Author Topic: Testing battery impedance  (Read 2338 times)

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Offline mrrrwhat

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Testing battery impedance
« on: January 29, 2017, 03:15:23 am »
Can i use dmm or lcr to test battery impedance?
I buy some lithium battery from china and i want to check the battery are real high drain battery or not |O
 

Offline jeroen79

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Re: Testing battery impedance
« Reply #1 on: January 29, 2017, 05:00:37 pm »
An LCR meter is for inductors, capacitors and resistors, not for batteries.

A DMM can measure current and voltage.
If you apply a load to the battery you can measure the load and the resulting drop in voltage.
That should tell you if the battery is fit for your intended purpose.
 

Offline eblc1388

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Re: Testing battery impedance
« Reply #2 on: January 30, 2017, 12:25:46 am »
That would be easy to do, as jeroen79 has suggested.

Get yourself a 1ohm 5W resistor. Connected one end to the negative terminal of the battery. Leave the other end unconnected yet. Now measure the battery voltage with a DMM. (e.g. 3.87V). Then with the DMM still connected, place the other end of the 1 ohm resistor to the battery positive terminal and watch carefully the DMM reading. (e.g. 3.45V). Remove the resistor.

Then everything is Ohm's Law from here.

The load current is simply 3.45A, voltage drop across the battery internal impedance is (3.87-3.45)V = 0.42V, so the battery impedance is 0.42V/3.45A = 0.122 ohm or 122 milliOhm.
 

Offline mrrrwhat

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Re: Testing battery impedance
« Reply #3 on: January 30, 2017, 03:23:14 am »
Thanks for reply my post :)
I find that the manufacturer give out the value of the battery impedance are measured by ac conductance method.
So i thank about using lcr meter in esr mode to measure may be better than using dc load method ???
 

Offline cs.dk

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Re: Testing battery impedance
« Reply #4 on: January 30, 2017, 05:57:27 am »
So i thank about using lcr meter in esr mode to measure may be better than using dc load method ???

Note that some ESR meters don't have protection on the input. ie. discharge the cap before testing, or something will fail in the meters input circuitry,
 

Offline kripton2035

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Re: Testing battery impedance
« Reply #5 on: January 30, 2017, 07:10:05 am »
yes with an lcr meter could be dangerous (for the lcr meter ...)
try to use some dedicated esr meter that are in fact like an impedance meter.
I know this one can measure battery impedance :
http://kripton2035.free.fr/digital%20esr/esr-kaspars.html

Online IanB

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Re: Testing battery impedance
« Reply #6 on: January 30, 2017, 07:26:32 am »
Thanks for reply my post :)
I find that the manufacturer give out the value of the battery impedance are measured by ac conductance method.
So i thank about using lcr meter in esr mode to measure may be better than using dc load method ???

You should measure the battery impedance in a way that is similar to the actual load that will be applied. If the battery will be used with a DC load then the AC impedance is not going to give you a good indication of performance. You should in that case measure the internal resistance using a DC method. However, if the load will have a large AC component (such as driving a switching power supply) then the AC impedance will be more relevant.

If you want to measure the AC impedance then I think you need a special instrument for that. I do not think a regular LCR meter is suitable.
I'm not an EE--what am I doing here?
 

Offline mrrrwhat

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Re: Testing battery impedance
« Reply #7 on: January 30, 2017, 07:41:35 am »
Thanks for help  ^-^
The battery will use to driver a high power brushless motor about 350W(replace the battery in dyson V6)
I think i need to buy a special meter to test battery impedance.
 

Offline Zero999

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Re: Testing battery impedance
« Reply #8 on: January 30, 2017, 07:32:47 pm »
Thanks for reply my post :)
I find that the manufacturer give out the value of the battery impedance are measured by ac conductance method.
So i thank about using lcr meter in esr mode to measure may be better than using dc load method ???
Presumably they would measure the impedance of the battery using a high frequency AC current source, connected to the battery via a capacitor. If the frequency is high enough and the capacitor's ESR is low enough, the the batter's internal impedance will dominate and the AC voltage across it will be equal to the impedance × AC current.
 

Offline Rerouter

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Re: Testing battery impedance
« Reply #9 on: January 30, 2017, 07:47:06 pm »
On the cheap to just measure the DC ESR of a battery, you can follow this approach, however it will not show you what the Impedance is vs frequency, just give you a baseline of go / no go.
 

Offline Zbig

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Re: Testing battery impedance
« Reply #10 on: January 31, 2017, 07:07:39 am »
Why the fixation on measuring the battery's impedance? If you are, like you said, trying to evaluate whether the battery is high drain enough for your intended purpose or not, measuring ESR is not the way to go. The right way to do it is to actually load it up with the current you expect in your target application and see how/if it delivers and for how long. One way to do that would be by using a device called Electronic DC Load. As you seem to be a beginner lacking much experience with this kind of stuff, I don't recommend you start with high capacity Li-Po packs. These things, when mishandled, can easily set you and your house on fire. Please be careful and choose a project more appropriate for your experience level. Get the basics right first.
« Last Edit: January 31, 2017, 08:34:07 am by Zbig »
 
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Offline jdraughn

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Re: Testing battery impedance
« Reply #11 on: January 31, 2017, 08:43:18 am »
Can i use dmm or lcr to test battery impedance?
I buy some lithium battery from china and i want to check the battery are real high drain battery or not |O

I stuck a flat lithium from a iPad in a little 1/12th scale RC car, and it hauled ass, after a couple of minutes I pulled the battery out and it was almost too hot to too touch. -Just because a battery is capable of dumping tons of amps at once, doesn't mean it should.
 


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