[RE-wrenches] concord batteries, EQUALIZE Them!

Tump tump at hughes.net
Wed Dec 2 04:39:54 PST 2009


Here is a good reason to spec out 2 volt cells, all of the manufactures have
DC input windows that will allow you to remove 2 volts while getting a
replacment.Conversly we have also installed 26/50 volt battery banks for hi
inrush loads.
Remember when you sized BB w/o charge controllers? 


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of R Ray
Walters
Sent: Tuesday, December 01, 2009 8:20 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] concord batteries, EQUALIZE Them!


Yes, I've had a 48 v system survive a dead cell (Outback inverter), but 24
or 12 v systems are done. So I guess the Sunnyboy can go down to 42 V?

R. Walters
ray at solarray.com
Solar Engineer




On Dec 1, 2009, at 3:41 PM, Richard L Ratico wrote:

> I believe the Sunny Island 5048 can be configured to remain "online" 
> with up to three cell failures. (Page 90, Sunny Island Manual). Of 
> course, it is a 48 volt inverter.
> 
> Dick Ratico
> Solarwind Electric
> 
> --- You wrote:
> I used to think that one string was optimal; until I had a single cell 
> failure take out an entire system for weeks. (try operating a 24 v 
> system at 22v! ) I now think that 2 parallel strings is optimum,  3 is 
> OK, and 4 is max. At 4 parallel strings, we start spending more time 
> looking to make sure all connectors are the same exact length etc. to 
> insure equal operation. But of course how do you account for varying 
> internal resistance of the batteries......?? I've done 4 parallel 
> strings at 144 DC of sealed batteries on an electric vehicle, but we 
> were very careful with our resistances, I even switched to smaller 
> wire, on closer strings, and calculated out the exact resistance, so 
> all strings were theoretically equal. This set actually just died, but 
> achieved its manufacturer's predicted cycle life. (B&B battery, 350 
> cycles to 80% DOD) So if you're careful, 4 strings can work well. 
> Worst I've seen was 20 golf carts paralleled in a 12 v system, (10 
> strings) and they didn't pull the main connections from across the 
> set, just connected to one end. The results were very predictable, 
> with the furthest batteries being chronically under charged, and the 
> closest ones being over cycled to a premature death.
> 
> Ray Walters
> --- end of quote --- _______________________________________________
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