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3 way Thetford fridge power consumption


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Our Pilote G600 has a 3 way fridge. On a recent trip I discovered that the charging voltage as indicated on the internal display of the vehicle (starter) battery dropped alarmingly when the fridge switched to 12v.


How much power should the fridge draw on 12v?


Should the alternator be able to cope with the fridge AND charge the vehicle battery?


We ended up running on gas only (we have crash protection on the gas cylinders) and then the battery charged properly

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I would start by investigating the charging voltages of both batteries and with fridge on and off using a decent multimeter. You may have a battery connection problem causing the low voltage issue.


The fridge will draw a reasonable current, possibly 10 Amps at 12 Volts from memory. If you look up the instructions for your model you should be able to find the exact spec.


Finally, some older models of MH wired the fridge in a short cut method, whereby the fridge was wired from the leisure battery with a second relay and often if the split charge relay connecting the leisure battery to the starter battery failed the fridge would then only run off the leisure battery and flatten that battery during driving. But this does not sound like your problem as you specifically said you were looking at starter battery voltage.


This may be an issue of the oft documented problem with failing engine ground straps!



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Brian Kirby - 2021-11-08 6:33 PM


Not an answer, but it may help if you give the year of your van, and the make and model of the fridge...


I think Tim's Pilote motorhome is a 2011 model and, if so, this advert would give an idea of its specification.




The fridge (as said in this thread’s title) was made by Thetford and the Southdowns’s photos suggest it was a Premium LCD N100 model (that was marketed in manual or automatic energy-selection versions),


The Thetford user manual for the N100 fridge provides no information on the appliance’s gas, 230V or 12V energy consumption - however, those data should (may?) be available on a Thetford label inside Tim’s fridge. That’s the case with my Rapido’s large Thetford N3150 fridge/freezer, with the label showing 190W at 12V (ie. 15.83 amps)


When a motorhome is being driven its alternator will need to power all vehicle ancilliaries (wipers, lights, heater-blower, etc.), plus charging the starter battery, powering a fridge running from 12V and charging leisure batteries. Normally (as Brian has said) this should not present problems, but if the batteries were heavily discharged to begin with (or past their best) and all the ancilliaries were on simultaneously, it might put the altenator under stress.


I’m a mite surprised that selecting the fridge’s 12V mode affects the starter battery. Historically, a 3-way fridge was wired to the starter battery, but I thought that practice would have ceased by 2011. On the other hand, it is a Pilote...

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Huge thanks for the helpful replies received. My van is indeed a 2012 Pilote. Starter battery is new and the problem was spotted having driven 500 miles or so, followed by a few days of pottering, but not with multiple starts.


I have not yet checked with a multimeter but was using the onboard voltmeter in the control panel. This is usually pretty accurate.


I have the van booked in with Marquis next week for a variety of things and have asked them to check it out. I'll post to let you know what transpires.


There was an issue whilst under warranty and the original Pilote connections were completely unacceptable, with lightweight cabling and contacts which burned out under the current load.


It's great to see how many have responded helpfully.



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timgriffiths - 2021-11-10 8:22 PM


Starter battery is new...

Has the problem only happened since the new battery was fitted?


If so look carefully around the battery for any signs of wiring not re-connected or possibly damaged, or maybe a blown fuse on the MH wiring side.



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timgriffiths - 2021-11-08 6:22 PM


Our Pilote G600 has a 3 way fridge. On a recent trip I discovered that the charging voltage as indicated on the internal display of the vehicle (starter) battery dropped alarmingly when the fridge switched to 12v...

Assuming that your Pilote’s onboard voltmeter gauge is OK, when the vehicle’s motor is running I’d expect the gauge to show over 14V (say 14.4V) for the starter-battery. readout, and I would not expect that voltage value to drop when the fridge was switched to 12V operation.




a) What starter-battery voltage does the gauge show with the motor running and the fridge not switched to 12V?


b) What starter-battery voltage does the gauge show with the motor running and the fridge switched to 12V?


The only time I’d expect to see a starter-battery voltage drop is if the motor were NOT running, the fridge takes its 12V power from that battery (and the fridge can actually be operated on 12V without the vehicle’s motor running).

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  • 11 months later...

My fridge works on mains and gas, but when on auto with engine running, the voltage as indicated on the display unit instantly drops from a charging voltage of aroud 13v to around 12v... well into the amber zone. It is, therefore, discharging the vehicle battery. Clealy the alternator os more than capable of handling the load, but someting it wrong! I raised this with Clive Mott who suggested checking the conncetions to the fridge fuse. These seemed to be OK but I put in a new fuse. It then worked beautifully... but only for a few minutes before the fault returned. Our workaround is to run on gas when travelling, but we'd rather not!

There was a fault from new and Johns Cross made new connections in the fridge itself as the Pilote ones seemed to have burned out! That solved it for ten years. I've checked the repair they did and it still seems fine.

I'm no ignoramous but don't enjoy meddling with MH electrics! Can anyone suggest a route forwards? As the gas jet may also need a clean, I'd be happy to engage the services of a mobile specialist if there is one who can be recommended. We're in central Hampshire.


ANy help/recommendations much appreciated.

Duplicate thread merged with original - Moderator.

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Hi Derek


I confess not to have seen your helpful response till now! The fault is still with us I'm afraid so I'm having to track down the cause. Charging voltage s definitely fine. New fuse 20A seemed to work intially with 12v driving the fridge and charging voltage still way up in the green zone, but fault soon returned. I may need to try to find a specialist repairer who really understands these systems.

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