12V Fridge Supply - from which battery? (1 Viewer)

[Lizbiebrowne]

I’m still at the planning stage for installing my B2B charger together with needing to replace my fridge which currently doesn’t work on 12V. I suddenly began to wonder where the 12 volt supply comes from the fridge and whether, if it came from the leisure battery, it would take a big chunk out of my 30 A B2B charger (I estimate the new fridge’s element will need about 150W or around 12 A of my 30 A). Am I right in thinking the fridge’s 12 V supply should come directly from the starter battery (suitably fused) and initiated by a D+ signal of course?

 

[68c]

Assuming it is not a compressor fridge, the 12v supply does come from the starter battery. However, as you suggest, this only happens when the engine is running triggering the D+ signal to connect the fridge. Of course the starter battery is being constantly charged at this time to replace the load from the fridge. For this reason some people prefer to state the alternator supplies the fridge, as it's output voltage is higher than the starter battery.

 

[funflair]

I believe that the fridge can be supplied from either starter battery or habitation battery, on our last van and this one it certainly came/comes from the habitation batteries but switched via a D+ signal when driving, if you select 12v manually it comes from habitation and will seriously deplete the batteries.

 

[Clivefog]

On many fridges there are 2 feeds one from leisure battery to energise control panel.
The other heavy duty one from D+ signal.

 

[StillGoing]

My Hymer fridge can be powered from the leisure battery when the engine isn’t running.

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[Sleeveless]

On many fridges there are 2 feeds one from leisure battery to energise control panel.
The other heavy duty one from D+ signal.

D+ is only a signal wire and "ground switched" on most PSA vehicles, so not capable of providing any power as such, but capable of switching a relay.

 

[Bessy765]

Our Dometic three way fridge freezer draws 17 amps on 12 volt

 

[Pausim]

On my Carthago with a CBE DS the fridge is powered by the leisure battery. In standard form it is of little importance because the D+ signal not only activates the fridge but links the engine and leisure batteries through a split charge relay. It only becomes evident when the split charge is disabled, to allow for a B2B, then the fridge load falls on the leisure battery alone.

 

[Lenny HB]

You need 3 connections to the fridge.

A low power feed from the leisure battery for fridge electronics.

A high power feed from the starter battery this needs to be switched via a relay which is switched by the D+ from the alternator so the fridge only runs from 12v with the engine running.

A D+ connection to the D+ terminal on the fridge. This is a safety feature so the fridge won't light on gas for 15min after the engine has stopped.

If you want to run the fridge from the leisure battery you can use a changeover relay with the N. O. contact connected to the starter battery & the N. C. contact connected to the leisure battery. This is what they do on a lot of German vans.

 

[autorouter]

together with needing to replace my fridge which currently doesn’t work on 12V.

Are you sure that it needs replacing? The fridge has a main coolant circuit, with a special liquid/gas mixture. When a small amount of heat is applied to the lower corner of the coolant circuit, it makes the coolant circulate and causes cooling. The small amount of heat can be from a 12V heater element, a 230V heater element or a small gas flame. If the fridge works on any one of the heat sources (12V, 230V, gas) then the coolant circuit (the expensive bit) is working fine. If it's not working on 12V, then it's a wiring fault, a heater element failure or maybe a control board fault. A wiring fault or heater element failure is usually easy to fix and not expensive.

I suddenly began to wonder where the 12 volt supply comes from the fridge and whether, if it came from the leisure battery, it would take a big chunk out of my 30 A B2B charger (I estimate the new fridge’s element will need about 150W or around 12 A of my 30 A). Am I right in thinking the fridge’s 12 V supply should come directly from the starter battery (suitably fused) and initiated by a D+ signal of course?

While you are wiring in the feed to the B2B, you could also run another wire for the fridge. You could run it from a relay triggered by the D+. It would take power from the alternator/starter battery while the engine was running, in a parallel path to the B2B, so that the full 30A of the B2B was available to charge the leisure battery. It should be fused, of course, maybe with a 20A fuse near the starter battery end.

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[Lizbiebrowne]

Our Dometic three way fridge freezer draws 17 amps on 12 volt

That matches with my experience; when on 240 V and powered via the inverter my KS Energy app reports 17 A being taken.

 

[Lizbiebrowne]

On my Carthago with a CBE DS the fridge is powered by the leisure battery. In standard form it is of little importance because the D+ signal not only activates the fridge but links the engine and leisure batteries through a split charge relay. It only becomes evident when the split charge is disabled, to allow for a B2B, then the fridge load falls on the leisure battery alone.

Yes, that's what I wanted to avoid, I didn't want to lose half the output of my B2B to running the fridge. Taking the high power feed from the starter battery as Lenny HB and others have indicated makes sense. I guess that that may already be the case with the EBL100 unit in my Hymer but I'll need to make sure.

 

[Lenny HB]

I guess that that may already be the case with the EBL100 unit in my Hymer but I'll need to make sure.

Hymers are normally wired with the fridge running from the starter battery with the engine running and the leisure battery with the engine stopped. The fridge relay is a changeover relay inside the EBL.

 

[Lizbiebrowne]

Are you sure that it needs replacing? The fridge has a main coolant circuit, with a special liquid/gas mixture. When a small amount of heat is applied to the lower corner of the coolant circuit, it makes the coolant circulate and causes cooling. The small amount of heat can be from a 12V heater element, a 230V heater element or a small gas flame. If the fridge works on any one of the heat sources (12V, 230V, gas) then the coolant circuit (the expensive bit) is working fine. If it's not working on 12V, then it's a wiring fault, a heater element failure or maybe a control board fault. A wiring fault or heater element failure is usually easy to fix and not expensive.

While you are wiring in the feed to the B2B, you could also run another wire for the fridge. You could run it from a relay triggered by the D+. It would take power from the alternator/starter battery while the engine was running, in a parallel path to the B2B, so that the full 30A of the B2B was available to charge the leisure battery. It should be fused, of course, maybe with a 20A fuse near the starter battery end.

No, I'm not sure but I'm losing confidence in the fridge. The 12V part has never worked (and I understand there can be a problem with the Thetford N145 with the fuse overheating and damaging a board somewhere - but I don't know where) but its always been OK on 240 V and gas. However, the last time I came to use it I couldn't turn it on or, rather, the green light wouldn't light up on the Control Panel although the fridge did come on and work OK. In fact the only way I could turn it off was to remove the EHU or pull the 20A fuse from the EBL. The other lights on the Control Panel, the AES/Mains/Gas/12V set and the Temperature, also don't light up and the button changing the power source also has no effect - it's always on 240 V. Also the fridge light doesn't work, so I suspect there may be a problem with the Control Panel - it looks something may have been spilt on it in the past (see photo)? My plan was to take the fridge out and have an unimpeded look at it to see if there's a poor connection somewhere.

 

[autorouter]

Taking the high power feed from the starter battery as @Lenny HB and others have indicated makes sense. I guess that that may already be the case with the EBL100 unit in my Hymer but I'll need to make sure.

There's a wiring diagram at the end of the manual. It's here if you haven't got it already:

https://res.cloudinary.com/lci-cloudinary/image/upload/v1694803226/lippert-eu/support/power-on-board/pdf/anleitungen/911/9110503/911503_20050112_EBL100-2_BA_EN.pdf

The 5-way connector is an input into the EBL, a separate feed from the starter battery for the fridge, also the D+ input signal. This starter battery feed has a 20A fuse, near the starter battery. Next to the big 50A fuse that's the feed for the split charge relay.

The 4-way connector is the output to the fridge. Pin1 or Pin4 for the power to the 12V heater element, Pin3 is the fridge negative, and Pin2 is the D+ signal for the fridge.

If the wire is to Pin4 (not Pin1) then there is an extra facility to run the fridge from the leisure battery. Not very useful normally, but handy when fault-finding or when gas can't be used, as on a ferry or in the Tunnel. If you put a 20A fuse in the 'AES/Kompr Kuhlschrank' slot, then the fridge will work on 12V when switched manually. That may allow you to rule out a fault with the heater element, or the wiring to the starter battery, or the auto-switching bit.

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