dc voltage readings 1

[Faseddie]

Greetings,
I am not an electrician or electronics anything beyond putting the stereo in the car. I have been troubleshooting a machine here a t work with the help of phone support technicians. It appears the problem is power, according to the techs. and thus we have been looking for a power drop in a dc circuit. Today I discovered there is a difference in the voltage reading based on where I ground the VOM. When checking voltage at the power amplifier on the hot wire and the ground pin on the amplifier I read the required 165 VDC. However when I use the chassis ground and the hot wire in I get 82 VDC. Checking the continuity between the chassis ground and the power amplifier I get a closed circuit. Why then is a 50% voltage drop?

Thanks

Fasedie

 

[Skogsgurra]

This is most likely because there is a bridge rectifier that feeds the DC Circuit.

As it happens, such a rectifier produces a symmetrical voltage with respect to supply ground (draw the diodes and you will see why). So, if you measure between DC Negative and Positive, you get one voltage and if you measure from Ground to DC Positive you get half that voltage. You may, if you measure carefully, get 82.5 V and 165 V.

Nothing wrong there. If you are satified with the 165 V is OK, that is.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[Faseddie]

Thanks - the actual read voltages were 164.4 and 82.2 so we are good.

Faseddie