Can you use LIPO's in an RC car?
Discussion
I'm looking to get an off road car like the Tamiya Hornet and have several 11.1v LIPOs knocking around from my RC plane plus charger so it would be a cheaper way to try the hobby.
I gather from other posts that the voltage is too high for a standard RC car motor, but if I got a suitable motor (if that's possible), would this setup work?
I know LIPOs have a lower discharge rate than NiMh and wonder whether they can cope with the higher drains in an RC car?
Your thoughts on this would be greatly appreciated! Am I mad?
I gather from other posts that the voltage is too high for a standard RC car motor, but if I got a suitable motor (if that's possible), would this setup work?
I know LIPOs have a lower discharge rate than NiMh and wonder whether they can cope with the higher drains in an RC car?
Your thoughts on this would be greatly appreciated! Am I mad?
The voltage difference is not significant enough to worry about (11.1 vs 9.6 for a typical 8-cell MiMH battery)
I think there may be an issue with the stall current demanded by the motor during the hard starts / stops associated with RC cars.
I use LiPolys in helicopters where the demands on the batteries are 'kinder' - i.e. The worst I can do is go full collective which will load the motor but never stall it.
However, that said, modern LiPoly cells are now getting very robust. As an example, a '30C' rated cell, which for a car sized application would be rated at about 2400mAH, is capable of delivering 72 Amps of burst current. Such a cell will normally be configured as 3 in parallel and 3 in series for 11.1V (3S3P), therefore the burst current capability will be 216 Amps.
Reduce this calculation accordingly for a 25 or 20C rated battery.
So long as the stall current of the motor does not exceed the burst current of the battery you should be fine. If you use a FET speed controller this will automatically limit the current since FETs increase in resistance as they get hotter.
Please read up on the dangers of using LiPolys though - although I imagine you are aware if you use them in RC 'planks'
I think there may be an issue with the stall current demanded by the motor during the hard starts / stops associated with RC cars.
I use LiPolys in helicopters where the demands on the batteries are 'kinder' - i.e. The worst I can do is go full collective which will load the motor but never stall it.
However, that said, modern LiPoly cells are now getting very robust. As an example, a '30C' rated cell, which for a car sized application would be rated at about 2400mAH, is capable of delivering 72 Amps of burst current. Such a cell will normally be configured as 3 in parallel and 3 in series for 11.1V (3S3P), therefore the burst current capability will be 216 Amps.
Reduce this calculation accordingly for a 25 or 20C rated battery.
So long as the stall current of the motor does not exceed the burst current of the battery you should be fine. If you use a FET speed controller this will automatically limit the current since FETs increase in resistance as they get hotter.
Please read up on the dangers of using LiPolys though - although I imagine you are aware if you use them in RC 'planks'
Thanks for your reply. I read up a fair bit on LIPOs before getting them for the plane and despite having bought very cheap packs (11.1v, 2400mah and only £12 all in) from Ebay, I haven't had one inflate yet. They're only connected with a 125w motor though.
I guess it is the large current draws that have stopped LIPOs "taking off" in RC car usage as the same capacity battery is about half the weight of NIMH which must be hugely useful in race cars.
I've since bought some Vapextech cells from the UK importer on Ebay 7.2v and 3700 for about £14 delivered - nice!
I guess it is the large current draws that have stopped LIPOs "taking off" in RC car usage as the same capacity battery is about half the weight of NIMH which must be hugely useful in race cars.
I've since bought some Vapextech cells from the UK importer on Ebay 7.2v and 3700 for about £14 delivered - nice!
Aha... 7.2V. I hadn't realised you were not using a 9.6V battery.
Why not try an 7.4V LiPoly (2S3P) with a decent 'C' rating? The power to weight ratio compared with using a 3700mAH NiMH battery would be superb.
I guess another side affect (as in helis) would be that less battery weight (ergo less capacity) means less current draw under acceleration - therefore more duration. There is a happy medium somewhere
Why not try an 7.4V LiPoly (2S3P) with a decent 'C' rating? The power to weight ratio compared with using a 3700mAH NiMH battery would be superb.
I guess another side affect (as in helis) would be that less battery weight (ergo less capacity) means less current draw under acceleration - therefore more duration. There is a happy medium somewhere
Edited by Spaceframe on Wednesday 3rd October 12:25
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