What an analog ESR meter will and won't do

[ratdude747]

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

ESR meters are AC ohmmeters. They work by passing high frequency AC instead of DC thru the tested component. The idea is that a resistor will still be a resistor in AC, but for a capacitor (which cannot pass DC from one side to another, so it just charges up with it), you will instead see how much resistance there is when passing the AC signal - ie, the ESR.

I wonder how hard it would be to DIY an esr meter then.... a digital one would be a pain as it would take an analog to digital converter and then lcd display drivers in addition to the transformers and whatnot needed to go from 120VAC to what was needed, plus the circuity to measure resistance.

it would be epic though.

[jcotton]

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

Just use a low frequency signal generator (10-100 kHz) and a scope. Here is one reference: http://www.anatekcorp.com/ttg/tiptrick.htm#Scope%20ESR
I used this method in the 1980's when I was a high school student.

I have the Badcaps ESR Meter from MiLuElectronics in ?Romania?, and the ESR-micro V4.0 from www.radiodevices.ru which is sold in the US on the www.prc68.com website at the bottom of the products page (no relation to seller).

The version of the MiLu meter I have does not have any protection for charged caps other than the thin trace on the board may fry and save the electronics (comment on
that issue seen in tekscopes, tekscopes2, or hpagilent Yahoo group). I have simply been careful since I saw the warning. Newer units may incorporate one or two additional parts to fix this. Several designs available on the web have this protection. I have had it for about two years and it has worked well for me.

The ESR-micro displays the resistance and capacitance on the LCD. It has different beeps including a unique sound for a cap with ESR of over ~3. It will display "only" for
the C value if there is no capacitance. The measurement method is similar to the Bob Parker Blue ESR meters. I have had this one for two weeks and like it so far.

I started with a DIY ESR meter based on several schematics available on the web. My junk box didn't have exactly what anyone else had used... I coupled an LCD to
a dual op-amp design with an input protection circuit. Just calibrate it with a real resistor of known value.

[TheLaw]

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

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.

Eventually I may want to try to make one of these cheap analog ESR meters...What modifications did you make (exactly) to achieve the range you got on yours?

Thanks.

[jsog]

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

I wonder how hard it would be to DIY an esr meter then.... a digital one would be a pain as it would take an analog to digital converter and then lcd display drivers in addition to the transformers and whatnot needed to go from 120VAC to what was needed, plus the circuity to measure resistance.

it would be epic though.

The AC signal is low voltage, my analog one is 0.25V. You can't go too high or it'll start triggering semiconductor junctions. AC, well a 100KHz square wave is pretty easy to generate from a microcontroller. Many have A/D inputs, and libraries for controlling character LCDs are common.

The hard part is doing it well. Input protection is really important on an actual tool. Accuracy, too.

[Th3_uN1Qu3]

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

Eventually I may want to try to make one of these cheap analog ESR meters...What modifications did you make (exactly) to achieve the range you got on yours?

Thanks.

I used a base drive transformer scavenged from an ATX supply. I'll have to look at it to tell you the pinout however... I used 1N5819 diodes in place of 1N4148. Also one of the 10 ohm resistors (doesn't matter which one) was replaced with a 1.8 ohm one to provide a lower impedance for the measurement signal. You can do better if you really make an effort to minimize series resistance of the secondary winding of the transformer, but it may not fit on a small core like an EE16 or EE19.

Other ways of generating a low impedance signal are valid too of course, but the transformer method has the advantage of being simple, and you can use a single dual opamp for the whole thing.

[TheLaw]

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

I used a base drive transformer scavenged from an ATX supply. I'll have to look at it to tell you the pinout however... I used 1N5819 diodes in place of 1N4148. Also one of the 10 ohm resistors (doesn't matter which one) was replaced with a 1.8 ohm one to provide a lower impedance for the measurement signal. You can do better if you really make an effort to minimize series resistance of the secondary winding of the transformer, but it may not fit on a small core like an EE16 or EE19.

Other ways of generating a low impedance signal are valid too of course, but the transformer method has the advantage of being simple, and you can use a single dual opamp for the whole thing.

Ahh. Is it possible you make a small write-up? Maybe some pics? I'm not sure if anyone else is following this thread, but this would be one of the only analog ESR meters that might be capable of detecting failure of lower-ESR caps, which is helpful.

If you're not feeling up to it, don't, but it might be a good resource.

[ipman]

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

@all: ther are no Fluke multimeters which can be used as ESR meter because they measure resistance by applying a DC current through resistor.
Earlier, when I compared the ESR meter with the Fluke, I was measuring a pure resistor out of circuit. On that kind of measurement, it does not matter which method you use, the result is the same. Then I've compared the values.

[TheLaw]

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

I used a base drive transformer scavenged from an ATX supply. I'll have to look at it to tell you the pinout however... I used 1N5819 diodes in place of 1N4148. Also one of the 10 ohm resistors (doesn't matter which one) was replaced with a 1.8 ohm one to provide a lower impedance for the measurement signal. You can do better if you really make an effort to minimize series resistance of the secondary winding of the transformer, but it may not fit on a small core like an EE16 or EE19.

Other ways of generating a low impedance signal are valid too of course, but the transformer method has the advantage of being simple, and you can use a single dual opamp for the whole thing.

I got interested in making one again. Can you explain what you mean by transformers and lowering their series resistance etc?

Thanks.

[BlackJack18]

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

I am retired, 40 years in the Electrical trade, and have always used an anolog triplet 630-A. It has served well for testing Caps, resistors and diodes. It is powered by two batteries, one 30 volt and one 1.5 volt.
All me crazy but I feel an anolog meter always tells the truth. The digital meter some times show untrue readings. This is my story and I am sticking to it!!

[PCBONEZ]

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

Analog meters can't read the 0.10-0.01 ohms range accurately [+/- .01 ohms or so] and that is what is needed for modern low ESR work.
Those numbers might be on the meter face but if you are using the bottom or top 1/4 of the scale on analog test equipment then you aren't using the meter ranges properly.
The highest accuracy is in the middle of the scale.
.
Analog meters are better for a lot of things but low ESR isn't one of them.
At ohms that low it takes too much meter current to move the needle and still get an accurate reading.
.