[RE-wrenches] Grid tie with BB

[Drake]

I just went through the same thing, and installed a 2205 Watt system 
on 4 Concord 224 Ah (24 hr rate) batteries.  I talked with the 
Concord tech support, and was told that this was fine.  Also, look in 
the SunXtender manual.  It says a very fast charge is good and allows 
for what would be brutal charge rates on a flooded battery.

At 12:43 PM 9/1/2012, you wrote:
>Rich,
>
>In your example you have 8kW feeding a 20kWh battery (assuming 400AH 
>bat). This is about 0.4C charge rate. If these were flooded 
>batteries, I might consider limiting bulk current to 0.2C because in 
>standby use they do not need to be fully recharged in one day. Slow 
>battery charging promotes longer life.
>
>Since you mention that these are AGM I would not worry about the 
>excess current, especially in a stand by configuration. Some AGM 
>manufacturers publish that you can provide charge current up to 5C 
>without harm. For your bank that would be 2000 amps at 57Vdc! I 
>believe all good quality AGM's can withstand high bulk charge 
>currents because of the efficient way hydrogen and oxygen are 
>recombined. Controlling voltage is the more important factor. So I 
>don't think you are missing anything.
>
>Larry Crutcher
>Starlight Solar Power Systems
>
>
>
>
>On Sep 1, 2012, at 6:35 AM, Rich Nicol wrote:
>
>Wrenches,
>I'm have a mental block with battery backup systems such as the 
>Outback Radian. Perhaps someone can help me get over it!
>Essentially these systems sell back power off the top of the battery 
>bank and the array is maintaining the state of charge of the battery 
>bank through traditional charge controllers. If you have a modest 
>battery bank sized for limited use on critical circuits and a good 
>size array for the benefit of net metering I would think it would be 
>necessary to limit the current the charge controllers are capable of 
>delivering to the battery bank to prevent damage to the batteries 
>when the controllers are Bulking or Absorbing, but then it would 
>seem that we limiting the utility of the larger array. If the 
>current from the controllers was not limited they will self-limit as 
>voltage rises, plus I suppose they will mostly be in float mode 
>except when the batteries are cycled but again it seems that we are 
>limiting the capability of the array compared to a straight grid 
>tied system with a traditional grid tied only inverter.
>An example would be a 8000 watt array using a couple of flexmax80 
>controllers with a string of 8 - L16 AGMs feeding a  Radian.
>What am I missing here?
>Thanks
>Rich
>
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