PSU filter cap leaked after a ground issue?

[CrysisLTU]

Hello everyone.

I've got a Smun AS-350-12 (12V 30A) power supply from aliexpress.com. Yes, it's a chinese cheapee, but it seems that it's quality isn't too bad.

Anyhow, I was using it with my HF radio transceiver. The PSU was causing lots of EMI/RFI on HF frequencies, and as a radio operator - that's super annoying.

To reduce that, I took some wire, connected it to the ground terminal of the PSU, and connected that wire to a hot water pipe (I live in EU, in an apartment - no third ground prong in the outlet). EMI got reduced! But just a little bit... The power supply wasn't radiating as much EMI/RFI, but the radio connected to the PSU was still suffering from RF noise.

I got frustrated after some time, and I've read that some dude with a similar PSU had a similar problem, and fixed it like this (quote): "removed the ac ground wire from the ground terminal and tied it to the DC ground on the power supply. Then I took a 250uf low ESR electrolytic, put the + side to the ac ground screw and tied the - to one of the dc ground screws as to make sure that any RF present on the chassis will have a definite low impedance to ground."

So, I tried the same. I remember that the cap I used wasn't 250uF, it was a little higher, and it wasn't marked as a low ESR. So, I plugged the cap in, plug the mains cable and... magic smoke coming out of the power supply! Yay...

I open the PSU up, only to find one DC filter cap that has leaked. It's some cheap SiQing 200v 680uF. There's another cap like that, but it didn't leak. AC Fuse is fine, no other burn marks or anything like that.

I've already got new same spec DC filter caps installed (yes, I've replaced both), but before turning on the PSU I want to know why the cap leaked in the first place, and will the new caps make it work fine again? Could something else have gotten broken because of what I have done? :/

I'm a quite a noob in grounding and AC, so help is needed! Thanks a lot.

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

"(I live in EU, in an apartment - no third ground prong in the outlet)"

How can you connect AC ground to anything when you said you have no AC ground? AC neutral is not AC ground.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

"(I live in EU, in an apartment - no third ground prong in the outlet)"

How can you connect AC ground to anything when you said you have no AC ground? AC neutral is not AC ground.

Well yes, there was no AC ground connected to the power supply, it's just not there. The other guy, that wrote that fix, does have AC ground.

[budm]

Re: PSU filter cap leaked after a ground issue?

"To reduce that, I took some wire, connected it to the ground terminal of the PSU, and connected that wire to a hot water pipe "

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

What did you wire the cap to? Oh, I missed the hot water pipe. Not supposed to use a hot water pipe for a ground, only cold and very close to the water service entrance of the building. Either that or a real ground rod.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

What did you wire the cap to?

It's written in the original post
Quote: "Then I took a 250uf low ESR electrolytic, put the + side to the ac ground screw and tied the - to one of the dc ground screws"
Again, the cap was not the same spec.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

Not supposed to use a hot water pipe for a ground, only cold and very close to the water service entrance of the building. Either that or a real ground rod.

Why can't I use the hot water pipe? I live in the second floor, no access to any other ground points.

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

The hot water line is separated by insulators at the water heater from the cold line. It would be better to use the cold line. It has a better chance at being close to earth ground potential.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

The hot water line is separated by insulators at the water heater from the cold line. It would be better to use the cold line. It has a better chance at being close to earth ground potential.

Oh, okay. Makes sense.
Any idea why the PSU's DC filter cap leaked then?

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

Cheap and ready to go is my guess unless somehow the cap you connected raised the voltage across the DC cap but I can't think of how that would have happened.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

Cheap and ready to go is my guess unless somehow the cap you connected raised the voltage across the DC cap but I can't think of how that would have happened.

It seemed the electrolyte came out from the bottom of the cap, together with some smoke. It was very quick. The power supply was bought new and used for a few days.
I still would want to know more correctly what happened, and if I'm okay to try to turn the supply on. I don't want the new caps to die, or the PSU to die in some other way now... Waiting for other people's thoughts

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

Can you post pictures?

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

Can you post pictures?

The old caps have been thrown away. I can post pictures of the PCB if you want.

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

Yeah, that's what I meant. I should try to be more clear.

If it was me I want to know why too. I'd disconnect the added cap from the DC ground before powering on the PSU and check for voltage between the DC ground and your external ground while it's on.

[CrysisLTU]

Re: PSU filter cap leaked after a ground issue?

Yeah, that's what I meant. I should try to be more clear.

If it was me I want to know why too. I'd disconnect the added cap from the DC ground before powering on the PSU and check for voltage between the DC ground and your external ground while it's on.

Here are the photos: https://imgur.com/a/8denv
Note the newly installed DC filter caps.
Oh, and yes, when I will try to turn it on, the cap wont be connected between DC ground and AC ground connection. I think I threw that cap away too

[budm]

Re: PSU filter cap leaked after a ground issue?

" "removed the ac ground wire from the ground terminal and tied it to the DC ground on the power supply. Then I took a 250uf low ESR electrolytic, put the + side to the ac ground screw and tied the - to one of the dc ground screws as to make sure that any RF present on the chassis will have a definite low impedance to ground."
I see the input Ground Earth terminal, but do not see the DC Ground terminal.
Can you show exactly how the 250uF cap is connected to this power supply terminals?

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

So you tied DC negative to chassis ground, right? If so I'd undo that too. Not having a schematic it's hard to tell what effect that would have.

[budm]

Re: PSU filter cap leaked after a ground issue?

I cannot find the info on the terminals of that power supply.
http://www.smunchina.com/html_produc...eries-396.html
The spec does not say that the V- is tied to the chassis Ground either.
I have a feeling that that cap was exposed to line Voltage AC so it smoked, he also did not indicate the voltage rating of that 250uF cap.

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

I think it's isolated. I can see from the pics there's one small blue cap that connect chassis grnd to V-, two to the input transformer secondary legs, and another one to - side of the 680uF cap on the end at the mounting screw hole. I don't see any other connections to chassis.

I suspect the blown cap got AC line voltage too.

[SteveNielsen]

Re: PSU filter cap leaked after a ground issue?

Concerning the RF noise problem, the standard methods of minimizing that on the DC supply lines to the radio would be using low-pass choke coils inline or pass them wrapped through torroids on the radio end of the supply lines, keeping the DC lines as short possible, and using a 2 conductor with sheild cable if the lines have to be longer than a few inches.