Newbie fridge question

[Woodster]

Another newbie question regarding compressor fridges in continental motorhomes how do you get on when you leave your van for five or six hours when you have no gas supply to fridge or no EHU I assume you leave it on the leisure battery but how long before battery goes flat. Years ago when we went to the nec show after only having the motorhome for a few weeks I forgot to switch over to gas and must of left fridge on leisure battery obviously when we came back flat battery all round 2hr wait for the AA.

 

[wiljoy]

Compressor fridges can drain your battery very quickly. If you intend to be off grid it may be best to fit a solar panel which will keep your leisure battery healthy.

 

[68c]

You seem to be mixing up two kinds of fridges. Compressor and Absorption.
The compressor fridge has a pump and needs an electrical supply, this should be from your leisure battery not from the engine starter battery so leaving it on should not flatten your starter battery. When on Electric Hook Up the van battery charger will keep the leisure battery topped up.
The absorption fridge has no pump and so it is silent, it works through a chemical process using a small amount of heat. The heat is provided by a selecting a small gas pilot light, or by a 12v heating coil which only works when the engine is running, or by a 240v heating coil.
First determine which sort you have.

 

[TheCaller]

A 3-way absorption fridge using the 12v supply as its heat source uses far more power than a compressor fridge does over the same period. Leaving a compressor fridge running while you go round a show shouldn't be a problem.

 

[Woodster]

Thanks 68c
Our new van has a compressor fridge our previous van was an autotrail Cherokee which had a three way fridge EHU L Gas. So I take it that was an absorption fridge. Told you I am a novice. Mind you that was 10 years ago.

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[68c]

Never had a modern compressor fridge so I defer to TheCaller.

 

[autorouter]

I forgot to switch over to gas and must of left fridge on leisure battery obviously when we came back flat battery all round 2hr wait for the AA.

Usually the fridge runs from the leisure battery not the starter battery when the engine is not running. There should be a relay that switches it automatically. This is specifically to ensure that the starter battery does not go flat. Some MHs have a manual override switch, which can of course be forgotten.

 

[Richard n Ann]

Absorption (3 way fridge) will use about 10 amps at 12v.

Compressor fridge uses about 3 amps at 12v.

 

[Woodster]

Thanks to all Funsters for all your help with my post. Great to know advice is not far away for us Newbies.
Very much appreciated. MIck.

 

[Graham of Madrid]

So are all modern 3 way fridges of the absorption type ?
I'm sure my fridge only works on 12 v with the engine running and that it won't run from the leisure battery when the engine is off. Does that sound right ?

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[Richard n Ann]

So are all modern 3 way fridges of the absorption type ?
I'm sure my fridge only works on 12 v with the engine running and that it won't run from the leisure battery when the engine is off. Does that sound right ?

Yes you're right, twice ?

 

[DBK]

So are all modern 3 way fridges of the absorption type ?
I'm sure my fridge only works on 12 v with the engine running and that it won't run from the leisure battery when the engine is off. Does that sound right ?

An absorption fridge just require heat to make it work. The "three way" bit is a reference to the three sources of heat they can use: 12 or 240 volt or gas.

 

[Allanm]

So are all modern 3 way fridges of the absorption type ?
I'm sure my fridge only works on 12 v with the engine running and that it won't run from the leisure battery when the engine is off. Does that sound right ?

Your absorption fridge will use 12v when the engine is running, gas when it’s not and mains when it’s hooked up to the mains. It will either switch between the 3 sources automatically or you will need to do it yourself. Most non auto switched fridges will however automatically switch to 12v when you start the engine but you will have to select gas or mains yourself when stopped. They generally won’t run on 12 v when the engine is off.

 

[autorouter]

The problem with running an absorption fridge from the leisure battery when the engine is stopped is that it takes 10 to 15 amps. If you have a 100 amp-hour battery, and you want to limit it to 50% discharge, then it will only last for 50/10 = 5 hours. In reality it's more than that, because the element is not actually on all the time, because the thermostat kicks in and switches it off maybe half the time. But basically it can completely drain a battery if left on overnight.

Because of that problem, most MHs are wired so that it's not possible to run the fridge from the leisure battery. However it can occasionally be useful - on a ferry crossing (gas flame not allowed), or when the gas has run out and you're parked for a few hours on the way to a campsite.

It's not easy to run an absorption fridge from solar power. You'll need about 200 amp-hours of charge per day, and for that you'd need at least 500 watts of panel, even in the height of summer