Shorted Kyocera Panel

[DStan]

Shorted Kyocera Panel

When I check the the resistance across the output of my Kyrocera panel it measures 0.2 ohms (about the lead resistance of my Fluke Model 77 multimeter) and the same with the leads reversed.

Kyocera Corporation
Model KC80
Serial 96833019
August 1996
80 Watt
21.5 Volt Open
4.97 Amp Closed
Polycrystalline Cells

There were three diodes clamped in parallel between each the panel output connectors and the external load terminals. When I removed the clamps to remove the diodes two of the six diodes fell apart, broken cleanly into two pieces across the center of the diodes body.

Externally the panel shows no evidence of physical damage.

I am unable to imagine how this sealed panel could develop a bi-directional short.

I am considering grinding down from the back of the panel to the foil strips that conduct the current to the panel output terminals so I can sever those connections there and directly measure the resistance of the series string of solar cells without the terminals connected to the cells.

Any comments or suggestions will be welcomed.

[inetdog]

Shorted Kyocera Panel

There were three diodes clamped in parallel between each the panel output connectors and the external load terminals. When I removed the clamps to remove the diodes two of the six diodes fell apart, broken cleanly into two pieces across the center of the diodes body.

Externally the panel shows no evidence of physical damage.

Any comments or suggestions will be welcomed.

I assume that the short was still there after you removed all of the diodes and connected to the panel terminal?

One of the things that can damage a diode is excess current, the other is excess reverse voltage. Either of those events, caused by accidental connection to an external power source, could also damage the internal bypass diodes (if this panel has them) and effectively short out the cells that way. The effects might not be visible in the cells themselves, since each cell is high resistance when not exposed to light, and so might not have been damaged by a short term external voltage.
Mechanical damage is very unlikely to cause a short unless you see broken insulating layers.

[DStan]

DStan replies . .

I measured the resistance with the diodes removed at the terminals connected to the series cell string.

This is not my panel. If the owner inadvertently connected the terminals to 120 VAC could that explain the damaged diodes and also shorted the cells in the series string?

[Mike90250]

Whatever fool at the factory decided that 3 diodes in parallel, is a proper replacement for a single heat sunk diode, deserves a special place in hell. Because thoses diodes are visible, everyone takes photos of them, and emulates it. But, what few realise, is the response curve in those diodes, means that 1 diode handles 95% of the load till it fails then ........

Those are "bypass" diodes. Panels seldom have blocking diodes, so they (panels) can be damaged (the PV cell junctions) if reverse battery power or AC is applied to their leads.


And if there is some sort of light on the panels, even indoors, your ohm meter may be driven nuts by some small voltage (even .1V) while in the ohms mode. PV panels are seldom tested as diodes, you have 17 or so, junctions in series, and so that would be at least a couple of volts needed to cause the diodes to conduct in 1 direction.

.2 ohms in both directions, in a very dark area, seems to indicate it's shot.

[DStan]

Panel Schematic from DStan

This is how the diodes are connected to the panel. I believe they are there to keep the battery from discharging when the panel is dark.

The resistance measurements at the panel terminal (with the diodes gone) with the panel face down on a table.

[DStan]

Ooops - Schematic didn't attach to the message - trying again.

Apparently I still cam' attach the schematic.

Description of image:

Terminal on left, labeled Minus Load.

Three diodes in parallel, arrows pointing to the right, connect to the Minus Load terminal at their left ends. The right end of these three diodes connect to a terminal labeled Panel Minus.

The negative terminal of the series string of Solar Cells is connected to the Panel Minus terminal.

The positive terminal of the series string of Solar Cells is connected to another terminal labeled the Panel Plus terminal.

Three diodes in parallel, arrows pointing to the right, connect to the Panel Plus terminal at their left ends. The right end of these three diodes connect to a terminal labeled Plus Load.

As stated above I believe these diodes are intended tom prevent the panel from discharging a battery directly connected to the panel from discharging the battery at night.

[DStan]

All my questions have been answered - thanks to everyone who helped.

All my questions have been answered - thanks to everyone who helped.