The battery engineers at the outfit that first taught me how to install
using buss bars cabling individual series strings in parallel to the buss
bars were also adamant that using that configuration would allow for
different size and capacity batteries to be installed in the same bank. I
also questioned them as you guys did and they assured me it would work. I
never did try it but I was also very satisfied with the stability of my
entire bank (12 series pairs paralleled through cables to +/- buss bars).
The bank voltage never varied much more than 1/10 volt differential from the
time I installed them until I sold the house a few years later.
Tom
-----Original Message-----
From: Ray Walters
Sent: Wednesday, November 18, 2015 5:18 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Mixing battery sizes in the same bank
Even if it works for short term testing, I would imagine long term
issues that would require more frequent equalization, and shorter cycle
life.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 11/18/2015 5:09 PM, Starlight Solar Power Systems wrote:
Just when I thought I was becoming a battery guru, this came up: A
customer asked me if he could purchase two different size 12 volt Lifeline
(Concorde) AGM batteries and connect them in parallel. Of course I told
him this was a bad idea and all his parallel batteries should be same
make, age, size. A few days later he called me back and said he talked to
Lifeline battery and they told him it was fine to mix any size of their
batteries together. Knowing that people sometimes hear wrong, I called
Lifeline to inquire. The answer, "yes, you can mix any of our batteries in
parallel. We have tested that and Concorde tested it and it’s no problem”.
Stunned, I asked him if this was in writing anywhere and he said no but I
could test this myself. So battery wrenches, what will happen if I have an
8D at 255AH paralleled to a group 24 at 75 AH and discharge this to 80%
DoD? How can this possibly be OK for the 75AH battery? And why would a
battery manufacturer say this?
Larry
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