[RE-wrenches] RE-wrenches] replace part of rolls battery bank

[greg egan]

Danny, My experience is if you are careful and use _equal length 
conductors_ for all 3 strings you can get good results.  The main 
problem I have with 3 strings of 6 V cells @ 48 vdc is leaving the 
customer with 72 cells to check and fill.  That's a lot of work if you 
don't have a watering system.

I totally get why you'd want to give them 2 strings in case they lose a 
battery or 2.  Most of my off grid customers live quite a ways from the 
battery store and it's not uncommon for it to take a month to get 
replacements - during the best of times.

Another option I've done is give them a string of 25 - 2V cells for a 
48V system.   You just set the charging parameters accordingly and go.  
That way if they lose a cell or two, the remaining battery bank should 
be able to keep them limping along until the replacement battery(s) show 
up.  Need to check and _make sure_ your charge controller and inverter 
can charge at the slightly higher V but usually that's not a problem.

Best,

Greg Egan
Remote Power Inc.

greg at remotepowerinc.com



Message: 1
Date: Tue, 4 Apr 2023 20:45:44 +0000
From: Daniel Young<danny at sesre.com>
To:"offgridsolar at sti.net"  <offgridsolar at sti.net>, RE-wrenches
	<re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] replace part of rolls battery bank
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Thanks all for the advice. I figured it was not worth trying on a different battery brand. I honestly needed to be able to tell them I researched it and asked my peers.

The client really uses the 3 x strings they have and did not really want to go down to 3. They are currently choosing to get the two Rolls under the prorated warranty, and hopes to get another 2 useful years out of the bank before planning to replace.

Already prepared him on the cost of the equivalent Li+ at todays prices. So he knows roughly where he is heading.

Side note: I am in the camp of trying for 2 x strings when possible (agree that 3 x strings is the absolute limit, and not the best option), simply because if a single cell goes bad, I don?t want a client with essentially nothing available until we can get a replacement and get on site. With 2 strings, they can make due at least. That?ll go out the window with Lithium though. Looking at Fortress Power for the next battery bank for this client. But we will see what changes in the market by the time it?s needed.

With Regards,
--

Danny Young
NABCEP PV Installation Professional #031508-90
Engineering Team Lead
Solar Energy Solutions
Lexington | Louisville | Bloomington | Cincinnati | Evansville | Indianapolis
513-448-5176 (mobile)
877-312-7456 (Main Office)
danny at sesre.com<mailto:danny at sesre.com>
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