[RE-wrenches] 10 kW Trace System

[Peter Parrish]

This one is for the grey beards.
 
I was asked to look at a slightly funky, ca 10 year old, Grid-tie Battery
Back Up System, with 2 ea SW5548s, 100 ea Astropower Ap-100s, 3 ea C-40 (I
think) charge controllers, 3 ea strings of 4 ea Sun Extender PVX12100T (100
A-hr) batteries. The PV modules are wired in strings of four. II strings
reside on a west facing garage roof (3:12) and 14 strings reside on a south
facing main house roof (3:12). Strings are combined using Pulse combiners
with up to 8 PV circuits on the input. Everything was buttoned up in rain
proof cabinets in such a way as to make inspection (including observation of
LCD displays) very difficult. Not a lot of wire marking, etc.
 
The client called us to look at the system. Prior to my arrival, the client
had done two things:
-          One battery string had been decommissioned due to a bad battery
and
-          One of the inverters had been put into bypass because of
fluctuating output and noise 
 
We put the inverter in question "on line" and sure enough the critical loads
(bathroom lights for example) began to fluctuate on a ~1 sec interval. The
inverter also had a fairly loud continuous hum punctuated by a "boing" which
occurred at exactly 1 sec intervals. After a while (10 minutes) the
fluctuations went away and so did the "boing" but the inverter still
exhibited a loud hum.
 
I spent a lot of time looking at the PV strings, circuit combiners and the
inputs to the CCs. Everything actually looked okay, except for one loose PV
circuit input at a circuit combiner. Due to the way the inverters and CC are
installed in the cabinets (CC in the back and inverters face up in front of
them), It is very hard to trace wires and view displays/LEDs.
 
The AC voltages appeared okay (117.5 to 119.6) and here is what we got on
the AC currents:
 
Inverter A (funky one)
AC Hot In1, 9.58 A 
Neutral In 1, 10.09 A
AC Hot Out, 1.47 A 
Vdc=56.4 V
 
Inverter B 
AC Hot In1, 7.2 - 8.4 A
Neutral In 1, 8.6 - 9.4
AC Hot Out, 1.57 - 1.86 A
(these currents were fluctuating and my clamp on ammeter has about a 1 sec
settling time) 
Vdc=54-64 V
 
 
Where do I start with this system? Obviously out of warranty, but people on
this email list seem to like these old inverters. What do the symptoms
suggest? Is there a company that repairs these inverters? What kind of
additional diagnostics should perform? The customer would like to keep the
battery back up functionality (which we didn't test), so for now I would
like to focus on determining the problem(s) and fixing it (them).
 
- Peter
 
Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

 
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