icy hot electricity: trouble measuring voltage

[sciencepunk]

I am doing the icy hot electricity project, and I'm having trouble measuring voltage. The device that I'm trying to measure voltage of is a 12 volt plug of a thermoelectric cooler. I am using a multimeter that I calibrated and checked with a 9 volt battery. (it's working fine) For my experiment, I set the meter to DC 20, and am getting a level of zero, when I should be getting just under 12 volts when I unplug the unit after running the unit for about 30 minutes. The top plate is about 0 degrees C and the bottom is about 33 degrees, so there should be some voltage. I put the red lead on the knob of the plug and the black lead on the side strip and cannot get a reading. Can you help me troubleshoot what my problem is? Thanks.

[rmarz]

sciencepunk - It sounds like your power connector is a plug to be used in a vehicle cigarette lighter. The tip of the connector is connected to +12 volts, and the metal connectors on the side (usually spring like strips) are ground. I have found that very often, only one of these side contacts is actually connected to the load. Try your voltmeter on the center connector and try both of the sides of the spring strips to see if that is the problem. There may also be a protective rectifier in the circuit (possibly in the connector itself) to prevent a reverse power connection. If that is the case, your meter will not detect any voltage at the connector. You would have to test at the actual Peltier diode in that case. Hope this helps.

Rick Marz