[SOLVED] ESR capacitor meter circuits

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pgr2002

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I tried several ESR circuits but all failed. Recently I tried Allan Willcox model using TL082 and Poptronix circuit using TL084. I used 250ua meter. In the case of Allan Willcox design the meter is going off scale and comes down slowly to 50 percent of the dial. And there is no movement of dial in the case of leads connected/shorted or connected to caps. I constructed only the meter circuit leaving the buzzer circuit. In the case of Poptronix one there is no movement of needle even if the leads are shorted or connected to caps. Can anyone explain this peculiar behaviour of the circuits. Are there any working model of ESR who have constucted and is working in which case I would like to desparately try one of them. I am attaching the images of the two model that I tried.
 

I build a poptronix some years ago and it's still working
I changed the output because I didnt have an analog meter
so I use a simple LM3914 and a bargraph display module, I copied the datasheet example.
and it works fine.
here is the original poptronix pdf, along with tons of others esr meters schematics (I did not try them all...)
**broken link removed**
 
The basic concept of measuring ESR, is that you send a low V, high frequency AC waveform through the capacitor.

A healthy cap will pass practically all of the waveform.

If it has any amount of internal ESR, it will raise the voltage. (V = R * A)

This simulation shows the output from a healthy cap (switch closed), versus one with 0.3 ohms ESR (switch open).



Notice the amount of current required, to generate voltage on the ESR. Your oscillator must produce this amount of current, or you won't get much of a reading. If you want greater output amplitude, you must inject greater current.

The input resistor is necessary.

Input voltage must be kept low (a fraction of a V), so as not to turn on neighboring devices.

The waveform does not have to be a sinewave. It can be most any type.

Generally speaking, a faster frequency is best, especially for smaller cap values.
 

I do have one circuit with LM3915, which is attached herewith. Will this work if I connect this to the circuit in place of the meter.
 

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The TL094 design uses a CC (constant current) square wave applied to probe and then precision peak detected to measure ESR voltage drop. With high impedance back to back (2) diode clamps limit the probe voltage to +/-0.7Vp or 1.4Vpp on a scope.

Make sure one side of probes is grounded as shown ( slight error in drafting crossed wires being joined ) and supply your DMM measurements on critical nodes (ac,dc)
Start with Vdc 9V,4.5V and 0V at every location, even those not shown on schematic.

Although no DC bias is supplied, Electrolytic caps are usually safe with 10% of the forward rated voltage in the reverse direction so +/-0.7V max ought to be safe, especially at fairly low currents.

Did I say where are your photo's & DMM measurements?

With enhancements you can change the R range on the emitter resistor after you get it working to change the scale of ESR. in 2 or more decades.
 

If you want my help, pls answer my questions.

THis is an old school design for old school caps with fairly high ESR and would not be able to detect any difference in new caps between 1 and 100 mOHms.
 

Thanks for the help. What type of transformer can I use? Can I make my own, then in that case what could be the number of turns required?
Click to expand...
Hi again
T1 can be calculated according to the operation frequency of your circuit . are you familiar with it's calculation ?

THis is an old school design for old school caps with fairly high ESR and would not be able to detect any difference in new caps between 1 and 100 mOHms.
Click to expand...

Hi Sunnyskyguy
Of course you are absolutely right , but i intentionally gave him/her that circuit because thus it will be much clear to him / her that how an ESR meter does work and after building that or perhaps similar simple circuits , problems will reveal themselves so the idea of optimization will come through the mind .

Best Regards
Goldsmith
 

goldsmith said:
Hi again
T1 can be calculated according to the operation frequency of your circuit . are you familiar with it's calculation ?
Click to expand...

I do have few transformers, and with one it did work well with 250ua meter. I do not have any bad caps as such now to test them, I tested with all the good caps and with low ohms resistors and i think it is working fine. Will it be possible to check caps which are in circuit without the leads soldered out?
 

I do have few transformers, and with one it did work well with 250ua meter.
Click to expand...
Hi again
I'm afraid but i didn't get your mean ! what thing worked fine ? with what ?
May you ask about your problem more clear ?
 

In response to your message I built as given by you the ESR meter. It did work fine with one of the transformers.
Click to expand...
Then nice to hear that . is there any other problem that perhaps i can help ?

Best Wishes
Goldsmith
 

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