PWM for High-Torque Motors

[Cursitor Doom]

Gentlemen,

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

TIA, CD

[Spehro Pefhany]

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

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

[jla...@highlandsniptechnology.com]

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

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.

[Cursitor Doom]

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??

[Rick C]

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
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[Cursitor Doom]

On Sat, 01 May 2021 16:07:08 +0100, Cursitor Doom <c...@nowhere.com>

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.

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.

[Ralph Mowery]

In article <4qrq8gpvg1kokmc0b...@4ax.com>, c...@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.

[jla...@highlandsniptechnology.com]

On Sat, 01 May 2021 16:07:08 +0100, Cursitor Doom <c...@nowhere.com>

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??

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?

[jla...@highlandsniptechnology.com]

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.

[Phil Hobbs]

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

[Ralph Mowery]

In article <110r8g9q6jd8qe5eq...@4ax.com>,
jla...@highlandsniptechnology.com says...

>
> The brushes might wear out or get hot from friction if run long-term.
> Starter brushes are big and crude, with strong springs.
>
>
>

Brushes are designed for a certain current density (think that is the
correct term but not sure). Too little current can be as bad for the
brushes as too much as far as brush wear.

[Cursitor Doom]

On Sat, 01 May 2021 09:20:51 -0700, jla...@highlandsniptechnology.com

I'll email you tomorrow.

[whit3rd]

On Saturday, May 1, 2021 at 6:48:21 AM UTC-7, Cursitor Doom wrote:

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

For starting a car, you don't need any control except on/off. And, you
don't make the motor good at keeping itself cool. So, what's the
non-automotive application that benefits from PWM?

[Cursitor Doom]

On Sat, 1 May 2021 22:20:19 -0700 (PDT), whit3rd <whi...@gmail.com>
wrote:

Proprietory ideas abound. Why not use your imagination? There are many
possible applications for a high-torque motor operating in short
bursts. I found mine, now it's over to you.

[chris]

No reason why not, though they are usually series wound, whereas a
separate field might be better from a control pov. Pwm for higher
power dc motors has been done for years and things like exercise
treadmills often use 1-3HP permanent magnet motors running at >
100 volts. The higher the voltage, the lower the ir losses, all else
being equal...

[whit3rd]

On Sunday, May 2, 2021 at 2:02:38 AM UTC-7, Cursitor Doom wrote:
> On Sat, 1 May 2021 22:20:19 -0700 (PDT), whit3rd <whi...@gmail.com>
> wrote:
> >On Saturday, May 1, 2021 at 6:48:21 AM UTC-7, Cursitor Doom wrote:

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

> >For starting a car, you don't need any control except on/off. And, you
> >don't make the motor good at keeping itself cool. So, what's the
> >non-automotive application that benefits from PWM?

> Proprietory ideas abound. Why not use your imagination?

Classically, for a burst one uses a regular-old-motor and a flywheel.
An electric clutch doesn't need PWM, and doesn't dim the lights when
engaged.

[Clive Arthur]

On 02/05/2021 16:22, whit3rd wrote:

<snip>

>
> Classically, for a burst one uses a regular-old-motor and a flywheel.
> An electric clutch doesn't need PWM, and doesn't dim the lights when
> engaged.

High torque short bursts? You need a Marinov motor...

http://www.electricstuff.co.uk/bbmotor.html#article

--
Cheers
Clive

[Rick C]

Interesting. I'll take the guy's word for it that it works. He says some things that don't make sense.

"One can see immediately that the baI1- bearing motor has no back tension because there are no magnets, and the magnetic field of the current in the "stator" cannot induce electric tension in the metal of the "rotor".

Thus the firm conclusion is to be drawn that the mechanical energy delivered by the ball-bearing motor is produced from nothing, in a drastic contradiction to the energy conservation law. "

There is "back tension" because of the resistance that creates the heating. I assume he means no inductive counter EMF, but that's not what makes a motor work so who cares? The statement that the motion is produced from "nothing" is absurd and violates no energy laws. Maybe he is speaking creatively, intending to mock what others might say?

This is a very low impedance device. I suppose the impedance can be increased by making the bearing balls smaller while keeping the radius of the race large. At some point this becomes counter productive to the lifespan of a high torque motor. The author also posts some errors. He claims the two motors have equal ohmic resistance, but says the larger motor draws a correspondingly higher current commensurate to the torque. If the current is higher, would not the resistance need to be lower? If he didn't use the same voltage in each case there is no comparison.

Two other statements offered apparently without evidence. ---
The driving force is higher for bigger bores, as the curvature of the races is less.
The driving force is greater for bigger balls, as their curvature is less.

I don't see this. A lesser curvature essentially lowers the leverage at a given distance from the point of contact. A greater rotation is required to accommodate the expansion. This would perhaps allow a larger speed of rotation, but either with no more force or with less force, but maybe I'm not grasping the full effect. I suppose since the expansion interaction area is greater this could result in a higher force. As the result is not so obvious at first glance, perhaps some measurement is in order. A lot would depend on the rate of cooling of the working area. I wonder if a thermal insulating layer might be of use? I'm also curious as to why box bearing don't exhibit this effect. Maybe there is too much area of contact lowering the electrical resistance and raising the thermal conductivity to a point the effect is nearly absent.

I wonder if there is any practical use for such a motor? I'm guessing it is not very efficient. It might however, be useful at the very low end of motor size where torque is very important to overcome stiction.

[Cursitor Doom]

On Sun, 2 May 2021 08:22:47 -0700 (PDT), whit3rd <whi...@gmail.com>

wrote:

>On Sunday, May 2, 2021 at 2:02:38 AM UTC-7, Cursitor Doom wrote:
>> On Sat, 1 May 2021 22:20:19 -0700 (PDT), whit3rd <whi...@gmail.com>
>> wrote:
>> >On Saturday, May 1, 2021 at 6:48:21 AM UTC-7, Cursitor Doom wrote:
>
>> >> Is it feasible to PWM a car starter motor or is there just too much
>> >> reactance in them?
>
>> >For starting a car, you don't need any control except on/off. And, you
>> >don't make the motor good at keeping itself cool. So, what's the
>> >non-automotive application that benefits from PWM?
>
>> Proprietory ideas abound. Why not use your imagination?
>
>Classically, for a burst one uses a regular-old-motor and a flywheel.
>An electric clutch doesn't need PWM, and doesn't dim the lights when
>engaged.

I'm familiar with that system but AFAIK it requires the flywheel to be
running *all* the time. I know they don't consume much energy to keep
'em running once they're up there at speed, but nevertheless, they do
still need to be powered constantly. Plus a flywheel by it's very
nature has to be *big* and *heavy* so that's a non-starter for my
purposes, I'm afraid.

[Cursitor Doom]

April the 1st was a month ago. I can't see any basis for this thing
working as described.

[Lasse Langwadt Christensen]

doesn't need t orun all the time, just needs to be "charged" before
you need the torque, https://youtu.be/ROnb5ouBjNc?t=65

how much torque do you need?

[Cursitor Doom]

Hmmm. Still doesn't do it for me I'm afraid.

>how much torque do you need?

Nothing stratospheric. 7.5 ft-lb should do the trick.

[Lasse Langwadt Christensen]

at what speed?

[Rick C]

What sort of speed? This is a motor that was considered for the vent project. It gets you about 10 ft-lbs at 14 rpm. Gear reduction. Seems to hold up to everything we throw at it, but the output shaft has its limits.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

[Cursitor Doom]

That's pretty much what I'm looking for, TBH. It'll be reduced by a
worm and nut arrangement anyway.

[Cursitor Doom]

On Sun, 2 May 2021 11:05:56 -0700 (PDT), Lasse Langwadt Christensen

See my follow up to Rick C. Don't over think this! I'm just fishing
for general and vague ideas at this stage.

[Rick C]

Sorry, forgot to add the link.

https://gimsonrobotics.co.uk/categories/dc-electric-motors/products/gr-ep-45e-medium-power-45mm-12v-planetary-gearmotor

In the UK. I'm sure there are others in the US. Much smaller than a starter motor, around $40 if I recall.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

[Rick C]

On Sunday, May 2, 2021 at 2:26:58 PM UTC-4, Cursitor Doom wrote:

It's all about speed. You can get any torque you want if you gear it down enough, but the speed will be slow, potentially glacial.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

[Cursitor Doom]

>> >> >you need the torque, https://youtu.be/ROnb5ouBjNc?t=65
>> >> Hmmm. Still doesn't do it for me I'm afraid.
>> >> >how much torque do you need?
>> >> Nothing stratospheric. 7.5 ft-lb should do the trick.
>> >at what speed?
>> See my follow up to Rick C. Don't over think this! I'm just fishing
>> for general and vague ideas at this stage.
>
>Sorry, forgot to add the link.
>
>https://gimsonrobotics.co.uk/categories/dc-electric-motors/products/gr-ep-45e-medium-power-45mm-12v-planetary-gearmotor
>
>In the UK. I'm sure there are others in the US. Much smaller than a starter motor, around $40 if I recall.

Thanks, Rick. THat's exactly the kind of thing I'm looking for - if I
can find a model with the right amount of power. Good link!

[TTman]

On 02/05

>> Sorry, forgot to add the link.
>>
>> https://gimsonrobotics.co.uk/categories/dc-electric-motors/products/gr-ep-45e-medium-power-45mm-12v-planetary-gearmotor
>>
>> In the UK. I'm sure there are others in the US. Much smaller than a starter motor, around $40 if I recall.
>
> Thanks, Rick. THat's exactly the kind of thing I'm looking for - if I
> can find a model with the right amount of power. Good link!
>

And here https://www.rapidonline.com/geared-motors



--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

[Clive Arthur]

Marinov was a bit of a nutter with all sorts of free energy type claims,
but his ball-bearing motor does work in that it rotates, albeit with
very poor efficiency. It would take an imagination far greater than
mine to envisage a sensible use for it.

I remember this being discussed in 'Wireless World' decades ago with
various theories to do with magnetics etc, when it was obvious that it
was really just a load of expanding balls.

--
Cheers
Clive

[John Doe]

Clive Arthur wrote:

> Marinov was a bit of a nutter with all sorts of free energy type claims,
> but his ball-bearing motor does work in that it rotates, albeit with
> very poor efficiency. It would take an imagination far greater than
> mine to envisage a sensible use for it.

Reminded me of Mazda's rotary engine (I know nothing about). There appears to
be a "return of the rotary engine" maybe 2019. So, apparently it was not very
successful.

[Lasse Langwadt Christensen]

it'll turn, but it won't be self starting and will ruin the bearings

https://www.plantservices.com/articles/2007/022/

[Steve Wilson]

Lasse Langwadt Christensen <lang...@fonz.dk> wrote:

Ceramic bearings can solve the problem. Scott Manley describes the
solution:

"Scientists May Have Figured Out Why So Many Spacecraft Were Failing"

https://www.youtube.com/watch?v=KibT-PEMHUU



--
The best designs occur in the theta state. - sw

[Cursitor Doom]

On Sun, 2 May 2021 22:40:22 -0000 (UTC), Steve Wilson <spa...@not.com>
wrote:

>Lasse Langwadt Christensen <lang...@fonz.dk> wrote:
>
>> søndag den 2. maj 2021 kl. 18.41.30 UTC+2 skrev Cursitor Doom:
>>> On Sun, 2 May 2021 16:38:18 +0100, Clive Arthur
>>> <cl...@nowaytoday.co.uk> wrote:
>>>
>>> >On 02/05/2021 16:22, whit3rd wrote:
>>> >
>>> ><snip>
>>> >>
>>> >> Classically, for a burst one uses a regular-old-motor and a flywheel.
>>
>>> >> An electric clutch doesn't need PWM, and doesn't dim the lights when
>>
>>> >> engaged.
>>> >
>>> >High torque short bursts? You need a Marinov motor...
>>> >
>>> >http://www.electricstuff.co.uk/bbmotor.html#article
>>> April the 1st was a month ago. I can't see any basis for this thing
>>> working as described.
>>
>> it'll turn, but it won't be self starting and will ruin the bearings
>>
>> https://www.plantservices.com/articles/2007/022/
>
>Ceramic bearings can solve the problem.

Trouble with ceramics is they're not very good conductors, though. ;-)