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Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC


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Old 09-20-2019, 01:31:49 PM
len k len k is offline
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Default Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

Low power Switching power supply ( 3.3, 5, 12V) in my 2 digital to analog TV converter boxes died. One ran ~ 5years, swapped in other never used box, it only lasted 2 months more. (Apex dt-502)

So I assumed AC ripple filter electrolytic caps dried up, I replaced 4 of them with others from my pile of used TV boards. Worked but new ones were too tall (3X), I installed others, now box only sort of works. So I want a way to measure uF before I install them, check if caps are any good.

With cap out-of-circuit, using analog VOM ohm setting , I short cap, attach ohmmeter, and watched SPEED of needle shoot up, and decay, the bad caps were definitely slower.

Nice crude test, but I'm looking for hard numbers on uF ......so I'm looking for cheap cap meter. Can you recommend one? I don't trouble shoot very often at all...so cheaper is better.

I'm ASSUMING uF changed, not ESR or leakage. Any insights ?

Would be nice to also ROUGHLY test caps in-circuit on board ......but that's not a requirement.

--------------------------------

For out-of-circuit .....I thought about using alkaline 9V transistor radio bat for bias and a small AC transformer for ~ 5 Vac 60 hz ...then measure current...... thing is any inductance of transformer would effect readings.... anyone try this. Any insights ?

I've done similar with AC motor caps and 120VAC utility power ......the uF readings were right on the money.... (so inductance of utility pole transformer was negligible). DO you think a small 120VAC transformer salvaged from a small portable radio would also have negligible inductance, so I can ignore it?
.

Last edited by len k; 09-20-2019 at 05:45:13 PM.
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Old 09-20-2019, 02:57:29 PM
dalmatiangirl61 dalmatiangirl61 is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

I'm far from expert status, but from what I've seen you need to test uf and ESR, a cap can show proper uf, yet still fail ESR test. Let me know what you find for cheap meters.
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Old 09-20-2019, 03:41:30 PM
dgibbs dgibbs is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

The ones I use at work are precision / high cost models, but Amazon seems to have a plethora of $20-30 models.
Can't speak for any of the models or brands they show as most I have never heard of, but the reviews didn't look too bad for some of them.
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Old 09-20-2019, 09:58:28 PM
Zephyr7 Zephyr7 is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

I was going to recommend the “almost all digital electronics” meter, but it seems to no longer be available.

I have a transistor tester from Peak Electronics in the UK and I’ve been both very happy and quite impressed with the little unit. They make an LCR meter too, so that might work for you:

https://www.peakelec.co.uk/acatalog/...nce-meter.html

Note that they make other useful stuff too so be sure to have a look at their other little testers.

Don’t try to test this stuff in circuit. There are too many ways to get goofy readings doing that.

BTW, caps come in voltage and capacitance ranges, but also lots of sizes and lead spacings. You can usually find a replacements that are the same size or smaller than the original parts for almost anything, but it can take some playing with the parametric search tools to find something that is both in stock and a functional replacement for your original part.

Bill
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Old 09-20-2019, 10:10:43 PM
len k len k is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

Looks like that one's ~ $75..... I was think around $20-40. Just something someone has ordered and found to work reasonable....plus not fall apart or die in 3 months.


In-circuit.......yes sneak path and funny reading potential.....but I've had good luck checking in-circuit diodes for basic open/short with analog ohmmeter. Think I only had one funny reading so I had to open the circuit. Transistors too..... usually....


For right now .....any ideas on my 9V bat + ~ 5VAC idea .....then measure the current, to determine uF. I have not measured DC caps yet.
.

Last edited by len k; 09-20-2019 at 10:46:24 PM.
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Old 09-20-2019, 11:16:19 PM
Pete Deets Pete Deets is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

Len,
Digikey has the cap you're looking for ranging from 12 cents each to $4.61 each here https://www.digikey.com/products/en/...=1&pageSize=25

Is your time worth a 12 cent part?..........PD
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Old 09-21-2019, 12:05:53 AM
len k len k is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

Well...... my scrap pile is available for immediate use... kinda helpful when the wife discovered it didn't work when she wanted to use it last night. Scrap pile let me get it working good enough for her to use last night.

Plus from what I'm seeing these filter caps likely also died on VCR that I liked.

Shipping is usually more than the parts.
.

Last edited by len k; 09-21-2019 at 02:33:56 AM.
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Old 09-21-2019, 09:03:30 AM
Jack Hottel Jack Hottel is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

I expect some of the cheap meters have capacitance capability, filter caps are probably 20% tolerance anyway so don't need to be too accurate. I have an Extech which works well. I considered it cheap when I bought it, but that was 10 years ago. I do not know of a cheap meter that will read ESR.
When replacing filter caps use higher voltage ratings if possible, that leads to longer life. Higher capacity gives better filtering.
If you don't have a supply house near you, Mouser or other mailer order is the only way. Even with one within forty miles I haven't been in years, too much traffic.
Jack Hottel
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Old 09-21-2019, 03:50:32 PM
Zephyr7 Zephyr7 is offline
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Default Re: Recomend a cheap DC electrolytic cap meter for me....~ 470uF 25VDC

Higher voltage rated caps don’t necessarily give you longer life unless the original cap was already running near the edge. Higher temperature ratings WILL ALWAYS give you longer life though. I like to use 105*C rated caps when I can on anything I want to last or make sure is reliable (like when I rebuild my generator voltage regulators, for example).

Len, $75 is crazy cheap for a decent LCR meter. My own LCR meter was around $1k. There are some little kits (I think velleman makes some) that let regular volt meters measure capacitance. Those circuits are an oscillator and a few other parts so pretty basic, but they work. That’s probably the only way to get down around your $20 range.

I suppose you could measure AC current through a cap and work out the capacitance value from that, but I don’t think you could easily linearize the result to get a direct reading on a basic meter. You’d also have the issue of calibrating it at a few points to have any idea of how accurate a reading you were making. For a simple pass/fail test though you’d probably be ok if checking against a known good cap of the same value.

Remember than an LCR meter can also read inductance and impedance, both of which are really useful when working with old transformers, motors, and generators. You can determine winding taps and other things that a simple ohmmeter can’t do.

Bill
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