Fridge and Battery Question...

[SoCal_80]

I have a 50q ARB fridge in the teardrop with a new Sears Marine group 31 AGM battery and 100w mono solar panel....All works very well but my question is this...If off for a while...lets say more than 24 hrs, the resting state of the battery may be at 12.45 volts and will obviously drop overtime. When the fridge cycles on, the voltage will drop....What is the lowest voltage I can let the battery drop to while the fridge cycles BEFORE I should worry about hurting the long term health of the battery?

thanks!

 

[jonyjoe101]

12.1 volts is 50 percent charge, thats where I aim for not going any lower. Once I reach 12.1 I start shutting down the non essentials. Even when I turn on my swampcooler which uses 7 amps (more than what a 12 volt fridge uses) I never see a big voltage drop, from 12.7 it might go to 12.5.
If the battery is dropping below 12.1 from a full charge, it means the battery is not getting a full charge. On my solar system, 240 watt panel. I bulk it at 14.4 and float it at 14.3 all day long. that way its always at maximum voltage while in sunlight. Some controllers dont stay in absorb mode (14.4) long enough to give the battery a good charge. Agm batteries can stay at 14.4 all day long with no issues. As the battery gets full it takes less amps.

 

[KevinsMap]

The battery life is certainly a concern, and the short answer for most AGM batteries is somewhere between 12.0 and 12.3 volts. Yes, is does vary by the type of AGM battery; a true marine deep cycle AGM capable of 400 cycles or more to 20% will shrug off 12.0 volts, no worries. So check the manufacturer spec. It is probably 12.2 volts or so, but be very sure.

But you have another issue to consider with a fridge; the motor. Motors really dislike operating below their rated voltage. You can burn out a motor this way, right quick, if the voltage drops low enough for a long enough duration. Similarly, a large startup voltage drop can damage the motor if that drop is low enough below spec, and it happens repeatedly. My Engel fridge has very specific specs for both; unfortunately those will not help you even a little, because the motor in your ARB is a very different design - completely different requirements.

 

[Ducky's Dad]

You can look it up on the Odyssey web site, but I'm pretty sure they say that anything below 10.6V can damage the battery. They have a chart on one of their tech pages that shows percent of charge at various voltage levels for their different batteries. All Odysseys are claimed to be deep cycle. If you regularly discharge to low levels, plan to use an Odyssey-approved conditioning charger to restore the battery to good condition after a trip. They also have a list of approved chargers on their website, and those vary by battery size.

 

[toyotech]

Good info in here. My 1st time using a 12v fridge was a few months ago when I went to the desert. Drove all day and engine of from 6pm to 7am. Cooler weather at night help keep the fridge cycling much. I also did a getto duel battery where I just brought a second battery that I hooked up together at night with jumper cables and start truck up in the morning to charge the second battery for the next night.

Just this weekend I did a trip to pismo and didn't bring a spare battery. Wasn't expecting pismo to be as hot as it was. Fridge cycle a lot but the truck was my base camp and I hooked up a portable solar system to keep it charged. Anyways by midnight it took my battery down to 11.95-12.1 when cycling and 12.3-12.4 when it was off. In the morning the solar charged my battery and by noon it was reading 13.0. Truck fired right up.

I really don't want to do a duel battery setup but this was the 1st time i experienced how much the fridge cycling so much. Hotter trips like this got me thinking I need a duel set up


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[AndrewP]

SoCal may be asking a different question. When the fridge is running the battery voltage transiently drops, then recovers to a somewhat higher resting voltage. I would not worry about the transient drop while running at all. Resting (no load) voltage is what counts here, and I would aim to stay above 12.1.