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Old 05-28-2019, 04:49 AM
superleccy68 is offline
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C ratings on larger capacity lipos

Just trying to reduce my level of ignorance here. I am looking at an aerobatic aircraft project (not multi-rotor) for 100 cc size motor. I notice that the larger capacity 6S-7S lipos of 8500mAh and above have comparatively low C ratings of 20C+. Is this really going to be adequate for this type of aircraft's performance? Thanks.
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Old 05-28-2019, 05:59 AM
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If you have an 8500mah battery that is 20c that is 170 amps

How much current do you anticipate pulling?

Also, many C ratings are more marketing than technical spec and some are, shall we say, more optimistic than others.
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Old 05-28-2019, 09:53 AM
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Thanks. I may be looking at this from the wrong angle, BarracudaHockey.
The intention is to use a Hacker A100-8 or A100-10 with with two 6s or 7s lipos wired in series of say 8.5 or 10 amp capacity. I guess the prop size would be in the region of 25x8 or 26x10. The ESC recommendation for these motors seems to Masterspin 170 Opto ESC. I am not sure what current I will be pulling at this point, just the rough parameters.
I take your point about C ratings being a marketing ploy though.
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Old 06-02-2019, 07:24 AM
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I believe this is due to the fact that very large capacities can already deliver higher currents. You can see exactly the opposite with the small batteries used by drone racers which have small capacity and extremely high discharge rates (above 120C).
As already mentioned by BarracudaHockey you can never know how accurate these numbers are until an industry standard for lipo testing is created.
Good luck with your 100cc project, I'm about to start my first 100cc plane but even being an electric addict I'm going for gas as I believe 50cc is the practical limit for electrics.
Ronaldo
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Old 06-02-2019, 09:20 AM
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Thanks for your input on C ratings, ronaldopn. You may well be right about 100cc electrics, but I thought I would at least research it leaving the battery cost option aside for the moment.
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Old 06-02-2019, 09:43 AM
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No problem, I'd love to make my first 100cc (GW 104" Extra 300LP) an electric project too, unfortunately, in a quick math, the weight of the complete gas system is almost equivalent to the electric (motor, ESC) without the main battery packs. When you add the main packs the numbers go really high.
Although you'll end up with a more powerful and reliable system, the weight penalty is too much for an aerobatic plane (IMHO). You'll have to sacrifice flight times even more to reduce weight.
Do the math for yourself and evaluate before you start purchasing the gear, for scale or sport planes it may still be valid but aerobatic planes will suffer performance-wise (short flight times are inevitable too).
Use PAR calc to make your simulations, this is my preferred software to dimension electric setups. It was created by one of the most knowledgeable guys in terms of power systems for aerobatic planes, his name is Jim (Aeroplayin here and on RCG), you may know him from the forums.
Ronaldo
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Old 06-12-2019, 02:22 PM
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Quote:
Originally Posted by superleccy68 View Post
Just trying to reduce my level of ignorance here. ...
About the marketing 'optmism', the nonsense and the outright C-rating lies, with standardized tests.
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