[RE-wrenches] Battery idle losses; Deka AGM

[Larry Crutcher, Starlight Solar Power Systems]

Hi William,

You asked how much energy the "battery" is expect to consume. At 300 to 1200 watts perhaps you mean how much the XW's consume from the battery? The idle current? Please clarify. The battery does not consume power except for self discharge which is very small. If healthy, the 8A8D will have about 2% per month self discharge, tested by open circuit voltage. As it ages, expect that to increase. 

If you have a defective 8A8D battery(s), it will usually exhibit high surface temperature and possible valve opening during the end of the absorb cycle (57.6 volts @ 77°). Check the current going to each battery. You can do this with two clamp on DC current meters on either side of the battery in test. Current should be about 0.5 to 1 amp across the battery at the end of absorb. High current and temperature indicate a defective battery. This battery(s) will act as a load and will lower the net bank capacity at night.  BTW, I have never been able to recover an AGM from this state.

Now...some bad news. The MK 8A8D is a Deka AGM battery. We have sold and installed these 8D's for many years with few failures. Lately we are having far too many Deka's going bad in just over 1 year. Since it only has a 1 year replacement, my customers are VERY upset. After speaking with my Deka rep. last week and I have decided to advise customers to not purchase the Deka 8D's.

Larry Crutcher
Starlight Solar Power Systems



On Oct 31, 2011, at 8:20 PM, William Miller wrote:

> Friends:
> 
> I have looked on the on-line literature but I can not find this answer:  I have a client with 16 MK 8A8D batteries in 48 volt configuration feeding 3 XW inverters.  How much energy will these batteries be expected to consume at night?  We simulated darkness measured a wide range of values, anywhere from 300 watts to 1200 watts.  Has anyone measured or calculated this?
> 
> Thanks in advance...
> 
> William