Electric Bikes Here's a place to discuss ebikes, from home grown to high-tech.

AC vs DC?

Old 10-18-09, 08:07 AM
  #1  
toyotaboy
Member
Thread Starter
 
toyotaboy's Avatar
 
Join Date: Oct 2009
Location: LITH, IL
Posts: 26

Bikes: trek 930

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
AC vs DC?

Ok, so I've decided to redo my bike project. I want to do an external motor and use gearing advantage (even though motors are efficient, it seems like a lot of these motors peak out in RPM and energy is wasted in torque). But my question is, I see some of the higher powered bikes here using AC motors. It would seem to me that it's a waste of energy to invert DC batteries into AC (10-15% loss) just so I can run an AC motor. Is there some torque advantage of using an AC motor that makes up for it?
toyotaboy is offline  
Old 10-18-09, 08:23 AM
  #2  
dougmc
Senior Member
 
dougmc's Avatar
 
Join Date: Jul 2008
Location: Austin, TX
Posts: 3,030

Bikes: Giant OCR2, Bridgestone RB-T, Bike-E, Vision R-40, Novara Safari

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Even DC motors `convert' DC to AC -- they just do it mechanically, via their brushes and commutators. I'm guessing that the AC motors you're referring to are also called brushless motors?

If so, they're good because you don't have any losses in the brushes and the ESC can do things like adjust the timing of the motor on the fly to make it more efficient. Ultimately, brushless motors tend to be more efficient than brushed motors. It's not a huge difference for good quality motors, but it's significant.
dougmc is offline  
Old 10-18-09, 11:29 AM
  #3  
cerewa
put our Heads Together
 
cerewa's Avatar
 
Join Date: Jun 2003
Location: southeast pennsylvania
Posts: 3,155

Bikes: a mountain bike with a cargo box on the back and aero bars on the front. an old well-worn dahon folding bike

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Brushless motors are MORE efficient than brushed motors (a.k.a. DC motors), not less.

For the most part the size and weight of an e-bike motor determine how much power you can put in to it, because they determine how much heat it can dissipate. (overheating is your limiting factor, except when brushes on brushed motors are the weak link instead).

This also means that more-efficient motors can accept more input power without overheating. (a more efficient motor is one converts more power into motion and less power into heat)
cerewa is offline  
Old 10-18-09, 01:54 PM
  #4  
rscamp
Senior Member
 
rscamp's Avatar
 
Join Date: Jun 2008
Posts: 251
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
DC brushless - switches DC current to create a rotating magnetic field to pull the permanent magnet rotor around
AC brushless - forms AC current waveforms electronically from a DC bus to create a rotating magnetic field to pull the permanent magnet rotor around

Our motors (for power) are DC brushless. AC brushless requires accurate rotation angle feedback and is only required where smooth and accurate positioning is required - i.e. brushless servo drives

Brushless are not only more efficient but have a wider operating power range. They are not limited by low and high current density capability of commutator brushes and some (particularly sensorless) adjust timing on the fly for different current levels.
rscamp is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
dbnm
Road Cycling
6
02-22-15 08:10 AM
geoluv
Bicycle Mechanics
9
08-30-11 07:13 PM
traumadogrn
Road Cycling
3
03-18-09 12:03 PM
travkat
Road Cycling
1
01-13-09 12:23 AM
benoist
Singlespeed & Fixed Gear
3
04-28-07 07:56 PM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.