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Author Topic: Homebrew Regulated Power Supply: How to test for noise, ripple??  (Read 321 times)

N2EYE

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Homebrew Regulated Power Supply: How to test for noise, ripple??
« on: February 13, 2021, 11:26:47 AM »

Any suggestions on how I can evaluate a homebrew Regulated Power Supply without a scope?

I'm concerned about Hum, noise. I discarded my old cathode-ray  when the spouse moved-in.  Anyway, it's a  LM723 based unit that I need to  yield 28vdc at 30 amp minimum.  I'm uncertain about the filter caps (Alibaba) and I'm worried about hum.

I do have a quality and calibrated analog VOM. 
Ned
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W9IQ

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #1 on: February 13, 2021, 11:46:59 AM »

Put your meter in AC volts and at its lowest voltage setting. Any AC reading is indicative of lack of power supply filtering.

The best condition under which to test this is at full load. I suggest a dummy load for the PS (e.g. car lights, salt water, higher power resistors, vehicle battery load tester, etc.) so as to avoid damaging any valuable gear.

Good luck with the project.

- Glenn W9IQ
« Last Edit: February 13, 2021, 11:50:43 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9AC

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #2 on: February 13, 2021, 12:08:55 PM »

Put your meter in AC volts and at its lowest voltage setting. Any AC reading is indicative of lack of power supply filtering.

- Glenn W9IQ

Yes!  For quick checks I use a Fluke 8060A DMM which has an AC response up to about 100 kHz.  That covers all but any high-frequency noise, especially from a switching supply or DC-DC converter where the switching frequency is well above 100 kHz.

Paul, W9AC
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K1KIM

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #3 on: February 13, 2021, 04:15:42 PM »

Noise and Ripple. 2 different things. You can always get on the air and get reports as well.
I try to shoot for 50mV or less ripple. I've seen some switching supplies up to 750.

A 47µf Tantalum capacitor in parallel at the output terminals will reduce ripple tremendously. In your case I would use a 40 VDC cap.

Some will say those caps explode. I haven't had any do that yet.
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W9IQ

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #4 on: February 13, 2021, 04:19:42 PM »

True, but ripple is the primary issue with a linear supply.

- Glenn W9IQ
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K1KIM

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #5 on: February 13, 2021, 04:59:46 PM »

True, but ripple is the primary issue with a linear supply.

- Glenn W9IQ

I think you meant “switching supply”

Linear supplies, though inefficient,
have inherently little ripple.
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W9FIB

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #6 on: February 14, 2021, 02:10:31 AM »

Yes, but how many are going to sit down and homebrew a switcher vs a linear?
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W9IQ

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #7 on: February 14, 2021, 04:35:55 AM »

True, but ripple is the primary issue with a linear supply.

- Glenn W9IQ

I think you meant “switching supply”

Linear supplies, though inefficient,
have inherently little ripple.

No, I meant ripple from an undersized or ineffective cap bank in a linear supply.

- Glenn W9IQ
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God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KU3X

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #8 on: February 14, 2021, 05:36:34 AM »

The one piece of test gear I never owned or use is an oscilloscope. Would not that be the test gear needed to check for ripple and / or noise?

I have plywood with big load resistors attached to it to test for load capacity of my HB supplies.

Barry, KU3X
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W9IQ

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #9 on: February 14, 2021, 05:42:33 AM »

The one piece of test gear I never owned or use is an oscilloscope. Would not that be the test gear needed to check for ripple and / or noise?

That certainly makes things easier, Barry but the OP stated he only has a meter so he was wondering what he could do to check thing out using his meter.

- Glenn W9IQ
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God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9IQ

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #10 on: February 14, 2021, 05:49:55 AM »

Just to elaborate a bit on my ripple comments, in a switching supply the ripple frequency tends to be coincident with the switching frequency. In a linear supply, the ripple frequency tends to be 1X or 2X of the mains frequency depending upon the rectification topology. In the US, linear supply ripple is therfore typically seen at 60 or 120 hertz.

The OP can readily detect mains based ripple by using the AC voltage capability in his meter as I described earlier in this thread.

- Glenn W9IQ
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KM1H

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #11 on: February 14, 2021, 10:00:34 AM »

Quote
A 47µf Tantalum capacitor in parallel at the output terminals will reduce ripple tremendously.

Why tantalum since a high tolerance isnt needed? Tantalums are a regular PITA in amps when used as part of the timer circuits and are the first thing I toss and replace with a regular aluminum cap that measures very close to what was used.

Carl
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K1KIM

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #12 on: February 14, 2021, 10:51:22 AM »

Quote
A 47µf Tantalum capacitor in parallel at the output terminals will reduce ripple tremendously.

Why tantalum since a high tolerance isnt needed? Tantalums are a regular PITA in amps when used as part of the timer circuits and are the first thing I toss and replace with a regular aluminum cap that measures very close to what was used.

Carl

I am trying to find the research article I read on using Tantalum in lieu of other caps. It was quite extensive data.

I’ll post it if I can find it
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AJ4SN

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #13 on: February 22, 2021, 04:11:00 PM »

The reputation for tantalum caps exploding was earned because, contrary to the typical electrolytic, the positive terminal is sometimes marked with a black stripe. Because of this, it was not uncommon for one of my students to put them in backwards, and they will pop like a firecracker!

Stan
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G3RZP

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Re: Homebrew Regulated Power Supply: How to test for noise, ripple??
« Reply #14 on: February 23, 2021, 02:31:00 AM »

Some of the small 'tear drop' tantalums had an applications warning about putting them across a power supply that had a fast rise time because of the high charging current. I had  a lot of failures on one equipment before reading that - back in about 1970.

Another point about ripple. Don't put the reservoir capacitor on a different lead to the load, i.e. 'daisy chain' things so in order, you have rectifier, reservoir cap, load. Otherwise the lead resistance can reduce the effectiveness of the reservoir capacitor.
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