Measuring voltage and current from a solar panel

[foolsday]

Hello,
I have been working on a project involving a small, off-grid solar setup. I am using a 175 watt panel (http://www.ecosolargy.com/products/alpha-series ), a 24 volt solar charge controller, two 12 volt deep cell batteries (in series), and a 24 to 120 volt inverter to provide usable power at the end. The entire setup is portable and intended to be used for educational purposes at my school. My basic setup seems to be running fine, but I have been running into problems when I attempt to measure output from the panel. My intent was to mount some analog voltage and amperage meters on the front of the unit to allow students to record changes throughout the day (see links at bottom). I initially wired the meters in series with one another. This gave me a reasonable voltage, but an amperage that never seemed to exceed one. Thinking this was odd, I then attempted to wire the meters in a parallel configuration. Now the amperage meter produced a sizable output, but the voltage read 0. What am I doing incorrectly here? Is it simply not possible to measure both values simultaneously, or do I need to create some sort of switch to measure only one at a time? Sorry for what is probably a pretty newbie question, and thanks in advance!

Volt meter:
http://www.allelectronics.com/make-a-store/item/PMD-100V/0-100V-DC-VOLT-METER/1.html

Amp meter:
http://www.allelectronics.com/make-a-store/item/PMD-30A/30-AMP-DC-PANEL-METER/1.html

 

[(*steve*)]

The voltmeter goes across the panels (between +ve and -ve).

The ammeter goes in series with one of the leads (+ve, or -ve, but more commonly +ve, although either will work).

Unless you have a maximum power point tracking regulator which has a load which demands as much power as you can generate (grid connected inverters are such a device) then the power you see coming from the panel is more to do with your load than the available power (e.g. you'll see no power from the panels if the battery is fully charged.

 

[foolsday]

Thanks for the quick reply, that was extremely helpful. It is now working perfectly! I have also noted how the amp value changes with the load being powered by the inverter and battery level, just as you commented.

Thanks again for the assistance.