Help Needed Please

 
hi there janet,

 sounds like things are running nicely on the charging side of your system.

 it's hard to guess exactly what your setup is. looks like about a 1.5kw pv array and producing/using about 110-160ah @ 48 volts nominal. that should make our battery bank in the neighborhood of 600ah @ 48vdc? does that sound about right. that would be 12 of the 200ah 12v batteries or 24 of the 200ah 6v batteries?....these battery bank sizes are based on a ~%20 depth of discharge. (%80 remaining) some schools of thought go with a ~%50 battery discharge limit and work them harder and replace them more often. that might make the bank about 8 of the 200ah 12v batteries or aprox 16 of the 200ah 6v batteries.

 i think jon is right on with the with the initial start of the compressor being the culprit. but your description of it happening at night smells more like voltage "droop" or sag, in that it does not drop out during the day when the pv array is holding up our voltage?

 one of the causes of dc voltage droop, besides an undersized battery bank is the size and length of the inverter cables. it is well worth the small effort and added expense to oversize this connection as well as the lugs and other battery cables.

 one other thing we might look at is giving the fridge its own separate ac branch circuit.

 hopefully we can find out more of what your running. ie: battery type and size, inverter model, fridge/freezer make, other loads, battery/inverter cable size and length. any inverter alarm codes. and are we using a battery monitor?

 sorry for all the questions..these kinds of problems are sort of fun to have a stab at and i'm sure we will get other folks interested in the "cure" for this one.

hang in there!
kind regards, dave

Hi again, Janet.  I did not mean to imply that you have a short circuit condition in your refrigerator load, but merely that it may appear as a short circuit to your inverter.  I don't know what inverter you have, so I can't make a judgement there.  When a refrigerant compressor first starts up, it draws an enormous load current, and the inverter may interpret this as a short circuit condition.  I would be hesitant to say that you have insufficient battery capacity, but more likely, an insufficient inverter surge capability.  In my case, I am running a 48v system as well, with 6 x 16 6v batteries, each with a capacity of 375 amp/hours, and inverter capacity of 11,000 watts, but this means nothing when I try to start up a heat pump compressor that draws a starting current in excess of 55 amps (off scale on my AC ammeter).  The inverters just go into fault mode and shut down due to excessive surge current. My solution was to operate the heat pump on its own dedicated line from utility power, and removed it as an inverter load.  My refrigerator is an older model (not high efficiency) and runs fine off the inverters.  This may or may not have anything to do with the problem you are having, but its my 2 cents worth anyway.   Best wishes with your RE system.  Jon C.