Fridge not working on 12V but element and fuse ok - time for creative thinking? (1 Viewer)

[Lizbiebrowne]

Had a thought during the night!

My Thetford N145 fridge won't run on 12 V. There are three fuses on the Control Panel: two blade fuses, 5A and 30A, and a glass fuse. I've removed the blade fuses and replaced them - no change, fridge still doesn't work. I've not been able to remove the glass fuse (too tight and don't want to break it) but it looks good through the glass.

There are three cables feeding the fridge from Block 1 on my EBL100: a Blue and Brown cable from Pins 3 and 4 that carry 14.4V at all times and a smaller Yellow cable from Pin 1 that reads 14.4 V only when the engine is running.

I've removed one of the 12V element wires (the one with the female spade connector) and measured the resistance across the element - 1.5 ohms (which I understand is expected for a good element). I've measured the voltage across the element's terminals with the engine running and the fridge selected for battery - 0V.

Now for the creative bit. If I arrange to power the 12V element from independent 12V supply, bypassing the fridge's electronics, will the fridge work?

 

[Richard n Ann]

If I arrange to power the 12V element from independent 12V supply, bypassing the fridge's electronics, will the fridge work?

Yes should do, although they use a lot of power so run the engine

 

[jezport]

Check the plug connection for the element. It's common for them to arc.

 

[Lizbiebrowne]

Check the plug connection for the element. It's common for them to arc.

Where should I be looking? The connector marked by the red arrow is labelled "DC_HEAT" and the other is labelled "DC_HEAT_GND".

Incidentally I assume that, because the connectors are different, it's important that the 12V element is connected with the correct polarity. Based on the labelling on the PC board I would guess the spade connector (DC_HEAT) should be connected to the +ve supply and the screwed-in fork connector (DC_HEAT_GND) to the -ve supply.

 

[Richard n Ann]

Check for burnt connectors and burnt tracks on the PCB. I'm not familiar with that PCB but a lot have relays on that fail, the contacts get hot and it's visible when they've failed. Also check the rotary switch spades and contacts for heat damage (if there is a rotary switch) anything that carries the element current really

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[Lizbiebrowne]

Check for burnt connectors and burnt tracks on the PCB. I'm not familiar with that PCB but a lot have relays on that fail, the contacts get hot and it's visible when they've failed. Also check the rotary switch spades and contacts for heat damage (if there is a rotary switch) anything that carries the element current really

The fridge is still in-situ in the van and I don't really want to have to take it out which I think I would have to do if I wanted to give the board a good inspection. I've taken several photos of the front of the board using my iPhone inside the fridge vents and I can't see an obvious problem.

That why I'm thinking - do I need to solve a problem with the board if I can arrange for a separate, fused, power supply for the 12V element IF that would work?

 

[oldiesontour]

Disconnect the element completely,then give it a known 12v supply connect element end first then neg securely to known supply then flash POS to known supply if a spark likely element is ok,(pref via a 20a fuse) leave connected fridge should work indefinitely BUT
as it won't be via a stat will draw circa 10ah ..24/7.if you can't find /rectify the cause a simple 12v digital thermostat (£10) best via a 30a relay (£5) could be used to replace the 12v side...only reqd IF the original system was static controlled...many aren't.

 

[Lizbiebrowne]

Disconnect the element completely,then give it a known 12v supply connect element end first then neg securely to known supply then flash POS to known supply if a spark likely element is ok,(pref via a 20a fuse) leave connected fridge should work indefinitely BUT
as it won't be via a stat will draw circa 10ah ..24/7.if you can't find /rectify the cause a simple 12v digital thermostat (£10) best via a 30a relay (£5) could be used to replace the 12v side...only reqd IF the original system was static controlled...many aren't.

By static do you mean the air isn’t circulated by a fan?

Thanks for the suggestion to look for a spark. I’ll try that this weekend.

 

[oldiesontour]

By static do you mean the air isn’t circulated by a fan?

Thanks for the suggestion to look for a spark. I’ll try that this weekend.

Sorry typo thermostatically controlled

 

[RedFrame]

Also disconnect the connector at the EBL and check for evidence of arcing/overheating.

Cheers
Red.

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[autorouter]

If you implement the fridge 12V function yourself, you need to be sure that the other heat sources are off when the 12V is on. Fairly automatic with the 240V side (no 240V when driving usually), but the gas could easily be left on accidentally when the 12V is on.

 

[Richard n Ann]

I fitted one of these on my fridge

Excellent quality, Big Clive stripped one down on YouTube and likes them. They can be powered from 12v if you bypass the tiny transformer inside
I think it would be right on the limit though switching 10 amps, they only have tiny relays inside

 

[Lizbiebrowne]

If you implement the fridge 12V function yourself, you need to be sure that the other heat sources are off when the 12V is on. Fairly automatic with the 240V side (no 240V when driving usually), but the gas could easily be left on accidentally when the 12V is on.

Well success. I connected up the 12V element to the fridge's own 12V supply from the EBL100 at midday and the freezer is now at -20C (despite having read on various occasions that the 12V element will not cool a fridge, only maintain the current temperature).

I plan to install a relay operated by the D+ signal from Pin 1, Block 1 on my EBL100 to turn the 12V element on when the engine's running and another relay, also operated by the D+ signal, that turns the fridge off when the engine's running to prevent any double operation.

One surprise - the 12V element draws 12 amps, but draws them from the leisure battery. I thought it would have been cabled from the starter battery? The voltage rises to 14.4V when the engine starts so presumably the split charge relay on the EBL100 kicks in as soon as the engine starts.

 

[oldiesontour]

Well success. I connected up the 12V element to the fridge's own 12V supply from the EBL100 at midday and the freezer is now at -20C (despite having read on various occasions that the 12V element will not cool a fridge, only maintain the current temperature).

I plan to install a relay operated by the D+ signal from Pin 1, Block 1 on my EBL100 to turn the 12V element on when the engine's running and another relay, also operated by the D+ signal, that turns the fridge off when the engine's running to prevent any double operation.

One surprise - the 12V element draws 12 amps, but draws them from the leisure battery. I thought it would have been cabled from the starter battery? The voltage rises to 14.4V when the engine starts so presumably the split charge relay on the EBL100 kicks in as soon as the engine starts.

Good news don't quite get 2 relays trying to make sense of your plan surely a DPDT relay is what's reqd ?

 

[Lizbiebrowne]

Good news don't quite get 2 relays trying to make sense of your plan surely a DPDT relay is what's reqd ?

Didn't know what a DPDT relay was until this evening. Wouldn't a SPDT be sufficient as I only need to switch the +ve side?

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[oldiesontour]

Didn't know what a DPDT relay was until this evening. Wouldn't a SPDT be sufficient as I only need to switch the +ve side?

Why did you think you needed 2 relays ?

 

[StillGoing]

One surprise - the 12V element draws 12 amps, but draws them from the leisure battery. I thought it would have been cabled from the starter battery? The voltage rises to 14.4V when the engine starts so presumably the split charge relay on the EBL100 kicks in as soon as the engine starts.

Have a look at the EBL 100 manual. There’s a 20A fuse for the fridge wiring.

 

[oldiesontour]

Why did you think you needed 2 relays ?

In reply to split charge relay yes it's doing what it should,also freezer at - 20 MAY suggest that a thermostat might be required if used on 12v for long periods fridge may become a freezer..I don't know if a stat was in the original system if so it may be the route cause

 

[autorouter]

One surprise - the 12V element draws 12 amps, but draws them from the leisure battery. I thought it would have been cabled from the starter battery?

You are right, it should be drawing from the starter battery. The current path is from starter battery (20A fuse) to Pin1 of the 5-way connector, through the internal fridge relay, and out on Pin1 and Pin4 of the 4-way connector.

There are two fridge relays, wired to Pin1 and Pin4 of the 4-way. The installer chooses which one to use. If you use Pin1 of the 4-way, it is a simple on/off from the starter battery when the engine starts/stops. However if you use Pin4 of the 4-way, the fridge supply switches between starter battery when engine is on and leisure battery when the engine is off. The leisure battery option also needs a 20A fuse in the 'AES/Kompr Kuhlschrank' slot. If that fuse isn't inserted, no power for the fridge is taken from the leisure battery.

That 12V power then goes from the 4-way EBL connector to the connections at the back of the fridge. So if you use that supply directly for the heater element, it will go on and off when the engine starts/stops.

I think you will still need the relay operated by the D+ to switch off the fridge to avoid double powering. That might be more conveniently done at the connectors at the back of the fridge. One of the wires is a D+, so everything is there for wiring a relay to cut off the fridge Low Current (LC) supply from the leisure battery to the control board.

 

[Lizbiebrowne]

Why did you think you needed 2 relays ?

I plan to power the 12V element using the existing cabling. I wanted one relay to switch the power on to the 12 V element when the engine started. To avoid the possibility of either the 240V element or gas being turned on I wanted a second relay to turn off the supply to the fridge when the engine started. I now realise I can use a crossover relay to achieve both this aims with a single relay.

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[oldiesontour]

I plan to power the 12V element using the existing cabling. I wanted one relay to switch the power on to the 12 V element when the engine started. To avoid the possibility of either the 240V element or gas being turned on I wanted a second relay to turn off the supply to the fridge when the engine started. I now realise I can use a crossover relay to achieve both this aims with a single relay.

Did you determine if the 12v side has a thermostat ?

 

[Lizbiebrowne]

Did you determine if the 12v side has a thermostat ?

I fired up the 12V element at around noon on Sunday. The ambient temperature was 15 C and after about 6 hours the freezer temperature was -20 C. I was quite impressed with that and, on the occasions I looked, the element was drawing 11-12 amps so I've no evidence that there is a thermostat but there are five temperature options on the Control Panel so perhaps these only apply to EHU or gas heating. Is there a definitive way to determine whether the 12 V heating element is thermostatically controlled?

 

[oldiesontour]

I fired up the 12V element at around noon on Sunday. The ambient temperature was 15 C and after about 6 hours the freezer temperature was -20 C. I was quite impressed with that and, on the occasions I looked, the element was drawing 11-12 amps so I've no evidence that there is a thermostat but there are five temperature options on the Control Panel so perhaps these only apply to EHU or gas heating. Is there a definitive way to determine whether the 12 V heating element is thermostatically controlled?

As you are bypassing any internal wiring of the fridge which is where any thermostat would be I can only suggest either hand book information,many do not have a thermostat on 12v .If it should have a stat that you have bypassed the fridge will get to cold may even freeze if left on long enough without the door being opened,they are not really intended to be on 12v for extended periods only whilst travelling so many do not fit a thermostat.
Maybe someone on here knows the actual set up you have,my knowledge is only general not specific to your fridge, personally I would not worry about a 12v stat but try it without and if it becomes a problem with the fridge getting to cold/freezing I would fit an after market digital or mechanical later if needed ( a simple enough job and under £10)

 

[Lizbiebrowne]

As you are bypassing any internal wiring of the fridge which is where any thermostat would be I can only suggest either hand book information,many do not have a thermostat on 12v .If it should have a stat that you have bypassed the fridge will get to cold may even freeze if left on long enough without the door being opened,they are not really intended to be on 12v for extended periods only whilst travelling so many do not fit a thermostat.
Maybe someone on here knows the actual set up you have,my knowledge is only general not specific to your fridge, personally I would not worry about a 12v stat but try it without and if it becomes a problem with the fridge getting to cold/freezing I would fit an after market digital or mechanical later if needed ( a simple enough job and under £10)

Yes, I should have realised that even if there is a thermostat it would'nt operate the way I've wired it up . We generally only travel 2-3 hrs a day when we're away so hopefully freezing up the fridge won't be an issue.

 

[Lizbiebrowne]

You are right, it should be drawing from the starter battery. The current path is from starter battery (20A fuse) to Pin1 of the 5-way connector, through the internal fridge relay, and out on Pin1 and Pin4 of the 4-way connector.

There are two fridge relays, wired to Pin1 and Pin4 of the 4-way. The installer chooses which one to use. If you use Pin1 of the 4-way, it is a simple on/off from the starter battery when the engine starts/stops. However if you use Pin4 of the 4-way, the fridge supply switches between starter battery when engine is on and leisure battery when the engine is off. The leisure battery option also needs a 20A fuse in the 'AES/Kompr Kuhlschrank' slot. If that fuse isn't inserted, no power for the fridge is taken from the leisure battery.

That 12V power then goes from the 4-way EBL connector to the connections at the back of the fridge. So if you use that supply directly for the heater element, it will go on and off when the engine starts/stops.

I think you will still need the relay operated by the D+ to switch off the fridge to avoid double powering. That might be more conveniently done at the connectors at the back of the fridge. One of the wires is a D+, so everything is there for wiring a relay to cut off the fridge Low Current (LC) supply from the leisure battery to the control board.

Thank you for that information.

I starting to understand now how the fridge/EBL100 electrics should work - I hadn't realised that Block 1 was powered from Block 4 and that there's a relay to switch Block 1 Pin 4 from Starter battery to Engine battery when the engine starts. So, today, using my multimeter I read 12.7V across Pins 3 and 4 Block 1 which rises immediately to 14.4V as the engine starts and which is maintained at 14.4V when the AES/Kompr Kuhlschrank fuse is removed (and which is 0 V when the engine is not running). So definitely the power is coming from the Starter battery/alternator when the engine is running.

I will fit a relay to allow the 12V element to be powered only when the engine is running and also a switch so I can prevent the 12V element from powering up unnecessarily each time the engine is started.

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[Lizbiebrowne]

6

You are right, it should be drawing from the starter battery. The current path is from starter battery (20A fuse) to Pin1 of the 5-way connector, through the internal fridge relay, and out on Pin1 and Pin4 of the 4-way connector.

There are two fridge relays, wired to Pin1 and Pin4 of the 4-way. The installer chooses which one to use. If you use Pin1 of the 4-way, it is a simple on/off from the starter battery when the engine starts/stops. However if you use Pin4 of the 4-way, the fridge supply switches between starter battery when engine is on and leisure battery when the engine is off. The leisure battery option also needs a 20A fuse in the 'AES/Kompr Kuhlschrank' slot. If that fuse isn't inserted, no power for the fridge is taken from the leisure battery.

That 12V power then goes from the 4-way EBL connector to the connections at the back of the fridge. So if you use that supply directly for the heater element, it will go on and off when the engine starts/stops.

I think you will still need the relay operated by the D+ to switch off the fridge to avoid double powering. That might be more conveniently done at the connectors at the back of the fridge. One of the wires is a D+, so everything is there for wiring a relay to cut off the fridge Low Current (LC) supply from the leisure battery to the control board.

Some follow up questions occurred to me. Can I simply connect the yellow D+ wire to the relay and run the other side to earth? Is there a fuse already protecting the yellow D+ wire in the EBL100? Does the D+ yellow wire have any other function apart from informing the fridge?

 

[autorouter]

Some follow up questions occurred to me. Can I simply connect the yellow D+ wire to the relay and run the other side to earth? Is there a fuse already protecting the yellow D+ wire in the EBL100? Does the D+ yellow wire have any other function apart from informing the fridge?

The D+ comes into the EBL100 on Pin3 of the 5-way connector, and there is a 2A fuse on that wire, with the 50A and 20A fuses next to the starter battery. The D+ is used for the split charge relay, and also things like the step alarm when the engine starts. It's a low power 'signal' circuit, but getting it to trigger another relay coil should be OK. If the alternator light on the dashboard doesn't go out fully, then you know you are loading it too much.