I'm sure part of the problem is no load current circulation, but much of
the problem can be seen with a clamp on meter while charging. I've seen
parallel strings pulling 10 amps on one string and 1 amp on the far
end. Not subtle at all, and very easy to understand why it would lead
to unequal battery charging. Let us know William what you find out with
your extra shunts; we always appreciate your keen mind and desire to get
to the root of the problem in a no nonsense manner. I think resistance
checks of the batteries and arranging the batteries into strings of
equal resistance might help too, but yes, less parallel strings is better.
Ray Walters
Remote Solar
303 505-8760
On 7/18/18 7:33 PM, William Miller wrote:
Colleagues:
I believe that circulating currents in multi-string battery
installations are a major cause of premature failure of such a
system. I think it is important to monitor these currents. Most
telling would be checking these currents in an at-rest scenario. It
would be helpful to have a baseline at install and then check
periodically.
Measuring these currents with any type of DC clamp-on meter can be
inaccurate at best. In a conversation with Steve Higgins at a recent
trade show I came up with this idea that may have some merit: If an
install has more than one string of batteries, install an
appropriately sized shunt in the negative lead of each string. At any
later date you can apply any decent voltmeter with a millivolt scale
and check for battery string imbalance with some degree of accuracy.
Shunts are cheap and readily available and if you avoid the brand that
Outback uses in the Radian GSLC cabinets, they are relatively rugged.
We will be trying this in any future install with multiple strings,
although we avoid this if at all possible.
William Miller
Gradient Cap_mini
Lic 773985
millersolar.com <http://www.millersolar.com/>
805-438-5600
*From:*RE-wrenches [mailto:re-wrenches-boun...@lists.re-wrenches.org
<mailto:re-wrenches-boun...@lists.re-wrenches.org>] *On Behalf Of
*John Blittersdorf
*Sent:* Wednesday, July 18, 2018 6:24 PM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Electrolyte Dilution vs Voltage
Mac,
I was about to ditto Ray with his more common than I would like
scenario of battery death when I saw your mention of the 2nd string
not connected. It is always nice to see
a solution that is simple and should have been considered, but wasn't.
The assumption with battery issues usually is that they are actually
hooked up! I often thought that it would be worth the money to supply
a cheap AC/DC clamp meter with every installation so that a phone
consultation could quickly determine if the strings were unbalanced
and what might be the reason. Bad cells and bad connection will
usually show up in a current check and then a quick voltage check of
each battery with a load on the system will show the culprit if a bad
cell and corrosion present might find the bad connection. I use
Interstate L16's most of the time and find that the life is typically
6 years. I used to call them a 7 to 10 year battery but kept
racheting back the claim until I now call them a 5 to 7 year battery
with more if properly maintained. I have seen 10 years but it is rare.
John Blittersdorf
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