Cheaper ESR meter

[notallbad]

Re: Cheaper ESR meter

Hi Mubashir
Just to confirm, is this the one your working on?
http://www.qsl.net/iz7ath/web/02_bre..._esr/index.htm

According to post No.4:
'At the output of the opamp we separate the AC and the DC components. First we see a low pass filter, composed by a resistor and capacitor, which allows the DC component to drive the base of the transistor which controls an LED. This LED will light if the capacitor under test is shorted or has high leakage current.'

My understanding would be that if you were to connect the 2 test probes together then this would act as a shorted cap and light up the LED.

Does your LED light up when the 2 probes are connected? This should work regardless of meter output.
This would at least show that something on your prototype is working.

Another point would be to check which resistors (R20, R21) you are using, the schematic shows 1k trim and 680ohm for a 500uA meter, what rated meter are you using? Have you made adjustment to R21 with any results obviously with probes shorted or with resistor across probes?
Rob

[mmir2012]

Re: Cheaper ESR meter

Thanks for quick reply. Yes that's the link. Two changes I have made or you can say deficiency. I saw another diagram that eliminated one NPN transistor TR1. May be this changes is making fault the move the meter needle. Second changes is that I am using 100 uA meter instead of 500 uA meter. Now what to do to use this 100 uA meter. As a trim pot I am using 2.2K preset and 680 ohm resistor too. Please help me how to use 100 uA meter instead of 500 uA meter. I have already bought it. I think I have cleared all the picture.

Wait for reply.

Thanks.

Mubashir

[budm]

Re: Cheaper ESR meter

If you eliminate TR1, then T2 will not get enough drive to drive the Bridge so the out from the bridge will be too low. You should build it as shown.an you show us the other circuit that only has one bridge driver transistor, they will have to set up one transistor to have enough gain to drive the bridge of set the receiving Opamp gain to be higher.

[notallbad]

Re: Cheaper ESR meter

Provide a link to the diagram that eliminates one NPN transistor.

I believe it is actually GS3's very own design modification but he also mentions that other components need tweaking.

I would recommend building as per the original circuit, prove it works and record your findings. Then make any modifications and prove it still works be referring to your recorded findings to compare results.

[mmir2012]

Re: Cheaper ESR meter

Thanks again.

You can see attached file for one transistor circuit diagram which I use. Now I am going to add transistor and other components value as per original diagram. Soon I shall back. One thing I want to ask again that I don't have 500 uA meter. But I have 100 uA meter. Is it possible to use this meter instead of 500 uA meter.

Mubashir

[budm]

Re: Cheaper ESR meter

You can use the 100uA, it will be more sensitive since it will only take 100uA to drive the meter full scale, so you will have to use larger resistor in series with the meter.
Here is the full text of the one transistor design which he indicated that the second transistor is needed.

[notallbad]

Re: Cheaper ESR meter

Mubashir

Find troubleshooting tips in the above link.

I shall be building various circuits in the next week or two, prototyped on a breadboard.

Keep going with yours and let us know how things turn out!

[mmir2012]

Re: Cheaper ESR meter

Good day for everyone,

I further worked on it and changed resistors,add one transistor as per original diagram. Now meter is working properly. But as I am using 100 uA instead of 500 uA Meter I have changed the resistor value as per circuit requirement. One problem I am facing now that when I am checking capacitor, LED lit every time when I checks capacitors. May be I have to increase the LED current limiting resistor 680 ohm to above. what u say ? Thanks again for helping me.

Mubashir

[notallbad]

Re: Cheaper ESR meter

I would leave R7 as 680 ohm but check that you are using the correct resistor at R15.
More likely is that Q3 transistor is incorrectly connected in your circuit. (Base is connected between R15 and C6, Collector is connected to the LED and Emitter is connected to GND).

Are you able to post a picture of your build?
I would be interested in seeing it!

[budm]

Re: Cheaper ESR meter

Yes, check your connection, the LED should only light up hwen you have unbalance DC on the bridge which will only happen when the capacitor is shorted, or when measure the resistor since short or using resistor will let the DC offset to go through the short or resistor, but it cannot go through capacitor, that is how the short LED indicator works.

[mmir2012]

Re: Cheaper ESR meter

Good day for everyone,

LED is now properly working. A capacitor was missing at that stage. A good news is that after checking and testing some capacitors I checked my oscilloscope which was out of order, horizontal line was missing only dot was showing there. I opened oscilloscope cover and checked power supply portion, one capacitor I found that was giving more difference than other. I simply changed that capacitor and ON power supply. I amazed to see that fault have been gone. I am very happy to make very useful gadget for my workbench.

After repairing oscilloscope I checked frequency at the end of both probes of ESR. Showing 153 KHz is there. If 100 KHz is necessary then I have to fix it, otherwise its working well. Thanks.

Mubashir

[notallbad]

Re: Cheaper ESR meter

Adjust resistor on TL084 pin 13 to bring freq close to 100khz.

[mmir2012]

Re: Cheaper ESR meter

Ok i shall try it. Today I am working on case/box for proper casing to protect it. Really found it very useful specially as I said that I have repaired oscilloscope which was out of order a long time. I am very happy. Thanks for reply.

Mubashir

[notallbad]

Re: Cheaper ESR meter

Keep us posted.

[budm]

Re: Cheaper ESR meter

That C5 you are using, is it ceramic X7R, Y5U, NPO, ETC? You should look and see if the freq changes with temperature.

[notallbad]

Re: Cheaper ESR meter

So, I built the meter as per link on post #1, prototyped on a breadboard using 1% 1/4w resistors throughout and a VU meter.
Supply voltage is provided by a 9v dc mains adapter.
+4.5v and -4.5v confirmed at IC TL084 Pins 4 and 11 measured across Pin 1.
With probes open, no LED and no movement on the meter.
When probes shorted the LED illuminates as expected and full deflection on the meter is achieved by adjusting the pot.

Issues I'm having:
When connecting a cap to test probes the deflection on the meter is more than full deflection (when probes shorted).
This may be correct but my logical thinking thinks otherwise.

I would like to confirm 100khz at the probes, I do have an oscilloscope (S51B) with probe but unsure how to use it.

[budm]

Re: Cheaper ESR meter

The cap you are testing, what kind and value?

[notallbad]

Re: Cheaper ESR meter

Thanks for getting back to me.

All electrolytic and new caps.

Axial 22uF 25V SU
Radial 47uF 35V Cosonic
Radial 1000uF 6.3v NHG
Radial 220uF 6.3v Samhwa
Radial 47uF 10v Rubycon

[budm]

Re: Cheaper ESR meter

Do you have 1 Ohm, 5 Ohms, 10 Ohms resistors to use and see what reading you will get?

[notallbad]

Re: Cheaper ESR meter

Hi I have known 5.1 and 10ohm 1% resistors and also a 2 ohm possibly 1w resistor.
The results are as illustrated which appear to be proportionate according to the resistance ranges.
Pic 1 - Probes shorted
Pic 2 - 2 ohm
Pic 3 - 5.1 ohm
Pic 4 - 10 ohm