Ultra cheap LCR meter to test capacitors in circuit?

[Peabody]

It seems Dave's $7 component tester generates 5V pulses, which I think would make it incompatible with in-circuit testing.  Is there anything available that would work in the $20 neighborhood?  I found a new meter from JYETech for about $55 that uses 0.5V pulses at 100 Hz or 1 KHz, which might work, but I'm just not sure I want to spend that much.  I very rarely need this capability at all, but in the last month have fixed a power supply and a TV where in-circuit capacitor testing would have been nice to have.  Would have to have ESR.

[abdulbadii]

https://www.ebay.com/itm/133262324817

~ $20

[BrokenYugo]

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/

[Per Hansson]

It seems Dave's $7 component tester generates 5V pulses, which I think would make it incompatible with in-circuit testing.  Is there anything available that would work in the $20 neighborhood?

If your component tester has been compiled with the menu and option enabled the feature is available:

C+ESR@TP1:3 The additional function "C+ESR@TP1:3" selects a stand-alone capacity measurement
with ESR (Equivalent Series Resistance) measurement at the test pins TP1 and
TP3. Capacities from 2µF up to 50mF can be measured. Because the measurement voltage is
only about 300mV , in most cases the capacitor can be measured "in circuit" without previous
disassembling. If the POWER OFF option is selected in the Makefile, the count of measurements
is limited to 250, but can be started immediately again. The series of measurements can
be finnished with a long key press.

Source: https://github.com/kubi48/TransistorTester-documentation/blob/main/pdftex/english/ttester.pdf

[Grandchuck]

Here is the waveform when testing a 220 uF capacitor with an ESR of 0.35 ohms using a BSIDE ESR02 Pro.

[Per Hansson]

Here is the waveform when testing a 220 uF capacitor with an ESR of 0.35 ohms using a BSIDE ESR02 Pro.

And here it is on the  BSIDE ESR02 Pro with the function "C+ESR@TP1:3" selected from the menu with a 220µF Suncon WX capacitor:


And for reference the default test mode:

[Peabody]

I've looked at the Github repo, and I think it's over my head.  It looks like I would have to install Linux, and deal with Make files that I know nothing about.  Are there any binary files with C+ESR@TP1:3 included that I could just flash to a 328P?

[Per Hansson]

My BSIDE ESR02 Pro that I did the above tests with still run the original firmware...
I think most testers will have this, but of course there is no guarantee what the Chinese sellers will implement...

[abdulbadii]

what tought there's a way to meter C in-situ as there'll be parallel line lowering the real C resistance measured?
must isolate at least a Cap pin

[Peabody]

My BSIDE ESR02 Pro that I did the above tests with still run the original firmware...
I think most testers will have this, but of course there is no guarantee what the Chinese sellers will implement...

Do you have a link to the one you bought?

[Per Hansson]

Do you have a link to the one you bought?

Here it is, I only paid $18.76 with free shipping for it back in November 2017 though...
https://www.aliexpress.com/item/32832292103.html

[Peabody]

It's somewhat more expensive now, and there's nothing in the listing to confirm that it has the low voltage option included.

In the past I've used a hand-held battery-powered scope to test capacitors, but only out of circuit.  It has a 1KHz 3.3V output test signal, and I connected the DUT across that output, along with the scope probes.  Shown below are pictures of a good and bad capacitor of the same nominal value.  The good cap looks pretty good at 2mV per division, but the bad one looks awful even at 200mV per division.  (At 200mV per division, the good cap is a straight line.)  Measuring only capacitance with another device didn't show much difference between the two caps, which is puzzling, but confirms that ESR is really what you need to know.

So instead of spending money on a new device, I wonder if I could modify the scope testing process a bit and be able to do in-circuit testing using stuff I already have.

First, the scope has a setting to change the test fequency to 10KHz, which I think should be done. 

Second, I would insert an opamp with negative gain to reduce the square wave to, say, 200mV, or even 100mV.  Then the scope probe and the leads to the  in-circuit caps would be across the opamp output.

What I'm uncertain about is what value the output impedance of the opamp should be.  I could make it 1K, or 47R, or something else, if it matters at all.  Of course I can just test different options and see what effect it has.

Of course this method wouldn't give me any numerical values at all other than what I can determine from the scope traces.  And I would need to have known good caps of various values to compare to.  But I have a pretty good selection to start with.

I know this seems a bit "how ya doin", as Dave would say, but it seems that this method would tell me which caps I need to replace, which is really all I need to know.

What do you think?

[Per Hansson]

It's somewhat more expensive now, and there's nothing in the listing to confirm that it has the low voltage option included.

I somehow got the word "and" in my reply above, it should have just said:
"If your component tester has been compiled with the menu option enabled the feature is available"

Basically what I'm trying to say is that any of these component testers that has the menu option compiled in will have this (and other measurement options) available.
And I think they basically all do, even the cheapest ones...

[Peabody]

I found a Youtube video showing the GM328 tester, and it shows that option on the menu.  The GM328 has a rotary encoder, which I assume is what you would want.  Without a case, it sells for about $17 at Aliexpress.

Well, I'm going to test my scope method to see if it will work.  I may buy a tester too, but really only need the ESR function.  But, you know, it's only $17.

[Peabody]

Just to complete the discussion on the option of using a scope to test ESR, I found that my little scope's function generator is adjustable up to 20KHz, and down to 50mV peak-to-peak.  Its ouput impedance is 100 ohms.  So I can use that to test for ESR in circuit.  I would probably run it through a 1K resistor just to not stress it.  The resulting waveform when testing a cap is reduced, but I can change the volts-per-division to compensate.  So the opamp isn't needed in this case, but I'm sure would have worked.

[Martini]

I basically have the same question but a lot less knowledge (and no scope with a function generator).

I've had a quick look at Github but there seem to be a pretty steep learning curve, starting with the difference between "k" and "m" firmwares, what sort of bootloader I need, what hardware is the most compatible, etc.


Is there someone who knows these little component testers well enough to advise me the best hardware and software for general use (identifying components off circuit and testing caps in-circuit, mostly)?

Capacities from 2µF up to 50mF can be measured.

What about values below 2 µF? I would like to test a 0.1 µF safety cap

[ingalopez]

For in circuit ESR test, Ive build it myself with the famous "5 transistor circuit", on an old analog multimeter. Never let me down!