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Author Topic: DC Battery Banks  (Read 13003 times)

Andre Blanchard

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Re: Just scored a battery bank
« Reply #15 on: November 14, 2006, 10:40:55 PM »

FYI - putting more than two batteries in parallel is a bad idea. Paralleling this many is a very bad move. Certainly they will work, but you're asking for trouble.... sorry.

Not necessarily, it is done a lot commercially, but with steering diodes in each string so that they cannot discharge into each other and walk the capacity down. It works if both batteries are exactly the same capacity and internal impedance, which they never are :-))
That works better on high voltage strings where the voltage drop across the diode is comparatively small.  On something like a 12 string the 0.5 to 1.0 volt lost to the diode is a big hit.  In a low voltage string it is better to use a relay or contactor in each string so that they are only paralleled when needed during discharge and separated during charging or testing.  This requires a controller or manual intervention and so is not as easy as the diodes.
 
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It is almost as much of a problem on 110V batteries to keep the cells all in balance, but most of these are on float charge all the time and have sufficient time to equalise.

We are fitting new 110V 200A battery sets into substations at present, next one arrives Monday, we take out the old ones for recycling. The new batteries are vented lead-acid with recombination filler/vents to trap any gasses and turn them back into water which runs back into the battery.

Peter
 

I know a guy thru an electric vehicle list who uses a very simple circuit across each battery to bypass some of the current so that the equalizing can happen faster.  It is nothing more then 2 ring terminals, 2 zener diodes, and a light bulb.  He uses two zeners because it increases the amount of current that can be bypassed, the voltage is dropped across two 5 watt diodes instead of one 5 watt diode, also the temperature voltage curve of the two lower voltage diodes is a better match for the battery charge curve.
He uses it on 12 volt AGMs and says it works great relative to the cost.  He has the pack inside a closed box that is painted white inside so that as one or more of the bulbs light up a sensor inside the box turns down the charge current so as to not over heat the zeners.

The list is here. http://www.madkatz.com/ev/evlist.html
The guys name is Lee Hart.
I can look up the component values if you like, if I remember tonight. :)
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horsefly76

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Re: DC Battery Banks
« Reply #16 on: July 21, 2007, 10:07:40 PM »
It pays to shop around and or have a friend on the inside.

I bought 6 DCS100L (100 Amp Hr) AGM batteries from Interstate battery (C&D technology) that were new but had sat 6 months on the shelf so they could not be sold as "new" They relabeled them as "Econo power" the name for their reconditioned batterys. 

I paid $160 for 6 batteries that normally go for $160 each! 
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