Series vs Permanent Magnet Starters

[John Park]

I have a circa 1978 starter - series wound field - that's almost as new, and a permanent magnet one circa 1982 that is in good condition but needs brushes. The PM one is Nippondenso and the wound one has a Suzuki logo and Mitsuba markings.

Is there a preference? I'm happy to use up the older one, unless there's some reason why I should repair the PM one instead.

[posplayr]

It would be interesting to see some data on the two. I have worked with large WARN winches that were series wound. They tend to create a lot of torque because the field is in series with the armature so at stall you have max current and therefore max magnetic strength. But at startup there is also a lot of startup current so there is a big kick even under no load. Basically the motor runs "balls to the walls" no matter what the load at startup making positioning tricky.

http://www.electrical4u.com/series-wound-dc-motor-or-dc-series-motor/

As you can read the series motors have poor speed control. I had to design a servo position control system using the series Winch. At zero load a small input created a big jump, whereas under load that same jump was relatively smaller in proportion to load. The control system had to adjust gain by about 10:1 on the fly based on inferred load.

None of this is relevant to a starter where you would like to get maximum output to spin the motor as fast as possible. Speed control is not an issue.

Speed & Torque of Series DC Motor

A series wound motors has linear relationship existing between the field current and the amount of torque produced. i.e. torque is directly proportional to current over the entire range of the graph. As in this case relatively higher current flows through the heavy series field winding with thicker diameter, the electromagnetic torque produced here is much higher than normal. This high electromagnetic torque produces motor speed, strong enough to lift heavy load overcoming its initial inertial of rest. And for this particular reason the motor becomes extremely essential as starter motors for most industrial applications dealing in heavy mechanical load like huge cranes or large metal chunks etc. Series motors are generally operated for a very small duration, about only a few seconds, just for the purpose of starting. Because if its run for too long, the high series current might burn out the series field coils thus leaving the motor useless.

[John Park]

Thanks for the reply, Posplayr. I recall that the 'old' starters used to work just fine, and maybe the high stall torque was what I liked in getting over the top of compression. I can see how the PM motors would be easier to make and be more abuse proof [like cranking until the battery goes dead, expecting some parameter to magically change and result in starting] and draw less battery.

One nice thing about twins is that, if it goes out, you can always bump start and change the starter later.

[John Park]

Upon further inspection, the end bell mounts are a different height, so the 400 starter won't fit the 450 case. And they're too low so you can't shim it up. I guess I'm looking for brushes after all.

[morganharri]

I have also tried to fit 400 starter into 450 case but it won't work.

[qcktvr]

I once owed an 83 Honda 650 CXTurbo, it was often tricky to start, needing a really good battery, it had a wimpy permanent magnet motor (maybe the magnets didn't age well?), switching to an 82 CX or prior motor with the field windings completely solved that problem...
So what does my GS1150 use? it can also be reluctant to crank strongly when the motor is hot...
Just unwrapped it, that new AGM battery is still at 12.68v, I'm impressed so far, getting warmer here but lots of sand on the roads yet..
Regards