Measuring output from used PV solar panels

[chrisstratton]

I just watched a video in which Will Prouse measured output from various panels using a depleted 12V battery and a Victron Solar Charge Controller apparently hooked up via BlueTooth to this phone. I believe I can measure "open circuit" voltage easily enough w/ a DC multimeter, but now that I know I'm "chasing" information to be measured in watts - both in PV panels and stored in batteries, I suspect I should get the right tools? Oh - that raises another question - is charging largely flat-linear? In other words, if my battery is 2/3rds full, would it start to accept few watts from the charger/pv panel? What about a lead acid battery? TIA!

 

[pollenface]

You could momentarily connect the panel directly to the battery and include a multimeter in the circuit to measure current. Volts X Amps = Watts.

Alternatively, most good quality charge controllers will display that information during charging.

 

[chrisstratton]

You could momentarily connect the panel directly to the battery and include a multimeter in the circuit to measure current. Volts X Amps = Watts.

Thank you!!! I like easy . Just checking - it's okay to feed 37VDC (or whatever) from the PV into a 12VDC battery???

 

[chrisski]

You could momentarily connect the panel directly to the battery and include a multimeter in the circuit to measure current. Volts X Amps = Watts.

The cheap multimeters I have are labeled 10 amp max. One, I can measure 6 amps with, the other one also labeled 10 amps max, the fuse blows. You can measure open circuit voltage, but for amperage I recommend shorting the leads and using a DC clamp meter.

Thank you!!! I like easy . Just checking - it's okay to feed 37VDC (or whatever) from the PV into a 12VDC battery???

Don't do that.

Not even for a 18 volt panel. That's too much for a battery. Might not kill it, but that would cause flooded lead acid to equalize, and the same thing with AGM, and that's bad because those are not designed to vent gasses excspt for emergencies and have no way to replace the lost electrolyte.

 

[efficientPV]

I recently got some questionable panels and did a quick test measuring open circuit voltage and voltage under load. I had connectors to connect to the panel. Dont just stick wires in when it can be under load. That can damage the connector. I chose a handy 50W 3 ohm resistor. The panel was 30V and a little over 200W. A momentary connection of a couple seconds will give a reading without burning up the resistor. Figure the voltage and resistance to calculate current.

I'm going to build a tester that plots current, voltage and wattage for an easy accurate scan. This charge controller stuff is hokum.

 

[chrisstratton]

You can measure open circuit voltage, but for amperage I recommend shorting the leads and using a DC clamp meter.

I've got a clamp meter. So, just temporarily "shorting" the leads from the PV panel won't cause damage? (I really am a newbie, lol).

 

[efficientPV]

Short circuit is a rough indicator, better than nothing. Short circuit current actually begins to happen not that far below power point voltage. You can have a couple bad cells which will force the bypass diodes to conduct. You get the same short circuit current, but the panel can produce no where near what the panel should produce at power point.