Testing solar panel current without frying multimeter

jef

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I see people are advising doing the dead short current test with a multimeter, which to the best of my knowledge is likely to fry the meter or at least blow the fuse.

Is it really standard practice to measure solar panel output by connecting a multimeter across the output of the solar panel?
Isn't the correct way to do this is to put the meter in series with a load, for example around a 3 ohm 100 watt resistor for testing current output on a 100 watt solar panel.
Or am I misinformed?
 

MisterSandals

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Is it really standard practice to measure solar panel output by connecting a multimeter across the output of the solar panel?
This is pretty standard practice. You need to make sure your panel amperage is lower than what your meter is rated for (its usually listed clearly near where the leads are plugged in for measuring current). And its important to not connect too long and provide plenty of time for your meter to cool before tests.

Its unlikely you will fry your meter. I have blown the internal fuses a couple times when testing things that exceeded my 10A meter (user error).
I have a 10 pack of 10A fuses so i can replace them in a minute or two.

Or, a clamp meter that reads DC current is surprisingly handy. When i got mine i could not believe how i got along without one...
 

740GLE

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Clamp meter and be done with it, they are pretty economical models out there that won’t break the bank.

Also what are you doing with the data once collected? Just verify each panel is in line with each other?
 

Don B. Cilly

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Most multimeters have a 10A (max) connector. If the single panel in question does not (likely) exceed it...
Or make yourself a "field ammeter" like mine :·)

fieldamp.jpg

[EDIT] I borrowed a DC clamp meter once. Not a Fluke, but supposedly a good one.
Compared the readings to the inline analog, they were way off. That was many years ago, though. They're probably better now.
-
 
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Hedges

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Avoid burning test leads or MC connectors.
You can connect leads with panel covered or turned away from sun. It will still have fairly full voltage, but low current.
I put cables into a suitable snap-action knife switch, so I can connect in the sun, then close switch. That works either to connect "A" terminal of meter, or short out for clamp meter.

Short circuit test may catch defects, but not all. I found some bad panels only showed up with a resistive load (I used oil-filled radiators.)
 

Bud Martin

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I always cover the panel with cardboard or blanket before connecting or disconnecting the meter/connectors.
 

Hedges

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Scroll down to second posting for picture of my open/short/load tester:

 

jef

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Clamp meter and be done with it, they are pretty economical models out there that won’t break the bank.

Also what are you doing with the data once collected? Just verify each panel is in line with each other?


Troubleshooting a new solar rig. Wanted to see how many amps the 100 watt panels were putting out without the charge controller.
Not getting much output from the panel, about 6 watts max from a Renogy 100w panel in full sun through a double pane window, connected to a renogy pmw charge controller which has bluetooth output. I know windows block a lot of energy but calculated it should be 20 - 25 watts when derated for the window and pmw controller. Maybe it's a defective charge controller.
 

Hedges

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Battery voltage? That can cause power harvested by SCC to drop if near full. Put a load on it.

Is this a lead-acid battery which can take some abuse?
You can use the battery as load for PV panel. You become the PWM. Just connect panel to battery and measure current.
 

Bud Martin

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Troubleshooting a new solar rig. Wanted to see how many amps the 100 watt panels were putting out without the charge controller.
Not getting much output from the panel, about 6 watts max from a Renogy 100w panel in full sun through a double pane window, connected to a renogy pmw charge controller which has bluetooth output. I know windows block a lot of energy but calculated it should be 20 - 25 watts when derated for the window and pmw controller. Maybe it's a defective charge controller.
Did you try to test it in direct sun to get comparison readings? Do you know what wavelength the the double pane block out, and do you know the PV panel wavelength it is designed for?
 

jef

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Did you try to test it in direct sun to get comparison readings? Do you know what wavelength the the double pane black out and the PV panel wavelength it is designed for?
That's probably where it's going eventually but -12 F here right now and battery doesn't have the low temp cutoff yet.
 

Bud Martin

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Well, at this point the test is not really valid. Please do the follow-up on the test result.
 

Hedges

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Take it out to your car, connect to 12V lead-acid starter battery, rotate panel to face sun and measure current & voltage.
 

jef

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Battery voltage? That can cause power harvested by SCC to drop if near full. Put a load on it.

Is this a lead-acid battery which can take some abuse?
You can use the battery as load for PV panel. You become the PWM. Just connect panel to battery and measure current.
It's a LiFep04 battery, and wasn't fully charged. Also didn't know you could short the solar panel output without damaging them, guess the internal resistance is high enough to prevent that.
 
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HRTKD

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In 2019 I tested all my panels for voltage before I installed them. Had I understood how to use the DC ammeter (non clamp-on) part of my multimeter I would have used that too. Once they were installed, the solar charge controller gave me a good idea of how well they were performing and I stopped worrying about it.
 

Hedges

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I hadn't worried before, but once I got a clamp ammeter, I checked parallel strings and saw major deviation.
That turned out to be 5 panels in one string (what are the odds??), so I swapped them for others.
These were about 17 year old Sharp polysilicon.

What is your series/parallel & multiple MPPT configuration? And panel brand/age? Oh, Duh! 2 years old.
 
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