C40's and SW's [RE-wrenches]

[Bill Brooks]

Graham,

I believe that bulk charging is meaningless in a grid-connected application.
Since the system is floated all the time, except during a power outage, the
focus is on the float settings. I would set the bulk timer on the inverter
to 0:00 so it automatically goes to float. The default for the inverter is
53.6 Volts for float and I think that is fine for most lead-acid batteries.
The key is making sure the C-40 is set at least one volt higher. It is also
critical that all controllers and inverters have temperature compensation
probes installed and sensing basically the same temperature.

Finally, check the C-40 while operating to make sure it is not controlling.
By testing the voltage drop across the C-40 positive battery and PV array
inputs, you can tell whether it is controlling. The voltage should always be
below 0.75 Volts, otherwise it is controlling. It should only control in an
outage. Set the C-40 bulk at the same as the float, since the array should
not be bulk charging the battery anyway. Bulk charging doesn't help a
battery that stays at float all the time. It can actually hurt a VRLA
battery by overcharging it if you allow it to bulk for more than a half-hour
or so. Hope that helps. Others may see it differently but I have over four
years of grid-connected experience with my C-40s and SW.

Bill.


-----Original Message-----
From: Graham Owen [mailto:graham at solarexpert.com]
Sent: Monday, February 03, 2003 9:01 PM
To: RE-wrenches at topica.com
Subject: C40's and SW's [RE-wrenches]


Dear Colleagues,

I need some Wrench assistance with a PV service call, for the Xantrex
Power Module system (or power panel for that matter), you have to set
the C40 charge controllers and the SW inverter so that the inverter can
sell PV power to the grid without the controllers restricting current
into the inverter in the first place. I am trying to determine which set
of values works the best.

Are these good figures?

C40  bulk   56.0
     float   55.0

inverter bulk  54.0
       float   53.2

Thanks in advance!

Graham

P.S. Joel, I am working on finding your CPUC answers, I was working out
of town today.

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