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C rating on Lipo's

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tigerman23/03/2019 14:58:02
156 forum posts

I fly a lot of EDF and all my lipo are 35c but I am being told that I should be using at least 50c for flying my EDF but does the so called c rate mean that much ????

J D 823/03/2019 15:40:58
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1058 forum posts
65 photos

I fly some EDF and find that unlike most discipline's one tends to fly at full power most of the time.This is harder on the lipo i recon an may limit their lifespan, However I only have 35c packs and given the extra cost of 50c packs will carry on the same.

Shaun Walsh23/03/2019 15:41:53
80 forum posts

Depends on the current draw of the motor and the ampere hour rating of the battery.

I fly using 3s lipos. My 2200 lipos are rated at 45c continuous which means that in theory they can supply 99 amps without going above their rating. My 3000 lipos are rated at 15c continuous which means they can supply 45 amps continuous, less than half the figure for the 2200s.

In practice there is no performance difference between the two because the motor they power draws a maximum of 25 amps, well within the rating both batteries.

So multiply the ampere hour rating of the battery by its c rating, If the figure you get is greater than the current actually drawn by the EDF then all is well and the bigger the margin the less strain on the battery.

Simon Chaddock23/03/2019 15:46:31
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5323 forum posts
2786 photos

The C rate is the maximum discharge rate for the battery. The value in amps is calculated by multiplying the battery capacity in Amp hours by tthe C rate.

So a 4000 MAh (that's 4Ah) x 35 C equals 140A.

To be meaningful you do need to know what is the actual discharge amps of your EDF.

If it is well below the C rate maximum then there is not much point in going to a higher C battery except being more expensive they might be better quality so better able to handle a lower discharge Amps with less cell damage.

Be aware C ratings can to be used as a marketing tool to persuade folk to buy a battery and pay a higher price for it rather than a realistic maximum current that will not damage the cells.

J Moyler23/03/2019 15:57:24
140 forum posts
56 photos

Please see link for useful information on LiPo batteries. Generally EDF tend to be a high power application (in other words high wattage, hence high current).

To work out if your batteries have the right range you need to measure the current using a watt meter. It might be that 35C batteries are suitable for your application but without further information we cannot say.

The information needed:

Model, Type of battery (how many cells, capacity eg on a battery your should have the following, 2200mAh, 3S1P 11.1v 20C and current draw (normally measured at full throttle ).

If you are drawing more the the C rating (in the example above 20C = 20 x 2.2Ah = 44 amph) the battery life will be short.

In the 4Max info sheet, what do the numbers mean regards to LiPo cells, it is suggested that you only draw about 60% of the max current for good battery life. In the example above this means 60% of 44Amph = 24.4 Amph

JM

Hope you find this helpful

Edited By J Moyler on 23/03/2019 16:05:44

Allan Bennett23/03/2019 20:11:13
1479 forum posts
38 photos

As for some of the others who have posted here, high C batteries are unnecessary for my LearJet edf because their mAh capacity is high enough to give a theoretical amps capability which is well above what the motors are actually drawing at full throttle. I'm actually using 30C packs.

It's always worth checking the weights of different packs, for you will probably find that for the same weight you can get more mAh at the expense of a lower C rating, but with a similar overall amps capability (Ah x C); and more mAh gives you longer flight duration.

As with many devices, treating them gently will prolong their overall life: With LiPos this means not charging them at more than 1C, not discharging them at anything near their theoretical capability (how far below is open to debate, but some brands are known to exaggerate their C ratings), not over- or under-charging them voltage-wise, and not storing them for prolonged periods at more than 50% charge. Note that their voltage can increase as they warm up so, if charging them at low temperatures -- such as in an unheated garage -- in winter it's advisable to only go to 4.1v or so, so that they won't exceed 4.2v when they warm up as you carry them to the field in your heated car. Some chargers do this automatically when they detect low ambient temperature.

MattyB23/03/2019 20:42:37
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1876 forum posts
28 photos

Short summary... almost all pack C-ratings are made up by manufacturers to sell their packs. If you have a decent charger that can measure the internal resistance (IR) of your packs you can estimate the max C rating of your packs using this tool; in my experience it tends to vary anywhere between 30-70% of the rating on the wrapper depending on brand, age and number of cycles.

Geoff Sleath23/03/2019 22:10:23
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3201 forum posts
247 photos

My Wayne--Giles ESR meter would agree with Marty as I've discovered lots of times - in fact I've yet to check a LiPo where the measured ESR justified the quoted C rating.

OTOH I don't know the criteria for setting C rating. Certainly it depends on the ESR because that's what determines the terminal voltage on load as well as the power dissipated within the battery itself but I don't know what the accepted terminal voltage nor the temperature rise over what load conditions.

I don't usually over stress my LiPos and particularly with large capacity ones get nowhere near the quoted C rating. Obviously EDFs need to draw a lot of current. I suppose a high C rating implies a better quality LiPo but I doubt if it's worth the extra outlay if taken to extreme.

Geoff

Ben B23/03/2019 22:22:04
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1386 forum posts
4 photos

Even within the same brand of batteries you'll find massive differences. Take HK Nanotech- I find the 2s 450s are really good - low IR and take a whooping nicely. Go up a few hundred mAh however and the IR drops massively and you're better going GNB (e.g. 2s 650 GNB beats the nanos hands down).! It's a bit silly really.

It's a minefield. Take C ratings with a MI inducing pinch of salt. If in doubt buy 1, check the IR and then decide on whether to buy more (bearing in mind IR changes massively with capacity). A tinywhoop size battery with a IR of 50 would seem ultra yet on a 2200 it's pants.

Mike Blandford23/03/2019 22:27:54
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477 forum posts
20 photos
Posted by J Moyler on 23/03/2019 15:57:24:. . .. In the example above this means 60% of 44Amph = 24.4 Amph. .

60% of 44Amps is 26.4Ampswink

Mike

J Moyler24/03/2019 03:03:37
140 forum posts
56 photos

Thank you Mike for the correction, mistyped and did not spot the mistake.

JM

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