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PWM for High-Torque Motors

Started by Cursitor Doom May 1, 2021
Gentlemen,

Is it feasible to PWM a car starter motor or is there just too much
reactance in them?

TIA, CD
On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <cd@nowhere.com>
wrote:

>Gentlemen, > >Is it feasible to PWM a car starter motor or is there just too much >reactance in them? > >TIA, CD
The problems usually arise when there is too little inductance, the I2R losses in the driver get excessive. Yes, you should be able to PWM a starter motor, but the MOSFETs had better be very hefty- hundreds of A honest rating, maybe more. -- Best regards, Spehro Pefhany
On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <cd@nowhere.com>
wrote:

>Gentlemen, > >Is it feasible to PWM a car starter motor or is there just too much >reactance in them? > >TIA, CD
It should work. It might help to drive the field and armature with separate PWMs. I think classic starters were series motors, optimized for starting and nothing else. Starter motors are brutes. Reactance helps! -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
On Sat, 01 May 2021 08:02:05 -0700, jlarkin@highlandsniptechnology.com
wrote:

>On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <cd@nowhere.com> >wrote: > >>Gentlemen, >> >>Is it feasible to PWM a car starter motor or is there just too much >>reactance in them? >> >>TIA, CD > >It should work. It might help to drive the field and armature with >separate PWMs. I think classic starters were series motors, optimized >for starting and nothing else.
Yeah, they were wound such that which ever polarity they were connected they would always turn in the same direction. Some had the direction of turn stamped onto them, too.
> >Starter motors are brutes. > >Reactance helps!
How does it *help* exactly??
On Saturday, May 1, 2021 at 11:07:14 AM UTC-4, Cursitor Doom wrote:
> On Sat, 01 May 2021 08:02:05 -0700, jla...@highlandsniptechnology.com > wrote: > >On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <c...@nowhere.com> > >wrote: > > > >>Gentlemen, > >> > >>Is it feasible to PWM a car starter motor or is there just too much > >>reactance in them? > >> > >>TIA, CD > > > >It should work. It might help to drive the field and armature with > >separate PWMs. I think classic starters were series motors, optimized > >for starting and nothing else. > Yeah, they were wound such that which ever polarity they were > connected they would always turn in the same direction. Some had the > direction of turn stamped onto them, too. > > > >Starter motors are brutes. > > > >Reactance helps! > How does it *help* exactly??
For PWM it smooths the current impulses to a more even level rather than literally on/off. -- Rick C. - Get 1,000 miles of free Supercharging - Tesla referral code - https://ts.la/richard11209
On Sat, 01 May 2021 16:07:08 +0100, Cursitor Doom <cd@nowhere.com>
wrote:

>On Sat, 01 May 2021 08:02:05 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <cd@nowhere.com> >>wrote: >> >>>Gentlemen, >>> >>>Is it feasible to PWM a car starter motor or is there just too much >>>reactance in them? >>> >>>TIA, CD >> >>It should work. It might help to drive the field and armature with >>separate PWMs. I think classic starters were series motors, optimized >>for starting and nothing else.
Yes, I neglected to mention about that. They are optimised for starting and are pretty much useless for anything involving more than around 30s operation at a time, given they have no cooling fins or vents to speak of.
In article <4qrq8gpvg1kokmc0bstsk1r5g44t9190tb@4ax.com>, cd@nowhere.com 
says...
> > > >>It should work. It might help to drive the field and armature with > >>separate PWMs. I think classic starters were series motors, optimized > >>for starting and nothing else. > > Yes, I neglected to mention about that. They are optimised for > starting and are pretty much useless for anything involving more than > around 30s operation at a time, given they have no cooling fins or > vents to speak of. > >
That is also what I was wondering about. What is the motor going to be used for ? As you said unless the appiation is for running it for less than 30 seconds and then giving it a 10 or more minuite cool off time it will burn out in a short period of time.
On Sat, 01 May 2021 16:07:08 +0100, Cursitor Doom <cd@nowhere.com>
wrote:

>On Sat, 01 May 2021 08:02:05 -0700, jlarkin@highlandsniptechnology.com >wrote: > >>On Sat, 01 May 2021 14:48:14 +0100, Cursitor Doom <cd@nowhere.com> >>wrote: >> >>>Gentlemen, >>> >>>Is it feasible to PWM a car starter motor or is there just too much >>>reactance in them? >>> >>>TIA, CD >> >>It should work. It might help to drive the field and armature with >>separate PWMs. I think classic starters were series motors, optimized >>for starting and nothing else. > >Yeah, they were wound such that which ever polarity they were >connected they would always turn in the same direction. Some had the >direction of turn stamped onto them, too. > >> >>Starter motors are brutes. >> >>Reactance helps! > >How does it *help* exactly??
Motor inductance lowpass filters the ripple current out of PWM, so you don't need separate inductors. At modern switching frequencies, a motor winding should have lots of inductance, but not enough to affect motion dynamics. What do you want to do with a starter motor? -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
On Sat, 1 May 2021 11:39:21 -0400, Ralph Mowery
<rmowery42@charter.net> wrote:

>In article <4qrq8gpvg1kokmc0bstsk1r5g44t9190tb@4ax.com>, cd@nowhere.com >says... >> > >> >>It should work. It might help to drive the field and armature with >> >>separate PWMs. I think classic starters were series motors, optimized >> >>for starting and nothing else. >> >> Yes, I neglected to mention about that. They are optimised for >> starting and are pretty much useless for anything involving more than >> around 30s operation at a time, given they have no cooling fins or >> vents to speak of. >> >> > >That is also what I was wondering about. What is the motor going to be >used for ? As you said unless the appiation is for running it for less >than 30 seconds and then giving it a 10 or more minuite cool off time it >will burn out in a short period of time. >
Depends on the load. It would be fine at reasonable loads. The brushes might wear out or get hot from friction if run long-term. Starter brushes are big and crude, with strong springs. A series motor can be weird. The theoretical unloaded RPMs is infinite, which might be a reason to drive the field and armature separately. The bearings may not be up to spinning fast and long either. -- John Larkin Highland Technology, Inc The best designs are necessarily accidental.
jlarkin@highlandsniptechnology.com wrote:
> On Sat, 1 May 2021 11:39:21 -0400, Ralph Mowery > <rmowery42@charter.net> wrote: > >> In article <4qrq8gpvg1kokmc0bstsk1r5g44t9190tb@4ax.com>, cd@nowhere.com >> says... >>>> >>>>> It should work. It might help to drive the field and armature with >>>>> separate PWMs. I think classic starters were series motors, optimized >>>>> for starting and nothing else. >>> >>> Yes, I neglected to mention about that. They are optimised for >>> starting and are pretty much useless for anything involving more than >>> around 30s operation at a time, given they have no cooling fins or >>> vents to speak of. >>> >>> >> >> That is also what I was wondering about. What is the motor going to be >> used for ? As you said unless the appiation is for running it for less >> than 30 seconds and then giving it a 10 or more minuite cool off time it >> will burn out in a short period of time. >> > > Depends on the load. It would be fine at reasonable loads. > > The brushes might wear out or get hot from friction if run long-term. > Starter brushes are big and crude, with strong springs. > > A series motor can be weird. The theoretical unloaded RPMs is > infinite, which might be a reason to drive the field and armature > separately. > > The bearings may not be up to spinning fast and long either.
Occasionally a starter drive will hang up, so that the spur gear doesn't get kicked out of the ring gear when the engine starts up. Makes very entertaining howling screeching noises, for awhile. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com