ESR / IR Meter fo Lipos - Page 59 - RC Groups
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Sep 01, 2017, 10:30 PM
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vollrathd's Avatar

A123 vs LiPo receiver battery packs


Quote:
Originally Posted by dcognat1
. But the Million dollar question is that would you trust these packs to power the Receiver and run the servos on a 10K jet?
I'm an admitted when it comes to using A123 battery packs for receiver power on our model airplanes. FYI, my RC models have over 150 A123 cells in them, mostly used for electric motor power, where up to 40 Amps per cell is pulled out of them on a regular basis.

I've got a Western Mountain CBA battery analyzer that has been used to conduct near 1000 discharge tests over the past many years on all sorts of batteries, including electric power, and receiver power.

Those tests have shown that the typical failure mode for a LiPo (And LiFe) is high internal resistance, or open circuit. The LiPos slowly wear out after many cycles, resulting in higher internal impedance. I've tested three of my RC club members LiFe's that had an open cell. A wild guess suggests that perhaps those 3 LiFe's had a pin hole in their plastic baggie.

That leaves the A123's for receiver power. These cells hold 3.3 Volts per cell, or 6.6 Volts per cell at current levels under 10 Amps or so. They hold that voltage until right before they are totally discharged. Compare that to around 7.3 Volts DC or so for a LiPo. I've only had two A123's from my RC friends that failed. One had been left completely dead for several years. That cell was jump started, and still put out 2.7 Volts DC at 10 Amps. But, it would go dead on its own after several months. The second A123 cell had an open circuit. El-stupido accidentally shorted bare cells against each other, and this cell had a hole burned completely through its case. Even with that, it took a year before it failed.

Take a look at the attached JPG that shows three tests pulling 25 Amps on three different A123 cells. The brown curve is a 2300 Mah cell with 500 cycles, and 5 years old on it. The blue curve is a 2300 Mah 2300 cell with a few dozen cycles on it. The violet curve is a brand new 2500 Mah (Type "B") cell. My models have a number of 6 - 8 year old A123 packs ranging from 4S1P to 6S2P that perform the same as the cell shown below. As these A123's get old, their internal impedance doesn't change a lot.

Note that these cells are measuring around 2.7 or 2.8 VDC at 25 Amps. After checking right across the cell with my $$$$ Fluke 87V meter, I found the voltage drop was on the test wires on my CBA analyzer. Those wires were beefed up to #12, and are now only one inch long. The actual voltage at 25 Amps is around 3.0 VDC per cell. That 25 Amps is several times more than most RC models ever pull out of their receiver battery packs.

For a $10K turbine model, IMHO, that plane should have primary/backup DC power to its receiver. My RC members are using a pair of 2S1P 2500 Mah A123's for 30 cc to 60 cc gassers, each with their own receiver switch, each switch with its own connection to the receiver. If you're using a power panel, the A123's should be equipped with #14 or #16 wires to the power panel.

Several of my RC members have 100 and 120 cc gassers. Those are equipped with a pair of 2S2P A123's. That's 10,000 mah, obvious overkill. But, they will never have to worry about sufficient receiver battery power for a days flying.

Ref: A123 use in receiver power should answer a few questions
A123 receiver pack posting
https://www.rcgroups.com/forums/show...-Battery-Packs

BattIR meter This meter shows that my various A123 cells match their IR values within a few percent.
https://www.rcgroups.com/forums/show...ircuitboard%21

A123 receiver pack supplier
http://www.radicalrc.com/category/A123-Cells-Packs-199

Raw A123 cell supplier (My source for the 200+ cells I've purchased over the past several years
http://www.a123batteries.com/product-p/anr26650m1-b.htm
Last edited by vollrathd; Sep 01, 2017 at 11:24 PM.
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Oct 12, 2017, 08:40 PM
Registered User
Ok next question on my Universal Analysis meter:

Trying to measure a new 1S Reedy Zappers 8000mAh hardcase pack we race in 1/12 pan car. I plug in the main power leads with converter XT60 to Deans that plugs into the Deans to 4mm bullet connects to Positive and Negative terminals. I get like 40 to 50 milli-ohms. I should see like 2 milli-ohms range here for this capacity battery.

Should I make a custom wire set for the 2 wire probe instead to this 1S pack? 4mm bullets at the battery with Positive and Negative little wires coming back to a Balance XH plug to 2 adjacent pins and then basically separately power the ESR meter with a 2S pack?

Pics of my connection below and the reading.
Oct 13, 2017, 08:14 AM
Registered User
190,

The problem you have is that there is no balance connector on the pack so that you are measuring the pack (IR + 2x4mm connectors + several inches of 16G wire + two poles of an XT connector + two poles of a Deans connector + a few inches of 14G wire).

To overcome this the meter normally uses the sense wires to measure the voltage at the cell which is accessed by the balance connector on the pack.. As there is no balance connector the best you can do is to measure the voltage right at the two power connections. You will still be reading the IR of the cell + two 4mm connectors but you can allow for the latter to some extent.
You cannot use a separate supply to power the meter because the measuring current pulse goes through the power leads and the voltage measurement is done by the sense leads. The meter will always measure the resistance in series with the voltage source up to the point where the sense leads are connected.
Default connection point, ie when the sense leads are not connected, will be at the meter.
You should use the best 4mm plugs you can; 4mm solid bullets show about 0.4milliohms each whilst the cheaper cage connectors are about 1 - 1.2milliohms and more variable
Ideally solder two thin wires to the 4mm solid plugs where the power leads enter and terminate the other end in a little JST connector which will mate with the connector in the sense leads of the meter which Rick now conveniently fits. Polarity must be observed of course.

You should now be able to read the lipo pack IR + 2 x 4mm connectors and subtract about 0.8 - 1 milliohms from the reading to get the Lipo IR.

This only applies to single cells as the sense lead max input voltage is limited to 5V.

Hope this helps

Wayne
Nov 10, 2017, 09:41 PM
Registered User
Is this meter still available to purchase?
Nov 11, 2017, 01:59 AM
Registered User
Quote:
Originally Posted by Flamewheel
Is this meter still available to purchase?
Very much so.
You can buy it from " RAMPMAN". (Rick Distler) on RC Groups who now makes it, ProgressiveRC in Seattle or HobbyKing who also now stock it.

Wayne
Nov 11, 2017, 05:58 PM
Frankenstein recycled packs
rampman's Avatar
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, 09:16 PM
Mansell Models
N827TM's Avatar
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
Quadaholic
--Oz--'s Avatar
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.
Mar 11, 2018, 04:46 PM
Registered User
vollrathd's Avatar
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
--Oz--'s Avatar
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
--Oz--'s Avatar
@ 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
vollrathd's Avatar
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
vollrathd's Avatar
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
Quadaholic
--Oz--'s Avatar
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!


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