Testing solar with multimeter

[camper101]

Hi,

I've got a new solar system and wanted to get an idea of how it's working. I've got a cheapo multimeter (measures volts but not amps) that I've been using.

When I checked voltage coming from the panel only, it was around 19 volts (cloudy day, 100w panel). When I attach the panels to the charge controller, I touch the charge controller screws (where the incoming solar is attached) directly with the multimeter leads, and it's only 11.75 volts. Is that normal?

The system isn't losing any power along the way -- I disconnected the terminals from the charge controller just to make sure I wasn't losing anything from splices/wire/fuses, and it's the same 19 and change. But the minute I attach the terminals to the charge controller, the voltage drops.

I hope I'm making sense... It seems as if once I attach the panels to the charge controller, it "sucks" some voltage out. If that's normal, then I'm happy - I'll hope it's getting sucked into the battery.

Thanks for any info.

 

[CaliMobber]

Its hard to get a real test of the solar panel with only volts. The 19v open is perfect. Its all voltage and no amp since its not flowing. The charge controller test has to many variables for me. I would have to know the State of the batteries, low or fully charged if using charge controller. Im not very smart in this area so someone can chime in.

I have a nice fluke meter with a DC amp clamp. What I do is clamp one wire during prime sun and see the amps flowing into the charge controller. Then amp*volts= watts and compare to the rating.

Hope this give you some idea's.

 

[camper101]

Thanks CaliMobber.

FWIW the state of charge was low according to the charge controller (Morningstar SunSaver). But yeah, it sounds like it's really hard to get an idea of how well things are working (I'm also not smart in this area, that's part of why it's so hard...).

 

[4x4junkie]

All sounds pretty normal to me.

Assuming your charge controller is a standard PWM type, it's normal to see voltage on the panel terminals near that of the battery itself, as it basically is just a straight-through circuit from the panel to your battery during the Bulk cycle. When the controller enters into Absorb mode as your battery nears full-charge, you'll then see a higher voltage appear across the panel leads, as the current drawn from the panel will be less.

 

[camper101]

Cool, thanks. It is PWM.

It was kind of suspicious that the 11.75 is awfully close to 12 volts, but my little brain couldn't make sense of how that would happen. Good to know.

 

[lysol]

Cool, thanks. It is PWM.

It was kind of suspicious that the 11.75 is awfully close to 12 volts, but my little brain couldn't make sense of how that would happen. Good to know.

If you want to learn how your system works, buy one of these:

http://www.amazon.com/Watts-Meter-A...UTF8&colid=FBSD1JSLBAXO&coliid=I2DUMWH2L6L0DH

I bought one and I now understand how many Volts, Amps, Watts, Amp Hours, and Watt hours I make. After a couple weeks, I had been able to predict how my setup would perform based on weather. I only have mine wired up before the solar charger so when I get my second one, I'll wire it up after the charger for a little so I can get a good idea of how much power loss is happening at the charger. Then I'll move it to the output LVD section of the charger so I can monitor my power consumption. That way, I can compare the incoming and outgoing against each other.