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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.
<br><br>
At 12:43 PM 9/1/2012, you wrote:<br>
<blockquote type=cite class=cite cite="">Rich,<br><br>
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.<br><br>
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.<br><br>
Larry Crutcher<br>
Starlight Solar Power Systems<br>
<u><br><br>
</u><br><br>
On Sep 1, 2012, at 6:35 AM, Rich Nicol wrote:<br><br>
Wrenches,<br>
I’m have a mental block with battery backup systems such as the Outback
Radian. Perhaps someone can help me get over it!<br>
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.<br>
An example would be a 8000 watt array using a couple of flexmax80
controllers with a string of 8 - L16 AGMs feeding a Radian.<br>
What am I missing here?<br>
Thanks<br>
Rich<br>
<br>
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