Originally Posted by
Turbo Joe
How are you guys measuring or inferring the current flow? Do you have some sort of inductive pickup on the battery wire?
Originally Posted by
Turbo Joe
I'm not really concerned the way you think.
Well now that's kind of harsh isn't it. You ask a question. A guy that actually knows, answers it, and you don't care what he thinks. How exactly are you getting your 12 amp average for a Mabuchi. Guessing out of thin air.
(It is interesting someone telling me how much I am on full throttle from a great distance. Usually that's something I can only report)
On this large track you gear the 3.5 motor to be in that high power band. Drew's math is in good order. That 95 amp value is representative for maximum accleration at full throttle (it is not peak current which may be double that or battery limited).
A motor does pull fewest amps at high RPM and increases amp drap all the way up to stall as load is applied to it. The following graph shows this for a stock motor. Stall speed is to the right and the line predicts an 80 amp pull on the start of the race. This data was extrapolated from data taken off a Turbo dyno. The Robitronic dyno which actually takes measurements near stall backs up this number. A test with a simple ammeter and a stalled stock truck backs up this number.
I doubt my 3.5 is pulling 150 amps except maybe very briefly at the start. I am able to maintain good corner speed. Traction is sufficient that traction roll is an issue to deal with this leads to high average amp draws as forward traction is also good.
So what evidence do I have of the high current. I use dean half plugs. If I plug the plug in backwards (not the wrong polarity but upside down) it will desolder after a few laps. (600F). And of course the calculations are accurate and have been repeated on a second battery.
My pan car pulls 38 amps average on the same track. Of course my stock truck on a sandy outdoor track pulls much less and has huge run time.
Note that peak power on an electric motor will occur just about in the middle of its RPM range or at about 1/2 of the amp draw at stall. For this stock motor peak power is at about 40-45 amps.