Internal Resistance tester

Has anyone used one of these?
I've decided to start IR testing cells before building packs and found this..

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com.au%2Fulk%2Fitm%2F252688203642

Yeah. Be aware they are ACIR though. So more impedance than resistance.

Great for weeding out outliers, but don't rely on it for doing any maths or for advertising your packs if you sell them. The "real world performance" for eBikes will be lower than the meter suggests.

You can calculate Ri by voltage drop on a cell under load, testig it at different loads and different states of charge. This is what the Cycle Analyst does during a ride.

the Grinspector station
http://www.ebikes.ca/product-info/grinspector.html
http://www.ebikes.ca/news/battery-grinspector/
can test batteries, too, and you could buld one rather than buy it if you have a CA you can flash with the firmware.

Or you can buy the new genuine SKYRC Imax B6 mini to test for DC internal resistance. Works pretty good in my experience

Sunder said:

Yeah. Be aware they are ACIR though. So more impedance than resistance.

Great for weeding out outliers, but don't rely on it for doing any maths or for advertising your packs if you sell them. The "real world performance" for eBikes will be lower than the meter suggests.

Click to expand...

Thanks for replies so far

Sunder, that's exactly what I want is to weed out the duds. I'm not so interested in the accuracy of the number, rather the consistency of testing accuracy.

Amber, I must get a cycle analyst but for this I'm just wanting a quick test to determine which cells are worth considering for a build.

Matador, I have a genuine imax b6, not the mini though. Have you ever been able to verify the results of the b6 with another instrument?

As long as you can get good contact, they are very consistent. There's two wires per probe, and both need good contact.

I tried it with my VTC4 cells. I would get reading of 21-22-23 mOhms DC resistance with the genuine branded SKYRC Imax B6 mini (or SKYRC ImaxB6AC V2). The older SKYRC IMaxB6 did not have the DCIR meter function I think...

Id also did some resistance tests on these cells using different resistor values while simultaneously measuring amp and voltage drop.
Values were in similar ranges..... 20 -22 millioms DC.

What I noticed is that sometimes values can be a bit off like as much as 25 milliohm instead of 22 milliohms with the ImaxB6 mini. But that can be solved by repeating the measure on the cell and eliminating measurement values at the extremes of the ranges.


Details of how I measured DCIR here
https://endless-sphere.com/forums/viewtopic.php?f=14&t=28285&start=175#p1299346

I compared with result I got with using different resistors and tracing graphs to get the slope (which gives the DCIR):https://endless-sphere.com/forums/viewtopic.php?f=14&t=87173&start=25#p1276187

These test I did last year when I was still in Canada. I'm now in NYC, stuck with no VTC4, but I bought 60 LG MF1 cells from alarmhookup. These are 2015 sept/october new old stock of LG cells. They measure around 65 mOhms in the Vruzend v1.0... 2150 mAh max 10A draw...

Matador

Matador said:

I tried it with my VTC4 cells. I would get reading of 21-22-23 mOhms DC resistance with the genuine branded SKYRC Imax B6 mini (or SKYRC ImaxB6AC V2). The older SKYRC IMaxB6 did not have the DCIR meter function I think...

Id also did some resistance tests on these cells using different resistor values while simultaneously measuring amp and voltage drop.
Values were in similar ranges..... 20 -22 millioms DC.

What I noticed is that sometimes values can be a bit off like as much as 25 milliohm instead of 22 milliohms. But that can be solved by repeating the measure on the cell and eliminating measurement values at the extremes of the ranges.


Details of how I measured DCIR here
https://endless-sphere.com/forums/viewtopic.php?f=14&t=28285&start=175#p1299346

I compared with result I got with using different resistors and tracing graphs to get the slope (which gives the DCIR):https://endless-sphere.com/forums/viewtopic.php?f=14&t=87173&start=25#p1276187

These test I did last year when I was still in Canada. I'm now in NYC, stuck with no VTC4, but I bought 60 LG MF1 cells from alarmhookup. These are 2015 sept/october new old stock of LG cells. They measure around 65 mOhms in the Vruzend v1.0... 2150 mAh max 10A draw...

Matador

Click to expand...

Thanks for the detailed response and tips.
I'll have a play with the imax, looks like it could better for this function than I first thought.

They are good cells the VTC4, I get a lot of them in the Makita packs among others.

Sunder said:

As long as you can get good contact, they are very consistent. There's two wires per probe, and both need good contact.

Click to expand...

Ok thanks. I'll probably get one, given the low price and recommendations here

It is pretty good considering the price.

But remember to measure at the right voltage/SoC of the battery. Resistance changes with charge.

flippy said:

It is pretty good considering the price.

But remember to measure at the right voltage/SoC of the battery. Resistance changes with charge.

Click to expand...

Good call. I don't suppose it matters what voltage, providing test cells are the same voltage, is that right?
(I'm talking li ion, not LiFe where SoC would need to be known)

Best situation is to test a single cell at the SoC stated by the spec sheet of the cell.

If you take a whole pack its generally best to take 2 measurements, one half charged and the other at full charge.

IR changes a lot with ambient temperature of the cells! Only way to get accurate cell IR is with a 4 wire method. The B6 IR will not be accurate especially on multi cell batteries.

Volt_Ampere said:

IR changes a lot with ambient temperature of the cells! Only way to get accurate cell IR is with a 4 wire method. The B6 IR will not be accurate especially on multi cell batteries.

Click to expand...

A totally agree. But comparing same type of cell at same SoC and same temps... I usually oberved less than 10% variation and at most in worst cases less than 20% variations in values. This is good enough for my purposes as ACIR might be precise but is totally useless for my purposes, with the load test method with different resistor values and graph method with great of the slope giving the DCIR value is propably 5-10% precise but way more time consuming in my experience.

I think precice DCIR meters do exists but they probably cost a few grands... maybe 500$ is you`re lucky and score an used model at cheap price...

I've ordered one of these units I'll get it in a week or two.

Just wondering if anyone can tell me what I should be seeing with 30Qs at a certain voltage using one of these?

My cells are recycled, so was also wondering what number you would consider acceptable for use in ebike packs?

Thanks in advance

there is no hard number for used cells. check the datasheet on the factory new IR and compare that to the current number.
as long as all cells are equal a higher number is not a problem. your heat production and voltage drop will rise the higher the IR is.
you have to decide what level of wear/IR is acceptable to you. usually there is a capacity loss when the IR gets notiably higher.

flippy said:

there is no hard number for used cells. check the datasheet on the factory new IR and compare that to the current number.
as long as all cells are equal a higher number is not a problem. your heat production and voltage drop will rise the higher the IR is.
you have to decide what level of wear/IR is acceptable to you. usually there is a capacity loss when the IR gets notiably higher.

Click to expand...

Thanks, i probably should have been more specific.
I was more meaning a range, or ball park number to look for using this meter and used 30Qs.
I'm sure a pattern or range will emerge as I start testing but wondered if anyone has done this testing with used 30Qs

You can also do the maths backwards, to make sure that under the loads you want to put it under doesn't cause sag big enough to trip LVC.

Thanks sunder.
I'll have a look when I get home on the computer, when ive got my glasses on

Sunder said:

ir.png

You can also do the maths backwards, to make sure that under the loads you want to put it under doesn't cause sag big enough to trip LVC.

Click to expand...

Wow my sony VTC4 kicks some asses indeed !
While in nyc i bought some LG MF1 2150 mAh 10A max cells from alarmhookup on ebay. Got 60 of these cells for 105$, including 3 BMSs. Manufacture date was between september and november 2015 in all cases. According to manufacturr theshoukd be 35 mOhm AC impesance at 1kHz. I Measured between 65 and 72 mOhm DC resistance on the Imax B6AC v2 in cells being in the 4.15 to 4.16V range.
Asides from capacity LG MF1 seem to be a good deal oneBay at around 1.75$ per cell... But I like Makita cells better of course... But in NYC i didnt have a good source for them curious to know about the ne VTC6