Floating 24VDC Power Supply ?

[ryguy1116]

I have a 24VDC power supply that does not have the common side connected to ground (floating). The Primary side is 120VAC. My question is what can I expect to measure from common to ground. Right now I am measuring very close to 24VDC from + to common.

I am also measuring 24-25VDC from common to GND. Is this expected? Is this to high? What would cause a high voltage between common and GND?

Any information would be usefull.

 

[RudyL54]

Normally the chassis or the power supply metal case is connected to ground. It may not be floating because if the outlet 120VAC is connected to ground, then effectively the chassis of the power supply is connected to ground.

 

[djs]

If the output of the PS is truely isolated from ground, then what you are reading is leakage from the power supply rails to ground. Rather than read voltage, try reading current. BE CAREFUL, if the PS is grounded somewhere, one rail or the other will supply full current through your meter (and blow the fuse!).

 

[stevenal]

I'm guessing you are using a nice digital multimeter with a high impedance input. These meters put very little load on a circuit, and can read induced voltages and stray capacitances that analog meters would drain away. You should be reading zero from either rail to ground if measured sequentially, or 12 V to ground if measured simultaneously, since the meter(s) represent the only connection(s) to ground. But use a low impedance meter, or a lamp.