M75 Siemens low voltage problem [RE-wrenches]

[Mark Downing]

Sounds like one or both diodes are shorted.  The panel
is most likely fine.  Shorted diodes are the most
common panel failure I have found.
Take the diodes out and measure the panel's OC
voltage.
I suspect it will be fine.
You should be removing the diodes to test them.
Resistance measurements are not made in live circuits.
To truly test the diode by itself, it needs to be out
of circuit.

If you put a jumper across the diode, you were
shorting out part of the panel, so the voltage would
remain the same or decrease.  The diodes operate
reverse biased, normally not conducting.

Mark, HAP

--- "David Palumbo, Independent Power & Light"
<ipl at sover.net> wrote:
> A fellow brought in a Siemens M75 (vintage 1994) 48
> watt module to me
> yesterday with a problem that I have never seen
> before.
> He reported that there was a lightning event close
> by and afterwards this
> one M75 (out of a simple 2 module array, daisy
> chained; the second module is
> OK) was draining his batteries. It was warm to the
> touch on the glass
> covering about one third of the cells.
> 
> I checked the modules operation with my Fluke and
> found the following. OCV =
> 6.05, ISC = 2.95 during a hot, sunny/hazy noon time
> with no shade on the
> module. The factory specs are: OCV = 19.8, and ISC =
> 3.35
> 
> It looks to me like only one third of the cells are
> now in the circuit. Is this a good assumption?
> 
> I checked the bypass diodes and the one in the
> positive box has continuity,
> it reads .1 Ohms in either direction with no sun on
> the module and it reads
> from 20 to 30 Ohms depending on the strength of
> sunlight in both directions
> (bad diode?). The negative diode has no continuity
> with no sun and has
> continuity in the sunlight in one direction only
> (which I think is OK). I
> put a jumper across the positive diode and the
> module output was still only
> 6 volts.
> 
> No physical damage is visible to my eye. Does anyone
> have any idea what is
> going on? And suggestions on how to fix it?
> Thanks,
> Dave
> 
> A thank you also goes out to Richard & Karen Perez,
> and Ian Woofenden for
> gracing Vermont's SolarFest with Home Powers
> presence a couple of weeks ago.
> It was great to have Richard speak during our
> battery workshop, we all
> enjoyed (and learned) from his battery sulfation /
> Dating Game analogy.


__________________________________________________
Do You Yahoo!?
Make international calls for as low as $.04/minute with Yahoo! Messenger
http://phonecard.yahoo.com/

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com

==^================================================================
EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9
Or send an email To: RE-wrenches-unsubscribe at topica.com
This email was sent to: michael.welch at homepower.com

T O P I C A -- Register now to manage your mail!
http://www.topica.com/partner/tag02/register
==^================================================================