Different C rating, same IR...

[Ahri]

I have two packs of Pulse Ultra 35C 5000mah 6S and 45C Gens Ace.
I've been using them for around 30 cycles. The IR rating of those two packs are all between 2.2-2.8 mOhm.
I'd like someone who has those high rating lipos(need to be same capacity) to test the IR to see if they are still the same. (I think there won't be any difference )
BTW, I read the IR using iCharger 309Duo

[HEXAHYDRATE]

You're probobly right on there will be no difference. C ratings should be taken with a grain of salt.

[mba83]

+1. The C-ratings seem to be comparable only within products of the same manufacturer.

[Xrayted]

I've never had a pack of any brand that had an actual C rating greater than 25-30 no matter what value was printed on the label. My Pulse 4500 65C packs are really 30C, and my Pulse 45C packs are all 20 or less.

I believe the Gens Ace 25C packs were the only batts that actually produced what they claimed during testing from multiple sources over the years.

Even the higher rated Gens Ace fell off quickly, so it was determined that purchasing anything more than their 25C was a waste.

[mba83]

How do you calculate the C rating? I would imagine just using some formula based on IRs would not work, as it depends on factors other than IRs.

[Ahri]

Originally Posted by mba83

+1. The C-ratings seem to be comparable only within products of the same manufacturer.

I just bought 2 Pulse 45C, will test and report

[jhamel]

Originally Posted by mba83

How do you calculate the C rating? I would imagine just using some formula based on IRs would not work, as it depends on factors other than IRs.

Justin Pucci goes over how to calculate the real C rating in his review of OptiPower Lipo's.

1) Always measure IR at the same temperature to keep the results consistent.

2) Figure out maximum heat dissipation. 6W per Ah is reasonable. If the pack can tolerate higher heat dissipation like 6.5W per Ah or even 7W per Ah, the calculated C rating would be higher. Manipulation of this heat dissipation is probably how LiPo manufacturers are able to fudge their inflated high C ratings.

3) Average the individual cells' IRs at full charge. For calculations use Ohms instead of milliohms. (2.9 mOhm = 0.0029 Ohm)

4) For calculation purposes enter pack capacity in Ah instead of mah. (4.4 Ah = 4400 mah)

5) Use formulas:

P = I^2 * R

I = (P/R)^1/2

So, assuming 6S 45C 4400 mah pack with average cell IR of 2.5 mOhm with an allowable safe heat dissipation of 6W per Ah use:
4.4 Ah
0.0025 Ohm

allowable heat dissipation would equal 6W * 4.4 Ah = 26.4

Divide this 26.4 by the average IR 0.0025 = 10,560

The square root of 10,560 = 102.76 Amp

Divide 102.76 A by the 4.4 Ah capacity = 23.4C

For the same size (capacity) pack with average IR of 2, the C rating would equal 26.1C. If the average IR is 1.8 per cell, the C rating would be 27.5C.

[mba83]

Originally Posted by curmudgeon

3) Average the individual cells' IRs at full charge.

Do most people measure IRs at full charge? I measure mine at storage, and wondering if I should change my procedures....

I wonder if there is a chart of C ratings somewhere based on this formula? With battery capacity on one axis, IRs on another.

[jhamel]

Originally Posted by mba83

Do most people measure IRs at full charge? I measure mine at storage...

My observations are that IR is higher at storage charge and lower at full charge.

[mba83]

Originally Posted by curmudgeon

My observations are that IR is higher at storage charge and lower at full charge.

Do you guys know what's the "proper" way to measure IRs? At storage or at full? I want to get values that are consistent with other members' measurements, especially when buying/selling packs.

[explorin]

it should be fully charged for consistency. a fully charged pack will be 5-10% lower than one at storage charge tho. Also, no one has a pack with cells that are 2 mOhms. chargers take readings in very different ways. you need a ESR meter to truly know what the mOhm is of the battery. I have pulse 6s 3700 45c batteries that after a flight when there 108 degrees read a entire 18 mOhms. Thats 6 mOhms per cell. the same pack after a charge is 77 degrees with 31 mOhms. alot of people would say that high of resistance the battery is toast. but they are not using accurtate equipment in measuring their packs. Heres a example, a brand new pulse 6s 3700 45c battery is 48 mOhm at 64 degrees. this was taken at 3.8v per cell so factor in the 5-10% so roughly 44 mOhms.

Many would say the pack is toast, but i say it has never been used and its cold. This is also why when i fly i let my batteries sit in the sun and get up to 85 degrees. i call it 'waking up' the battery. that way its warm and ready to deliver full power when i lift off and to limit damage to the battery as little as possible. Cause i know when i take off, i hammer the heli till the end of the flight and by 'waking up' the battery i feel its not so hard on it.

Also, because no one uses a standard tool measuring IR its impossible to know the true health of the pack. the proper way to measure IR is using the proper tool. http://www.progressiverc.com/univers...sis-meter.html

[Xrayted]

Its doesnt matter what state of charge they are in as long as you do it the same way every time for comparison. The battery would have to be in such a low/dead state that there was a large drop in voltage with the slightest current load placed on it for testing in order for the IR values to be way off simply due to its charge state, in other words the battery would be complete toast already and unchargeable for it to matter.

The reason IR may appear lower after full charge is because charging is heating the cells a small amount and warmer packs will always show lower IR than a cooler pack will. The only caveat here is charging a warm pack immediately after flying it, in which the charging process may actually cool the pack down from its beginning temp depending on how hot it was to begin with.

As Explorin said, there is no consistency between measurement methods we discuss here in this forum, so the values we see are only comparable to our own individual packs and equipment . You get a baseline using whatever method you have at whatever point in the charge cycle you choose at the same ambient temp every time, and in theory you should see any changes that are occurring with a particular cell if its going south on you, otherwise your readings dont mean squat to someone else with the same packs and vice versa.

I have a Giles ESR meter which I feel is the most accurate method of testing since it applies a higher current load during the test and can take into account the resistance of the packs wiring, connectors and my solder job, or not if I wish to see only the cells of the lipo IR themselves without any of the connectors factored in. It always reads a higher IR than my 4010 Duo charger does, but I still use the charger value as a monitor simply for convenience sake. It's not the precise number I care about, but trends or change over time.

[explorin]

I have a Giles ESR meter which I feel is the most accurate method of testing since it applies a higher current load during the test and can take into account the resistance of the packs wiring, connectors and my solder job, or not if I wish to see only the cells of the lipo IR themselves without any of the connectors factored in. It always reads a higher IR than my 4010 Duo charger does, but I still use the charger value as a monitor simply for convenience sake. It's not the precise number I care about, but trends or change over time.

this is a perfect answer.

[jhamel]

Originally Posted by Xrayted

I have a Giles ESR meter which I feel is the most accurate method of testing...

I believe the Giles ESR meter only works for 2S to 6S packs. I don't believe it will work with my 7S packs.

[Xrayted]

Originally Posted by curmudgeon

I believe the Giles ESR meter only works for 2S to 6S packs. I don't believe it will work with my 7S packs.

True, good point there.