Why is 30-35mph such a hurdle for Electrics?

5 posts / 0 new
Last post
leopardpm
Offline
Last seen: 15 years 4 months ago
Joined: Friday, July 25, 2008 - 14:00
Points: 19
Why is 30-35mph such a hurdle for Electrics?

Hi,
I just read yet another thread where someone was trying to push their scooter to or past 35mph - why does this seem to be such a hurdle? I mean, all the motor specs I see rate the motor in RPMs/Volt which implies a linear MPH improvement from just upping the voltage (which also seems to be the standard Mod). So, if any given motor takes a vehicle to 20 mph at 36 volts, then doesn't that mean that increasing the voltage 50% (batteries + controller) would result in a direct speed increase of 50% (30mph in this sample case)?

Also, what about gearing? I mean, even using standard cheapo bicycle hub gearing gives you the ability to dramatically increase speed vs constant drive sprocket speed... so use a low gear for starting out (and higher amps), then gear up for higher speeds (also drawing more amps, but not as much as the high torque starting from zero speed uses). Doesn't the motor draw the most amps (and total power) from the start and at top speed it doesn't really draw alot (unless carting around a ton of weight, I suppose, but even then once you got it moving it is alot easier to keep it moving, right?).

Just a beginner here with beginner type questions...

nasukaren
nasukaren's picture
Offline
Last seen: 14 years 3 months ago
Joined: Sunday, July 6, 2008 - 04:05
Points: 188
Re: Why is 30-35mph such a hurdle for Electrics?

Air resistance starts becoming a significant factor after 20mph and increases exponentially!

Karen

Working on a Piaggio Boxer (mo-ped) EV conversion: http://gpsy.com/ev

dogman
dogman's picture
Offline
Last seen: 14 years 4 months ago
Joined: Tuesday, April 29, 2008 - 15:41
Points: 830
Re: Why is 30-35mph such a hurdle for Electrics?

Its not a hurdle for electric motors. It is a hurdle for any type of very low horsepower motor. Gears would help, but for electric motors aren't really needed if the motor is big enough and power supply is adequate. The cyclone motors use gearing of the bike, and I hear work good for hills and heavy weight trailers. On the high speed end, as you raise the gear, the tiny motor works like its starting out if the gear gets too high, so range will then suffer if geared too high. On a car, in overdrive, the motor is nowhere near its capacity so while that is a very high gear, the motor could handle quite a bit more in most cars.

Wind resistance is a big factor too, but just as much for power consumption as for speed. Weight is a biggie also. At some point, carrying more battery to go fast gets so heavy you don't gain as much speed or range as you did with the first set of batteries.

For bike hubmotors, carrying enough volts to go faster than thrity leads to battery packs that either don't go so far, or weigh more than is comfy to carry. The compromize point seems to be around 48v and 25-30 mph. This is also the case for scooters with up to 1000 watt motors or so. To go faster, with a bigger motor, and more batteries starts to need a stronger, heavier frame, sturdier tires etc, and before long you are now a motorcycle, not a bike or small scooter.

Be the pack leader.
36 volt sla schwinn beach cruiser
36 volt lifepo4 mongoose mtb
24 volt sla + nicad EV Global

noobster
noobster's picture
Offline
Last seen: 15 years 4 months ago
Joined: Friday, May 16, 2008 - 20:11
Points: 45
Re: Why is 30-35mph such a hurdle for Electrics?

The big factor is wind resistance. My bike is only 24volt and goes 27mph after a fresh charge. It's using 65:11 gearing powered by two kollmorgen 400w brushless motors and goes up hills fine too. At 27mph if I tuck in like one of the motorcycle racers I can hit 30mph. Wind resistance plays a huge role in mph but I think multiple gears would help for a well rounded bike.

go green

decibel1
Offline
Last seen: 13 years 1 week ago
Joined: Wednesday, December 13, 2006 - 09:49
Points: 170
Re: Why is 30-35mph such a hurdle for Electrics?

All the above is true, but another factor is that electric motors produce their highest torque at 0 rpm, and it decreases as speed is increased. This is not true for ICE's. This would argue for a multi-speed transmission for electrics, though some efficiencey is lost there.

Log in or register to post comments


Who's online

There are currently 0 users online.

Who's new

  • Juli76
  • xovacharging
  • stuuno
  • marce002
  • Heiwarsot

Support V is for Voltage