AC vs Dc Q's.

Hi,
Thanks everyone who has answered my questions so far.
I have had a little bit of a think about my goals and needs for creating my electric bike, and after some reseach and deliberation have abit of predicament.

I live on top of a mountain, with a lot of hills, some of which have a 12 - 17% gradability rating. My bike will be primarily be just to cruise around "town" where the max speed limit is 60km\h although higher speen would be great.

I was looking at the the MARS M0709 motor and running it at 72v off a direct chain drive with a single gear ratio. Although I think it may be too underpowered.

My second thought would be a L91 - 4003 ADC motor running at 72 with a 11.5hp. off a direct chain drive and single ratio.

But due to the inheret characteristics of a perm dc motor and its ability to only run really within a narrow powerband and gearing is not really an option.
Would a DC motor be impractical for my intended desire, a relitively high speed, the need for alot of torque setup?

Range is of secondary consideration and maybe 20 - 30km's max, drivability is of up most importance, speed and hill climbing.

Would a AC induction setup be more suited to my needs, as the AC motor relies on its behavior as aposed to speed to get max performance.

My undertanding is that an ac motor is best loaded up high and rpm is not a limiting factor, although it loses torque.

Although the sheer amount of work required for AC is alot more.
Future plans are hopefully to build a Ev car and run a AC motor.

Could anyone suggest anything better to me?

Edited by highfaultcurrent - 13 December 2009 at 5:19pm

Originally posted by highfaultcurrent But due to the inheret characteristics of a perm dc motor and its ability to only run really within a narrow powerband and gearing is not really an option. Would a DC motor be impractical for my intended desire, a relitively high speed, the need for alot of torque setup?

other way round.
a perm mag motor run with a controller supplied with a high enough voltage has a *very* wide power band.
a DC motor, due to other constraints does not.

the MARS motor is a BLDC, controllers for BLDC are plentiful (when talking less than 100kw)

i actually have such a controller sitting on my shelf im trying to get rid of.
72v 400A with a MARS will give you way more than 60kmh, with the right gearing and battery. (peak power would be ~28.8kw if limited only my motor and controller).

btw, if you're only aiming at 60kmh, an L-91 is overkill.
actually, the MARS is probably overkill aswell.
those hp ratings are continuous ratings.
having too much motor does give a fair bit of safety margin, but it robs you of space/weight capacity that would be better used for batteries.

Matt

My view is, more power the better.
Id rather have overkill, that way I won't ever be dissapointed.

I know the L-91 would be major overkill,
I am building the bike around the motor, so a larger motor can be compensated with batteries and weight can be compensated with the exter power to an extent.

Really my constraint is the price of a motor controller and batteries, hence why I was looking at overkill for the motor to compensate for the lower voltage.

i figured get the most powerfull motor at 72V which is where my price consraint ends at a 72V and 450A motor controller, and battery pack to suit.

Thanks for your replies.

Have you thought about the open source controller?

http://www.aeva.asn.au/forums/forum_posts.asp?TID=1160