Output of DC power supply contains unwanted AC

Thread Starter

Ready or not

Joined Jul 27, 2023
1
My new, low cost, 15 VDC power supply actually outputs that voltage, however, the output also contains unadvertised and unwanted 45 VAC to ground. Could someone help me find a way to block the AC?
 

BobTPH

Joined Jun 5, 2013
9,189
How did you measure that? What ground, the earth ground on your AC power?

Does the AC power have a two-pin or 3-pin plug?

I would check the outlet to make sure it is wired correctly. It might have ground and neutral reversed.
 

crutschow

Joined Mar 14, 2008
34,717
If the AC is from one of the outputs to earth (safety) ground, then that's likely just from small, stray capacitive coupling through the supply, and is not of concern for normal supply operation.
Connect a 1kΩ resistor from the output to ground and see what you then measure.

Is there any significant AC across the two DC terminals?
 

Jon Chandler

Joined Jun 12, 2008
1,073
I can tell two things instantly from your post:

○ It's a switch mode power supply

○ You're in North America or other location with ~120VAC power.

As @crutschow said, it's a tiny leakage current across caps in the power supply and extremely common with smps.
 

MisterBill2

Joined Jan 23, 2018
19,086
The supply may be of the non-isolated variety, or it may be defective or damaged. Given that we have no information provided the very best possible is guesses.
 

MaxHeadRoom

Joined Jul 18, 2013
28,782
My new, low cost, 15 VDC power supply actually outputs that voltage, however, the output also contains unadvertised and unwanted 45 VAC to ground.
Often possible to read that effect when using a hi impedance meter, i.e. leakage.
Place a 10K across the leads and see if the reading collapses
 

MisterBill2

Joined Jan 23, 2018
19,086
My new, low cost, 15 VDC power supply actually outputs that voltage, however, the output also contains unadvertised and unwanted 45 VAC to ground. Could someone help me find a way to block the AC?
So the supply delivers 15 volts of DC between the positive output terminal and the negative output terminal?? And also, at the same time, delivers 45 volts AC between the positive output terminal and ground, as in the AC mains neutral line ground???

Are you able to open the supply and examine the connections?And maybe, with it disconnected from the mains, measure resistances??? I see indications that it is not an isolated supply, but one with the output tied to the mains input in some manner.
It would be OK for charging an isolated battery, but not for much else, if that is the case.
 

MaxHeadRoom

Joined Jul 18, 2013
28,782
So the supply delivers 15 volts of DC between the positive output terminal and the negative output terminal?? And also, at the same time, delivers 45 volts AC between the positive output terminal and ground, as in the AC mains neutral line ground???
Does not necessarily mean that it would supply any thing like significant current, if it is leakage.
With a high impedance VOM it is often a normal experience..
 

MisterBill2

Joined Jan 23, 2018
19,086
That amount of leakage is enough to cause al sorts of problems in an electronic circuit, and probably indicates that there is some level of shock hazard present.
So I would be reluctant to use it for anything where serious leakage might cause a problem.
 
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