Nov 11, 2017, 06:58 PM Frankenstein recycled packs Thanks Wayne... FYI - HobbyKing asked me to build an extra 50 last month so now HobbyKing has stock in the USA warehouse. We are working on getting stock in the Europe warehouse soon but I do not know the schedule for this but know it is in their plan. Rick
 Nov 11, 2017, 10:16 PM Mansell Models These meters are awesome! I bought one earlier this year and I use it all the time to compare the C rating on other batteries similar to mine. Rick, I cannot thank you enough for showing me this meter a couple of years ago. It is well worth the money for any one serious about flying electric models. Cheers, Tom
Mar 11, 2018, 12:28 PM
What voltage resolution is needed to calc IR?

3 digits (1mV),
4 digits (100uV)
5 digits (10uV)
6 digits (1uV)

I have access to a bunch of 6 digit bench DMM's if needed, this is one of my benchs at work.

### Images

Mar 11, 2018, 04:46 PM
Registered User
Quote:
 Originally Posted by --Oz-- What voltage resolution is needed to calc IR? 3 digits (1mV), 4 digits (100uV) 5 digits (10uV) 6 digits (1uV) I have access to a bunch of 6 digit bench DMM's if needed, this is one of my benchs at work.
Just about any 4 digit multimeter is sufficient to calculate battery voltage IR values. You need to check the voltage on each cell while load testing. For best results, use the two resistor load test where all of the cell voltages are measured at one test current, then all of the cell voltages are measured at a second test current. It's a bit of work, but it will be accurate.

IR values calculates as follows:

Cell_IR = (Voltage_Low Amps-Voltage_HiAmps)/(Amps_High current-Amps_LowCurrent)

I did this project awhile back that does all of this stuff automatically.

BattIR meter

https://www.rcgroups.com/forums/show...ircuitboard%21
 Mar 11, 2018, 09:40 PM Quadaholic Thanks vollrathd! EDIT: What is the formula that calculates the max amps for the pack at the end in your program? Last edited by --Oz--; Mar 12, 2018 at 04:48 PM.
 Mar 16, 2018, 06:59 PM Quadaholic @ vollrathd, can you take a peek at my post in your thread? https://www.rcgroups.com/forums/show...8&postcount=57
Mar 16, 2018, 07:40 PM
Registered User
Quote:
 Originally Posted by --Oz-- @ vollrathd, can you take a peek at my post in your thread? https://www.rcgroups.com/forums/show...8&postcount=57
Responded to in the above post.
Mar 16, 2018, 07:54 PM
Registered User
Quote:
 Originally Posted by --Oz-- Thanks vollrathd! EDIT: What is the formula that calculates the max amps for the pack at the end in your program?
The formula for maximum Amps was derived by Forsyth, Julian, Giles who ran a whole series of tests on a variety of batteries for the calculation. Credit for the work of Forsyth, Julian, Giles is displayed on the BattIR meters LCD display during the test routine of the BattIR meter.

The formula is the square root of (6,000 * Batt_ AmpHrs)/(BattIR) where BatteryIR is measured in milliohms.
Last edited by vollrathd; Mar 16, 2018 at 11:51 PM. Reason: Forgot the square root calculation
Mar 31, 2018, 11:13 PM
Quote:
 Originally Posted by vollrathd The formula for maximum Amps was derived by Forsyth, Julian, Giles who ran a whole series of tests on a variety of batteries for the calculation. Credit for the work of Forsyth, Julian, Giles is displayed on the BattIR meters LCD display during the test routine of the BattIR meter. The formula is the square root of (6,000 * Batt_ AmpHrs)/(BattIR) where BatteryIR is measured in milliohms.
Thanks again!
Mar 05, 2019, 07:28 AM
Registered User

# john61CT

I work with LFP prismatics, 20Ah at the smallest, up to 180Ah cells, plan to go over 1000Ah when I'm rich.

I do not need "objectively true" numbers, just consistency in identifying weak cells in a set, and measuring deterioration over thousands of cycles.

Also use load testing of residual Ah compared to the first 50 cycles, after break in period.

Winston and CALB mostly, but want to be able to start trying out cheaper no-name stuff as well.

Is this device going to be useful in this context?

As a side note, always looking for reliable & trustworthy sources for US delivery of the above type cells. Currently looking to source 20-25Ah qty 18+.

PM on that last to keep the thread clean

thanks
Mar 05, 2019, 12:21 PM
Registered User
Quote:
 Originally Posted by John61CT I work with LFP prismatics, 20Ah at the smallest, up to 180Ah cells, plan to go over 1000Ah when I'm rich. I do not need "objectively true" numbers, just consistency in identifying weak cells in a set, and measuring deterioration over thousands of cycles. Also use load testing of residual Ah compared to the first 50 cycles, after break in period. Winston and CALB mostly, but want to be able to start trying out cheaper no-name stuff as well. Is this device going to be useful in this context? As a side note, always looking for reliable & trustworthy sources for US delivery of the above type cells. Currently looking to source 20-25Ah qty 18+. PM on that last to keep the thread clean thanks
These battery IR meters apply a load current to the battery, and then measure the battery voltage drop caused by that current. The battery internal resistance is then calculated by dividing the change in voltage under load by the change in current. As the ability of the battery to put out high current increases, the resulting voltage sag tends to decrease.

When that voltage sag drops to a few millivolts, the accuracy of the test starts to drop off, especially if the voltage measuring device has only one millivolt resolution, for example.

The only way around that is to either increase the test current to much higher levels, or increase the resolution of the test metering, or both.