[RE-wrenches] Float, Sell Voltages

[Maverick Brown [Maverick Solar]]

Mike,

I approached it as if the batteries where installed in a UPS system. What
constant float voltage would the batteries be charged at during grid-up, so
they would be ready for grid-down? 

I would use 53.2V for Float and for Sell. 

I also recommend to use software on the inverter to automatically bring the
batteries to Absorb periodically. Most inverters have a setting to do this
daily. The Absorb Time can be rather short since the Depth of the Discharge
is so low. Of course, I would use different Absorb settings for an off-grid
location.

I am not sure what you mean by "wide open". The Charge Controller should go
wide open so long as it can stay in Bulk mode while the inverter is selling.
I have seen settings on the CC that cause it to go into Float and then the
inverter has nothing to sell.  

I would not set the float to 55V for hours on end. The batteries might start
to off-gas. At the same time, you can adjust Sell seasonally for inverters
that do not Temperature Correct the Sell Voltage. Concorde's Lifeline AGM
Technical Manual has a temperature chart that explains the V/T relationship.

Good Luck,

Maverick

Maverick Brown
BSEET, NABCEP Certified Solar PV Installer R # 091209-26
President & CEO
Maverick Solar Enterprises, Inc.


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of
holtek at sbcglobal.net
Sent: Thursday, April 07, 2011 8:31 AM
To: RE-wrenches
Subject: [RE-wrenches] Float, Sell Voltages

Trying to tweak a couple of battery based grid-tie systems.Trying to
maximize sell back without frying or draining the batteries. Have gotten
various opinions from manufacturer's techs, so why not a few more......
Concord AGM's set now as follows:
Bulk = 57.2v
float = 53.2v
sell = 52v
It is my understanding that sell is actually a "low end float" on a grid-tie
system and to keep the CC "wide open" for sellback, I might set the float to
around 54.5v+ ( and maybe even as high as 55v?) and the sell voltage a bit
higher - (53.2?) with the understanding that if grid goes down for extended
period of time that the float must be set back to 53.2.  Any thoughts?

One other thing....with 4.3kW PV array, what would you expect as the maximum
sell wattage to show up at peak sun? (my guess is 3.3 - 3.5)



Holt E. Kelly
Holtek Fireplace & Solar Products
500 Jewell Dr.
Waco TX. 76712
254-751-9111
www.holteksolar.com

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