Ground fault [RE-wrenches]

[William Miller]

Rick:

Sorry I didn't answer this question sooner, I have been meeting some
deadlines.

The PV modules are old Cariso modules mounted in racks of 8.  Each 8 are
wired in series for and OC voltage of about 50.  SC amperage was measured
and averages between 2 and 2.6 amps per rack.  There are 12 racks connected
to the charge controller for a maximum total short circuit amps of about
30.   This should be well under the approved rating for this unit.

It seems unlikely that 30 amps could fry the SB50.  If, however, the fault
current was from the battery bank, I wonder why the 60 amp breaker between
the battery and the SB50 did not trip?

The damaged SB50 is on its way to you.  Unfortunately, the circuit board
was so fragile that the slightest tug on the wires disintegrated a good
portion of it.  I always assume fire damage will travel upwards, and
significant damage is seen about 1.5 inches above where the display cable
plugs in, so I speculate the damage could have started lower down than
where the shunt is.

Thanks for considering all of the data that is developing in this.

William Miller




At 05:44 PM 11/14/02 -0800, you wrote:
>I have talked to William Miller on this several times and have reviewed
>communications on the wrenches and information on his site. The shunts in
>the SB50 between Bat- and PV- can easily carry the 50A continuously. I don't
>see at this point how a properly sized system with 40A of Isc could cause
>this. Looking at the photos and circuit diagrams it's somewhat hard to be
>certain exactly where it all started inside the SB50. A PV input short can
>take out the FET's in an SB50, but we have never seen anything like this
>before. The shunt area of the board in the photos is quite burned. This
>makes me wonder how much PV was actually connected to the controller. Also,
>48V PV's seem high for a 24V system and I wonder if the modules properly fit
>within the 57V max input voltage spec of the SB50. I would agree that PVGFP
>would have certainly stopped the situation from progressing as it did.
>
>Rick Cullen
>RV Power Products, Inc.
>Providing quality MPPT solar charge controllers
>Phone 760-597-1642 x102
>Fax 760-597-1731
>
>mail to: rick at rvpowerproducts.com
>www.rvpowerproducts.com
>
>----- Original Message -----
>From: "Allan Sindelar" <allan at positiveenergysolar.com>
>To: <RE-wrenches at topica.com>
>Sent: Thursday, November 14, 2002 11:27 AM
>Subject: Re: Ground fault [RE-wrenches]
>
>
>>
>> ----- Original Message -----
>> From: "Electrical Energy" <solar at eagle-access.net>
>> > This is a very informative thread.  I noticed on your web site that the
>> > negative lead measured - 48 volts to ground.  Was that after the wire
>was
>> > disconnected, or was there a grounding problem?
>>
>> If these Carrizo modules are set up as Quad-Lams, 48V dc could be VOC on a
>> 24V nominal array, as these Lams are about 6V VOC each. Is it a 24V
>system?
>> What are the specifics of the input current and voltage?
>>
>> (Three in series won't always charge a 12V battery in hot weather, but
>four
>> is higher than needed. A Solar Boost lets you harvest that extra
>voltage--I
>> have seen a 50% boost in winter on a QL/SB50 setup; the MPPT trim pot was
>> maxed out.)
>>
>> As the PV- and B- are isolated from each other at the SB50, a ground fault
>> could indeed send full array current from PV- through the controller to
>the
>> grounded B-, and overcurrent protection wouldn't catch the fault. Rick
>> Cullen, could this cause the fire?
>>
>> Allan at Positive Energy
>>
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>
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William Miller
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