ian.mich said:
what?? any 9c or pro 901 will take 4kw without giving two shits because if you actually sustain 4kw, you're going to deplete your batteries in no time.
That depends on the size of your batteries. If your'e just using some little 44V 5Ah pack, sure.
I'm pretty sure I could melt (or at least damage) my air-cooled 9C 2807 before I ran out of power, with 20Ah at ~66V hot-off-charger, even if I only ran it down to 15Ah used. If I added on my other packs for more range, I just about guarantee it's destruction.
It gets too hot to touch the windings just doing stop-and-go traffic using only partial throttle for startups, trying to keep it under 2KW most of the time for acceleration, for 2.5 mile commute to/from work, max 20MPH speed, 14-16MPH average depending on traffic and lights. I want to measure it's winding temperature, but havent' yet setup temperature probes for this. (mostly because it takes a couple of hours to get the wheel off and back on the bike, not counting the time tot ake it apart and run the sensor wires thru it and moutn the sensor. but also because I don't yet have an appropriate sensor/thermometer).
I imagine if I let it run at the 4KW+ I get at full throttle from a stop, every time, or kept full throttle so I end up at 30-35MPH and try to cruise at that full throttle, it'd damage something quickly. (this is assuming I upgraded the phase wires, because the factory ones it has right now would melt insulation and short out long before the motor failed).
I don't remember what the wattage Dogman was running at the DeathRace last year, but he pretty well overheated (was smoking) his front 9C in the race, and probably still had plenty of battery left. I think it was around 3KW, though it might've been 5KW.
And both of thsoe sitatuions I describe above aren't using 4KW constant, just during the hard acceleration part, getting up to speed, repeatedly. If you put one on a dyno and put a 4KW constant load on it, I expect it'd smoke well before a "48V" (60-ish really) 20Ah pack ran out of power, even aircooled or oil-cooled. Some run even bigger packs.
Now, if you're talking 4KW *bursts* during acceleration only, and running less than 500W the rest of the time, like I normally do on CrazyBike2, then sure--I coudl do that probably all day long even in the 120F heat, and still not destroy teh motor, although it would likely smell funny.