i know this subject has been done to death, but need a simple answer. I have a 100ah d/c battery, myportable fridge draws approx. 2amps. how long should it power the fridge before it reduces the battery to 50% capacity? thanks in advance.
You may have a 100 ah battery at new but with age and cycles you may already be down to a much smaller capacity which you have to allow for.
Best to monitor battery voltage and don't go below 50% =12.2 v with no load, the time you run the fridge to reach this at a constant 2 amp rate will determine your capacity of the battery.
A better measure of the batteries 50% mark is 12v under a load of no more than 5 amps per 100Ah advertised capacity. A sulphated battery will bounce back to better than 12.2v no load but drop to 11v or less under load resulting in a burnt out fridge compressor if it uses one of the Chinese Danfoss copies. Bob from Mildura can repair them but a replacement battery is a lot cheaper so best to either have a low voltage cut off set to 12v or at least a monitor that you can keep an eye on.
T1 Terry
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I was hoping that those of you with more experience than me might have come up with a reasonable compromise for setting the LVD. The real unknown that might make such a rule of thumb improbable is each and every system will experience different loads. I think I will begin with erring no the side of being safe and set it a 12 volts even. If the thing is always tripping I will consider a lower figure if it never trips I will consider a higher number. For the uninitiated out there you might be wondering what all the fuss is about. Stated simply discharging your battery bank too deeply is very detrimental. Consider the attached graph. Ignore the little comment tags this was converted from a PDF file. The graph is also a depiction of a AGM battery, expect less from the standard golf cart battery. Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50% The most practical number to use is 50% DOD on a regular basis. This does NOT mean you cannot go to 80% once in a while. It's just that when designing a system when you have some idea of the loads, you should figure on an average DOD of around 50% for the best storage vs cost factor Now I for one am not willing or perhaps not able to constantly monitor the battery bank voltage to ensure the best life for my batteries, hence the load controller.
so best to either have a low voltage cut off set to 12v or at least a monitor that you can keep an eye on.
