The result of removing the 3A fuse is the LC supply now remains on when the engine is running, (good) however it appears to cause the HC feed to go intermittent. On inspection in the Dis. box there is a Relay that is now active causing this HC switching. (?)

2. Location 12 on the Dis. board, where there are 2 male connectors:- Described as AES Fridge connection. "It is a bridge which excludes the 3 way fridge function and is used to connect the AES fridge directly to the B2 (which is the leisure battery)
The result of the bridge appears to be that HC supply now is constant at 12.2v when the engine is off, but the LC feed still drops away once the engine is started.

Essentially the root of the problem is the LC feed being cut once the engine is running, this probably wasn't an issue with the old fridge as there was no digital controls as such which likely meant that losing that feed when on the move was not a problem.
hope this makes some sort of sense and there may be some ideas on how to resolve
thanks

 

[autorouter]

The result of removing the 3A fuse is the LC supply now remains on when the engine is running, (good) however it appears to cause the HC feed to go intermittent. On inspection in the Dis. box there is a Relay that is now active causing this HC switching. (?)

When you say intermittent, do you mean the HC supply comes on only when the engine is running, and goes off when the engine stops? If so that's what it's supposed to do. It avoids running the fridge from the leisure or starter battery 12V when the alternator is not supplying power. If it's an AES fridge it should automatically switch to gas when the engine stops.

There is an automatic delay of about 15 to 20 minutes before the gas comes on when the engine stops. This is for safety, so that the gas doesn't fire up when you stop for fuel.

 

[Cavingaz]

Hi thanks for the reply.
When I say intermittent, I mean that I have the engine running and the 12v HC is not stable, every few seconds the voltage drops away. When I am in the van I can hear and feel a relay operating on the main distribution board.
thanks

 

[autorouter]

As I understand it, the LC supply to the fridge is a 'permanent supply', ie it doesn't switch off either from the panel switch or when the engine starts/stops. I think it should be wired via pins 5 or 6 on the 6-way connector, protected by Fuse 9. Other permanently on devices like the heater controls are also wired through this fuse.

The HC supply should be wired via pins 2 and 3 of the 6-way connector, protected by Fuse 6 (30A). The current will be quite high, maybe 15A or more, so it would be a good idea to wire to both pins (2 & 3) to share the amps load. You can join the wires together near the connector, and run a single (maybe thicker) wire to the fridge 12V element. Pins 2 & 3 should be ON (+12V) when the engine is running, and OFF (no volts) when the engine stops. They should not be 'intermittent'.

I don't think the terminals at Location 12 are relevant. I think they are intended for something like a compressor fridge that works from 12V all the time, not just when the engine is running.

 

[Cavingaz]

Thanks again - having checked the 6 pin there are 3 wires in this block.

1. Position 4 - Motorised step.
2. Position 1 - Aux feed that supplies the rear radio and cigar lighter
3. Position 3 - Fridge HC supply, with the 30A fuse as you mentioned. Is it worth wiring to position 2 as well?

Therefore no LC wires in this block. I am pretty sure the LC feed is on the 9 pin block in position 9 together with the Group B lights (7,8).

After starting the engine the LC feed cuts out , likely due to a habitation relay(?)(not sure where that is) to avoid the lights being active whilst travelling. As you say, putting the LC onto the 6 pin would sort this out.
Earlier, I disconnected the LC supply that comes from the van and wired a separate supply from a spare 12v battery directly to the LC fridge wires including wiring in the D+. As expected this provided power to the fridge display/control panel (I had removed the van feed as there is access behind one of the vents on the side of the van)
On starting the engine, this time the fridge control panel remained on a it has a directly LC feed.
However the HC 12v continues to be intermittent and measuring the voltage at position 2, the value rises to ~13.6v and then drops to around 12v, this coincides with the relay on the Dis. board clicking in and out. As yet I can't work out if the fridge switches off as the voltage drops or as it peaks - I'll do a more thorough test tomorrow.
I can get around the LC cut off by removing the 3A fuse from position 6 which is the "cutting out device of all 12v whilst travelling"
but the main issue seems the 12v HC supply. Is there a possibility that the fridge is pulling too much current from and causes a drop sufficient to activate/deactivate the relay on the board?
thanks again

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[GeoffnDee]

Cavingaz Are you trying this with the bridge connection removed or in place , I think that it should be removed in your case, if you have not tried already , to avoid an extra link to the leisure battery that may not be needed.

 

[GeoffnDee]

To add to the above, The Thetford N4090 shows a D+ ,as well as HC and LC , at the fridge wiring connection point and maybe this other D+ signal is also needed for correct 12v operation ?

 

[autorouter]

We are running a DS-300UK distribution box and having read the manuals it suggests a couple of options that we have tried.
1. Remove the 3A fuse in position 6 which "gives power to the cutting out device of all 12v mains during the trip, except the 12v refrigerator"
The result of removing the 3A fuse is the LC supply now remains on when the engine is running, (good) however it appears to cause the HC feed to go intermittent. On inspection in the Dis. box there is a Relay that is now active causing this HC switching. (?)

For some reason, on UK MHs there is a relay which switches off all habitation circuits when the engine is running. That is what this 3A fuse in position 6 will enable. The bit "except the 12v refrigerator" means that the LC supply to the fridge should NOT be wired into this circuit. The supply to an AES 3-way fridge needs to be wired so that it is permanently on. Pin 5 or 6 of that 6-way are suitable supply points for the LC supply.

For some reason they do not give an amps value or a watts value for the 12V fridge element. However usually they are about 10A on the smaller fridges like this one, and about 15A on the larger fridges. The connector pin can carry about 16A I think, so would have no problem with a smaller 10A element. For the 15A element it's a bit near the limit, so would be worth thinking about doubling up the wires to share the load on the pins, but for 10A it's not really necessary.

 

[Cavingaz]

Cavingaz Are you trying this with the bridge connection removed or in place , I think that it should be removed in your case, if you have not tried already , to avoid an extra link to the leis

Hi
I don't have a bridge across position 12, I tried this earlier and as you say that seemed to mean that there was a connection to the leisure battery directly and as such the voltage was around 12.2 volts on the HC.

 

[Cavingaz]

For some reason, on UK MHs there is a relay which switches off all habitation circuits when the engine is running. That is what this 3A fuse in position 6 will enable. The bit "except the 12v refrigerator" means that the LC supply to the fridge should NOT be wired into this circuit. The supply to an AES 3-way fridge needs to be wired so that it is permanently on. Pin 5 or 6 of that 6-way are suitable supply points for the LC supply.

For some reason they do not give an amps value or a watts value for the 12V fridge element. However usually they are about 10A on the smaller fridges like this one, and about 15A on the larger fridges. The connector pin can carry about 16A I think, so would have no problem with a smaller 10A element. For the 15A element it's a bit near the limit, so would be worth thinking about doubling up the wires to share the load on the pins, but for 10A it's not really necessary.

I tend to agree, ideally the LC should be moved over to the 6 pin at position 5/6. However I am not sure this will stop the HC switching in and out. I've had a guy over earlier who did my habitation check a few weeks ago, and whilst not fully familiar with all auto electrics had spoken to another contact and seemed to think the current draw on the HC side was causing the Relay in the centre right on the DC300 to flip the supply from the alternator on and off??
Worth also saying ( in response to a point from GeoffnDee) that I have the D+ wire connected to the LC supply, with the D+ connected the fridge doesn't operate at all.

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[Cavingaz]

*without the D+ connected I meant to say....

 

[autorouter]

Something is not right with that D+. I think the fridge should work on gas and 240V with the LC supply connected, and the D+ entirely absent. However the wiring diagram has the D+ wired to the connector so maybe it is required to be wired.

Try wiring the LC supply to that permanent 12V supply on Pin6, and wire the D+ wire from the DS300 to the D+ fridge input.

If the fridge doesn't work on any power source (240V, gas, 12V) then there's something wrong. Check that the D+ is about 12V when the engine is running, and is a low voltage, about zero, when the engine stops.

 

[Cavingaz]

Something is not right with that D+. I think the fridge should work on gas and 240V with the LC supply connected, and the D+ entirely absent. However the wiring diagram has the D+ wired to the connector so maybe it is required to be wired.

Try wiring the LC supply to that permanent 12V supply on Pin6, and wire the D+ wire from the DS300 to the D+ fridge input.

If the fridge doesn't work on any power source (240V, gas, 12V) then there's something wrong. Check that the D+ is about 12V when the engine is running, and is a low voltage, about zero, when the engine stops.

Update:
I've wired the LC now to position 5 on the 6 pins connector. So LC is now constant. BTW the fridge runs fine on EH and on Gas. The issue still remains when I start the engine. I've done a few more measurements this morning.
With the fridge switched off at the panel and engine running the HC feed to the fridge from the board out of position 3 (it's not currently wired across 2 as well) is 13.9v. When I switch the fridge on, the voltage drops to around 12.6v as measured at the HC connector at position 3, after maybe a second the relay on the board clicks and the voltage drops completely to zero and the fridge goes off. There is another click and HC power is restored with a reading that ranges from a high of over 13v but very quickly drops to 12.6v before another click of the relay and the HC is cut again.
Regarding the relay on the board it is a 1038++which I assume is soldered to the board? Is this likely to be the cause or perhaps another relay in the fridge circuit somewhere?
thanks

 

[GeoffnDee]

The Electronic battery separator signals the fridge relay and it links the batteries when the alternator output is above 13.3v , maybe the 12v heaters coming into use is causing a voltage drop and switching the link and relay signal in and out.
The same battery separator signal operates an awning light relay (if you have a light fitted) to turn the light off with the engine running and perhaps the problem is in that circuit causing a voltage drop problem ?

 

[autorouter]

If you remove the HC fuse (the 30A one) so that no fridge HC current flows, the relay should click on when the engine is running, and click off when the engine stops. Does the relay do that, or does it still click on and off?

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[Cavingaz]

If you remove the HC fuse (the 30A one) so that no fridge HC current flows, the relay should click on when the engine is running, and click off when the engine stops. Does the relay do that, or does it still click on and off?

yes with the fuse out the relay operates as you say.
we have run the engine at 2500 rpm for a minute or so and then switched the fridge on. The relay remained stable for a little longer than earlier today, as the voltage on the HC held up at 12.8v before dropping to around 12.5 which seemed to activate the relay cutting the feed momentarily

 

[Cavingaz]

The Electronic battery separator signals the fridge relay and it links the batteries when the alternator output is above 13.3v , maybe the 12v heaters coming into use is causing a voltage drop and switching the link and relay signal in and out.
The same battery separator signal operates an awning light relay (if you have a light fitted) to turn the light off with the engine running and perhaps the problem is in that circuit causing a voltage drop problem ?

We have an awning light and yes it goes off when the engine is running. Not sure where that relay might be? Also where is the battery separator typically located and what does it look like - would it be the PCT Volton ZR1220

 

[GeoffnDee]

The awning light relay looks like it is in the Ds300 as does the Electronic Battery separator, the only information I have regarding the DS300 is what I found at Broken Link Removed , where you can download information at PC-100/ PC-200 DS300 section that you may find useful (if you do not have it already.)
www.apluljackelectronics.co.uk repair CBE items and it could be worth talking to them to see if they can help with information regarding the wiring of your new Fridge through the DS300

 

[autorouter]

The Electronic battery separator signals the fridge relay and it links the batteries when the alternator output is above 13.3v

I hadn't realised that the trigger for the split charge relay, fridge, awning light etc was a voltage-sensitive circuit rather than a direct D+ signal from the alternator. As you say, it looks like the fridge heater connection is causing a voltage drop, and the voltage-sensitive battery separator circuit is erroneously sensing that the engine has stopped, so it's switching off.

I don't like voltage-sensitive circuits for this reason. And also, the chances are if you install solar and charge the starter battery, the Electronic battery separator will sense the charging voltage and assume the engine is running. So it kindly switches off all your habitation circuits.

I don't know a simple answer to this problem. It would be a matter of substituting the Electronic Battery Separator output with either a D+ signal from the alternator, or maybe using a device made by Votronics, which outputs 12V when it senses engine vibration.

 

[Cavingaz]

Hi Autorouter/GeoffnDee,
thanks for continuing to try and work this one out. I'll give the folks who repair CBE units a call.
I have a local auto-electrician who I have spoken with today who happens to have a motorhome of his own.
He suggested take a new input feed and wiring in a fuse and new relay then disconnect the HC feed for the fridge from the board and wiring this to the new relay (along with a earth). Whilst this is bypassing the problem he suggested this might be a reasonable workaround.

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[GeoffnDee]

Hello Cavingaz Yes, by-passing the DS300 could be the answer to getting your new fridge electrical /control system to work as it should , Unless The CBE repair people www.apuljackelectronics.co.uk (I put the wrong spelling before) have any better ideas.

 

[Cavingaz]

Hello Cavingaz Yes, by-passing the DS300 could be the answer to getting your new fridge electrical /control system to work as it should , Unless The CBE repair people www.apuljackelectronics.co.uk (I put the wrong spelling before) have any better ideas.

thanks - I had a couple of thoughts overnight (!) I'm going to test the voltage on the inputs to the board, before going down the bypass route, as I wonder if what you mentioned in the earlier thread is occurring, in that there is a loss of voltage due to the battery separator?
I'm not clear yet where this is in the circuit,- I assume that given there is a fuse in the dis. board for the separator it sits after the main input to the board? If so then the bypass will work.(I hope).
I also may and try and look where the drop might be happening... your suggestion of the awning light - again there is a fuse for this in the Dis board I think so could remove it and see if that makes any difference. Last thought was if the earth on the fridge was sufficient when pulling on the HC, perhaps this itself is causing the issue, so maybe I could connect a temporary earth, again to see if that makes any difference. (bit of a shot in the dark!)

 

[GeoffnDee]

The other way you could look at doing this is to use the +B2 for LC and +B1 for HC (both fused) or the batteries direct to the fridge connections which would mean you would just need the D+ connection into the fridge which could be either from the Ds 300 (via the battery separator ?) or the alternator D+ signal. Then I think you will find that the switching of the 12v HC will be controlled by the fridges own built in Power control board.

 

[autorouter]

Before you go looking for voltage drops in the wiring, you could check to see if the voltage at the starter battery terminals drops when the HC load switches in. If it does, then no amount of thicker cables and extra earth wires is going to make any difference.

 

[Cavingaz]

Update -I focussed my attention on the split charge relay and also the awning light circuit. Firstly removed the 5A fuse on the board for the awning light and refitted it. Then after discovering the cover on the split charge relay was on upside down, I decided to check the earth connection. It wasn't loose but was arguable not fully under the clamp.
Anyhow restarted the engine and had 13.3v at the HC Fridge output from the board, and the good news is that it remained constant meaning the relay didn't switch!!
Problem appears to be solved and look forward to cold beers on our next trip.
Huge thanks to Autorouter and GeoffnDee who directed me to the areas to check.

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