5 Transistor ESR Meter Design

[Jay_Diddy_B]

JLLE21,
The frequency of the oscillator is not very critical. 100kHz is the industry standard for ESR measurement. When troubleshooting equipment the idea is to find bad capacitors.

If you don't have or unable to find the 1500pF capacitor you put 1000pF and 470pF in parallel. With SMD capacitors you solder them on top of each other.

The 555 timer will also work. Connect the output of the 555 timer to the base of Q3 with a 10k resistor.

If the capacitors are good they will not conduct dc, the resistance will be high. A good capacitor will have a low impedance at 100kHz. The short detector is to detect parts with a low dc resistance.

Regards,

Jay_Diddy_B

[JLLE21]

JLLE21,
The frequency of the oscillator is not very critical. 100kHz is the industry standard for ESR measurement. When troubleshooting equipment the idea is to find bad capacitors.

If you don't have or unable to find the 1500pF capacitor you put 1000pF and 470pF in parallel. With SMD capacitors you solder them on top of each other.

The 555 timer will also work. Connect the output of the 555 timer to the base of Q3 with a 10k resistor.

If the capacitors are good they will not conduct dc, the resistance will be high. A good capacitor will have a low impedance at 100kHz. The short detector is to detect parts with a low dc resistance.

Regards,

Jay_Diddy_B

Hello friend, it has been difficult to me this project, i'm stuck and feel ashamed about it.
started colecting the components following your schematic and thinking the anakiev board posted was exact to your design, but now looking closely is different, has 28R, an TP are different.
can you please post a non-SMD board view? (still missing components to find for mine)

i'll appreciate your help

best regards.

[Jay_Diddy_B]

Hello friend, it has been difficult to me this project, i'm stuck and feel ashamed about it.
started colecting the components following your schematic and thinking the anakiev board posted was exact to your design, but now looking closely is different, has 28R, an TP are different.
can you please post a non-SMD board view? (still missing components to find for mine)

i'll appreciate your help

best regards.

Forum user Anakiev posted a design in this message:

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg5137590/#msg5137590

I have not made a thru-hole version myself.

Jay_Diddy_B

[Anakiev]

@JLLE21 I've uploaded the schematic in the original post.
R28 isn't something I've added this is the pot for calibration. All TPs are where my wires are coming from.

This is R28 in the original schematic:


Edit: Maybe you are looking an older schematic because all of my TPs match with the original ones.

[DiodeIndia]

This circuit is very good and very simple to make I used old component from PC motherboard and it's working fine but it's showing 112ua in digital metre and also in my area they are no suitable metre in good price I have one with the range of 250ua 

[RoGeorge]

Try to increase the gain of the last 2 transistors, so to use the 250uA analog uA-meter as indicator.

For both Q4 and Q5, replace their resistor in the emitter with a smaller one (the resistor for AC, the one in series with a capacitor, not the resistor for DC bias).  In the schematic from the very first post of this thread, the AC gain resistors are R16 and R21, replace them with something like 10..15 ohms instead of the original 33 ohms.

[Jay_Diddy_B]

DiodeIndia asked:

This circuit is very good and very simple to make I used old component from PC motherboard and it's working fine but it's showing 112ua in digital metre and also in my area they are no suitable metre in good price I have one with the range of 250ua 

Welcome to the forum!!

Have a look at this schematic, it shows the modifications required for a 250uA meter:

Further details can be found here:

https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg2457936/#msg2457936

Regards,

Jay_Diddy_B

[DiodeIndia]

Thanks  :-+by the way in place of C2 I am using 1nf capacitor instant of 1.5 nf so what will be difference in circuit and I have some more problems when I move the testing leads the value is getting about 5 to 10% change and my maximum short circuit current is 130 UA or sometime 140 but I am using 1% tolerance resistance so what is the problem 

[Jay_Diddy_B]

Thanks  :-+by the way in place of C2 I am using 1nf capacitor instant of 1.5 nf so what will be difference in circuit and I have some more problems when I move the testing leads the value is getting about 5 to 10% change and my maximum short circuit current is 130 UA or sometime 140 but I am using 1% tolerance resistance so what is the problem 

DiodeIndia,

If C2 is smaller, the frequency will be higher. With C2 = 1nF the frequency will be around 150 kHz.

The meter, described here, measures impedance. The inductance of the test leads is part of that impedance. Keep the test leads short or twist them together to reduce the inductance.

To increase meter deflection reduce the value of the fixed resistor in series with the meter. As a starting point reduce the value by a factor of 2.

Jay_Diddy_B

[ME]

I just looked at the datasheet for my 18650 cells , The ir is tested at 1khz , If the freq of this esr meter was lowered to 1khz could it be used to check the ir of these 18650 cells , Datasheet attatched.

[Jay_Diddy_B]

I just looked at the datasheet for my 18650 cells , The ir is tested at 1khz , If the freq of this esr meter was lowered to 1khz could it be used to check the ir of these 18650 cells , Datasheet attatched.

This ESR meter will be damaged if connected to a battery.

In this thread I describe a circuit can be used for measuring the ESR of cells:

https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/msg3296986/#msg3296986


Regards,

Jay_Diddy_B

[RoGeorge]

A 0.68uF or so capacitor in series with the battery would do it, and calibrate the zero with the 0.68uF in series with a short circuit instead of battery.

I didn't try, but my guess is, the frequency won't matter that much when measuring batteries.  So, it might not be necessary to change the frequency when measuring batteries ESR.  After all, this instrument produces a square wave, which means the spectrum would be more like a frequency comb anyway, and not like a single spectral line.

[Fr_J_K]

Hello Jay_Diddy_B,
Congratulations on a lovely and practical design. I put together the 1mA version:
https://www.eevblog.com/forum/projects/5-transistor-esr-meter-design/msg3008380/#msg3008380
It works but still only up to 150uA and for that I had to raise the supply to 9V. Changing the resistors around Q4 and Q5 made v. little difference. It works as intended but only with a 50 or 100uA meter. I'm thinking about swapping Q4 and Q5 for Darlingtons and see what happens. Will post the results later.

[Fr_J_K]

Hello Jay_Diddy_B, hello All,
I substituted the output transistors Q4, Q5 for a pair of home made NPN Darlingtons and it works great now with 500uA. I piggy-backed two 2N3904 for each replacement. You could also use a factory NPN Darlington in TO-92 casing, such as BC517. But then the E C pins are reversed.

Voltage on the probes is 86mV, freq. 86 kHz measured with Fluke 87V. Supply Voltage has to be precisely regulated for consistent readings.

Beautiful design overall. Thank you, Jay_Diddy_B.
Try a pair of Darlingtons on the output if the meter you have requires more oomph to deflect.