Ground fault [RE-wrenches]

Rick Cullen - RV Power Products rick at rvpowerproducts.com
Thu Nov 14 17:44:48 PST 2002


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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