Power supply.... what's going on here? (Electronics project)

[Scarletpimpofnel]

I have a 5v 3A wall block type PSU to power an electronics project I'm building but have a couple of odd things. I thought I'd test it just to see what voltage it kicks out and found:

1 - Upon turn on the blue aluminium plate the connector is attached to seems live. It tingles to the touch in an unpleasant way. Like a high voltage constant static.

2 - When I put my multimeter on the power lines with no load it starts at 5v (correct) but then quickly climbed to 12v then out of range (was on the DMM's 20V scale so no idea where it ended up)

With a light load it seems to settle at 5V but what is happening on no load? Why am I getting a "shock"? By circuit has an electrolytic and ceramic capacitor across the incoming 5V supply so if its some stray noise hopefully that will deal with it, but will it?

Any idea what is going on, do I need to do anything in my circuit to handle it. TIA

[outnumbered]

It's not really a shock you're getting, that tingle is a characteristic of type ii insulated power supply. You can Google why it happens, but it's safe.

[Scarletpimpofnel]

Thanks, so basically a Y class capacitor passing a bit of HV side current through to the LV side then passing through me to earth. All normal.

The thing is I don't want everyone handling my project's enclosure thinking they are getting a shock!

I'm wondering if there is a 5V wall block that has an earth pin rather than double insulated that would solve this???...

[Murph7355]

Can the connector mount to the blue plate be better insulated?

[spikeyhead]

Can your project go in a plastic box?

[Scarletpimpofnel]

Murph7355 said:

Can the connector mount to the blue plate be better insulated?

TY. That was the solution I came up with. I've used nylon shoulder washers to insulate that connector (and others) from the case. But I still don't know if that leakage current on the 5V rail will affect by electronics within the enclosure.

A cheaper solution might have been to get a 5V supply with an earth pin on it!

[Scarletpimpofnel]

spikeyhead said:

Can your project go in a plastic box?

I usually do use plastic but wanted this project to look decent so used a blue anodised aluminium case. Usually the surface of these are insulating (they are to my DMM) but not to the mains leakage current it seems.

[ATG]

So long as your project on average draws enough current to stop the PSU's output from drifting, I'd have thought it should be fine. Worse case, you could always stick a resistor across the PSU. I'm guessing you'd only need to draw a few micro amps to stabilise it.

[OIC]

Don't switching adapters fail to mains fairly frequently?

I've got a knackered one that gives you quite a bump if you touch the +ve.

Keeping it for a special occasion.

[Scarletpimpofnel]

ATG said:

So long as your project on average draws enough current to stop the PSU's output from drifting, I'd have thought it should be fine. Worse case, you could always stick a resistor across the PSU. I'm guessing you'd only need to draw a few micro amps to stabilise it.

Interesting thanks. My project definitely will be drawing 0.1Amps typically spiking up to 2.5Amps (when actuators activate etc) so comfortably surpasses what you suggest ty.

[Scarletpimpofnel]

OIC said:

Don't switching adapters fail to mains fairly frequently?

I've got a knackered one that gives you quite a bump if you touch the +ve.

Keeping it for a special occasion.

Hmmm hope not :-(

They should have a Y class capacitor preventing such a failure to mains but who knows. My adapter is some Chinese supplied item so who knows what components it has in it. But I haven't heard of anyone dieing from one in this country???