Help Needed Please

2 Posts
May 26, 2009 09:35 pm
Help Needed Please

Hi there, we are relatively new to RE, and wondered if anyone could advise on the following problem we are experiencing.

We have a 48v system, our panels are collecting normally, and we are absorbing at 57.6v daily, we average around 110 to 160 amp hours per day. Batteries are water checked and equalised regularly.

In the evening with battery levels anywhere from 50 to 48.5v the system trips out.  When we unplug our energy efficient fridge/freezer, reset and we are ok with the exception we cannot get the fridge back in without tripping the system.

Any advice or suggestion would be welcome.


Janet Gregory
97 Posts
May 26, 2009 11:58 pm
Re: Help Needed Please

Hi Janet.  My first thought is that the inverter you are using is sensing a short circuit load when the refrig/freezer compressor initially starts, and is shutting down.  Do you get a fault light on the inverter when this happens, indicating an overload condition for the inverter?  I had a similar situation with a heat pump...also uses a compressor, and so this thought registered.  Jon C.
220 Posts
May 27, 2009 01:50 am
Re: 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

2 Posts
May 27, 2009 09:24 pm
Re: Help Needed Please

Hi there Dave & Jon,

Many thanks for your ideas and suggestions.

We will check out the short circuit first.

But it seems to me that maybe we have an undersized battery bank.  We have 8 x 6v giving 232ah per battery, wired in series, so if my understanding is correct we only have 232ah storage.

This might be the answer.

We will check into this and I will let you know the outcome.

Many thanks for your help guy.

97 Posts
May 27, 2009 10:53 pm
Re: Help Needed Please

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. Smiley  Best wishes with your RE system.  Jon C.
May 29, 2009 07:55 pm
Re: Help Needed Please

Assuming that your fridge is vac powered from an inverter - is there any mention or warning in the inverters literature about using capacitor start motors?

Just a thought.

We tried using a conventional clothes washer on a DR1512 and it did fine as long as it was a Sunny day and we gave the PV time to bring the voltage of the batteries up higher than nominal. The worst time was at the beginning of the spin cycle. There were times when a cloud would move in and get between the Sun and PV array, just at the start of the spin cycle and, we weren't looking and this would cause an overload on the DR1512.
 Watching the dc amperage on our Bogart 2020 monitor while the washingmachine was going through a complete wash cycle, (about as much fun as watching paint dry) it would get to the spin cycle and stop for a moment, the battery voltage and the charge amps would go back up then the spin cycle would kick in and I watched the charging amps go from +45 down to -70. Of course the voltage went down just as dramatically. Once it was up and spinning at speed though, the 2020 would show amperage getting right to the point of a + charge and thats where it stayed until finished spinning. We stopped using that washingmachine cause we didn't want it to smoke the 1512. Cheaper to replace a washingmachine than a DR1512. Can you believe that?
« Last Edit: May 31, 2009 05:33 am by Thomas Allen Schmidt »

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