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Unread 01-12-2018, 10:57 AM
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Internal battery resistance test tools

I have been actively working on a team releated prototype project (this applies to FRC approved batteries and other kinds of batteries) and find myself frequently needing to measure the internal resistance of batteries.

I was wondering if anyone has experience with the
All-Sun EM3610 meter and measuring battery internal resistance.

I need to be sure to account for the lead resistance on the battery so I find myself using 4 lead milliOhm meters measuring the resistance of the leads to the battery and subtracting that from a reading across the battery and the leads with the measurement from the charger. I'd like something more direct. Just hoping someone else can comment on the experience of using that product?

Last edited by techhelpbb : 01-12-2018 at 12:12 PM.
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Unread 01-12-2018, 11:14 PM
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Re: Internal battery resistance test tools

Well I just got that All-Sun meter.

I tested it against 1% tolerance: 200mOhm, 100mOhm, 10mOhm and 2mOhm resistors.

It read all values but the 2mOhm adequately and there it read 3mOhm on the 200mOhm scale.

I put it on a very lightly used FRC battery at near full charge and off charge for a few days and got 12.5mOhm to 13mOhm which sounds about right.

I'll try some more batteries soon but this may not work well on my LiPo packs because they read 1mOhm per flat pack with 2 in series when charged.
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Unread 01-13-2018, 08:19 AM
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Re: Internal battery resistance test tools

Awesome, thanks for testing this! That looks like a nifty tool.

Not nearly as accurate or nifty: We wrote some code in 2016 to calculate it at runtime:
https://github.com/RobotCasserole173...Estimator.java

The numbers that came back seemed reasonable (especially since they also included battery cables, connectors and main circuit breaker). But, never had much to cross-check it against besides the datasheet.
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Unread 01-13-2018, 09:38 AM
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Re: Internal battery resistance test tools

The CTRE Battery Beak has been used by quite a few FRC teams (mine included) for several seasons now. It measures internal resistance using DC loading, by a procedure that is similar to the one described in IEC 61951-1 (2005); that method is recommended for batteries that serve DC power loads.

The All-Sun tester that the OP referenced uses a different method, based on 1000 Hz measurements. That method is recommended for batteries that serve digital device loads.

For a little more depth on battery internal resistance test methods, look here.

For a lot more, maybe Mike or Omar from CTRE will weigh in.
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Unread 01-13-2018, 10:21 AM
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Re: Internal battery resistance test tools

Did the meter come with a manual? Does it indicate what the test current is?

What value did it give for each of the resistors you tested?

The concern is that the method used still includes the resistance of the two probes to the battery and at low internal resistance values, this can become a significant but inconsistent error.
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Unread 01-13-2018, 10:36 AM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by gerthworm View Post
Awesome, thanks for testing this! That looks like a nifty tool.

Not nearly as accurate or nifty: We wrote some code in 2016 to calculate it at runtime:
https://github.com/RobotCasserole173...Estimator.java

The numbers that came back seemed reasonable (especially since they also included battery cables, connectors and main circuit breaker). But, never had much to cross-check it against besides the datasheet.
This is a good way of measuring the source resistance (= battery internal resistance + cable resistances + connection contact resistances + breaker internal resistance). For FRC, this is probably at least as useful than just the battery internal resistance since one never uses the battery alone without all those other pieces and the resistances of many of those other pieces can change or degrade over time just like the battery internal resistance.

What is the current when the measurement is made? Is the current dependent on the components (loads) connected to the PDP? I am not a programmer and could not find what sets the current in your (very well documented) program but I could find where it is measured and used in calculations.

Is it possible for you to make this measurement many times, starting with tight bolted connections and a new SB connector then unplug and re-plug the SB connector before making the next measurement? The reason I am asking this is I have noticed some SB connectors where the silver(?) plating is noticeably/visibly worn off the contact areas and I was wondering what impact this has on the contact resistance. If it does have a significant effect, those aiming for the highest level of performance might want to crimp on new contacts periodically.

Sorry to Techhelpbb for taking this thread in a different direction.
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Unread 01-13-2018, 03:38 PM
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Re: Internal battery resistance test tools

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Originally Posted by techhelpbb View Post
I was wondering if anyone has experience with the All-Sun EM3610 meter and measuring battery internal resistance.
FWIW, All-Sun's product webpage for model EM3610 does not list lead/acid as one of the supported chemistries.


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Unread 01-13-2018, 05:01 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by philso View Post
What is the current when the measurement is made? Is the current dependent on the components (loads) connected to the PDP? I am not a programmer and could not find what sets the current in your (very well documented) program but I could find where it is measured and used in calculations.
https://www.chiefdelphi.com/media/papers/3364 describes it in more detail.

At least for our purposes, there was nothing to "set" the current per say. We ran this while the robot was on the field doing it's thing. We would track a short history of samples, and every loop analyze the sample set to look at the standard deviation.

If the robot was under the right conditions, we would use the voltage/current history buffers to do a best-fit line to calculate resistance. The criteria for "right conditions" was more than a 7A standard deviation of our measured current. (7 was kinda just a made up number, but was enough to ensure our V/I point cloud was spread out enough to make the information in the best-fit line meaningful). The slope of the best-fit line correlates to resistance.


Quote:
Originally Posted by philso View Post
Is it possible for you to make this measurement many times, starting with tight bolted connections and a new SB connector then unplug and re-plug the SB connector before making the next measurement? The reason I am asking this is I have noticed some SB connectors where the silver(?) plating is noticeably/visibly worn off the contact areas and I was wondering what impact this has on the contact resistance. If it does have a significant effect, those aiming for the highest level of performance might want to crimp on new contacts periodically.
Yup, I think i know what you're saying, and it should be possible. This estimator was more designed to track degrading battery ability over the course of a match, but you could average out the estimates and try with a bunch of different input permutations (such as connector changes like you mentioned) to generate samples.

PM me for details, or feel free to comment on the paper thread if we want to move this conversation
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Unread 01-13-2018, 07:06 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by philso View Post
Did the meter come with a manual? Does it indicate what the test current is?

What value did it give for each of the resistors you tested?

The concern is that the method used still includes the resistance of the two probes to the battery and at low internal resistance values, this can become a significant but inconsistent error.
The meter manual is in not in English.
I'll try to get one in English but there are a few things that could be the values you are asking about.

It's got 2 wires to each probe hence the probe resistance is not much an issue. I tested by shorting the probes together and got zero Ohms. It's likely it's using the 4 wire method to measure the resistors but I can check that with another meter.

I don't have the values from tests in front of me, but I should be back in my home state on Monday and I can post them. The resistor values are within 1% of the readings and I can provide the Mouser part numbers...for all except the 2mOhm where that value is really low on the 200mOhm range.

Last edited by techhelpbb : 01-13-2018 at 07:21 PM.
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Unread 01-13-2018, 07:14 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by Ether View Post
FWIW, All-Sun's product webpage for model EM3610 does not list lead/acid as one of the supported chemistries.

What's interesting is they sell this on AliExpress as an automotive tester. I have to dig out my Battery Beak and see if the readings are different. However so far the readings for internal resistance I got with it from a 9.6V NiCd pack, 9.6V NiMH pack, 6.6V LiFePo4, 6.4V LiFePo4 and this FRC battery seem pretty close based on what the load circuits have been demonstrating.

Most important to me...these internal resistance readings are way closer than the internal resistance measurement function of my Turnigy Reaktor 250 charger which is only 2 wires and consistently off as much as 50-60% because of the leads to the battery. It only reads close on batteries with the short balance charging connector (makes sense cause it makes the battery leads really short).

My issue with the Battery Beak is the opposite. I don't want to potentially do something bad to my Battery Beak testing battery chemistries that are not normally on FRC robots.

Last edited by techhelpbb : 01-13-2018 at 07:51 PM.
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Unread 01-15-2018, 06:30 PM
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Re: Internal battery resistance test tools

Battery beak 2.0 with June 2015 firmware
Versus
All-Sun Em3610

On AndyMark crimped 1foot 6AWG leads.
Measured at the connector.

Very lightly used battery Beak reads 17mOhm 4 times and 18mOhm once.
Rates battery at charged to 77% of capacity.

Em3610 tried 5 times as well 15.2-15.6mOhm with probe tips held firm against blades of connector by hand.
I got my lower reading before because with these probes I can get against the battery blades themselves removing the cable and connector as other sources of low resistance in the circuit.

I am charging that FRC battery on my Turnigy Reaktor 250 charger with a RadioShack 15A 13.8V power supply set at 0.5A while I am gone. The charger display says the battery is taking 160mA right now.

Probes touched together:

Code:
3 tests per setting
Range 20Ohm: 0.0 Ohm, 0.0 Ohm, 0.0 Ohm
Range 2000mOhm (2Ohm): 0.0 Ohm, 0.0 Ohm, 0.0 Ohm
Range 200mOhm (0.2Ohm): 0.0009 Ohm, 0.0012 Ohm, 0.001 Ohm = Average error 0.00103 Ohm
Hence on the lowest value resistance I have below of 0.002Ohm this is going to read incorrectly.

Passive resistance measurements:

Code:
Mouser Part #: 588-650FPR002E
  Maker:        Ohmite
  Resistance:   0.002Ohms (2 mOhms)
  Tolerance:    +/-1% = +/-0.00002Ohms
  Power rating: 5Watts
  Package:      Through-hole
  Datasheet:    https://www.mouser.com/ds/2/303/res_...rm-1265426.pdf
  Qty to test:  1

  Readings:
    Resistor A:
     Range 200 mOhm
     Attached leads by hand pressure
     3 readings: 2.5-2.6 mOhm, 2.6-2.7 mOhm, 2.5 mOhm

Mouser Part #: 588-12FR010E
  Maker:        Ohmite
  Resistance:   0.01Ohm (10 mOhms)
  Tolerance:    +/-1% = +/-0.0001Ohm
  Power rating: 2Watts
  Package:      Axial
  Datasheet:    https://www.mouser.com/ds/2/303/res_10-1265495.pdf
  Qty to test:  2

  Readings:
   Resistor A:
     Range 200 mOhm
     Attached leads by hand pressure
     3 readings: 10.2 - 10.3 mOhm, 10 mOhm, 10.2 mOhm
   Resistor B:
     Range 200 mOhm
     Attached leads by hand pressure
     3 readings: 10.1 mOhm, 10.2 mOhm, 10.1 mOhm

Mouser Part #: 588-12FR100E
  Maker:        Ohmite
  Resistance:   0.1Ohm (100 mOhms)
  Tolerance:    +/-1% = +/-0.001Ohm
  Power rating: 2Watts
  Package:      Axial
  Datasheet:    https://www.mouser.com/ds/2/303/res_10-1265495.pdf
  Qty to test:  2

  Readings:
   Resistor A:
     Range 200 mOhm
     Attached leads by hand pressure
     3 readings: 101.8 mOhms, 101.7 mOhms, 101.5mOhms
   Resistor B:
     Range 200 mOhm
     Attached leads by hand pressure
     3 readings: 101.6 mOhms, 101.2 mOhms, 101.2-101.3 mOhms

Mouser Part #: 588-13FR200E
  Maker:        Ohmite
  Resistance:   0.2Ohms (200 mOhms)
  Tolerance:    +/-1% = +/-0.002Ohm
  Power rating: 3Watts
  Package:      Axial
  Datasheet:    https://www.mouser.com/ds/2/303/res_10-1265495.pdf
  Qty to test:  2

  Readings:
   Resistor A:
     Range 2000 mOhms (exceeds 200 mOhm range)
     Attached leads by hand pressure
     3 readings: 198 mOhms, 198 mOhms, 198 mOhms
   Resistor B:
     Range 2000 mOhms (exceeds 200 mOhm range)
     Attached leads by hand pressure
     3 readings: 199 mOhms, 199 mOhms, 199 mOhms
I am definitely not making these readings more stable by simply pushing the leads into a non-conductive surface with my hands, but in fairness, the meter comes without clips and this is what will happen if you push the probes onto the connections.

Last edited by techhelpbb : 01-15-2018 at 11:56 PM.
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Unread 01-15-2018, 10:41 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by techhelpbb View Post
Very lightly used battery Beak reads 17mOhm 4 times and 18mOhm once.
Rates battery at charged to 77% of capacity.

Em3610 tried 5 times as well 15.2-15.6mOhm with probe tips held firm against blades of connector by hand.
+- 1.3% variation in the readings from the Em3610 is pretty impressive.

The difference between the Beak and the Em3610 is only just over 10% which is also pretty good correlation considering they are probably measuring using different current levels.
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Unread 01-15-2018, 10:53 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by philso View Post
...considering they are probably measuring using different current levels.
Not just different current levels. They are using different technologies.

Beak uses DC ΔV/ΔI

EM3610 uses 1000Hz AC


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Unread 01-15-2018, 11:59 PM
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Re: Internal battery resistance test tools

Quote:
Originally Posted by philso View Post
+- 1.3% variation in the readings from the Em3610 is pretty impressive.

The difference between the Beak and the Em3610 is only just over 10% which is also pretty good correlation considering they are probably measuring using different current levels.
As others have noted it's also likely because of the different methods of testing internal resistance between the Battery Beak and the EM3610.

I don't have any more time to play with this tonight. I'll try to connect my oscilloscope across a passive resistor under test with the EM3610 and see if I can determine what it's doing.

I don't know if merely placing a fixed resistance across the battery is a good test when one considers that the ESC are chopping the DC to power the motors who's windings are clearly not passive resistive loads. However the measurements produced don't deviate so much that I am as confused as I was when I was trying to reconcile the internal resistance measurements from the Turnigy Reaktor 250 and it was doing stuff like this:

Code:
Battery            Voltage     Reaktor 250     EM3610      Approx Error % (EM3610/Reaktor250)
FRC lead acid      13.8        92mOhm          12.7mOhm    63% (accounted for readings of wires for 45 mOhms)
LiFePo4 custom     6.4         139mOhm         75.7mOhm    53%
LiFePo4 Zippy RC   6.6         56mOhm          29.5mOhm    53%
DeWorld NiMH       9.6         405mOhm         251mOhm     63%
NiCd pack          9.6         410mOhm         220mOhm     53%

Reaktor 250 charger readings are 1.8x - 1.9x higher or 1.6x - 1.7x higher than the EM3610 readings.
The increased error tracks circuits with very different wire gauge sizes in the path to the battery assembly.
Basically I'd take these readings over the 2 wire readings from the Turnigy Reaktor 250 charger across the board.
The Reaktor only behaved itself with the balance charging connectors in use.

Last edited by techhelpbb : 01-16-2018 at 01:02 AM.
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Unread 01-16-2018, 07:55 PM
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Re: Internal battery resistance test tools

The seller has sent me the English manual for the EM3610.
It's attached here.

I found these 3 things interesting:

Page: 7
"For measurements in the 200m range, set the range switch in the 200m range position and short the two test probes, the display will show a reading. This reading must be subtracted from all the measurements in the 200m range."

Notably this means the resistance reading of the 2 mOhm passive resistor is now too low, instead of too high.
The rest of the measurements from the passive resistors now seem just a little more accurate on that 200m range.
Except for the 200mOhm resistor which I measured on the 2000m range.

This also then applies to the FRC battery measurements which were done on the 200mhm range.
This means at the battery terminals I was reading:
12.5 mOhm - 1 mOhm on average = 11.5 mOhm
to
13 mOhm - 1 mOhm on average = 12 mOhm

Which for a battery where we commonly believe the internal resistance averages 11 mOhm that's very close.
On the end of the AndyMark lead kit the measurements then become:
15.2 mOhm - 1 mOhm = 14.2mOhm
15.6 mOhm - 1 mOhm = 14.6mOhm

Manual says the error for the EM3610 could be 10% so let's take the average of 14.4mOhm.
14.4 mOhm + (14.4 mOhm 10%) = about 15.8mOhm if the EM3610 is low

The Battery Beak manual says it has an error of about +/- 1 mOhm no mention of rounding.
So 17 mOhm might be 16 mOhm if the Battery Beak is high.

So pretty close between the EM3610 and Battery Beak.

Page: 8
"Do not apply a voltage higher than 50V between the test probes; otherwise the meter will be damaged."

Page: 9
"To avoid damage to the meter, do not apply any AC signal between the test probes."

Moving on...

I was curious about the 11 mOhm average I have seen used for FRC batteries (look around ChiefDelphi it's come up in several posts over the years). The InterState batteries on AndyMark's website right now say 12 mOhm-15 mOhm internal resistance I don't see if they mention how they measured that. The SLA1116 datasheet link on Andy's website is broken right now I got that from the PowerPatrol datasheet below that.

The FRC battery I bought from AndyMark that I have been testing is an ES17-12.
The datasheet is attached to this post.
It clearly says: "Internal Resistance (at 1kHz): Approx. 12 mOhm"

I looked at the datasheets for all these other FRC compatible batteries listed here:
https://www.chiefdelphi.com/forums/s...78&postcount=1
I found the 11 mOhm measurement only on the Yuasa NP18-12 datasheet as attached.
None of the other datasheets mention more detail other than tested at temperature 25C (my shop is 68F-71.5F as measured by AcuRite 06044 sensors and graphed on their App on my Android phone and I can set them up to read in Celsius but internally they read in Fahrenheit so just do the conversion: 20C-22C).

Generally if you test the internal resistance of the battery when it's just off the charger and still settling you'll read as high as 19 mOhm on the Battery Beak with this same battery I have been testing in these posts. So when it completely settles and hits room temperature (for me) is when the Battery Beak reads 17 mOhm. So if my room temperature is a little lower than 25C that might account for reading a little less than 12 mOhm they probably measured at 25C.

Basically I'd love to know what methods and tools all these other battery manufacturers were using to measure these batteries and post those results on their datasheets.

Not going to have time for any oscilloscope readings tonight either.
Attached Files
File Type: pdf EM3610+ENGLISH.pdf (148.9 KB, 5 views)
File Type: pdf ES17-12.pdf (343.0 KB, 1 views)
File Type: pdf NP_18_12_DataSheet.pdf (260.8 KB, 1 views)

Last edited by techhelpbb : 01-16-2018 at 10:34 PM.
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