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Hi

Well, both?+ and - output from a psu may be totally isolated from chassis/ground, but if its not and? - / 0v is connected to ground, and you connect wires to a pcb that also has - / 0v connected to chassis/ground, then you will have a ground loop from the - output of the psu trough the wire to the pcb, then to ground in the pcb, and back to the psu trough the chassis.?

The length of the loop will affect what frequencies its worst at, the longer it is, the lower frequency.

But very often the - / 0v is not totally isolated and not directly connected to ground, it's connected with a capacitor.? This was the issue withe the PSU we had problem with at work, due to a sensor that was sensitive to noise between the power lines and ground.

You can break the loop for higher frequencies by adding a power filter like this:

This is made for AC line filtering, but works well to to stop high frequency noise on DC as well, just be aware of current rating.?

I don't have a book advice, maybe someone else does, but here is some quick google findings:

They focus mostly on filtering the input, due to the regulations, but sometimes you can need the same type of filtering on the output. Or maybe just a simple LC filter will do.

Just have to try, and see.

?

Askild

On Tue, Oct 16, 2018 at 9:54 AM Tam Hanna <tamhan@...> wrote:

Hello Askild,

sorry to ask stupid, also to the quorum. Ground loops in power supplies?

So far, I mainly worked on process computers. If you can give me some advice, I would be very thankful. Telling me about a book to buy also works!

Tam

On 16.10.18 09:36, Askild wrote:

Hi Tam

My best advice would be to only use the datasheets as rough indication, but do not trust them before you have done your own measurements on ripple and noise generation.

If using DC/DC converters, remember to measure noise on the input as well, not only on the output.

And most datasheets do define the noise with and external capacitor, and measured with 20MHz bandwidth limit.?

Be careful how things are grounded, if ground loops is?unavoidable, use ferrite core/toroid to block it at high frequencies.?

I will??of course let you know how things go with my project, but it will probably be some time before I have something to share.

Askild

?

On Tue, Oct 16, 2018 at 8:24 AM Tam Hanna <tamhan@...> wrote:

Hello Askild,
sorry to ask, but I have a similar replacement job upcoming for an LC334 which my father bought at a vultures market and whose PSU blew up.

If you could elaborate on your experiences a bit, I would be much obliged. Also, I live in Eastern Europe - in the worst case, we can meet in the middle or you can fly in to my lab if you need help.

Tam

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With best regards
Tam HANNA (emailing on a BlackBerry PRIV)

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Am 15. Oktober 2018 20:09:46 MESZ schrieb Askild <megafluffy@...>:

Thanks all for your input.

I would be nice to have a spare unit, then I would get my hands on the top, bottom and left side panels that was missing as well when I found it, but it's unlikely to show up any locally, I'm in Norway (Europe)

And shipping from US for this heavy beast will be a lot.

So far it has not cost me much to get it where I can do some testing on it, only $47 for the ref osc, where I got half refunded because the connector with the flex-cable was missing (it was on the ebay picture), so I took the connector from the toasted osc that was in the generator when I found it. And e few SMC connector that where broken.

I did find the A7A2 (new) at ebay for $250 + shipping and the A7A3 (used) at BMI Surplus for $149 + shipping

I will first see what it will cost me to build it up with separate units, if I find a combination that will fit in the small space...

I have done a lot of testing on AC/DC and DC/DC converters at work recently, due to a DC/DC PSU generating a lot of noise between power out and ground (box), it ended with that we ditched the expensive Phoenix for a cheap Mean Well.

So doing this testing I have learned a bit on what to look for, and how to reduce the influence of the PSU noise.

Askild

?

On Mon, Oct 15, 2018 at 6:37 PM Peter Gottlieb <hpnpilot@...> wrote:

Oh, entirely humorously.?

Peter

On Oct 15, 2018, at 12:27 PM, Tam Hanna <tamhan@...> wrote:

Folks listen up. I've got like an insane fever and am flying out to a tradeshow in hell tomorrow.

All I know was that the guy got the MDO working, but then it showed spurious responses.

I apologize, I meant well and wanted to help.

p.s. in case this was ment humorously, I apologize. My humor detector is currently shut down due to overheating...

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With best regards
Tam HANNA (emailing on a BlackBerry PRIV)

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Am 15. Oktober 2018 18:24:27 MESZ schrieb Adrian <Adrian@...>:

Don't know either, but given how Tam said it produced them I'll bet it's painful?

Adrian

On 10/15/2018 5:15 PM, Peter Gottlieb wrote:

What is a quine?

Peter