[RE-wrenches] AC Coupled Magnum Issue

[Drake]

Hello Wrenches,

I had an unexpected glitch in AC coupling a Magnum 4024 PAE 
inverter.  The system utilizes AGM batteries, which (according to 
Concorde tech support) have a very strict upper voltage limit.

The relay used to stop the current input from the direct grid tie 
inverter, when battery voltage is high, is controlled by a 
Morningstar Relay Driver.  The relay driver is set to shut off the 
charge at 28.8 volts.

The charger on the Magnum is set to charge the batteries to  28.6 volts.

The plan was to be able to charge batteries from the Magnum without 
tripping the AC connection between the grid tie inverter to the 
grid.  The Magnum should charge to 28.6 volts, 0.2 volts below the 
relay driver's programmed trigger point.

There is one catch to using this approach. The Magnum inverter has a 
remote temperature sensor in the battery bank. The relay driver is 
not temperature corrected. Therefore, when the batteries are cold, 
the charging voltage goes up in the Magnum.  This higher voltage 
trips the relay controlled by the driver, and disconnects the grid 
tie inverter from the grid.

I've played with the voltage set points, but the charge voltage on 
the Magnum would be too low for good battery maintenance.  If these 
were liquid electrolyte batteries, I'd crank up the voltage on the 
relay driver.  Since they are AGM batteries, it doesn't seem like a 
good idea to do that.

The work around for this at present is to;
    * Charge batteries at night in the winter
    * No problem is expected in the summer
The batteries are in an insulated box in a shed connected to the 
house. The inside of the battery box has a screened hole that is 
supposed to allow heated air into the box.  This vent doesn't keep 
the batteries warm enough to prevent the problem.

Is there a temperature sensitive, voltage controlled relay or diver 
available?  Has anyone used a temperature bulb with the relay driver 
in a way that could solve this problem? Has anyone else come up 
against this issue, and if so, what was your solution?

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/>http://athens-electric.com/
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