Maybe a bit off point, but when ever I install anything over two strings (and sometimes even then), I set up each string on it's own OCPD / Disco. like in the marine industry. Sometimes even with a trimetric on each string.
I have one Off Grid customer (yes, a bit of a character, but smart enough to pull it off), with an Outback VFX7248 operating at 120VAC and an old Trace SW4024. A 48V 1300Ah Solar One Bank, a 24V 4 string T105 bank and 2 48V strings of L16.. He also has three generators, one for each fuel type.. We were hired to install the 48V system. Each string (even the T105s) has it's own OCPD / Disco. The two systems can be linked either way on the AC side. (Yes, this was his design - But I do enjoy a good challenge.. occasionally). Likewise, the Solar is set up to be able to charge any bank / string (with appropriate reprogramming). Last I knew, the way he operates, He runs the 48V Outback system as his main and feeds AC to the 24V SW system and runs the 24V system like a UPS for critical loads.
The idea here is that he can use most any battery available if need be.
Of course he also has most of his basement hermetically sealed and full of doomsday provisions, a 1000 square foot root cellar, a 13,000 gal. fresh water tank buried up the hill (gravity fed), and a small airstrip out back.. just in case.
Oh, and he paid in cash but did ask if I could take gold (the office folks didn't think it was a good idea).
They're out there people. db
Dan Brown
Foxfire Energy Corp.
Renewable Energy Systems
(802)-483-2564
www.Foxfire-Energy.com
NABCEP #092907-44
-------- Original Message --------
Subject: [RE-wrenches] Mixing battery sizes in the same bank
From: Starlight Solar Power Systems <la...@starlightsolar.com>
Date: Wed, November 18, 2015 7:09 pm
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
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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