Analog ESR meter design

[ben7]

Re: Analog ESR meter design

Ok, I built a ~50khz, ~50% duty cycle LM555 timer circuit. That drives a transformer via a coupling capacitor. The transformer takes in 5vac and puts out about 225mV open-circuit. I used this page and the diagram on it to get my ideas from.

I can post some pics tomorrow, but so far I have only made the capacitor testing portion. I tested a 63v 330uF NCC LXZ -> 216mV. I tested a bulged capXon KF (1000uF 25v) ---> 43mV!!!

The 555 has no problem powering the transformer, as its 200:15 ratio. As described on this page, the transformer takes the high-voltage, high-impedance, and makes it low-voltage, low-impedance.

[vhr]

Re: Analog ESR meter design

ESR meter for capacitor LOW ESR in circuit.
http://radiokot.ru/konkurs/10/

[ben7]

Re: Analog ESR meter design

ESR meter for capacitor LOW ESR in circuit.
http://radiokot.ru/konkurs/10/

Wow, good link! Never seen that one before. Interesting how the circuits aren't even in a box xD

[budm]

Re: Analog ESR meter design

Double WOW!, it can test any form factor CAPS, I like the way he made the testing pads for testing the surface mounted cap.

[vhr]

Re: Analog ESR meter design

ESR meter with indication of leakage and short circuit.
ESR-0...75Ohm
F-80kHz
Vp-p<30mV
HL1-leakage 0...100Ohm
http://radiokot.ru/konkurs/21/

[Agent24]

Re: Analog ESR meter design

I wonder how easy it would be to replace the analog meter with a digital readout using 7400\4000 series logic

[ben7]

Re: Analog ESR meter design

I wonder how easy it would be to replace the analog meter with a digital readout using 7400\4000 series logic

I think it would be quite complicated, using at least half a dozen IC's

-Ben

[tom66]

Re: Analog ESR meter design

Here's my stab at an ESR meter. It passes a constant current sine wave thru the cap (converts square wave to sine), picks up the voltage and outputs an AC (100kHz) voltage with an amplitude approximately equal to ESR. A scale factor control would allow for compensation for true-RMS or average-reading multimeters. May as well use the meter's conversion circuitry...

In theory, as it is all ac coupled, it can handle a fully charged capacitor with no problems. Maximum voltage would be 630V or 1000V depending on cap limits.

TODOs - think about AC-to-DC conversion, think about split supplies (try and avoid them.) Ideal meter would run off either 2pc or 3pc of 1.5V AA.

[budm]

Re: Analog ESR meter design

The circuit in post 45, the output is rectified to feed analog meter, you may be able to just use cheap DMM that can read low DC mV range.

[budm]

Re: Analog ESR meter design

This my experiment with ESR meter using some scrapped parts I have in my parts bin, LM555 and 2N3904. Works pretty well compared to my SECORE LC75 for the reading range I want.

[momaka]

Re: Analog ESR meter design

This my experiment with ESR meter using some scrapped parts I have in my parts bin, LM555 and 2N3904. Works pretty well compared to my SECORE LC75 for the reading range I want.

Cool.
Mind posting a schematic or link where you might have gotten the schematic? I need to build me one as well.

[ben7]

Re: Analog ESR meter design

Good job!

[budm]

Re: Analog ESR meter design

Thanks, here is the Diagram & BOM. I am going to make smaller board to fit into old RadiShack Analog meter, since proof of ciruit is verified and it works.

[budm]

Re: Analog ESR meter design

By the way, for more bias stability of Q1, you can add 100 Ohms between Emitter and Ground and bypass it with 0.47uF cap, and if you want adjustable gain, then put that 0.47uF cap in series with 500 Ohm trimpot for gain adjustment.

[budm]

Re: Analog ESR meter design

Rev2 with added Adj gain and bias stabilizer for Q1.

[sebr]

Re: Analog ESR meter design

Rev2 with added Adj gain and bias stabilizer for Q1.

Thanks for the update, just what i was looking for

[momaka]

Re: Analog ESR meter design

Thanks, here is the Diagram & BOM. I am going to make smaller board to fit into old RadiShack Analog meter, since proof of ciruit is verified and it works.

Thanks.
I think I will be building one as well sometime this week.

[sebr]

Re: Analog ESR meter design

Just to make sure: this meter isn't capable of testing caps in circuit, or?

Maybe in next revision you could add diodes + bleed resistor to protect the circuit if a charged cap is connected?

[Agent24]

Re: Analog ESR meter design

Even the meters that can test in-circuit can still be fooled by paralleled capacitors or other components, as always, the best test for just about anything is out-of-circuit.

I don't see a huge reason for testing in-circuit anyway. When doing a recap it's usually because you have crap brands and some have already failed.

In such a case it's more sensible to replace the lot anyway for better reliability in the future. Testing their ESR becomes more of an informational postmortem exercise.


Still, I guess it's better to have the feature and not want it than want it and not have it.

[budm]

Re: Analog ESR meter design

agent24 is correct, if you have a bunch of caps in parallel, the bad one will not show up as having the high ESR. I always test component out off the circuits.
@sebr: I did add the 1N4007 Diodes to the test terminal, you can add it if you worry about accidentally attach a charged caps to the tester, and if you want more complex, you can add the cap and a bleeder resistor also.