Thread: Fridge Battery Cutoff

I understood that 10.5V was considered 100% discharged and an AGM battery would withstand around 200 100% discharged cycles. The specification sheet for any given battery will show how many 100% discharged cycles it can withstand. I thought I had the spec sheet for my AGM but haven't found it quickly.

If you have a Waeco fridge (as I have), they all cut out at 11v to preserve your battery. You'll find it a PIA if you have it cutting out much higher than 11V as you'll find your beer warm and food going off all the time as we did when we had a voltage drop problem due to the cabling not being heavy enough for the distance from the 2nd battery in the vehicle to the cargo area.
I've regularly run my sealed ordinary (not AGM)deep cycle downt to 9.5v and no problems getting it to charge again, I've been using the same battery in the camper for ages (3 years plus).
We now run all LED lighting around the camp so as to reduce battery drain also.

PS: once we get the battery down to where the fridge won't run, we connect it to the 2nd batter in the vehicle if we're not going to be moving the camper.

I think you will find that 11v is OK. Remember this is measured at the fridge compressor not the battery. As the compressor tries to start during its cycle it draws quite a bit, the power lead for these fridges is not real heavy so voltage drop between the battery and compressor is actually quite high – especially if it runs through a cig light conection. My Evacool will run off the battery in the car until it cuts out, at that point the car will still start – I tested this several times to decide whether I wanted a 2nd batt in the vehicle for day trips.

As Wardy suggests you may be better off concentrating on what else is running of the battery overnight.

Hi Gary.

I'm running with what was in the vehicle when we purchased it, and have yet to finalise my re-hash of the setup ...

.. however, what I notice is that when my fridge (ARB 47L) goes in to low voltage shutdown (set at 10.5v), the voltage at the aux battery in the engine bay reads around 11.6-11.8v .... 1.1-1.3v voltage drop.

Fridge is plugged into the rear aux power socket in the back, and at the fusebox the supply has been disconnected from the starting battery and rewired to the aux' battery ... obviously the wiring from the fusebox to the rear aux socket is way too light, but it works in my favour with the LV cut-out at 10.5v to not take the aux' battery down below approx' 11.5v.

I need to upgrade the wiring to that aux' power socket.

50A/Hr wet lead acid deep cycle battery. Fridge & 2x LED camping lights only and depending on ambient temps, current setup is good for 1-1.5 days before LV shutdown.

Thanks for all the responses - looks like they are really not needed.

My fridge does not run from the starting batteries at all and is only about 3 feet from the aux battery. The battery when the engine is off only feeds the battery and a clock nothing else. While the starter motor runs off 24v my electronic ignition (and the exciter coils in the 12v alt) do run from the aux battery - however I have a 24v -12v power supply if the aux battery were to be totally flat. But I normally also carry a self contained 12v pwer pack for emergencies.

I haven't let the fridge switch itself off as yet so I might try just to see that it does work as advertised and if it does then i will not worry about an additional cut out.

Cheers

Garry

In our set-up the fridge also cuts out at 11 volts. Having said that, we can still start the car the next morning on the same battery on which has the fridge will no longer run.

Erich

Hi Garry and as above, and something to try, to see what your battery is actually being discharged down too low.

Park your vehicle where you can get at a battery charger if you need to and just run your fridge till it trips.

Most vehicles can easily be started using a cranking battery with 11.75v and modern vehicles will often start from as low as 11.5v.

But in your case and for the benefit of getting a long life out of any cranking battery, see if it drops below 12.0v, if so, then charge the setting on your fridge.

But, it is amazing just how much voltage drop occurs through a few metres of thin wire and this will happen even when there is a low current draw like your fridge.

Cigarette lighter power sockets are designed, as the name implies, to power a cigarette lighter. These devices will work form quite low voltages, so vehicle manufacturers don’t need to factor in voltage drop when they wire their vehicles.

Then along comes the fridge manufacturers and, knowing how most vehicle power sockets are wired, they factor in the voltage drop and you then have a fridge that cuts out at 11v at the fridge but it is highly likely that the voltage at the battery is still in the 12v range.

So carry out your test an see what you come up with.

Thanks for the good advice - I am not so worried about getting the car going if the aux battery gets flat as it is completely separate for the cranking system but it does power the coil and electronic ignition but I can 12v from anywhere to get. In an emergency I can tap off one of the starting batteries for a start and likewise even though the cranking circuit is 24v I have found that jumping to one of the 12v starters from the 12v aux provides enough oomph to crank.

What I am worried about is battery maintenance on the aux 12v (105Ahr Allrounder). I accidentally let it get a bit low last year when the truck was off the road and even "shocking" it back to life with 12 amps for a short period and then letting the charger do its automatic thing it only ever gets back to 13v and tends to hang on at 12.5v (measured at the battery). My ebay fridge is actually uses very little power (about the same as the brand names)but the cutoff is set at 11v and non adjustable.

Likewise in the RRS - I have not done any electrical work on it at the moment - the fridge works OK from the switched 12v in the rear and the small wiring does not seem to impact on the operation of the fridge. From what you have indicated that if the fridge was to turn off at 11v there should be enough to start and run the cars systems.

In due course I will need one of you systems to run one or two batteries under the bonnet, as well my camper with additional heavy duty 12v plugs in the rear wired direct from the aux battery - but for now things to do in the future.

Cheers

Garry