Fridge operation on 12 volt

Remember, when you see people running fridges on 12v here they are almost universally compressor fridges which are designed to run on 12v fairly efficiently. A 3-way fridge draws a lot of current if you run it on 12v instead of propane as it the 12v is running a little heater in place of the propane flame. I imagine if you have a modern 3-way fridge it will have some form of battery protection circuitry, but I recall my old 3-way had nothing of the sort, and a small heater element like that will just keep draining and draining the battery until it is completely dead and fit only for the trash can.

Steve.

The thing is Jim, were not talking about doing lots of other stuff like charging low batteries, just keeping up with the 15A needed by the fridge. When that's all the charge circuit has to do then the truck can keep up with a fridge just fine.
BTW, if your alt only puts out 13.8 then there's something wrong with it. S/B more like 14.2~14.8 depending on temperature.
I and many other people I know have used 12V fridges for many years.

ScottG wrote:
Even the biggest 3 way fridges only use 15 amps so any alternator should be able to keep up no matter what is running:

6 cuft Norcold

One of the main reasons many TC folks abandoned using 12vdc for cooling is the issue of having low house batteries and running the fridge. You could have a demand of 15 amps for the fridge and who knows how much for the house batteries....
So even 20amps for the house batteries and 15 for the fridge is 35 amps which exceeds the 30 amp factory fused/relay controls for trailer/camper. Some trucks stock fusing/relay may be more.

Wire gauge considerations are also an issue. I have measured a 1vdc drop from the truck battery to the house battery just to charge it... (2x amps). So 13.8 alternator voltage drops to 12.8 by the time it gets to the house batteries and you are not going to charge very much if at all and this is not taking into consideration of a possible absorb fridge running on 12vdc.

Many TC folks have rewired and added relays/solenoids and big wire to compensate.

Jim

I agree it would charge slower but just to keep up has never been a problem for me. Neither my 82 Chev or my 93 Dodge with puny factory wires had any problem running a fridge in my TC.
This isn't the OP's problem anyway.

Problem isn't the alternator keeping up, it is the factory wiring usually will not carry 100% of the frig 12v load.

When checking battery level by voltage, you need to disconnect all loads, wait a few minutes for the battery to equalize, then measure the voltage. When the load is still applied, the voltage will be much lower than true voltage.

However, a group 24 is only rated at 90A/hr. 14A for two hours is 28A/hr or about 31% of battery capacity. If the fridge was still on when voltage was measured, 11.77 would seem about right.

Even the biggest 3 way fridges only use 15 amps so any alternator should be able to keep up no matter what is running:

6 cuft Norcold

Run the refer on LP and 120 volts AC when available.
You could run on 12 volts DC only when the truck is running. It could be difficult for the truck to keep up, if you are running with lights on, heater on, radio on and wipers on.

The truck shouldn't have any problem keeping up with the fridge on 12V while it's going down the road because it's only drawing 10~15 amps but when your stopped then that's a pretty good load for the battery alone. The amount of time your battery lasted is normal but I would switch it to gas anytime you stop for any length of time.

Not too many people run their fridge on 12v because it uses too many amps. You could use 12v while driving only if you alternator can keep up, and that's asking a lot. I am able to use 12v only while driving because my truck came with a heavy duty 200 amp alternator.