Car starter motor

babydark

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Feb 9, 2008
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What do you think about using a car starter motor on a bike ?

I've build a motorized bike with a old Lawn-boy 2cycle engine, it work well and do 27 miles/liter of fuel.
With the gas engine, I was able to go up to 53 mph but now I want to convert it to electric power.

I have a Bosch starter motor form a jetta diesel with permanent magnets and internal gear reduction.
This motor turn around 6000 rpm at 12v and draw something like 40 amps at no-load.
On my bike the motor won't be able to turn faster than 3000 - 3500 rpm and will be controlled with a homebuild pwm controller.


I have some doubts about the efficiency of this motor on my setup.
 
babydark said:
and draw something like 40 amps at no-load.

:shock: I'd say your efficiency concerns are WELL founded. The ratio of stall current to no-load current is a good indicator of motor efficiency. A ratio of 50:1 or greater is good. The other thing I'd be concerned about is duty-cycle. As a starter motor, this motor is probably designed to run for 10-30 seconds and then rest for a half hour or more. Running it for hours at a time in a bike could over heat or wear out the motor quickly. At least it's not a series wound starter motor :twisted: them's good at making stuff GLOW.

marty
 
Heavy and not designed for continuous duty, so likely to get hot. You'll also have to gear it down.

On the plus side, it is cheap and runs on 12v. Built tough.

I'd say it will be a fun project build, so try it without a lot of expectations, and maybe it will turn out to be more practical than it sounds.

It would be interesting to hear about the cheapest ebike designs people have come up with.
 
babydark said:
This motor turn around 6000 rpm at 12v and draw something like 40 amps at no-load.

Holy crap! I draw less than that MAXIMUM!

Ditch it! Ditch it fast!

Starter motors are basically designed to be cheap and that's about it. They only need to run for a few seconds at a time, so you don't have to worry about overheating in normal use. Running it for as long as you would be on an ebike would almost certainly destroy it. Not to mention that the thing is probably 15% or less efficient (wild guess).
 
car starter motors are often shunt wound and do not have any magnets. unless they are connected to a load they can rev to unbelievably high rpms and the rotor could fly apart.

shunt motors are used because they can produce extremely high startup torque.

rick
 
About twenty years back there was an old guy, retiree went by the name Metro, who tooled around town on a homebuilt electric delta trike.

The trike was FWD with this huge starter motor angled up alongside the front fork as a friction drive.
It looked so lopsided heavy as tho it would flip the bike on it's side like a farm tractor at any moment, but he was one proud & happy camper with his creation.
He lugged a 3.5hp Honda generator on the the back of the delta for the power source which charged a single 12V car battery.
The one time I got a chance to talk to him that he wasn't zipping along he filled me in that the starter came from a GM delivery cube van & that the motor required extensive re-wiring, but he wouldn't elaborate.
 
rkosiorek said:
car starter motors are often shunt wound and do not have any magnets. unless they are connected to a load they can rev to unbelievably high rpms and the rotor could fly apart.

shunt motors are used because they can produce extremely high startup torque.

rick

Don't you mean series?
 
oops, uh errr.

yeah i meant series.

what can i say it was late, no coffee.

rick
 
Many of the newer starter motors have permanent magnets.
40A no load is way too high to be useful, but the magnets might be good for something.

You need a motor with more turns on the armature to get the current down. Rewinding is one option, but a real PITA with a motor like that.

I would suggest a different motor. Something like a MY1020 is fairly cheap.
http://tncscooters.com/partsdb.php?type=ES (toward bottom of page)
 
You can get 250 and 300 watt 24v scooter motors for $10 from Apex Electronics http://www.apexelectronic.com/

They've got shelves of them. I ran one at 36v and it was as fast as my 600w hubmotor. Kind of noisy, though.
 

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If you pulse it and let off so it can cool, as you ride, it may give you lots of pleasure before it craters. I have built 2 treadmill motor ebikes with belts that work almost as well as my hubmotor ebikes. You will need to run at least 24v to get moving.
 
Treadmill motors weight about 25 to 30 lbs. The one I replaced brushes on says 130 V DC, 2.5 HP. It looks like more work, weight and costs using a treadmill motor than just buying a used hub.
 
Car starters have been used, and of course they "work". Results were poor.

If you are desperate to make the cheapest possible scavenged system, consider an 18V cordless circular saw.

Sourced from a pawn shop. With a near dead battery. Very cheap.
 
I cant rave enough about the treadmill motor, it was free, though some fabrication was required, it is silent and goes about 18mph I guess on a 36v battery. It works best with a trike setup, and can sit in the rain all year long. The belt slips a little upon takeoff, so pedal and pulse until 10mph and then it grips great!
 
I also attempted to make a DIY eskate with a 36v cordless Greenworks weedeater. It spins stupid fast on 36v, but didnt have alot of torque. I have a few hoverboard motors and they will fly on an ebike controller, but again, fabrication is the tricky part when adapting to your bike. Hoverboard wheels and treadmill motors are the most promising for DIY!
 
One more thing, controllers are usually the weak link in the chain, and you wont need one, or a throttle, when doing a treadmill motor DIY. Reverse thread the heavy wheel and cut it so you can reinstall the small threaded pulley. This will give you clearance to make fabrication simple.
 
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