[RE-wrenches] Xantrex C-40 Drifting

[Drake]

I have a Xantrex C-40 that won't keep its settings. It is important 
that it does because it is for a maintainer array (80 W) on an AGM 
battery bank, on an AC coupled backup system. Not only could high 
voltage damage the batteries, but when the voltage goes over 30 
Volts, the AUX relay opens and the grid tie inverter is isolated from the grid.

After numerous sessions of reprogramming, Xantrex tech support sent 
me a new unit. The problem persisted as before. A new temperature 
sensor helped, but the settings still drift. It seems that rebooting 
the charge controller helps for a day or so, but then it drifts again.

The potentiometer settings are way below the calculated setting for 
29.4 V, but it still peaks in the high 30s. I check the temperature 
compensated voltages on the Outback Mate, and the temp compensated 
voltage runs high.

In a related side issue, the AUX relay of the FX inverters is not 
based on temperature compensated voltage, which makes setting AC 
coupling charge set points more problematic.

Has anyone experienced a C-40 CC that drifts in its settings. What 
would be a good (inexpensive) charge controller to accurately control 
80 W of PV?

Thanks,

Drake

Drake Chamberlin
Athens Electric LLC
OH License 44810
CO License 3773
NABCEP Certified Solar PV
740-448-7328
<http://athens-electric.com/>http://athens-electric.com/
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