DC motor ? for our resident EE's, JT and BD

Many years ago I saw a very old offset press with a large flywheel powered by a universal motor. The shaft of the motor had a small rubber like wheel that rubbed against the flywheel. There was a foot peddle that changed the position of the brushes on the motor, which in turn would increase the speed of the motor.

So, I've seen the speed of a universal motor controlled by changing the position of the brushes.

So is it possible by altering the position of the brushes on a 6v starter we could slow it down a little? That way when we use a 6v starter on 12v conversion, the starter drive so won't engage so hard, which can possibly damage the starter drive and or starterring? At the same time the starter will produce enough power on 12v to start the engine?

Some of the 12 volt starters have a field coil with what I remember called a shunt coil ? That may be what it was in there for ?
I'd see if you can either get a 12 volt starter for your application or 12 volt field coils and or armature.

See TIP #43 of the 75 Tips (part 2) TO SAFELY start your tractor and to avoid several problems. Advise if you DO NOT have this valuable 7 page info or can't find it on this site. The starter brushes are not adjustable because of the thru bolts in the starter.

Are you our resident EE's?

I know how starters are made. I even made a dc motor in the 5th grade as a science fair project. I could alter it speed by relocating the brushes.

One can always cut off the indexing pin on end bell, drill new holes and alter the position of the brushes. It's not rocket science, more like grade school science.

Yes, to all, I know I can buy 12v starters. Have one in the mail. But what's the fun in that if all you have to do is reposition the brushes?

A lot of tractors have been converted to 12 volts without changing anything on the starter. No problems with the starter due to higher voltage. Just don't crank too long and overheat the 6 volt starter.

I built a few of those motors way back when but you know I do not remember how to do one now but that was say 50 or so years ago LOL. Built more then one and also built a simple radio or 2 also. Also cooked more then one hot dog with a couple nails and a power cord

If your 12V conversion using a 6V starter, bangs in hard enough to break drive cushion springs, just replace one of the heavy battery cables with a cheap Walmart type 12V cable. This will reduce the starters "kick" just enough to prevent drive breakage, while still cranking 3 times better than the 6V setup. Done that successfully several times. No need to over think this deal.

(quoted from post at 16:36:37 02/16/15)
... So is it possible by altering the position of the brushes on a 6v starter we could slow it down a little? That way when we use a 6v starter on 12v conversion, the starter drive so won't engage so hard, which can possibly damage the starter drive and or starter ring? At the same time the starter will produce enough power on 12v to start the engine?

Click to expand...

First the qualification: I'm not a degeed EE, but I do motor and electronic work professionally, and have seen exactly what you are describing.

Yes, you can change the brush position and slow the starter, but the current will not really drop much, which just makes the starter far less efficient with the energy provided (more heat than movement). Universal motors are designed A LOT different than a starter (a lot more poles on the rotor and more field windings), even if the same basic principles apply.

I just had my 6v starter rebuilt with 12v field coils - not that it wouldn't work at 12v when I converted the electrical system, but the bendix was shot (and I was hand cranking it a 6v) long before it had the chance to be "abused" at 12v. Cold weather made the starter fix a necessity.

Maybe the extended cold weather cranking necessary at 6v ruined the bendix. I know it does a lot better now at 12v.

I've had nothing but problems on two different tractors snapping off starter drives. Hopefully I didn't damage the teeth on starter ring.

Use a long thin cable and wrap some of it into a coil. If it isn't enough, do it to the ground too. When not using the starter it will still carry all you need.

If I wanted to experiment with brush timing/position I would try putting a bevel on one side of the brush. This would make the brush thinner, perhaps decreasing the life. However, it should give some indication of what happens without a major machining project.

George, once again I think we need to back up a couple of steps. Why do you want to slow down the starter in the first place? The whole point of a 12 volt conversion is to crank the engine harder and faster than the original starter can do on six volts. The downside is you're putting more current through the starter than it was originally designed for, but most converted tractors start so fast that's a non-issue.

What is your intended goal? Less current? Slower acceleration? Slower cranking? Less torque? The easiest way to achieve all of these is to install a twelve volt starter, or convert the machine back to six volts. There's no easy way to reduce the current inrush when you hit a motor wound for six volts with twelve volts.

I suspect the motor you saw was not a universal motor but rather a repulsion motor, which is an AC motor which uses brushes for speed control.

Its possible to change brush position to change speed, but that's a lot of work and engineering and some machine work to accomplish in my opinion. Its already pretty crowded inside the brush area on the starter.

To reduce the hard engage you get when you apply 12 volts to a 6 volt starter you could use a smaller wimpy battery, say a 500 CCA or less battery instead of a 700 to 900 etc. Also if you use maybe 4 gauge cables instead of say 2 or 0 etc that can soften the impact. Usually a 6 volt starter with 12 volts applied spins plenty fast so I don't think a lighter battery and smaller cables will prevent a good start.

John T

Because I've already lost 3 starter drives and may have damaged the starter teeth on flywheel.

The battery on Farmall is 450CCA. I was planning to try a 300 CCA lawn mower battery. When it gets warmer I'll take starter apart and I see if I can move brushes in the same direction the shaft rotates. I too am thinking there may be an issue with drilling new hole in end bell. The brushes or wires may get in the way of the 2 bolts that hold starter together. If I rotate it the wrong direction, starter will rotate backwards.

Already ordered a 12v starter for Jubilee. Plan to see how much damage is done to the starter ring on flywheel tomorrow.

Thanks
George

George,you have something else wrong then 12 into 6 starter.Cheap bendix,or misalined somehow.We have been running a Jub.over 50 yrs.on 12 volt and are still on the original starter-bendix with an engine load that takes all a good 800-900 CCA battery will deliver in 20F and lower temps.So stop trying to reinvent the wheel and look for the problem,because there are thousands out there NOT HAVING PROBLEMS.

FOR BEST RESULTS: If your engine is prorerly tuned(Ignition,valves,proper OIL for the season-temperture) the Tractor will Start and run without changing to 12 volts !!!. That said I use my 8N-b with the 6 volt system year round. It start on about the 3rd revolution with the chock on.T use 10-30Wt oil and live just outside Chicago in Valparaiso Indiana.Please read TIP #43 FROM The N-News Magazine BELOW:To jump start a 6 volt tractor with a 12 volt battery, put the tractor in neutral,block the wheels an turn the key on. Put one jumper cable on the stud of the starter (-) polarity . Standard wiring polarity is is(+) ground Double check this. Make sure the transmision is in neutral because when you place the other jumper (+) on the frame of the tractor thr STARTER will ENGAUGE and turn the motor over. This bypasses the neutral safety switch and the solenoid. The 12 volt battery will not harm the 6 volt starter unless you crank it for more than a minuate or so. HOWEVER if you jump the 12 volt battery directly to the 6 volt battery you stand a good chance of a battery explosion! I know I did this on a 6 volt !950 chevty truck.
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