esr meter build

[ronsimpson]

The meter reads in mΩ and therefor above 32Ω will display as negative.

o.k I got up to 65 ohms display did not turn negative. at 66 ohms the meter stopped reading esr,

Post #16 testes for this. Seems to work up to 65/66 ohms.

 

[Pommie]

That is strange and, in that case, I have no idea what is going on in the software. Shame we can't get the source code.

Mike.

 

[ronsimpson]

Is it true this only happens on Ele. caps.? (stated several times)
Maybe the "L" of the Ele cap is the problem. (inductance)
Can we try small amounts of L added to a known cap and see what happens? Some thing like the "add a resistor" test above.

 

[peter g]

hi mike, any suggestions on how I can fix it?

 

[peter g]

ignore last post.

 

[peter g]

o.k i'll try adding inductance. are we looking for/if the reading goes negative?

 

[peter g]

hi, trying to get a supply of inductors. i'am going to repeat the resistor test again.

 

[ronsimpson]

trying to get a supply of inductors.

I think 5 to 10 turns of wire around your finger. (air coil)

 

[peter g]

in the resistor test I kept adding resistors. how do I test with an inductor?

 

[ronsimpson]

What size of capacitor are you using where the ESR=negative? Brand and voltage?
I might be able to find out the inductance. (data sheet and some math)
Then we will add that amount of inductance to a cap that reads good. (series)

 

[peter g]

hi ron, I will check that out and let you know. thanks, pete.

 

[peter g]

o.k., the first cap is a nichicon 4700mfd@25v, the second is a elna@35v 1000mfd. I might add a 10mfd shows normal. I think what nigel said about a software problem has merit the only confusing thing is that many people have constructed this meter and very few report the problem i'am having. i'am using the same componets and pcb that others are using, so why is there a problem with my meter?

 

[Nigel Goodwin]

o.k., the first cap is a nichicon 4700mfd@25v, the second is a elna@35v 1000mfd. I might add a 10mfd shows normal. I think what nigel said about a software problem has merit the only confusing thing is that many people have constructed this meter and very few report the problem i'am having. i'am using the same componets and pcb that others are using, so why is there a problem with my meter?

It's difficult to know without the source code, as I've said I consider it's badly written as it has the capability of displaying negative values, but presumably there's a problem somewhere that's causing it to give those values (as others have suggested, probably because it uses signed variables instead of unsigned ones). The source code would at least show how it's trying to do the reading, and give you a chance to workout why it might be reading wrongly.

 

[ronsimpson]

many people have constructed this meter and very few report the problem i'am having.

I have a meter that looks like it BUT does not have the ESR function.
Maybe a very old version.
I use the meter mostly on pF parts. I use it to measure pF between layers in transformers. Measure a trace on a PCB to a ground plane.
My meter works well from 0.1pF through 10uF. (most meter I have used do not do well at "pF")
I do not trust any of the meters for 1,000.uF ele. caps.
One of my meters, I can set what frequency to measures the cap at. It seem right to measure a 22pF at 10mhz, and a ele cap at 100hz. With a big ele. cap, at 10mhz, the cap seems to go away.

 

[Nigel Goodwin]

It seem right to measure a 22pF at 10mhz, and a ele cap at 100hz. With a big ele. cap, at 10mhz, the cap seems to go away.

Quite correct, however for ESR you commonly measure at 100KHz - and with the most common fault (over the last 20-30 years) been high ESR electrolytics, an ESR meter is particularly important.

 

[ronsimpson]

however for ESR you commonly measure at 100KHz

Many Ele. Caps have a current rating at 100khz and 50-60hz. Probably they will be used as input or output filter on PWM or as filtering right after a full wave bridge (power line transformer).

I don't know how "this meter" works for ESR?
I some times put the cap in a network analyzer and see how close the cap is to an ideal part. The difference will show the R and L inside the cap.
If you put a known L across the unknown C and sweep frequency with a network analyzer you will know resonance frequency and thus C. and at resonance the Z of LC goes to zero leaving R.
The other choice is to jam 1A square wave current wave into the cap and watch the voltage across the cap.
I think, at only one frequency, it might be hard to see R and not see L. (hard to tell the effect of one and not the other)

After all that I did not add anything to the conversation so will sign off.

 

[peter g]

hi guys, I added an attachment to a website where this project originated. maybe something helpful there.https://www.hobbielektronika.hu/cikkek/lcm3_alkatresz_mero_muszer_-_kit_lehetoseg.html?pg=4

 

[jjw]

Have you calibrated the ESR measurement according the instructions.
The measurement of an elcap is based on charging the capacitor from 5V through a 180 ohm resistor.
I guess the capacitance and ESR are calculated by the charge time to a fixed voltage and the extra voltage step due ESR at the beginning of charging ?
The leakage of the capacitor might give negative readings ?

 

[peter g]

hi jjw, I have calibrated the meter ad nauseum, the negative value occurs only on large value caps(1000mfd on up). thanks for your input. pete

 

[dr pepper]

I have 2 meters that measure esr, one digital, one analogue both work well, I also have a pic based lc meter, its very accurate but soetimes it too reads negative, I wonder if a component is incorrect on yours or something, if the device doesnt see a pure reactance like theres dc resistance or inductance or maybe even dc that could throw your readings off.