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Jul 21, 2019, 06:21 AM
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New Product

The official new ESR/IR Mark II meter thread – NB: READ THE FIRST 10 POSTS


For almost 10 years the Wayne Giles designed, LiPo ESR/IR meter has been the gold standard on which modellers who are serious about preserving the life of their expensive LiPos, getting packs with the best performance, and sorting out the marketing rubbish on the label from the real performance of a LiPo have relied. The meter measures the Effective Series Resistance or “Internal Resistance" of each cell in a LiPo pack. This provides a direct measure of relative cell condition and comparative pack performance. Used in conjunction with a very simple web based “LiPoTool” the meter provides an extremely fast non-destructive indication of the sensible maximum current limit for any model LiPo to preserve its life and avoid overheating. It has brought some sanity to the often outrageous claims of C-rate on the label of some vendor’s packs.

Almost 1900 of these meters are in use worldwide and now…….

There is a new version with the same accuracy and reliability - but much quicker and more convenient to use. It is a development of Wayne’s design by well known RCGroups modeler Rick Distler (rampman) who has been making the original version for some years now.

The purpose of this thread is to provide a place where people can ask questions about the new meter, discuss its use, and get help.

There are plenty of other threads for the discussion of the merits of particular LiPo brands and formulations, or the actual in-flight performance and bench testing results. Please take the “Brand X is complete junk” and the 20-minute Youtubes of your favourite pack powering a speck around the sky there.

So why the change in a very successful meter?

The original ESR/IR meter measured each cell resistance one at a time. It is extremely accurate and reliable but a bit tedious to use as you have to re-enter the pack capacity every time you connect a new pack, manually enter the pack capacity, and measure each cell individually. The new version has a built-in list of most popular pack sizes (which can be simply edited on the fly), stores the last value used, and measures all cell IR values at one time.



The picture shows an original meter (we will call it a Mark I or Mk I) on the left and the new Mark II version on the right. Note that the original meter has come in a few variants over the years. The very first had a front panel toggle switch to choose between cell or pack IR, there has been a manually switched dual range version to allow measurement of smaller packs, and finally the “Universal” version shown in the photo which covers all pack sizes. The firmware has also been updated over the years to show more information. There is also a specialised 1S version for the tiny indoor 70-200mAh single cells which was produced in small numbers.

So, what does the new Mk II version do?

Usage could not be simpler:

1) Plug in the LiPo main lead
2) Plug in the balance lead. Individual cell voltages and state of charge are displayed.
3) (Optional) Hold down the left button for about 2 seconds to change the pack size if required.
4) Press the right button to display all the individual cell IR values, the pack IR, the recommended maximum current draw for the pack and a Figure of Merit used to compare packs.
5) Press the left button to toggle the screen to display the recommended maximum current draw for each cell and a conservative realistic true C rate for the pack.

That’s it. Takes less than 10 seconds if using the same pack size.

Here is what the two display screens look like using a 3S pack as an example.



The new meter is available now directly from Rick.
Just email him at [email protected]
The cost is US$149 plus shipping.

It is also available through ProgressiveRC

https://www.progressiverc.com/lipo-e...r-mark-ii.html

and will be from HobbyKing in due course.
Last edited by jj604; Jul 29, 2019 at 07:11 PM. Reason: Added ProgressiveRC availability
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Jul 21, 2019, 06:21 AM
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How it works

The original ESR/IR Mk I meter is classic “old school” electronics of the best kind. A power transistor is pulsed on for a precise interval by an operational amplifier which accurately controls the constant current load. In the original meters this was a 16 Amp load for 15mS. In the later Universal Mk I meter the load is reduced to 8 Amps which has little effect on accuracy but allows the meter to be used with smaller packs. A fully floating operational amplifier measuring circuit attached to a 2-pin probe that can be inserted in the balance connector, one cell at a time, accurately measures the voltage drop when the load is applied. The circuit is individually hand calibrated for each meter for accuracy before shipping. Measuring the IR of each cell individually is a bit tedious but has the important advantage of eliminating any measurement errors between the cells as the same circuit is used each time. The resulting voltage drop is divided by the current and displayed as an IR value by a small PIC microcontroller. The later version 2.0 of the PIC firmware in the Mk I meters also calculates and display a recommended maximum continuous current and a recommended maximum C rate based on the assumptions of the LiPoTool.
The values of current for the load, and the time for which it was applied, were determined by a great deal of experiment with real LiPo packs to ensure consistency and accuracy.

This is typically how the Mk I meter works, using a single push button to do all the settings, and displaying its results. You have to reset the capacity every time you connect a new pack.

The initial screen on power up looks like this.



Pressing and holding the red button for a second or so takes you to this screen.



Pressing the button toggles through the 100’s of mAh values.
Pressing and holding moves to the 1000’s of mAh values.



When done, pressing and holding takes you to the main screen.



From there, moving the cell voltage sense lead and pushing the button after each move measures each cell IR value.

Originally the ESR/IR meter was a DIY project entitled “Build Your Own ESR Meter” published by Wayne Giles in a British vendor model forum in Feb 2010. Wayne is a retired professional electronics and electrical power engineer and keen modeller and this project was a simplified development of a Battery Performance Meter which had been used to assist some of the UK International competitors obtain maximum performance. Wayne is someone who really understands power measurement in high current circuits with its arcane demands of star points and consideration of thermal junction heating effects. This kind of measurement is a long way from the high impedance, high frequency, logic-level digital electronics that is common today and needs a special understanding to obtain accurate, reliable and repeatable results. Wayne anticipated that maybe a couple of people would be interested - but the DIY project was so popular the demand for ESR/IR meters became a retirement hobby project and almost 1100 meters were eventually sold, many through ProgressiveRC in the US. Rick Distler began assembling them in the US when Wayne got tired of making them and produced another 800 with many being sold through Hobbyking. That’s nearly 1900 meters worldwide – not bad for something that “maybe a couple of people would be interested in”. Variants included the original 16A single range model, a dual range 16A/1.6A switched version for smaller packs, the final Universal 8A version and a specialised meter for measuring small 1S cells for indoor models. One of the originals was even assembled in Australia and modified to log IR over long periods to investigate the effect of temperature on IR.



The new Mk II meter

Wayne has now fully passed the torch to Rick Distler in the US, and Rick has just done a complete redesign in conjunction with a very clever electronics whiz (although he has kept exactly the same case for the meter - which is kind of neat). The meter now has two push buttons on the front which allow pack capacity selection, switching between the display of mOhm IR values and recommended currents, and the initiation of IR measurement.



The new meter still has six OpAmps as differential input buffers for the cell voltages, but the PC board now has SMD components, an 8-channel multiplexor SP8T switch, a 13-bit AD convertor, an Atmega 328 microprocessor and an 128x64 serial graphic LCD display. The 2-pin probe has been replaced by a 1-6S capable balance connector. The JST-XH balance connector is modified so that you can connect any LiPo between 1S and 6S to the socket.



The meter cell lead on actual production meters may vary from this picture as later production versions will have longer 12” leads.

The Mk II now displays all the results for all cells at once, including IR and recommended maximum current draw. This is much more convenient, and eliminates any errors due to the time delay between measuring the first and last cell, but puts real demands on the design since all of the cell readings must now be consistent and equally accurate. A look at the interior shows different generations of electronics. Mk I on the left, Mk II on the right. The internal 9V battery is used in both meters when testing a 1S pack or well discharged 2S which cannot deliver a high enough voltage to run the meter. The individual cell voltages can be accurately read down to 0.8V; below that they do not display. However, the other cell voltage readings are unaffected by a missing cell value.


[IMGhttps://www.rcgroups.com/forums/showatt.php?attachmentid=12332839[/IMG]

Most important however is what has not changed. The core circuit that applies the 8 Amp load for 15mS is identical to that in the original meter. Since the main aim was to design a meter that is more convenient and faster to use BUT with no reduction in accuracy, and that returns the same result as the original, this was a crucial design decision. See posts #6 and #7 for a discussion of why the consistency and actual mechanics of measurement are so important in determining reliable, repeatable and comparable IR values.

The new Mark II meter uses software averaging of the last 2, 3 or 4 reads in addition to all the other usual measuring circuit tricks to obtain reliable, consistent and accurate results. This technique using multiple readings is necessary because of the high resolution of the circuit which causes fluctuation in displayed values. Another critical operating difference is that the meter stores a wide range of different LiPo capacities and remembers them, even when turned off. This is a very big convenience. There are 5 display pages of included pre-set pack sizes with each page having 5 different values. You can edit any of the values to 100mAh increments. The meter remembers the last size you used.
Last edited by jj604; Jul 22, 2019 at 06:04 AM.
Jul 21, 2019, 06:22 AM
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Accuracy

So how good is it? I built a test rig that puts a known resistor across each cell in addition to an A123 single cell to provide sufficient voltage to overcome the “low cell voltage” condition. This is essentially identical to the manual calibration rig that was used for the Mark 1 meters. It has the great advantage that it eliminates any variability due to the LiPo battery. The value of the resistor is unaffected by normal temperature variation or state of charge.



I tested a prototype Mk II meter and 3 different Mk 1 meters that I own. One of these is a recent 8A Universal meter, the second is an early production 16A Dual Range and the third a very early 16A single range meter, probably a prototype. I first used a resistor that is approximately 12 mΩ and then another that is approximately 2.5mΩ. This is typical of cell IR values of smaller 1000mAh and larger 5000 mAh packs.

Here are the results.



Notable is the agreement of the three Mk I meters, two of which are almost 10 years old and have never been recalibrated! It’s pretty hard to beat individual calibration by a master. The auto-calibrated Mk II meter reads fractionally lower than the Mk I meters but the difference is very small and the meter is consistent. When measuring IR values around 2-3 mOhm, we are working in an area where very slight environmental and test condition differences can cause significant differences in the actual readings.

Rick advised me that the very first prototypes (like this one) had a bit of variability due to their hand manufacture. Production meters are even more consistent as they are built on an automated pick-and-place line.

A production Mk II and a production Mk I were then compared with two different size packs that cover the range most modellers use – 1000mAh and 5000mAh. The meters were set up with a Y harness to take the readings at essentially the same time to eliminate as many variables as possible.



The MkII meter measures both cell and pack voltages to a high resolution. For the 8A test current pulse load, this results in cell ESR values being resolved to significantly better than 0.1mOhm. Additionally, the meter calculates and displays a moving average of up to the last 4 ESR readings which increases the effective resolution. The final result is thus not limited by the resolution of the meter.

But the result of measurement of LiPo ESR is subject to a number of other factors. Repeatability, consistency and accuracy can all be affected by them, including cell heating due to the test pulse. It is normal for there to be some spread of the values of ESR, especially when testing is repeated.

In summary: the new Mk II meter returns results essentially the same as the original meter within the range of fluctuation and error expected.


IMPORTANT: The Effective Series Resistance or “IR” of a high rate model LiPo is EXTREMELY temperature dependent. There is more information on this in Post #7.

The values the meter returns for a recommended C rate and maximum recommended current are based on IR values measured at a standard temperature of 22°C/72°CF.
Last edited by jj604; Jul 22, 2019 at 06:06 AM.
Jul 21, 2019, 06:23 AM
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Using the Mk II meter - details

The new meter, like the original, can measure up to 6S packs. If you plug a 6S into the power and balance leads you will initially get a list of individual cell voltages, the pack voltage, the assumed capacity based on the last value you set (incorrect in this picture because the capacity has not been set for the new pack), and an indication of the charge state of the pack.



If you plug in a pack with less than 6 cells the display shows only those cells.



If you plug in only the power lead and not the balance lead, the meter warns you like this.



You can still press the right-hand button and the meter is smart enough to report the pack voltage, and the total pack IR. It cannot measure the individual cell IR values. It functions in this case as a very quick pack IR checker as shown below.



If you press the left button it will give you the recommended maximum C rate (based on the pack IR value).



On the other hand, if you press the right-hand button with only the balance lead connected and without the main lead, then the display shows cell voltages along with pack charge state - but a warning buzz will sound as it cannot measure the IR values. It functions in this case as a very accurate cellmeter (capable of measuring down to 0.8V/cell) as shown below.



Normal use

The first thing you should do after connecting the power and balance leads is to set the pack capacity if it is not the same as the displayed value. This is done by holding down the left button for about 2 seconds then releasing it.

This menu will appear.



Select the correct capacity for the pack by using the left button to scroll and the right to select. When you have chosen a capacity, you get a final choice to edit the value or use it.



If you are in this screen changing pack sizes and decide you did not want to do that after all, press and hold the left button for about 2 seconds and you will be returned to the main screen. Pack size will be edited if that is what you did - but it will not be selected when you return to the main screen.

After selecting the capacity (“Use it”), the left button toggles between the raw IR values like this ……



….. and the recommended maximum current for this pack – for each cell. On the top line in both screens is a “Figure of Merit” FoM. This is a value based on the calculated C rate of the pack. A FoM around 1.0 or greater indicates an excellent pack, although packs with a much lower FoM are perfectly satisfactory for most applications. Also, on the top line of the second screen is the C rate (the Greek "alpha" on the screen) that the LiPo tool calculates for this pack.



Now here is an old 6S, 2200mAh “50C” pack that is past its prime. Note that the meter recommends only a 31 Amp maximum continuous current which is equivalent to a 14C rate.





Finally, if the pack has less than 6 cells the meter will simply display only that which it can measure.



Last edited by jj604; Jul 22, 2019 at 06:37 AM.
Jul 21, 2019, 06:23 AM
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How tough is it?

Well, it is possible to wreck any precision instrument but the ESR/IR meter is actually pretty tough.

• It is protected against polarity reversal on the main leads provided the balance wire is not connected.
• It is protected against forcing the balance connector in the wrong way around.
• It doesn’t matter which pins on the balance connector you plug a smaller balance plug into (although the cell labels on the display will not match the battery).
• It will buzz angrily at you as a warning if you try and take repeated readings too quickly as the power FET has to dissipate the heat from the test load.

What cannot be protected against is:

• Connecting the meter to packs with a large number of cells. It is designed for 6S packs or less. The power FET has both a power and voltage limit and is protected up to 40Volts but over that and you will fry it. For example, a fully charged 10S pack exceeds this limit. An 8 cell will just shut down the meter but cause no damage.
• Polarity reversal of the main lead IF the balance lead is already plugged in. Doing this will require the replacement of one diode.
Last edited by jj604; Jul 21, 2019 at 07:47 AM.
Jul 21, 2019, 06:24 AM
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What do we currently know about LiPo performance and IR?

The short story.

Internal Resistance (IR) is an empirical (measured) value that describes observed behaviour; it is not a precise description of what the cell is doing internally.

A LiPo battery, used in the way modelers normally use it, behaves to a reasonable approximation as though it were a voltage source in series with a small resistance inside the battery - hence Internal Resistance. A LiPo is not however actually a perfect voltage source containing an internal resistor. It just behaves roughly as though it was and that makes it easy to make some predictions about battery performance without having to analyze the electro-chemistry of the internal workings in awful detail. The equations involved, and their solution, is not the stuff ordinary folks want to be involved in.

Here's the variables we know about:

1) Test method. IR of batteries is calculated either by measuring the DC voltage change between loaded and unloaded state, or applying a known AC frequency and measuring the impedance. The latter is the standard industry way of doing it, is rapid and easy to do, and is fine for Quality Assurance in LiPo manufacturing - but it returns “IR” values that are significantly lower than DC values. The impedance of a LiPo is lower than its DC resistance as the LiPo has significant capacitance. Vendors like this, as it makes their packs look better than they actually perform in DC applications like ours. DC load methods are more realistic for flight packs but are very dependent on the time you apply the load for - and that's why values from the Wayne Giles ESR/IR meter, which is a pure DC load method, are sometimes different from values returned by some chargers, which stop charging briefly and measure the cell voltage difference between the charging and unloaded state.

However, even if you use the same measurement method without fail there are still significant variables:

2) State of Charge. The measured IR varies a bit with the state of charge (SOC) of the LiPo but it's not actually a big variation. A LiPo is fully charged at 100% SOC and completely exhausted at 0% SOC. IR is minimum at 100% charge and rises very slightly as the pack discharges until you get to about 10% SOC at which point it shoots up.

3) Pack size. The measured IR for a particular chemistry is inversely proportional to the capacity of the pack. A larger pack contains a larger electrolytic pathway for the electrons to move across, so the resistance to travel is less. Think of how a single lane highway can accommodate only a quarter of traffic at the same speed as a four lane one. The “resistance” to traffic flow is 4x that of the bigger highway.

4) Age of the pack. IR rises as packs age. Provided there is no actual cell failure, it seems as though this is again dependent on cell chemistry and construction. Reliable genuine cycle life numbers are very hard to come by, but the collective wisdom is that "heavy" packs like the Turnigy Graphenes and Panthers have a much slower increase in IR over elapsed time and number of cycles than HV packs and lightweight graphene packs. It is plausible that this is related to internal temperature rise, as heat is pretty much the enemy of any consumer battery. Note that this is not an absolute judgment as a pack that runs hot will have lower IR (see 5 below) and may perform better even although it won't last as long.

5) Temperature. This is the biggy. The measured value of IR is very dependent on the measurement temperature. Different chemistries have quite different IR vs. Temperature curves but all show a very dramatic increase in measured IR as temperature drops below room temperature. The changes can be large. A drop of 10°C can nearly double the IR value. That's why Wayne Giles, Mark Forsyth, John Julian and others are obsessive about emphasising that IR must be measured at a standard temperature - normally 22°C or 72°F if you want to compare results of different packs. In practice no one has the means to measure the internal temperature of a LiPo so the standard advice is to leave the pack in a 22/72 degree environment for at least 2 hours before measuring IR. Of course, if all you want to do is an instant check on the consistency of each cell IR across a single pack, the temperature and state of charge can be ignored. This temperature effect also explains the good performance of some otherwise high initial IR packs. The large internal heat generation of a high current load rapidly reduces the IR and reduces the internal voltage drop. This is evident in high current constant load tests by a dip and then recovery in the cell voltages in the first seconds of discharge. If it doesn't destroy the pack prematurely it is almost certain it accelerates its demise. Such packs may "flare brightly but briefly". In practice they might still perform well for as long as required, depending on the expectation and requirement.

Bottom Line:
IR measurement is not a substitute for proper load testing. But, provided you maintain consistency in test method and conditions, it is a very convenient, quick and non-damaging way to get an indication of the relative quality of different packs. And it provides a simple numerical measure that is easy to understand rather than complex graphs which need to be interpreted.

Note that you can use individual cell IR or total pack IR (the sum of the individual cell IR values since all the cells are in series) whichever suits. Individual cell IR, normally using the highest individual IR value as the IR “bottleneck”, has the advantage that you can compare the quality of packs of different cell counts directly without any mental arithmetic.
Last edited by jj604; Jul 21, 2019 at 07:49 AM.
Jul 21, 2019, 06:25 AM
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Why is Internal Resistance useful?

The long story

To repeat: Internal Resistance (IR) is an empirical (measured) value that describes observed behaviour; it is not a precise description of what the cell is doing internally.

Critically, it is important to understand there is no actual “internal resistor” so you can use some resistor rules (two cells in parallel have half the IR of one) but not others (IR varies dramatically with temperature in a way a resistor does not). That is why the ESR term, used here to mean Effective Series Resistance, is really preferable. ESR is normally used for Equivalent Series Resistance which is the series resistive in-phase component of a reactive AC circuit which also has inductive and capacitive values. When applied to LiPo measurement, it just means the effective resistance to current flow within the battery measured in Ohms. Importantly, IR is a measured number not an intrinsic property, so that different methods of measuring IR give different numbers.

Of the various tools used to measure IR, the Wayne Giles ESR/IR meter uses the Kelvin (4-wire) method of measuring cell voltage separately through the balance leads to avoid errors caused by resistance of the battery leads and connectors. At least one other meter and most chargers that report an IR number use the 4-wire method. A number of Wattmeters also report an IR value. However, if they have only two wire connections to the battery and load as most do, it can be assumed that the IR values are nonsense. It has been determined that although the numbers measured by different 4-wire methods are all slightly different, they are generally fairly consistent across different batteries if using the same method.

The important caution is that, when comparing IR numbers, you can only reliably do so if you know at least:

• the test temperature; AND
• the method used to measure them.

Why use this number?

If it is so prone to measurement variables, why use IR at all? Well, C rating is largely now meaningless since that also needs to be specified under particular conditions - and never is, and never will be, since it is not in the manufacturer’s interest to do so. However, a great deal of practical experience by a number of knowledgeable folks over several years and in several countries suggests that, properly specified, IR is a “good” measure. It is fairly easy to do with the right equipment, easy to understand and, with relatively few controlled conditions, values can be compared. Practical experience to date has shown it is a good guide to real performance. For example, there is some evidence that different manufacturer’s batteries respond differently to temperature - IR predictions for Brand A vs. Brand B in Norway in winter and Arizona in summer are a reasonable predictor of actual behaviour.


What is the importance in practice?

Typically a LiPo discharged under increasing currents displays a set of voltage/time curves something like this picture. The graph is of measured cell voltage on the Y axis against elapsed time on the X axis at very high constant current discharge rates for a high performing pack. As the discharge current goes up the cell voltage drops because there is a higher voltage drop within the cell due to IR and at the same time the heat generation within the cell increases.



Note how that as the discharge rate increases - measured as “C” which equals the actual current divided by the manufacturer’s mAh rating - the available voltage to the power system drops and the final pack temperature rises Eventually at high enough C, the cell simply cannot maintain any useful voltage.

Temperature rise is a function of the internal heating (high IR and/or higher current means that more heat is generated inside the battery), the physical configuration of the battery (big batteries have lower IR but poorer surface/volume ratios, multiple cells have poorer heat dissipation than a single cell since they have less surface area exposed), and the external cooling conditions (ambient temperature, air flow etc.).

Normally up to a certain discharge rate the voltage curve falls with increasing current and continues to decrease with time. However, at some fairly high current, the curve dips, and then rises again as the internal heating of the battery accelerates the chemical reactions inside and produces more volts. This is the blue line in the graph. The battery is certainly being abused at this point and will have a short life.

Wayne Giles and Mark Forsyth developed a simple tool to predict a “reasonable” maximum current drain based on the heat dissipation inside the pack calculated from the measured internal resistance. It is available on my website here at:

http://jj604.com/LiPoTool/

The aim of the maximum current calculator is to give a very simple tool to estimate the maximum current any particular battery is capable of while maintaining a decent cell voltage and limiting the internal thermal heating.

It is not a theoretically derived tool, but one based on a number of years of observation of the performance and heating of batteries under test and in flight. The conclusion is that placing a limit on the power dissipated in the battery as a function of its capacity is a remarkably good guide to the maximum current rating. This has proved true over a range of commonly used battery sizes down as far as the tiny single 150mAh cells used in the micro fliers from Parkzone. It is a conservative estimate and suggests a maximum current for any pack that will optimise both performance and life of the pack.

Note that other Lithium chemistries may be different and you should not assume that "known" facts for other packs, such as the common LiIon cells or LiFe, necessarily apply to LiPo model flight packs.

As emphasised previously, actual IR values are very dependent on how you measure them. This cannot be over emphasised. Unlike "intrinsic" properties like weight and size, the values are not invariant. If you measure the weight of a sealed LiPo pack then, assuming your instruments are accurate, you should get exactly the same weight (allowing for a miniscule variation in the force of gravity at a different location) as anyone else. IR is not like that. It is a "derived" value and depends on the simplifying model you assume for a real LiPo. A real LiPo is a very complex little electrochemical factory and most of us don't pretend to understand exactly what is going on inside in all its detail. Like most things in electricity however the behaviour can be simplified by a model that puts together a few well understood fundamental components that mimic the behaviour of the real thing. A battery model may consist of several ideal voltage sources, several ideal resistors, several ideal capacitors and several ideal inductors and possibly some complex temperature dependant components. The simplest practical approximation to a real LiPo is a single ideal voltage source in series with a single internal resistor. The more current you pull, the bigger the voltage drop over the internal resistor, the more the voltage drop at the pack terminals and the more the internal heating. But this is an oversimplification. Real LiPos don't behave like this. However, adding more and more "corrections" makes it impossible to do any meaningful analysis and predictions so this very simple model is pretty good provided you keep all the other variables constant. The 5 key variables that need to be controlled were listed in Post #6. Of these, the one that probably cause the most cases of differing results for the same pack is temperature.

Here is a set of curves showing dependence of IR on temperature for a number of different Turnigy packs of the same size. They were measured with a Mk I ESR/IR meter over a temperature range mostly from 50°C (122°F) down to well below freezing (0°C).



Analysis of a large number of these curves shows no straightforward mathematical equation that fits the curves. They seem to be unique for each pack chemistry.

The 4 significant take away messages are:

• All curves show a decrease in IR with increasing temperature
• As it gets significantly colder the IR shoots up extremely rapidly. This is recognised in cold climates as the “Winter failure” problem if you do not pre-heat your LiPo packs.
• Curves for different chemistries, even from the same vendor, can cross over. This means that a pack which might have higher IR at room temperature than another could actually perform better than the second when it warms up.
• The curves demonstrate how vital it is to standardise on test temperature. There can be over 50% difference in cell IR value for exactly the same cell measured at 20° (68°F) and 30°C (86°F).

What is meant by the statement that the value of IR is “dependent on the measuring method”?

No one suggests that the value of IR is only dependent on measuring method but it is a critical factor to understand. What is meant is this.

There is no actual resistance inside a LiPo that we can measure with an Ohmeter and get the same and identical result no matter when or who the measurement is done by. The "internal resistance" is a component in a simplified conceptual model as noted previously. We know it is not entirely accurate and folks doing more sophisticated work on things like electric traction batteries may use a much more complex model with a greater number of individual elements to analyse. But for most of us, this is beyond practical and the simple model is good enough to predict performance. All “modelling” in science is a compromise between simplicity and accuracy of similitude and this compromise is at the simplicity end of the spectrum.

Although we cannot directly measure an internal resistance in Ohms, what we can do is measure current and voltage with precision when we put a load on the battery. The drop in voltage divided by the current has the value of Ohms and is a measured value of the ‘internal resistance’.

So we know we can measure voltage and current to high accuracy, and the various meter and chargers measuring IR are unlikely to suffer from lack of precision. However, there is one big variable that is not present in normal resistance measurement. How long, and how often, and in what manner do you load the battery to get the measured voltage drop. This is what is meant by "Measured IR values are very dependent on how you measure them." Extremely precise meters that are properly calibrated will return different results if you load the cell for different times, or use several pulses and average rather than a single pulse, or measure the voltage rebound during charging when the charge current is removed and so on. None of these values is intrinsically the ‘correct’ one. Provided the meter/charger is well designed to be stable and accurate, then any of them can be taken as correct.

Three things follow:

• If you want to monitor the performance of your own packs then you should always use the same method and tool under the same conditions. Temperature constancy is the big one as noted earlier.
• If you want to compare IR values with others you need to know how the IR values were measured. You cannot directly compare a value from Wayne's ESR/IR meter with that from a typical charger as they are measuring the IR differently.
• The big question is how you relate a particular IR value to "real life" performance. No one who is serious about LiPo IR has ever suggested that measuring IR is a proper substitute for actually testing packs under load conditions. The sort of comprehensive and well controlled testing that you see reported on this web site. https://www.rcgroups.com/forums/showthread.php?1767093-Battery-Load-Test-Comparisons/page1

What IR measurement is, is a very quick and simple way to get a reasonable approximation of how a pack will perform in actual service. That approximation in the case of the Giles meter is based on a great deal of empirical evidence. That is, Wayne and others have tested lots of different packs and found that the IR value measured by the meter correlates pretty well with most LiPo pack performance if you make a simple assumption that the internal heat generation calculated from the measured IR value should be kept below a maximum. The important point is that this is empirical - that is, based on a lot of observation of real performance and not some theoretical reasoning. This simple assumption is taken together with a second. The meter design uses a DC pulse load that was again derived empirically by observation of a lot of load curves to give repeatable and representative results. The second assumption that the DC load should be measured after the initial drop has levelled out, but before significant internal heating occurs also seems a reasonable one.

The LiPoTool calculator at http://jj604.com/LiPoTool/ uses these simple findings to predict a "safe" maximum current for any pack. This same calculation is built into the Mk II meter. The recommended value is a bit arbitrary and deliberately conservative to maximise the life of the LiPo. You can certainly discharge packs at higher currents but eventually you will see shortened lifetimes, puffing etc. We know that some of the modern graphene formulations can do better than predicted by the LiPoTool and we suspect this is because of their very low intrinsic internal resistance to begin with, so that internal heating is less with this kind of pack. The Turnigy Graphene/Panthers seem to manage this and provide high C rates but still have a long cycle life. Other graphene formulations have higher internal resistance initially but this drops off as they heat up so they may perform similarly at high rates. The question of their longevity is a matter for real world experience.
Last edited by jj604; Jul 22, 2019 at 06:10 AM.
Jul 21, 2019, 06:25 AM
ancora imparo
jj604's Avatar
Thread OP
Useful links

• The LiPoTool
http://jj604.com/LiPoTool/
• The IR/LiPoTool discussion thread
https://www.rcgroups.com/forums/showthread.php?1577989-A-simple-LiPo-performance-tool
• The original ESR/IR meter threads
1) https://www.rcgroups.com/forums/show...%20ESR%20meter
2) https://www.rcgroups.com/forums/show...5#post16305234
• The Mk I ESR/IR meter v2 thread
https://www.rcgroups.com/forums/show...5#post41087393
• The LiPo Ratings website
http://www.liporatings.com/index.html
• The definitive LiPo performance thread on RCGroups
https://www.rcgroups.com/forums/show...parisons/page1
Last edited by jj604; Jul 21, 2019 at 08:22 AM.
Jul 21, 2019, 06:26 AM
ancora imparo
jj604's Avatar
Thread OP
Reserved for update information on the meter including any improvements of modifications.
Last edited by jj604; Jul 21, 2019 at 08:02 AM.
Jul 21, 2019, 06:27 AM
ancora imparo
jj604's Avatar
Thread OP
Reserved for interesting stuff that comes up that we didn’t think of.
Last edited by jj604; Jul 21, 2019 at 08:02 AM.
Jul 21, 2019, 10:13 AM
HAL... Open the damn doors!
jfetter's Avatar
Ordered! Thank you for your great work!

Jack
Jul 21, 2019, 10:48 AM
Registered User

Ordered!


Mine is on the way, too!!!
Jul 21, 2019, 11:26 AM
Frankenstein recycled packs
rampman's Avatar

Some additional notes


Thanks Jack and Tim and the recipients of the other 21 meters that I am shipping on Monday.
I will NOT be able to ship after noon this coming Wednesday - Monday as I will be doing what I love most, flying at a RC fun fly, and I will not have cell coverage during this time.

Greg and I began this project 2.5 years ago and he was, no, IS the most amazing EE I have ever worked with. Knowing software and hardware, he could not point his finger at "the other guy" and kept coming up with new features like storing pack sizes, reset option, automated test and calibration fixture...
I have been so blessed to have met Greg and also working with other very knowledgeable engineers such as John, Wayne and mrforsyth and a few others to help bring this nice tool to reality.
Also, I want to thank David Gray and Robin Wilkes of Progressive RC and Hobbyking Richard from Hobby King for pushing me to invest time and money into a new designed meter. Progressive is already requesting a Mark III but I need to catch my breath a bit first. LOL

Lastly, a HUGE shout out to Wayne Giles for passing the torch to me to allow the original Lipo ESR Meter to still be built and sold to the masses (it was, and still is, too good to die) and of course, JJ604 for his extensive technical knowledge and writing skills. I read his review and ordered one first thing this am. LOL

I originally wanted to call this a Lipo Dyno (think of race car dynamometers used to test motor horsepower and torque) but Richard from Hobbyking (Hobbyking Richard on RCG's) objected as it sounded too much like Dynogy through I am sure MarkF would have approved. LOL
It was Wayne that suggested the Mark II and I really liked that as it retains most of the original name. John decided to name the old meters Mark I so it was easier for us to know what version we were discussing at the time and it is helping to identify different versions of meters in this thread also.


I will use this post to put other information and updates as needed

1. The voltage is calibrated to a calibrated 6.5 digit digital multi-meter (DVM). While I have only compared a few of the early models to the calibrated DVM I found them to be only a few thousandths of a volt variance. With this said, you should be able to trust these voltages as accurate, at least more accurate than most or all other hobby specific hand held cell checkers and the free meters we can get from Harbor Fright Tools.

2. If you have a pack with a dead cell, as long as the balance wire is connected to the cell, we will still accurately read/post all of the other cell voltages. We MUST have a connection to the dead cell to have a reference to the "ground" for the next cell to read accurately. IF the wire is broken (common) or the cell is OPEN (really rare) the next cell in Series will have a floating ground and not record correctly.
Remember, this will measure a cell down to just below 0.8 volts. If the cell voltage value disappears after taking an ESR measurement and then re-appears it is due to crossing this low voltage threshold and is normal.

3. When changing pack sizes, if you decide to not use that pack size next after all, push and HOLD the left button for 1 second and you will be returned to the last screen (HOME) and still have the same pack mAh size selected.

4. When taking a Pack ESR measurement, which is a reading without the balance lead connected, the ESR value posted will NOT be the same as when taking a reading with the balance tap connected. This is expected and due to a pack reading including the length of discharge wires from the pack to the meter and the connector that connects the pack to the meter. It is NOT a Kelvin 4-wire Measurement so the total ESR value displayed will be much higher than if you add all of the cell ESR cell values after a Kelvin reading it taken.

5.


Cheers,
Rick
Last edited by rampman; Jul 21, 2019 at 11:43 AM. Reason: Added 4.
Jul 21, 2019, 12:15 PM
big ignore list/drama is dumb
brushless55's Avatar
This new unit is very cool..
I will have to pick one up!
Jul 21, 2019, 05:06 PM
Battery Puffer
Funny when I first read where you say Lipo dyno, I didn't think of Dinogy, but find it funny that Richard did. Good job Rick on getting this to where it is today.


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