Problem with used solar panel:

[billthedog]

I bought a panel about 5' by 3' with 72 cells, no glass damage.

At the junction box on the back are 4 terminals, (relative to the negative
terminal) I can read 12 volts, 24 volts, and 36 volts.

But when I use a amp meter, (with or without a load in series) the meter reads zero. Tried a different meter, same thing.

Measuring across the 3 diodes in the junction box, same thing.

Good looking panel, no visable damage front or back, measurements taken
with panel in full California sun.

I am a electronics hobbyist but this has me stumped. ?

[sensij]

Are you measuring Isc (short circuit current)? You would take the plus lead of the panel, connect it through your ammeter to the minus lead. Current is very sensitive to irradiance, so your highest value should come on a clear day, at solar noon, with the panel oriented to be directly facing the sun.

[inetdog]

I bought a panel about 5' by 3' with 72 cells, no glass damage.

At the junction box on the back are 4 terminals, (relative to the negative
terminal) I can read 12 volts, 24 volts, and 36 volts.

But when I use a amp meter, (with or without a load in series) the meter reads zero. Tried a different meter, same thing.

Measuring across the 3 diodes in the junction box, same thing.

Good looking panel, no visable damage front or back, measurements taken
with panel in full California sun.

I am a electronics hobbyist but this has me stumped. ?

The first thing you need to apply your electronics hobbyist knowledge to is that the individual cells in the panel are current sources, where the available current is proportional to the intensity of the sunlight hitting them. A defective cell can produce full voltage (~.5V) but next to no current and will resist attempts to force more current that that through it.

Each terminal in the box is wired to a point in the series string of cells that makes up the panel, as you can tell by the 0, 12, 24, 36V reading (essentially 12V for each of the three sections.)
The bypass diodes are there so that if there is one defective (or shaded) cell in a single section the other two sections can still produce useful output current, just at 12V lower voltage than normal for the panel. If it were not for the bypass diodes, a single shaded cell could drop the total panel output to close to zero and also damage that cell.

Since you have placed your ammeter across each step of the series circuit, it does not matter whether the bypass diodes are good or not, you would have to have one or more defective cells in each panel section.

(Just for completeness,
1. does your multimeter have a separate jack into which you plug one of the test leads when measuring on the 10A range?
2. Are you absolutely sure that you have not blown the fuse for the high amp range in both meters?)

[billthedog]

1. does your multimeter have a separate jack into which you plug one of the test leads when measuring on the 10A range? Yes. Both multimeters have the 10 amp jack on the left.

2. Are you absolutely sure that you have not blown the fuse for the high amp range in both meters?) Yes, Both are Fluke multimeters, fuses in both checked.

Strange isn't it ?

[LETitROLL]

1. does your multimeter have a separate jack into which you plug one of the test leads when measuring on the 10A range? Yes. Both multimeters have the 10 amp jack on the left.

2. Are you absolutely sure that you have not blown the fuse for the high amp range in both meters?) Yes, Both are Fluke multimeters, fuses in both checked.

Strange isn't it ?

Find an old style incandescent light bulb of 100W (or higher) and hook your panel leads straight to it with full sun and panel at good angle to sun, you should see the filiment turn orange and or the globe will get warm, if so obviously you have current flow regardless of what any meter says.