Author Topic: ESR Meter Adapter Design and Construction  (Read 112883 times)

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Online Johnny10

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Re: ESR Meter Adapter Design and Construction
« Reply #250 on: May 08, 2020, 01:21:04 pm »
Great Thread !
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Online trobbins

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Re: ESR Meter Adapter Design and Construction
« Reply #251 on: May 15, 2020, 01:34:40 am »
I have powered up my variant of Jay_Diddy_B's ESR meter, and it is performing very nicely indeed.

The IA certainly allows easy setup up for 0 milliohm (+/- less than 0.1 milliohm) and 1.000V for 1 ohm 1%, and appears to be dead accurate down to the 47 milliohm 1% reference I have, when using a nice 30cm long Kelvin clip lead set with 4mm plugs.

I haven't yet played with the 555 oscillator, which is running at 18kHz, to see if the setup can support similar results at 100kHz.

Aiming to set up the IA gain for 1V/ohm and 0.1V/ohm to allow up to about 16 ohm max range (open circuit reads about 1.65V at the moment), and use switched fixed resistors and a trimpot for gain setup with sufficient offset trim range (which I aim to change to fixed and trimpot to reduce the present trimpot sensitivity when setting 0 ohm end).

I found a practical 'zero ohm' link to keep the Kelvin clip contact faces flat over their entire length, in the form of an 8mm wide, 0.9mm thick flat bar that had a previous life as a contact link bar in a high current contactor.  There are a few parts that show some temperature sensitivity (a few milliohm change when squirted), so packaging the circuitry to minimise local temperature changes seems worthwhile.

PS. it does work with capacitors, even the bigger ones with readings down around 10 milliohm, although ESR of a cap may be quite temp sensitive and so absolute ESR should really note the temp, and comparisons should use caps at the same ambient temp.

 

Offline ogden

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Re: ESR Meter Adapter Design and Construction
« Reply #252 on: October 24, 2020, 09:05:03 pm »
As ESR Meter Adapter is safe to measure charged capacitors, most likely it can be used to measure ESR of the batteries too. I would love universal battery/capacitor ESR meter. Hint: LTC6900 as configurable by resistor(s), clock. Please do not hesitate to post if you are interested in measuring ESR of the batteries.
 

Offline Jay_Diddy_B

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Re: ESR Meter Adapter Design and Construction
« Reply #253 on: October 26, 2020, 06:51:06 pm »
Hi group,

I have looked at measuring the ESR of cells before. You can find the message in this thread:

Link: https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/msg2798498/#msg2798498

ESR Meter Adapter - Modification for 1 kHz (nominal)

Now I am going to share modifications that can be made to the ESR Meter Adapter to lower the frequency from the 100kHz, normally used for electrolytic capacitors, to 1 kHz for batteries and cells.

LTspice Model

[attachimg=1]


I have indicated the changes and addition on the LTspice schematic.

The LTspice model shows an output of 100mV /  \$\Omega\$

[attachimg=2]


This is nice and linear just like the 100kHz version.

Modified Circuit Board

[attachimg=3]


All of the parts will fit the original except for the 100uF electrolytic capacitor.

Testing

[attachimg=4]


Here I am using the test resistors described here:

Link: https://www.eevblog.com/forum/projects/esr-meter-adapter-design-and-construction/msg343855/#msg343855

to confirm the operation.

Attachments

I have attached a pdf of the modified schematic and the LTspice model.

Regards,
Jay_Diddy_B

[attachurl=5]
[attachurl=6]
 
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Offline ogden

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Re: ESR Meter Adapter Design and Construction
« Reply #254 on: October 27, 2020, 02:37:30 am »
ESR Meter Adapter - Modification for 1 kHz (nominal)

Now I am going to share modifications that can be made to the ESR Meter Adapter to lower the frequency from the 100kHz, normally used for electrolytic capacitors, to 1 kHz for batteries and cells.

Wow, you are so fast! Thanx. Any chances to have 200 mOhm or at least 1 Ohm range? 20 Ohm is good for CR2032 and similar low capacity cells.
 

Offline hugo

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Re: ESR Meter Adapter Design and Construction
« Reply #255 on: October 27, 2020, 07:49:31 pm »
It looks like the output voltage is not quite linear below 2 ohm ... ;)
 

Offline floobydust

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Re: ESR Meter Adapter Design and Construction
« Reply #256 on: October 27, 2020, 08:09:04 pm »
I've often wondered why this meter intentionally has such high output impedance with R3  :-//
Usually you want to pump some current, several mA's or more through the DUT to swamp out wet effects. In the case of lead-acid battery ESR I would think the measurement is corrupted. Car battery ESR measurements are several amp pulses for this reason I think.
 

Offline Jay_Diddy_B

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Re: ESR Meter Adapter Design and Construction
« Reply #257 on: October 28, 2020, 08:42:01 am »
Hi group,

Here are some test results using Li-ion cells.

Laptop Battery Pack

[attachimg=1]


I broke apart an old Asus battery pack and separated four of the cells.

[attachimg=2]


I have numbered the cells 1 to 4.

HP 4328A Measurement

This is a 1 kHz (+/- 100 Hz) sinewave ac coupled milli-ohmmeter.

Sample reading:

[attachimg=3]


1 kHz ESR Meter Adapter

[attachimg=4]


The adapter was read with a Fluke 289. The Fluke 289 has been set relative to remove the offset.

[attachimg=5]


Results

The two methods gave very similar results. The difference are probably from the connections made with the 4328A.


[attachimg=7]


Regards,
Jay_Diddy_B

« Last Edit: October 28, 2020, 08:54:38 am by Jay_Diddy_B »
 
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Offline ogden

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Re: ESR Meter Adapter Design and Construction
« Reply #258 on: October 28, 2020, 04:38:43 pm »
I broke apart an old Asus battery pack and separated four of the cells.
Wow, very promising results. Difference between instruments below 10% and battery impedance spread below 10% as well - cell pack looks like well-balanced. Any chance for you to discharge one cell and measure ESR with both tools again? Asking to disassemble all the battery packs around until you find one with bad cell would be asking too much :)
 


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