Jumper parallel battery strings? [RE-wrenches]

[Gary Higbee]

Your free subscription is supported by today's sponsor:
-------------------------------------------------------------------
Claim your tickets to Universal Orlando now
http://click.topica.com/caacQ4Kbz8Qcsbz9JC9a/PermissionData
-------------------------------------------------------------------

Wrenches,

I'm attempting to make the most of a challenged battery bank, and would
appreciate your thoughts.

This bank is comprised of two 24-volt banks tied in the middle, and each of
the two banks has six parallel strings of two Concorde PVX1080's in series.
I know, bad news having six parallel strings. There were reasons for it 2
1/2 years ago (though perhaps not good enough ones!) and I'm attempting to
make the most of the way things are. This system is grid-tied, and the
batteries are for standby power.

Here's what's going on with the battery banks. Essentially all the
individual batteries (parallel strings disconnected) in what I'll call Bank
1 (48V positive) read around .5 volts higher than those in Bank 2 (negative
end). That voltage is at rest with no loads or charge for over 12 hours.
When charging or selling the difference is several volts between parallel
strings of bank 1 and bank 2. Bank 1 is hot, Bank 2 is cold. There is no
24-volt tap for any charging or loads.

So for some reason one entire bank is running high, and the other is running
low, thus some batteries are running hotter than I'd like while others are
not receiving an adequate charge. Within each bank individual batteries read
relatively close to each other--I'm not seeing much difference in parallel
strings.

Two questions:

1) How could this situation evolve?

2--MORE IMPORTANT) What is the best way to deal with it?

The Concorde technical person I spoke with had no idea what would explain
why a 24-volt bank in series with another 24-volt bank would do this.

I suggested moving things around to balance out the banks--putting higher
voltage strings in parallel with the lower, and the Concorde person thought
this was worth it. He then suggested tying the banks together at the 12 and
36 volt points (by layout they are already tied together at 24 volts). He
told me that I could do this with #6 wire, since the current would be very
small.

I thought this was a good idea, but then started looking at potential
current flows. It now seems to me that the jumpers would need to be 2/0 or
so, because we are introducing a different potential current path. For those
who are visual like me envision a mini-circuit that has batteries 1 and 2 in
series. These are in parallel with batteries 3 and 4, which are also in
series. OK, we've got two strings of two as a series-parallel system. Now if
we jumper together the electrical midpoints of the series strings we could
have current flowing through 1 and 3 or 2 and 4, or some mix. Right (or
Wrong)? If one or more batteries had a higher internal resistance we might
push a lot of current through the jumper, and our #6 would fry. Or would it?
Would the higher resistance of this jumper prevent large current flows,
because taking the course of the original series path would be lower.

WHAT TO DO?

It seems reasonable to me to rearrange things to put higher-voltage
batteries in parallel strings with lower-voltage. This should at least even
out the voltages.

What about the additional jumpering at 12 and 24 volts? Do you think this is
worth the time? I'd sure rather not have to do this unless it would yield.
Since I see very little variation in individual batteries from the existing
parallel strings I'm inclined to not do the jumpering. If there was a good
case for jumpering then what size wire makes sense--#6 or 2/0?


Thanks!!

Gary

Your free subscription is supported by today's sponsor:
-------------------------------------------------------------------
4 Free Low-Fat recipes
http://click.topica.com/caacQ4Nbz8Qcsbz9JC9f/PermissionData
-------------------------------------------------------------------

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & etiquette: www.mrsharkey.com/wrenches/etiquette.php

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------