Starter motor amperage and e-start nirvana

LeFrog · Sep 11, 2007

If one Mitsuba SM-14 runs at 12.6 A and the other one at over 16.4 A, which one has the most cranking power?

In all seriousness, is there a good way to determine the torque produced by an electric motor?

Then, how much punch can a new starter sprague take before being shot?

I am trying to reach the e-start nirvana, and right now I have the following ingredients:

1-SEM rewound by Steve "Sparks" (sorry, buddy, could not test it tonight either)
2-Trusty Dellorto jetted by Dale L.
3-Beefy SM-14 (not new, usual CBR scavenging)
4-New sprague (former was shot)
5-New IXU24 plug
6-Upgraded auto decomp weight
7-Spot on timing
8-The will to make it work

Will it work, is the question. If I get a better restarter in the process, I'd be just as happy.

Simon · Sep 12, 2007

Hey LeFrog,

The simple answer is:

Power = Voltage x Current

So clearly given the same voltage it should the the one with the greatest current assuming there aren't any serious losses somewhere in the system...

You've read my guide on setting up the autodecomp which should help.

Good luck.

All the best,
Simon

LeFrog · Sep 12, 2007

Simon, I know the formula, but it's not necessarily because a starter motor uses more electricity that it is a more efficient starter motor. It can also be a good heater.

But in this case I can tell you the one which pulls the most amp is quite torquish, because I accidentally closed circuit while it was not secured in place and it jump at my face. It also shorted the poz on the body, produced a lot of sparks, complete with the welder effect and melted wire.

The issue is that the beefy guy has the wrong back (won't work with the current bracket).

I decided to swap back and, to my dismay, I only got 14.5 A stabilized (after an initial spike at 18 A). But the other motor now gives over 18 A stabilized (initial spike over 20 A).

I guess the issue is with the brush plate. I could swap them and see... I will probably do that this week-end.
I could also get a brush plate kit but is it necessary?

I was wondering if someone could measure the draw in Amps from his starter motor on a newer Berg, because SM-14s are advertised at between .5KW and .6KW according to the specs I found, and 20A would not even give half of that (probably the top you can get, if you use 24V for instance).

Thanks for the help!

sparks · Sep 13, 2007

Re: RE: Starter motor amperage and e-start nirvana

Hi Frog,

The speed and torque are dependant on three things, two or four brushes, two or four pole magnet stator and the winding spec of your armature, lap or wave wound.
Your current drew is dependant on two things the internal resistance of the windings and load put upon it.
The CBR600 starter which I think most people change to is a two brush pole four stator, this should be well man enough for the job.
I've rewound many starter motor armatures over the years.

Regards

Sparks.

LeFrog · Sep 13, 2007

RE: Re: RE: Starter motor amperage and e-start nirvana

Thanks, Steve.

I have found many docs about starters and they give much information on how these little technological marvels work.

http://members.aol.com/pullingtractor/starter.htm
http://www.misterfixit.com/starttst.htm
http://www.samarins.com/glossary/starter.html
http://home.clara.net/hallvw/starter.htm

Some sell expensive rebuild kits and services, which make the eBay way still the most interesting.

I guess that any Mitsuba SM-14 can be used to fix a defective Husaberg starter motor or upgrade it to the longer size (650-style), since the internals of the newer motor can be used on the defective one.

Still much cheaper than buying a new motor.

The hardest part of the operation for me was to find a 7mm socket in my drawer.

Starter motor amperage and e-start nirvana

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