SW Tripping DC 250 Breaker [RE-wrenches]

[Roy Dyngen]

Hi Travis,

I assume that the TM is reading current going through both of the breakers.
Have you measured the current in the line where the tripping breaker is
separately?  The reason the inverter isn't giving you an "over current"
error is that the trip limit is 78 amps AC and you must be under that.  It
seems to me that the problem is following one particular breaker, which
would explain why the problem went away when you switched to the other
inverter/breaker.

Roy Dyngen

-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net] 
Sent: Thursday, September 18, 2003 9:12 PM
To: RE-wrenches at topica.com
Subject: SW Tripping DC 250 Breaker [RE-wrenches]


Hello All,

I've recently set up a weekend hunting property with a pair of rebuilt
SW4024MC's stacked for a 120/240 output.  One string of Surrette 4KS25PS
rated 1904 AH @ C/100.  Outback PSDC with a 250 amp breaker for each
inverter, a pair of 4/0 cables less than 8' long for each inverter.

Batteries have been equalized. All cells check out fine with the hydrometer
with no variance and their voltage stays within .05 volts loaded and
resting.

The inverters start and run the 2 wire 3/4 hp 240 well pump easily.
Trimetric read less the 65 amps for the well pump.  No problem with the 120
volt RV rooftop Air Conditioner either.  TM reads 80-85 amps while it's
running.  Unable to get starting surge readings with my clamp-on meter that
day since it had failed.  From my experience the TM meter doesn't read near
as fast as a clamp on with the "peak" feature.  My estimate is that starting
surges are twice I'm seeing on the TM.

If the RV air is running WHEN the well pump tries to start, the 250 amp
breaker trips on the SW4024 that the RV AC is on before the pump can start.
I can watch the amps on the TM climb to just under 400 before the breaker
trips.  Remember that the TM is a little slow so I'm guessing that means
something like 600-800 amps.  The 4/0 battery cables don't even get warm
while this is going on.  My fluke 87 was working that day and I was able to
record the lowest AC voltage as 205 from phase to phase.  The TM shows the
battery gets pulled down to the lower 21's.  I did this at least 5 times and
not once did the inverter give an over current error message.  I'm really
confused at this point because I set up a lot of stacked pairs of SW's and
they have always ran anything I've asked them to.

While on site I called Xantrex tech support.  They suggest switching the RV
air conditioner from one inverter to the other but not to reverse the well
pump.  After doing that, everything works fine?????  The tech support person
wasn't really able to adequately explain to me what was going on (I don't
think he really knew) but he blames it on the well pump.  So what's going
on?  Is it the well pump?  If it is how do I articulate this to the well
service guy and the customer?

Thanks in advance,

Travis Creswell
Ozark Energy Services, Inc.
Joplin, MO 

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