Gary,
I have just two methods I use to test all batteries. I do a voltage
check of each battery under load with solar input shut off. You will
quickly find a battery with a bad cell or two.
It is best to do this test when the batteries are already somewhat
discharged to see clearer results. When under charge, and even floating or
with a light load, a battery with bad cells can look OK in the voltage
check. Bad cells can show up as down about 1.5 to 2 volts for each bad
cell from normal. I have also seen batteries that not only dropped in
voltage but actually changed polarity. Had a 6volt L16 read -2 VDC. That
dropped the string by 8 volts!!! Typically bad cell problems will show up
after some discharge and if a single string, the string voltage suddenly
drops down. In parallel strings the numbers get really random but other
batteries in same string will rise high to compensate for the low battery.
I have seen a 6 volt go to +9 volts and was boiling violently. (hence why
multiple strings are not the best design). If the above checks are OK,
batteries still appearing to be weak have reached the twilight of their
lives and a plan is needed to retire them. $$$$ 9 years seems about right
from my experience to see serious decline in output.
The other quick test for parallel string batteries is to use the DC
clamp meter to check each string as being roughly equal in current under
load or under full charge rate. This will find bad cells, different aged
batteries, and /or bad connections. When you lose a string, that will
definitely reduce the coasting time.
I don't check specific gravity for two reasons. It is time consuming
and moving acid around is not good in my book. I have found individual
batteries with low specific gravity readings that went on to work OK for
many years, If the batteries pass my voltage and current checks, I call
them good to go.
John Blittersdorf
Solar Guru
Rob Stubbins Solar (division of Rob Stubbins Electrical and General
Contractors)
280 Quality Lane
Rutland, VT 05701
802-775-1484 ext 512
On Thu, Sep 1, 2016 at 8:51 AM, Gary Bassett <g...@hudsonsolar.com> wrote:
> We have a grid tied battery backup system that uses 8 Sun Xtender
> PVX-2120L batteries, about 9 years old. The grid has been going out
> frequently – about 4 times in the past 3 weeks. When the grid goes out, the
> battery voltage gets too low and shuts the system down pretty quickly. One
> of the times, this happened within 4 hours. We want to test the capacity of
> the batteries and we have a testing procedure from Concorde that seems like
> it would take a lot of time. Is there a quick way to test the battery
> capacity?
>
>
>
> Gary
>
>
>
>
>
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