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'[OT]: Need ideas for supply for 90V motor drive...'
2002\11\21@171505 by Chris Loiacono

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Once again, I'm not looking for anyone to do my work for me - just hoping
someone can give me a little push down the hill.

I'm after the lowest cost way to make the 90V needed for a brush motor PWM
speed control w/ current limit.....Any ideas as to where I might start
looking?

TA,
Chris

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2002\11\21@172745 by Mike Poulton

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Chris Loiacono wrote:
> Once again, I'm not looking for anyone to do my work for me - just hoping
> someone can give me a little push down the hill.
> I'm after the lowest cost way to make the 90V needed for a brush motor PWM
> speed control w/ current limit.....Any ideas as to where I might start
> looking?

You want to make the 90V, or the controller, or both?  If you want to
make the 90V, then what are you starting with?  Do you want
bidirectional operation?  What type of motor is it?
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2002\11\21@175314 by Lucas Thompson

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I'm looking for nearly the same thing but for a 30-volt, 15-amp
reverse capable PWM speed controller for brushed-DC permanent
magnet type motors. The +-30V is going to be supplied by a big
ni-cd pack.
I've looked around on the PIClist site and found some promising things
but they seem to lack reversability. Ideally, it'd be able to brake the
motors with a PWM-to-ground short circuit type mechanism instead of
trying to apply opposing voltage to get the motors to stop.

Maybe someone else has already done this exact thing. Gladly take any
suggestions!

Chris Loiacono wrote:
> Once again, I'm not looking for anyone to do my work for me - just
> hoping someone can give me a little push down the hill. I'm after the
> lowest cost way to make the 90V needed for a brush motor PWM speed
> control w/ current limit.....Any ideas as to where I might start
> looking?

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2002\11\21@185956 by Spehro Pefhany

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At 05:21 PM 11/21/02 -0500, you wrote:
>Once again, I'm not looking for anyone to do my work for me - just hoping
>someone can give me a little push down the hill.

Right there behind you. ;-)

>I'm after the lowest cost way to make the 90V needed for a brush motor PWM
>speed control w/ current limit.....Any ideas as to where I might start
>looking?

From 120VAC? FW bridge with appropriate fusing and surge suppression and
EMI filtering, followed by a BFC filter. Limit the duty cycle of your PWM
to less than about 55 or 60%. Optically isolate the PIC (presumably, eh?)
controller and power it from a separate transformer power supply if possible.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2002\11\21@194831 by DFansler

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Take a look at http://www.robot-power.com/ and the Open Source Motor Control
(OSMC).  They have the design published for a PWM power unit that is a  160
A, 50V H-Bridge.  They supply both the schematic and a kit.  I purchased the
kit and assembled it with no problem.  Unit works good.  While you  may not
want the kit, the schematic should help you design what you need.  The PWM
control is from an Intersil HIP4081PWM controller that controls external
FETs for power.  I used it in another project (zero shift focuser for my
telescope).

David V. Fansler
@spam@DFanslerKILLspamspamMindSpring.com
http://www.DV-Fansler.com

{Original Message removed}

2002\11\22@041241 by Alan B. Pearce

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>I'm looking for nearly the same thing but for a 30-volt, 15-amp
>reverse capable PWM speed controller for brushed-DC permanent
>magnet type motors. The +-30V is going to be supplied by a big
>ni-cd pack.
>I've looked around on the PIClist site and found some promising things
>but they seem to lack reversability. Ideally, it'd be able to brake the
>motors with a PWM-to-ground short circuit type mechanism instead of
>trying to apply opposing voltage to get the motors to stop.

This is exactly the area that the Intersil HIP4080 is great for. Colleagues
of mine are using these to build a PWM driver to go on space craft to
operate from 29V supply. In our case we need 10A peak, but for your use just
use beefier output FETs. You will have the advantage of being able to use
the most recent fast switching/low input capacitance FETs that will suit.

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2002\11\22@090856 by Chris Loiacono

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So, if I understnd you correctly, simply make DC from the line and since it
will be more than 120V, limit the max pwm output to equal 90V.........is
that what you mean?
Certainly sounds inexpensive.
I'll have to see how much resolution this will take away....

>  From 120VAC? FW bridge with appropriate fusing and surge
> suppression and
> EMI filtering, followed by a BFC filter. Limit the duty cycle
> of your PWM
> to less than about 55 or 60%. Optically isolate the PIC
> (presumably, eh?)
> controller and power it from a separate transformer power
> supply if possible.

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2002\11\22@212005 by M. Adam Davis

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What's the load (5A?  50A?), and the required regulation (5%, 10%, in
the neighborhood, etc)?

If 10% under is ok, then make a full wave rectifier from AC mains.

120V RMS = 169.68V p-p
Full wave with appropiately sized caps = ~84vdc

-Adam

Chris Loiacono wrote:

{Quote hidden}

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2002\11\22@222238 by Chris Loiacono

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I really like this idea.... almost too simple!
The motor is a 1.75 HP gear motor. I'll have to check on the gear ratio to
see if I can achieve the speed range in the spec. since it could be only 81V
if the line is as low as 115VAC....
I don't have a specification for the regulation, but my guess is that it is
in the 5 to 10% range since it is for a small roll converting machine....
{Quote hidden}

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2002\11\22@225620 by Spehro Pefhany

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At 09:19 PM 11/22/02 -0500, you wrote:
>What's the load (5A?  50A?), and the required regulation (5%, 10%, in
>the neighborhood, etc)?
>
>If 10% under is ok, then make a full wave rectifier from AC mains.
>
>120V RMS = 169.68V p-p

You're off by 2:1, it's about 340V p-p.

Best regards,

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2002\11\22@231942 by Paul Hutchinson

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> >What's the load (5A?  50A?), and the required regulation (5%, 10%, in
> >the neighborhood, etc)?
> >
> >If 10% under is ok, then make a full wave rectifier from AC mains.
> >
> >120V RMS = 169.68V p-p
>
> You're off by 2:1, it's about 340V p-p.
>

And with full wave rectification and filtering there will be about
169.68VDC. Not good for the 90V motor ;-)

Paul

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2002\11\23@004058 by Sean H. Breheny

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I think by "full wave rectification" he means using a center-taped
transformer with two diodes, NOT a four diode bridge. That does indeed
divide the voltage by two.

Sean

At 11:16 PM 11/22/2002 -0500, you wrote:
{Quote hidden}

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2002\11\25@211844 by Dwayne Reid

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At 05:21 PM 11/21/02 -0500, Chris Loiacono wrote:
>Once again, I'm not looking for anyone to do my work for me - just hoping
>someone can give me a little push down the hill.
>
>I'm after the lowest cost way to make the 90V needed for a brush motor PWM
>speed control w/ current limit.....Any ideas as to where I might start
>looking?

If this is something like a treadmill motor, all you should need is a phase
controlled full wave bridge rectifier (2 diodes, 2 SCRs) operated directly
from the 120 Vac line.  This is how most tread mills do their speed control.

The 90V rating on the motor comes from full wave rectifying the incoming
120 Vac but not filtering it; and operating a somewhat less than the full
180 degree conduction for each half-cycle.  Most older blueprint machines
use similar motors (smaller, of course) and control techniques.

For a simple test, just grab a fan-motor rated speed control and connect it
to a bridge rectifier feeding the motor.  Should work just fine.

dwayne

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2002\11\25@233802 by Chris Loiacono

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Thanks, Dwayne. Not only is this simlpe and inexpensive, but it lets me use
some h/w & code from recent projects to modernize the basic idea. I remember
fixing bench-top machines that formed axial component leads with this type
of driver back in the 70's. It may not be as efficient as PWM driving via
FET's, but I can see how it would be clean and simple. For this little
laminating machine it should be fine.
Now for the catch - current limiting - at AC freq it's always fun getting a
good running current averaging circuit with impedance a PIC ADC will
handle.....
But then again, I did ask for a starting point.......

Chris
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