Thoughts on current, wattage etc on r/c stuff
 

Hello all!

I'm kinda confused about what hardware should be used for 1/8 racing because of amps and watts are being used and can be deliverd..

Because of the Motor being the end user the most current will be used by the motor.. (Like a light bulb will only use the wattage it is produced to use)
In this example i'm looking at a 2100kv Turnigy redcan. This motor has a peak wattage of 2100W, this corresponds to a maximal current at the rated 15V of 2100W/15V=140A (Peak current usage) This is also stated in the turnigy specs so guess this should be the truth..

Now when i'm looking at ESC specifications for 1/8th scale everyone i tolk to tells me i need a 150A ESC. I bought a Hobbywing XR8 Plus, this ESC should be capable to do 150A contant and a deliver a peak current of 950A.
(Now why would i need a ESC that can do that when the peak current will not be higher than 140A!!?!!)

But the story continues on batteries.. Most people i talk too state that i need a high mah lipo with a C discharge rating as high as possible. So i got a 7600mah 4S 75-150C lipo.. Now when i'm calculating the amps this beast can deliver i'm going nuts: 7600mah=7,6A
7,6Ax75C=570Ah while i could do perfectly with a lipo of 140A (max current of Motor): 140A/7.6A=18.4C

Why are current and wattage rates of Lipo's and ESC's so much hyped up when it seems to be completely useless? And how come ESC's and Lipo's that should be capable of delivering so much current still get warm or even catch on fire when only a fraction of their capabilitys is being used? :weird:

Sorry for my dutchy english :sweat:

IIRC motors have a much higher peak than that (e.g. when starting to turn from a standstill), and they are not really comparable to light bulbs or other simple resistors.

C-Ratings on batteries are not realistic. So much so, that calculating it the way you did doesn't really lead to useful results any more. But higher C-Rating usually means lower IR, and that should lead to a battery that stays cooler and is less stressed by the load you put on it and deliver more punch or voltage under load.

Then why can't i find any motor with a max current higher then 160A?

That the motor peaks at 140A is not true, that would be the savest limit by the specs. With a bad gearing the peak can go higher before you know it....

The same with batteries and ESC, using them on the limit will give a shorer life and a bad performance.

Well, when a motor shorts out(& there are a few ways it can happen, even physically locking one up will have similar results), its amp draw will spike at CONSIDERABLY higher levels than 120-150 amps(at least the serious mod motors will, the smaller 540-sized mild wind spec motors will draw closer to 120-150 amps max. under such conditions), so if an ESC can't handle such spikes it can be damaged more easily.. Not to mention, every motor is a little different, even with 2 motors of the same wind & type, manufacturing tolerances alone will produce 2 motors that draw a little differently from one another, so some will be more efficient than standard, & some less so. Just remember that it is ALWAYS good to have room for emergencies when looking at ESC specs....:cool: