Classic cars forum & vehicle restoration.

pigtin · Joined: 23 Nov 2007 Posts: 1879 Location: Herne Bay

I recently exchanged the starter motor on my Sprite for a more up-to-date item with the disc type commutator.
I am interested to know if these are more efficient than to old barrel type or it was just to reduce the length. My A7 special has the battery mounted under the boot and the voltage drop, while not appearing to affect the starter motor, seems to affect the power of the spark.
The simple answer would probably be to run a dedicated wire, direct from the battery, for the ignition or to fit a lower voltage coil with a ballast resistor. There are practical difficulties with running the extra wire and a starter motor with a lower power consumption is a more attractive proposition. Confused

ukdave2002 · Joined: 23 Nov 2007 Posts: 4105 Location: South Cheshire

At the end of the day you can't change the laws of physics, size does matter Confused

but one thing I never got my head round as an electrical & electronics engineer was magnetism! I learned all the theory to pass exams, but never really understood it well enough to comment, is there any spec supplied with this new motor?
My modern, a 6 series BM has the battery in the boot (in the spare wheel well Shocked

but you dont get a spare wheel these days! just a run flat tyres) and has a dirty thick cable to the front of the car, just like mini's used to have Very Happy

UKD

peter scott · Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh

pigtin · Joined: 23 Nov 2007 Posts: 1879 Location: Herne Bay

Didn't occur to me until I'd put the new motor into the Sprite that it may have improved the starting on the special. It's a pig of a job to change and I was being lazy hoping someone might know. Of course checking the relative voltage drops on one, or the other, in the same car would give a clear indication of which draws the least current. The disc commutator motor is, of course, shorter than the other but the armature and field coils seem to be the same size. Perhaps the efficiency is the same.
In the end I shall probably have to do as you suggest Peter. Many thanks.

And thanks UKDave I have no spec as the motor has been used. Like you, I studied electrical engineering and the family firm are involved with the repair of motors, but these are AC and I'm not up-to-speed anymore on DC motors. Confused

Don.

Mog · Joined: 30 Dec 2007 Posts: 661 Location: Sydney

I love A.C. speed controllers, when you can crank them up to 100 hz. It has saved me many hours of work to get the exact speed I want. We had to stir up some heavy mineral slurry , after 1 hour at 50 hz. nothing was happening. So at about 80 hz. it was all stirred up in 10 mins. !