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Ground on AC DC Converter

I have a 5V and a 12V power supply. Both have a N, L, Ground connections for the AC side. Both also have a V- and V+ connection. Measuring between V- and V+ I get the correct voltages, i.e. 5V and

12V. Measuring between ground (AC side) and V- on both the 5V and 12V gives 0V. Measuring between ground (AC side) and V+ on the 5V supply gives 0V and on the 12V supply 12V.

Why does the 5V power supply not show 5V from ground to V+? Note that the 5V can deliver up to 6A and it is under a 0.6A load when I measure the voltage.

Thanks

Reply to
hufaunder
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** Use a * ohm * meter to check for continuity.

Bet the 5 volt one has no connection from AC ground to the DC output.

Most simple PSUs have the DC output "floating" ie not connected to safety ground.

........ Phil

Reply to
Phil Allison

So if both the 12V and 5V need the same reference then could I connect V- on the 5V PS and the V- on the 12V PS and the ground on the AC side of the 12V PS all together? Are there any safety issues with this?

Thanks

Reply to
hufaunder

There should not be any issues with this - safety or otherwise. As Phil says, output ground is often floating, but just as commonly, if the power supply has a metal enclosure, it will have an AC-side safety ground, and the output ground will likely be tied to it.

Arfa

Reply to
Arfa Daily

You have already stated that with the 12V supply, V- and AC-ground are connected? That is, you did what Phil suggested and looked for continuity between the -12V and AC-ground?

Keep in mind that some (cheap) power-supplies use autotransformers, such that the LVAC side is still directly connected to the AC mains... meaning that the DC side also remains connected to the AC mains. Others use step-down transfomers with the secondary isolated from the primary. You need to determine which is which in your case. More work with the VOM, but easily determined.

Unless both supplies are isolation-type and writing for myself, I would not connnect the two together without further testing for potential between the two, or between the workpiece (what you are powering) and the two if connected together. If they are isolation- type, then there should be no safety issues.

But test for AC and DC potential between the two supplies anyway before making any common connections.

Next question: Does the 12V supply have enough capacity that you could use it to provide 12V and 5V via a divider?

Peter Wieck Wyncote, PA

Reply to
pfjw

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