[SOLVED] Help to build a working model of ESR meter

[pgr2002]

I tried to make several ESR meters but all failed. I am attacing the images of the ESR I tried to build. Has anyone know the working model of the ESR meter and may be pleased to send/attach the circuit diagram of the same.

 

[chuckey]

Your first three diagrams are too small to read. So circuit 4, what did you use for the transformer? The pot should be set to give 1/2 the supply voltage output (not critical). If you short out the capacitor terminals , does the meter read full scale+++?
Frank

 

[Kripton2035]

build the poptronix one here : **broken link removed**

it works, and uses simple components like opamps and resistors, no difficult-to-find-or-build transformers

 

[pgr2002]

Thanks for response. I used a small transformer. the meter does not read full scale (no response) if the leads are shorted.

 

[pjmelect]

I don't think that any of the circuits is very good, but they should work. Why did your builds fail? The main failing of the non transformer circuits is that the test voltage is to high to measure the ESR in circuit, however you do not need to use a transformer to do this.

 

[pgr2002]

Thanks for the reply. I will go ahead with the circuit and let u know.

 

[D.A.(Tony)Stewart]

It would help if we knew what Caps you wanted to test for ESR. Batteries and capacitors alike have a wide range in ESR spanning many decades.

 

[chuckey]

If the meter does not read, full scale when the leads are shorted then there is a serious fault. Either the oscillator is not running or the opamp does not work. First unsolder one end of the 22 ohm resistor going between earth and the 1MF cap. Touching the input pin 6 should make the meter read something, if it does not, the circuit needs checking out. Once you have got this bit to work, you can use it to measure the output from the oscillator.
Frank

 

[pgr2002]

As suggested by you, by touching pin 6 did make the meter to read and there was viz.2v on 10v scale (approx.). but still the entire circuit does not show any deflection even after shorting the leads. please can you suggest something about the circuit.

- - - Updated - - -

the meter does not read evenif the capacitor terminals are shorted. could you please have any suggestions to this behaviour.

 

[chuckey]

It would seem that the metering circuit is working after a fashion, so the problem must be that the oscillator is not running. What transformer are you using? To check the oscillator direct, connect the 1 MF capacitor unsoldered before to PIN 1 of the first TL072. There should be a lot of AC there. The 100K pot should be set so its output is 1/2 of the battery voltage.
Fraank

 

[pgr2002]

I connected 1mf capacitor to pin 1 of TL072 the same deflection i.e. 2v on 10v scale. i also attach the spice list of the circuit if this helps to find the fault

 

[chuckey]

From your multisim listing :-
*## Multisim Component T1 ##*
xT1 5 0 8 0 Tran_T1
.subckt Tran_T1 p1pos p1neg s1pos s1neg
***Primary coil 1
G1 p1pos p1neg value={-1/400*(20*I(Es1))}

***Secondary coil 1
Es1 s1pos s1neg value={V(p1pos,p1neg)*20/400}

.ends
Err, what this in English?, turns ratio and the primary inductance? - micro H?, milli H? Henries?
Frank

 

[pgr2002]

Sir,

the transformer used here is based on turns ratio - pri/sec as 400/20.

 

[chuckey]

And its primary inductance is. .. . .? Or does your simulator regard it as a perfect transformer with infinite primary inductance?
Frank

 

[pgr2002]

No and there is no indication as such that it is the perfect transformer and also there are no errors as such.

 

[D.A.(Tony)Stewart]

ESR meters are great for measure the state of charge of Amp hr capacity of batteries too.
Mallory Energizer uses the method of measuring the voltage using two current limited sources 5 mA and 505 mA thus the difference in voltage is the ESR . It does this after 50ms of chemical equilibrium.
LiPo battery ESR meters use the max safe current of eight (8) watts ( dumped into battery ESR) per Ah capacity for testing batteries and from this you can compute the ESR and State of Charge.

I suggest you use the same approach for measuring ESR in shorted boards and capacitors. TO perform this you need a capacitor with LOW ESR ~ 1mOhm and a 100mV shunt resistor or 0.1V/0.5A= 200 mOhm and a switch gate pulse of 50ms with a Sample & Hold to measure the voltage after the discharge is opened.

apply 1mA measure Vf on 200mOhm shunt thru probes to target, when instrument reads 200uV it knows you made contact and then switches to 505 mA constant source
then charges up a S&H and turns off the power MOSFET in 50ms and takes the reading.

YOu can then repeat this every second to see if the ESR changes with probe pressure or probe position.

It is automatic if you sense 5mA then zap, hold, open ADC read and loop.

If you want to fuse the short open. Switch to a higher Capacitor voltage discharge and apply for 0.1 second so you do not waste much battery power. YOu can work out the I*t fuse time constant of the short you wish to blow and calculate the Joules of 1/2CV^2 required to blow the short, without burning up your tracks.

For inductive loads a back to back diode clamp will work without affecting the shunt reading.

extra [points] if you measure voltage rise during the current source to measure inductance, for limited range.