What an analog ESR meter will and won't do

[ipman]

Re: What an analog ESR meter will and won't do

@ ipman: Isn't that the one from x-roast.home.ro? I wanted one myself but i wasn't sure how well it did.

Yes, this is the one. Works just fine.

I've just aquired today a 1964 analog volt-ampermeter for two bucks. Works like new, hard to believe.


@Longbow: such fine resolution and accuracy will be required only in very special and particular applications and caps will be expensive and big. Never seen one of these, but as far as I've encountered caps (until now) had no such low values. In usual device repairs, like monitors, TV's, motherboards, etc.

[Longbow]

Re: What an analog ESR meter will and won't do

I did say prefer, and if caps with ESR at that ultra low range didnt matter beyond the 100th then why even bother having specs for them to the 1000th. My guess is because sometimes it does matter.

It was the original question that caught my eye, namely what an ESR will and won't do. Apparently a lot of people expect them to do everything. But it is a fact that a piece of test equipment no matter how wonderful is only as good as the person operating it.

Objectively speaking, manufacturer's data sheets are almost always massaged to indicate the best possible spec under conditions that will never exist in the real world. Any specification may be claimed on these data sheets, and often can be grossly incorrect. Designers do not take these numbers as fact, but rely on their own testing to establish the working values of capacitors, semiconductors, etc. Having said as much, the data sheet is all you have as a starting point for selecting components. Also, good engineering practice always adds a comfortable de-rating factor even if the claimed specification is accurate.

As far as an ESR meter that could be accurate to the 1/1000 of an ohm - would that level of accuracy assist anyone in repairing faulty equipment, or in the evaluation of an individual part? Answer: no. I've never seen such a unit, but you can be certain it is not a troubleshooting aid. Similar to high end digital multimeters, resistance reading can be made at extremely low ranges, and usually demand 4 leads, careful attention to lead lengths, shielding and connectors. So if it were possible, we could cull out the questionable capacitors with an ESR of .008 ohms, from the good ones showing an ESR of .002 ohms?

[Th3_uN1Qu3]

Re: What an analog ESR meter will and won't do

As with voltmeters, I prefer the digital ones, since they are easier to read (no parallax error).

Me too. I don't even own an analog multimeter... But you do need all those fancy goodies like TrueRMS to replace a good analog meter. An analog will not lie regardless of the waveform of the voltage it is measuring. For a digital one to do the same you need some extras.

@ ipman: Isn't that the one from x-roast.home.ro? I wanted one myself but i wasn't sure how well it did.

[japlytic]

Re: What an analog ESR meter will and won't do

As with voltmeters, I prefer the digital ones, since they are easier to read (no parallax error).

[ipman]

Re: What an analog ESR meter will and won't do

There is an ESR-meter made by somebody here in Romania which has 2 decimals.
It's spot-on compared with a Fluke 189, which also can measure with 2 decimals.
Not bad for a device that costs around 30 euros, but still not as stable and calibrated against standards like the Fluke.
Here's a picture measuring a (still) good low-ESR 470uF/25V cap, Hermei LL series.

To add some on-topic: with a digital ESR meter you can choose the best piece in a batch of caps.

[brethin]

Re: What an analog ESR meter will and won't do

I did say prefer, and if caps with ESR at that ultra low range didnt matter beyond the 100th then why even bother having specs for them to the 1000th. My guess is because sometimes it does matter.

[Th3_uN1Qu3]

Re: What an analog ESR meter will and won't do

A design i have seen even included shorted cap detection. I've never gotten that particular one to work though. You DO have a continuity function on your multimeter though, don't you.

In fact, the ESR value can often be 5 to 10 times the advertised value before it affects circuit operation.

Exactly. And this is something that a simple analog meter WILL detect reliably.

[Longbow]

Re: What an analog ESR meter will and won't do

I'd say the above information is misleading at best. The Blue meter is the only ESR meter that comes to mind that gives a 2 digit readout below 1 ohm. There may be more accurate digital readout meters, but the cost would be prohibitive and unnecessary. Is the Blue meter precise to the 100th of an ohm? I don't know and it doesn't matter anyway. People incorrectly assume that a capacitor's ESR must closely equal the manufacturer's claimed value, or else it is faulty. In fact, the ESR value can often be 5 to 10 times the advertised value before it affects circuit operation. As with most test equipment, an experienced technician is required.

For the most part, the equipment is a troubleshooting aid and not a laboratory calibration standard. Analog meters have one advantage - you can get an instant relative measure and do not have to concern yourself with actual numbers. Therefore, an analog meter such as the Capacitor Wizard has that advantage.

In fact, the one thing an ESR meter cannot do is detect a shorted capacitor, since it will read a low value on the meter, and look like a perfectly good ESR reading.

[brethin]

Re: What an analog ESR meter will and won't do

I would prefer a meter with a range of .001 to say 5 ohms for it to be useful to me.

[Th3_uN1Qu3]

I'm sure you've all seen those analog ESR meters which use a microamp meter (or really, any meter with a needle, mine for example uses a cheap dB meter), and some of you may wonder whether they will be enough for finding bad caps that aren't bloated.

Short answer: Yes.

I have built this one: http://ludens.cl/Electron/esr/esr.html and with a few small modifications it can easily spot differences of 0.1 ohms, the other end of the scale being at roughly 15 ohms. This makes a good all-rounder, and it's suitable for checking high voltage capacitors as well, which generally have a few ohms ESR.

What this type of meter won't do is spot a cap that is low-ESR and not yet bad, just out of its tolerance. It does not have enough resolution for that (unless you've got your hands on a really big meter movement). If you work only on computer stuff with ultra low ESR caps, you're better off buying a digital ESR meter, but i bet 95% of capacitor problems can be diagnosed with one of those analog meters built from scrap parts...

Most of the non-commercial digital ESR meter designs i've seen so far are pretty dodgy, so if you really want a digital one, i'd say buy it. Or wait for me to design one.