Testing solar panel current without load

[workmaster2n]

I have 3 x 240 watt panels that are wired in series. I’m in Australia, where the sun is fierce. On a good day, I see a maximum of 330 watts from this series of panels (should be 720, in a perfect world) at the charge controller.

The panels are cheap and old. I’m trying to figure out if the panels have outlived their usefulness, or if the wire run to the controller is bad.

I individually tested each panel and they all output about 130 watts when connected to the charge controller.

If I connect a multimeter across each panel’s leads when disconnected from the controller, I get the expected voltage. But I can’t get a reading for amps. My guess is that the multimeter isn’t putting enough load on the panel to induce a current. When connected to the controller, the panels output about 1/2 their rated amps.

Is there a way I can check the amperage of these panels? If I go get a sizable resistor from the electronics store, might I have some luck?

Or is there some other way I can check if the cable run to the controller is the culprit?

[Seaslug Caravan]

Normally open cct voltage and current specs are on the underside of the panel.
What multimeter are you using cause if it’s a cheap’n then you have already blown it up, because most only read to 10 amps.
No reason why your panel isn’t reading short cct current other than operator error.
Assuming 12 volt system.

[donradcliffe]

Buy a multimeter with a clamp on DC ammeter. Take the two wires from each panel and short them together. Put the ammeter on the wire and measure the short circuit current. Compare it to the short circuit current on the panel label.

[workmaster2n]

Originally Posted by Seaslug Caravan

Normally open cct voltage and current specs are on the underside of the panel.
What multimeter are you using cause if it’s a cheap’n then you have already blown it up, because most only read to 10 amps.
No reason why your panel isn’t reading short cct current other than operator error.
Assuming 12 volt system.

It’s a 600 amp clamp on meter. I came across another thread somewhere that mentioned the panel wouldn’t show proper output unless under load.

Could be user error, but the fact that I’m getting voltage readings makes me think I’m missing something else.

For reference, there are only 2 plugs on the multimeter, so I’m not plugging the cables into the wrong ports.

[workmaster2n]

Originally Posted by donradcliffe

Buy a multimeter with a clamp on DC ammeter. Take the two wires from each panel and short them together. Put the ammeter on the wire and measure the short circuit current. Compare it to the short circuit current on the panel label.

I’ve got a clamp on meter. Didn’t think of this approach. I’ll give it a go!

[workmaster2n]

Originally Posted by donradcliffe

Buy a multimeter with a clamp on DC ammeter. Take the two wires from each panel and short them together. Put the ammeter on the wire and measure the short circuit current. Compare it to the short circuit current on the panel label.

This worked a treat. Thanks for the idea!

[senormechanico]

Don't leave the panel leads shorted any longer than you actually need to.
In full sun, overheating can result.

[donradcliffe]

Originally Posted by senormechanico

Don't leave the panel leads shorted any longer than you actually need to.
In full sun, overheating can result.

I have no idea where you came up with that one. The rated short circuit current is only a bit higher than the operating current, and it takes special conditions to achieve it

[senormechanico]

I read it somewhere on the internet, so it MUST be true.
Not sure, but it might have been from that guy in Oz who posts the off grid garage.

[goboatingnow]

Originally Posted by senormechanico

Don't leave the panel leads shorted any longer than you actually need to.
In full sun, overheating can result.

No heating results as the voltage Is very low and little power is being generated. It’s z current source notes voltage source.