[RE-wrenches] Small battery bank vs too large array

[Jason Szumlanski]

I could be wrong, but I thought the FM60 and FM80 charge controllers have
adjustable current limits that apply to battery charging, and I think when
integrated with GVFX inverters in sell mode and a Mate controller, you will
be able to accomplish what you need to do without a relay. I always thought
when the charge controller indicated GT Mode and was in bulk charging mode
that the current limit would be essentially ignored because the battery
voltage is above the sell voltage and any available DC current would be
inverted and sold to the grid. In other words, the batteries are full, so
they are not being charged - the FM60 and GVFX communicate and balance the
current available for selling.

You may want to talk to Outback about that, because I don't think it is
documented all that well, and again, I could be wrong. I've never installed
that much solar on a small battery, so it never came up! Incidentally, I
have someone that came in today looking for a 5kW grid-interactive system
and a small battery to handle critical loads. I was leaning to an AC
coupled system to get away from the issue you describe, but now I am
second-guessing that theory. I'd be interested to learn what you discover.

Most inverter manufacturer's have a minimum battery size, but that
seemingly is there to address the maximum possible current out of the
battery, not the charging rate because that can be limited, too.

Jason Szumlanski
Fafco Solar


On Thu, Jul 19, 2012 at 5:20 PM, Drake <drake.chamberlin at redwoodalliance.org
> wrote:

>  Hello Wrenches,
>
> Where can I get a device that will measure current through a shunt and
> create a signal to trigger a relay?
>
> We want to be able to use a 2 kW array with four, 200 AH sealed batteries
> on an Outback system.  2 kW of PV would be too much amperage for the
> batteries.  The idea is to open relays to disengage strings in conditions
> of high current to the batteries.
>
> The reason for this is to create backup systems where power will be
> abundantly available when the sun shines. The system will normally connect
> to the grid, except during outages.  In normal charging conditions the
> power will go straight to the grid.  When the grid is down, power will be
> available for loads and battery charging, but batteries will be protected
> from overcharge?
>
> Any suggestions on ways to accomplish this are welcome!
>
> Thanks
>
> Drake
>
>
> Drake Chamberlin
> *Athens Electric LLC
> OH License 44810
> CO License 3773
> NABCEP Certified Solar PV Installer
> 740-448-7328
> *http://athens-electric.com/
>
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