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Old Aug 18, 2014, 04:36 PM
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Originally Posted by gtxkid View Post
Is there a charger that has it integral in one of the i-chargers.
No, the i chargers use a similar system at a much lower current, but this means that they only have a resolution of 1 milliohm., which is ok for small lipos but does not enable you to compare larger cells.
If the cell value is about 2 milliohms, a resolution of 1 milliohm is obviously insufficient.

Wayne
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Old Aug 18, 2014, 06:37 PM
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There are two diferent one's to choose from on ProgressiveRC.
I want to check some 6s 10000 packs.
I also have some single cell and a variaty of 3s and 4s
Hmmmmmm What do i do.
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Old Aug 18, 2014, 07:07 PM
ancora imparo
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Joined Jul 2005
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Wayne will advise, but in the meantime:

A 10,000 mAH true 30C pack is capable of delivering 300Amps and for that to happen without excessive heating the individual cell resistance needs to be about 0.65mOhm.

You cannoy meaningfully measure and compare resistance at that level with an instrument that only has a resolution of 1mOhm.

The iChargers have proved accurate and reliable IR testers but really only for cell IR's of a few mOhm or more.

John
Quote:
Originally Posted by gtxkid View Post
There are two diferent one's to choose from on ProgressiveRC.
I want to check some 6s 10000 packs.
I also have some single cell and a variaty of 3s and 4s
Hmmmmmm What do i do.
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Old Aug 18, 2014, 11:13 PM
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New iChargers (308DUO, 4010DUO, iCharger 406DUO) have resolution 0.1mOhm.
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Old Aug 18, 2014, 11:56 PM
ancora imparo
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That's useful to know. I have only had experience with the 3010B and other single channel iChargers.

Thanks.
Quote:
Originally Posted by vlad_vy View Post
New iChargers (308DUO, 4010DUO, iCharger 406DUO) have resolution 0.1mOhm.
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Old Aug 19, 2014, 03:16 PM
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Rugby, UK
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Quote:
Originally Posted by gtxkid View Post
There are two diferent one's to choose from on ProgressiveRC.
I want to check some 6s 10000 packs.
I also have some single cell and a variaty of 3s and 4s
Hmmmmmm What do i do.

If you only want to ,measure 10,000mAh packs I would advise the Hi Res unit as it has a resolution of 0.01milliohms. As you want to measure smaller 3 and 4S packs and single cells the standard unit with a the single cell modification. (1S. - 6S) is probably more suitable with a resolution of 0.04milliohms..
The Hi Res unit will only read cells up to 8millihoms and packs up to 65milliohms so that smaller packs of less than 2600mAh may be outside its range. The standard unit has range limits of 35 and 250 milliohms so it will cover any lipo but has less resolution.

Wayne
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Old Aug 19, 2014, 03:44 PM
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Quote:
Originally Posted by Wayne Giles View Post
If you only want to ,measure 10,000mAh packs I would advise the Hi Res unit as it has a resolution of 0.01milliohms. As you want to measure smaller 3 and 4S packs and single cells the standard unit with a the single cell modification. (1S. - 6S) is probably more suitable with a resolution of 0.04milliohms..
The Hi Res unit will only read cells up to 8millihoms and packs up to 65milliohms so that smaller packs of less than 2600mAh may be outside its range. The standard unit has range limits of 35 and 250 milliohms so it will cover any lipo but has less resolution.

Wayne
I am dreaming of a unit that has a selector dial on the front to switch between 1S 2s 3s 4s 5s 6s 7s 8s .
And a switch for different ma
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Old Aug 29, 2014, 07:39 PM
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I have become very interested in ESR after almost losing a plane to to LVC due to a worn out Lipo that had a huge voltage drop. I have ordered one of Wayne's meters and intend to measure all of my batteries.

I have a question about how much of the energy in a pack is lost due to the heat developed due to the resistance of the pack. Lets just say for example that I had a good Lipo with the following numbers: 2200 mah, 5.5 ESR per cell, FOM .99, 49 A. Suppose I put this in my EDF jet and flew the pack drawing 49 A until it I had depleted half of its capacity, or used 1100 mah. How much of the 1100 mah would have been dissipated as heat in the battery? I know that the ESR would decrease as the battery warmed up, and there are many other factors involved, but lets pretend that it didn't. Just curious if the heat loss in the battery is a significant energy loss.

Second, is the loss proportional to the resistance, ie., if the same battery had twice the ESR would it lose twice as much energy from battery heating?
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Old Yesterday, 03:10 AM
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Originally Posted by u2builder View Post
I have become very interested in ESR after almost losing a plane to to LVC due to a worn out Lipo that had a huge voltage drop. I have ordered one of Wayne's meters and intend to measure all of my batteries.

I have a question about how much of the energy in a pack is lost due to the heat developed due to the resistance of the pack. Lets just say for example that I had a good Lipo with the following numbers: 2200 mah, 5.5 ESR per cell, FOM .99, 49 A. Suppose I put this in my EDF jet and flew the pack drawing 49 A until it I had depleted half of its capacity, or used 1100 mah. How much of the 1100 mah would have been dissipated as heat in the battery? I know that the ESR would decrease as the battery warmed up, and there are many other factors involved, but lets pretend that it didn't. Just curious if the heat loss in the battery is a significant energy loss.

Second, is the loss proportional to the resistance, ie., if the same battery had twice the ESR would it lose twice as much energy from battery heating?
Joe,
The 1100mAh is not energy until you bring the voltage into the equation, so the nominal energy capacity of a 3S2200 pack is 11.1V x 2.2Ah. = 24.42Wh.

So half the capacity is 12.21Wh. The energy lost in the pack ESR at 49A for 50% discharge is 0.89Wh, so that the percentage of energy lost in the internal resistance of the pack is 7.3%.

If you double the ESR, it will double the losses.

More noticeable is that the 7.3% energy and voltage loss translates into a power loss at the prop. of nearly double so that you would expect a power loss of about 14%.

Wayne
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Old Yesterday, 05:55 AM
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Thanks. That is a fairly significant loss.

I have a fairly large number of batteries that are either more than a couple years old, quite a few cycles, and perhaps not the best in the first place. Since I have added telemetry recently I have started to notice large voltage drops under load on many of these batteries. I suspect that quite of few of my batteries have FOM's below .5 and some perhaps well below that. In other words, they are "toast". So in addition to reaching LVC on my ESC much sooner than I would expect, even if I back off on the throttle I am seeing significantly reduced flight times due to energy converted to heat in the batteries. It will be very interesting to sort them out with your meter.
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Old Yesterday, 08:20 AM
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Originally Posted by u2builder View Post
Thanks. That is a fairly significant loss.

I have a fairly large number of batteries that are either more than a couple years old, quite a few cycles, and perhaps not the best in the first place. Since I have added telemetry recently I have started to notice large voltage drops under load on many of these batteries. I suspect that quite of few of my batteries have FOM's below .5 and some perhaps well below that. In other words, they are "toast". So in addition to reaching LVC on my ESC much sooner than I would expect, even if I back off on the throttle I am seeing significantly reduced flight times due to energy converted to heat in the batteries. It will be very interesting to sort them out with your meter.
Joe,

You will probably find that the poor packs have one weak cell which is dying so that most of the voltage drop will be in that cell. This means that the weak cell gets much hotter in operation which accelerates its demise.
It is an enlightening experience to see how the lipotool results, using the highest Cell IR in a pack, correlate with the actual pack performance in flight.

Your meter was posted this morning, BTW. Hope you find it useful.

Wayne
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Old Yesterday, 11:02 AM
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Originally Posted by Wayne Giles View Post
Joe,

You will probably find that the poor packs have one weak cell which is dying so that most of the voltage drop will be in that cell. This means that the weak cell gets much hotter in operation which accelerates its demise.
It is an enlightening experience to see how the lipotool results, using the highest Cell IR in a pack, correlate with the actual pack performance in flight.

Your meter was posted this morning, BTW. Hope you find it useful.

Wayne
Thanks so much. I am really looking forward to sorting my batteries. All but a couple are Gforce Nano's,2200 and 3300 3S listed as 40 and 60C, some two or three years old and a couple are almost new with just a handful of cycles. I am pretty sure the meter is going to tell me the older ones are ready for disposal. Plus I just ordered a couple of Revo Diamond 60C so it will be very interesting to compare the new Revo's with the almost new Gforce. I'll give the Revo's a few cycles to settle them in. Very exciting.
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Old Yesterday, 02:37 PM
aka JetMan Joe
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That's interesting Wayne, now I understand how one can use ESR values to estimate lost or wasted power in a pack. Thanks!

I hope you will extend grace and allow me to swing off your topic a little. Now that the rain is back here I'm turning back to my battery testing, specifically the life cycle testing we've talked about. I'm trying to settle on a simple method of determining and showing if a pack is actually delivering on the capacity it claims and also to determine when to call it depleted.

I really have not grown comfortable with the idea of taking a pack down to 3v/cell or there abouts as part of the testing process. I've always tried to model my testing on our real life use patterns and I think I've come up with a way that would be easy to manage and tell us what we need to know. It may not be the "best" way but I don't want to complicate the process. However I do want to make sure my thinking is sound so I'm running this by you before proceeding down this path.

It's simply to calculate 80% of a packs stated capacity, pull it out and evaluate what's left. So after fully charging a 5000mah pack I would pull out 4000mah. The voltage level remaining is the metric by which we can judge the pack.

Using the voltage/capacity table that Mark published (thank you Mark) we can determine that a new "5000mah" pack should have an average cell voltage level no less then 3.73v or 20% left after 4000 mah is pulled out of it. If it does then we have a rightous brand. Proceeding on to the life cycle testing the pack is subjected to 25 charge/4000mah discharge cycles and then tested again to determine if 3.73v/20% still remains. This process will repeat until the pack is depleted. At what value would you consider one of your packs "dead"? If it were mine I would say that 3.61v/5% is pretty definitive but I'm open to other opinions.

Joe
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Old Yesterday, 05:17 PM
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Joe (G),

I really think that the only way to accurately amd consistently measure the real capacity of a pack is to discharge it fully to 3V / cell at aspecified low rate (1C?)

If you only discharge to 80%, then I believe we are assuming that the cell capacity remaining is an exact analogue of the remaining capacity which is not necessarily so for several reasons.

1). The loss of capacity is not necessarily linear over the discharge curve.
2). You cannot assume that the original capacity is correct, although you could measure it with this method initially.
3). The slope of the discharge curve is very shallow at 80% discharge and therefore likely to introduce errors unless you discharge at a high rate in which case the IR, and change of IR with age and temperature, will introduce different errors.
4). We are looking for small differences and they may well be swamped by such errors. The 100cycle testing I was involved in (each cycle down to 3V/ cell) resulted in capacity losses varying from 12% max down to only 2.8% min. for the 100 cycles.

If you fully discharge from 4.2V down to 3V at 1C, the curve at 3V is going over the "knee" and has a steep gradient so that there is a sharp and obvious cutoff point.

We are all drilled not to discharge below 80% and warned that 3V is armageddon, but I have never yet damaged a lipo by discharging to 3V.
The 80% rule is important in real flying situations to ensure that the weakest, ie lowest capacity, cell in the pack is never fully discharged as the load current could then drive that cell voltage to zero or even negative in only a few seconds.

This situation does not exist in your capacity testing and you can use JJ's Cellog cutout circuit to ensure that the discharge is stopped instantly as the first cell falls to 3.0V

I do think that it is a good idea to stop your high power 25 cycles of discharge at 80% as that is a closer replica of real world use, but I believe the measurement cycle needs to be a full discharge to achieve accurate results.

Wayne
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Old Yesterday, 05:37 PM
aka JetMan Joe
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Ha! So much for my easy way out. I have to bow to your experience and go with the 3.0v for the qualifier.

However can I get away with a 2C discharge down to 3v? That's what I have on hand and I can catch the voltage at 500ms intervals and keep from going below. Or do I need to do what it takes to make the measurement discharge at 1C?

Joe

(BTW Thanks Wayne, I appreciate your wealth of knowledge)
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