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        New Product ESR / IR Meter fo Lipos

#1 Wayne Giles Oct 16, 2010 07:41 AM

ESR / IR Meter fo Lipos
 
3 Attachment(s)
ESR / IR Meter for 2 – 6 Cell Lipo Packs
A unit to measure and track the deterioration of your Lipos and compare different makes.

BACKGROUND

This is not a serious commercial enterprise, just a hobby extension. As an active modeller and retired power electronics engineer, I have a particular interest in battery performance and have built myself a unit to measure the internal resistance (ESR or IR) of Lipo packs and cells. It worked so well that I have had a PCB laid out and have built a small batch partially to recover some of the engineering cost, but also to offer the unit to other modellers because it is so useful. It measures both total pack ESR and individual cell ESR , the latter using a Kelvin 4 wire system at high current levels.
Many Lipo chargers read ESR, but they are measuring the charging ESR at low currents, which is very different from discharging ESR at high current, which is what the user is interested in. The difference is often more than double and is further distorted by the endothermic charging effect as the ESR of lipos has a negative temperature coefficient.
ESR tells us more about the likely performance and life of Lipos than any other measurement.
As a pack ages it’s ESR will increase and a serious mismatch of cell ESR usually occurs as a pack nears end of life. The meter allows the user to monitor and measure the deterioration of a pack and individual cells within it. Thus you can accurately measure and quantify the declining performance of your lipos as they age.

DESCRIPTION

The unit is self powered by the pack under test, the only controls are a mode switch and an operate button.
ESR is measured at high current to simulate real operating levels.
When connected to the pack, the display will read the voltage of the pack if switched to ‘Pack’. If the meter is switched to ‘Cell’ and the search connector plugged into the balance connector, the meter will read the voltage of the cell corresponding to the pin positions. Moving the search connector allows measurement of any cell in the pack.
Pressing the operate button will display ESR for about 3 seconds and then revert to voltage. In ‘Pack’ mode it will read the ESR of the whole pack plus the connector and leads. This is a practical measurement as it is measuring the total resistance that the ESC will see in practice.
In ‘Cell’ mode it will read the ESR of just the individual cell that the search wire is connected to, excluding all leads and connectors. In the ‘Cell’ mode the instrument is using a true 4 wire Kelvin connection enabling the user to very accurately compare the ESRs of each individual cell in the pack.

SPECIFICATION

Mode--Measurement Range---ESR Resolution---Accuracy---Volt Res.---Volt Acc.
Pack---0–250 Milliohms--------0.3 Milliohms-----<3%-------40mV------<0.5%
Cell-----0–30 Milliohms--------0.04 Milliohms----<2%-------10mV------<0.3%

Measurement current: 16A.
Maximum Pack Voltage: 30V.
Protection: Unit is protected against reverse polarity on both main power and search wire inputs.
Range: The unit can measure any Lipo pack of 2 – 6 cells in the range of 500mAh – 6000mAh.
Size: 45mm x 100mm x 130mm (1.8” x 4” x 5”)
Weight: 200g (7 oz)
Standard Connector: Deans.

NOTE :THIS UNIT IS NOW REPLACED WITH AN AUTOMATIC RANGING UNIT.
SAME BASIC SPECIFICATION.

FOR DETAILS AND PRICING SEE http://www.rcgroups.com/forums/showp...&postcount=249
Will answer any technical questions I can.


To buy one contact me by PM initially and I will give e-mail address and details.
Wayne

#2 N2UMK Oct 16, 2010 01:48 PM

ESR/IR meter
 
Wayne -
Very cool! I was just talking about internal resistance with a fellow e-pilot.
He bought a cell-pro charger because it measures ir. Your meter looks very practical.
Nice work!
Pat
N2UMK

#3 Cody f86saber Oct 16, 2010 02:03 PM

Good work Wayne Giles. Nice to have someone else with an engineering background around.

#4 rick.benjamin Oct 16, 2010 02:08 PM

I agree, and am interested in purchasing one
pm sent

#5 biskit Oct 16, 2010 02:47 PM

How exactly does it measure IR? Have you compared the values your device gives to those obtained from chargers that measure IR? Can it measure other chemistry cells?

#6 Wayne Giles Oct 16, 2010 03:09 PM

Quote:

Originally Posted by biskit (Post 16305575)
How exactly does it measure IR? Have you compared the values your device gives to those obtained from chargers that measure IR? Can it measure other chemistry cells?

It measures the effective resistance by applying a pulse load of controlled constant current load of 16A to the pack, measuring the voltage just before the start of the pulse and again just before the end of the pulse. It then does the maths of subtracting the last figure from the first figure, divides the answer by 16 to give result in ohms and divides that by 1000 to display the answer in milliohms.
I have compared the results with those from chargers and generally they vary by up to 150% more. The meter agrees with the figures from actual loading results when power testing whereas the charger results are higher, I think because of the endothermic effect of charging and because most chargers do not use a 4 wire Kelvin connection so that the connectors are included in cell figures.
The unit will measure any chemistry provided that the pack is between 7V and 30V and the cell voltage is less than 5V.

Wayne

#7 rick.benjamin Oct 16, 2010 03:40 PM

1 Attachment(s)
Sent $70.40 by paypal
Oh boy, oh boy!
Is it here yet?!

#8 Wayne Giles Oct 16, 2010 05:04 PM

Quote:

Originally Posted by rick.benjamin (Post 16305886)
Sent $70.40 by paypal
Oh boy, oh boy!
Is it here yet?!

I'm sending it, I'm sending it!!

Wayne

#9 mtnflyer44 Oct 18, 2010 07:00 PM

Wayne,

PM sent, I will be travelling until Wednesday pm. Hold one for me.

#10 JimDrew Oct 18, 2010 07:21 PM

We would like to purchase one ourselves.

#11 Wayne Giles Oct 19, 2010 05:18 AM

[QUOTE=Cody f86saber;16305316]Good work Wayne Giles. Nice to have someone else with an engineering background around.[/Q

There are a lot, of engineers/retired engineers on the forum, I think because modelling is miniature engineering without the responsibility - you get the high, without the hassle!
I found Phil_G on the forums who has done the PIC and software for me on the meter. I just worked out a basic system, sent him a spec, he sent me a board with the display and PIC on it, I built my power operating and analogue measurement system onto it, pressed the button and hey presto! it worked first time. I just had to calibrate it and we had a working system. We have changed and added bits since then such as the voltage measurement facility, but the co-operative excercise worked perfectly and first time.

Wayne

#12 Wayne Giles Oct 20, 2010 01:27 PM

Quote:

Originally Posted by mtnflyer44 (Post 16323295)
Wayne,

PM sent, I will be travelling until Wednesday pm. Hold one for me.

Marvin,
OK, Will do.
Re: your PM, I'm sure you will find that the accuracy and repeatability of the meter will allow you to compare cells within a pack. The resolution of 0.04milliohms means that you can measure a cell on the outside of a pack, place the palm of your hand on the cell for only 5 - 10 seconds, take another reading and see that there is a measureable change in ESR.

Wayne

#13 mrforsyth Oct 20, 2010 01:56 PM

Nice work Wayne.

Quick question - Have you had the opportunity to corroborate the readings from your meter with any of the commonly used hobby grade chargers that incorporate IR measurement features? (FMA CP10, PL8, iChargers, etc.) And with greatly varying cell capacities? Also wondering how the results compare with a lab grade kelvin meter...

I (among others) have long complained that C ratings are basically useless since there is no test standard. Sadly, C ratings have proven to be an extremely effective marketing tool however as most modelers are not aware that they are very arbitrary. As such, I have been using cell IR as my primary performance indicator for the last few years as it's much simpler than firing up my CBA.

I would be much happier if lipoly manufacturers would print measured cell IR on their packs rather than arbitrary C ratings. This will obviously never happen though as it would likely expose the largest lipoly vendors in a less than favorable light.

Mark

#14 Wayne Giles Oct 20, 2010 03:20 PM

[[SIZE="2"]QUOTE=mrforsyth;16338611]Nice work Wayne.

Quick question - Have you had the opportunity to corroborate the readings from your meter with any of the commonly used hobby grade chargers that incorporate IR measurement features? (FMA CP10, PL8, iChargers, etc.) And with greatly varying cell capacities? Also wondering how the results compare with a lab grade kelvin meter...

I (among others) have long complained that C ratings are basically useless since there is no test standard. Sadly, C ratings have proven to be an extremely effective marketing tool however as most modelers are not aware that they are very arbitrary. As such, I have been using cell IR as my primary performance indicator for the last few years as it's much simpler than firing up my CBA.

I would be much happier if lipoly manufacturers would print measured cell IR on their packs rather than arbitrary C ratings. This will obviously never happen though as it would likely expose the largest lipoly vendors in a less than favorable light.

Mark[/QUOTE]

Thanks Mark,

The only Charger I have which reads IR is a Hyperion EOS0610iNET which is a great charger but not very good at measuring IR. It reads between 150 and 250% of the IR I measure, varying with pack size and other factors which I cannot quantify. So much so that I quickly gave it up as a measurement source.
The meter gives the same results that I see in power testing ie the figures agree with the initial drop when the a controlled CC load is applied. Obviously I have checked this against the step change on a memory 'scope using reasonable length pulses of significant load, 10- 20C. I don't have a lab grade Kelvin meter, but have calibrated 10 and 45 milliohm resistors which I use to calibrate the 'Cell' and 'Pack' ranges respectively, and all the meters so far have shown figures within 1% on the Cell range and 3% on the Pack range. Latter is more difficult to be precise as it is not a Kelvin measurement so we have a (variable) connector contact in series.
I agree with you about "C" ratings. They were a joke a few years back and I was beginning to think they were more realistic when claims were 25 and 30C. I now think we are into another lunatic claiming era.
Whilst I agree with your last paragraph, the pack must be soaked at a known temperature (25deg.cent/77deg.F?) and given time to settle if you are comparing packs.
When looking for degradation between cells within a pack this is obviously not a problem and the advantage of the meter it gives an instant answer.

Wayne

#15 mtnflyer44 Oct 23, 2010 07:46 AM

Wayne, money is on the way.

Marvin


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