HIGH TORQUE DC MOTOR CONTROLLER

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badtube
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HIGH TORQUE DC MOTOR CONTROLLER

Post by badtube » Thu Feb 21, 2008 5:19 pm

I need a controller to soft start an auto engine starter and increase the rpm's
to full. This is to turn an auto engine, not for cranking, but to be able to watch the moving parts of the engine. Where to purchase a controller or the schematic to build one would be of great help. Thanks

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jwax
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Post by jwax » Thu Feb 21, 2008 5:30 pm

Do you want a fixed ramp-up to a set slow speed, or do you want full control of the motor speed, with for example, a potentiometer?
Is this a full size automobile gas engine that you're spinning?
Curtis Instruments makes great DC motor controllers, but that may be overkill, depending on your needs.

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Re: HIGH TORQUE DC MOTOR CONTROLLER

Post by Bigglez » Thu Feb 21, 2008 5:42 pm

Greetings (No Name Supplied),
badtube wrote:I need a controller to soft start an auto engine starter and increase the rpm's
to full. This is to turn an auto engine, not for cranking, but to be able to watch the moving parts of the engine. Where to purchase a controller or the schematic to build one would be of great help. Thanks
I don't think this will work for you. An auto self-starter
motor has two motions, the armature spins up
and a solenoid forces the pinion gear to engage
with the teeth on the flywheel. (Removing the
power stops the motor and a spring retracts the
pinion). The pinion gear has a special mechanical
structure called a bendix or sprag clutch.

Trying to reduce the speed of the starter by
lowering the voltage will interfere with the pinion
solenoid.

What you need is a gearbox to reduce a motor's
speed to slowly turn over the engine.

If the engine is being prepared to be a display
the friction from the engine can be reduced by
venting the cylinders and possibly removing the
piston rings. Perhaps you plan to section the valve
cover, engine block, and sump to make other
moving parts visible?

Comments Welcome!

badtube
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Post by badtube » Thu Feb 21, 2008 5:58 pm

jwax wrote:Do you want a fixed ramp-up to a set slow speed, or do you want full control of the motor speed, with for example, a potentiometer?
Is this a full size automobile gas engine that you're spinning?
Curtis Instruments makes great DC motor controllers, but that may be overkill, depending on your needs.
Thanks guys for the replies. I want full control like with a pot .
I am not concerned about the bendex. I will use a belt or gear drive with a clutch. Do you have a web site for curtis instruments?
Thanks

Roger

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jwax
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Post by jwax » Thu Feb 21, 2008 6:04 pm

http://curtisinst.com/
You'll save on the size of controller you need by reducing the mechanical load as much as possible in that engine. Good luck!

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Joseph
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Post by Joseph » Fri Feb 22, 2008 6:23 am

Hi,

I would like to show you an image, but it just seems so hard, or my brain refuses to do the effort. Please go here http://tech.groups.yahoo.com/group/switchmode/ and then I can help you freely. Let me know who you are.

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Joseph
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Post by Joseph » Fri Feb 22, 2008 8:11 am

Here is a reprint from my description of one of my circuits that I recommend for what you want to do. It is relatively simple and uses basic and universal parts. I have built it point to point. You can play with it LTspice because the .asc file is located at the group I linked to above.
The PWM controller especially designed for my electric
bicycle oscillates at a relatively low audible frequency
for efficiency and simplicity. The LTspice version uses
a 1uF oscillator capacitor, but the real circuit may
give a better sounding result using a 0.33uF one which may
produce approximately a 300Hz motor whine.

The circuit is configured so that if the wiper inside the throttle
potentiometer loses its contact with the resistive strip, the
motor will cut out. In practice, this may cause jitter in the power
to the motor, but it seems to be the simplest effective safety
option.

In the LTspice version, four Schmitt trigger gates are
stacked on top of each other. The real circuit gets extra gate
drive for the MOSFETs from the four unused CMOS gates on the
74C14 chip.

If eight 55v 70a MOSFETs are paralleled, the efficiency
should still be about 98% if the load current is about 50a.
My old controller design did not have current limiting
like this one has, so I needed extra MOSFETs for
robustness. Now the main advantage of extra MOSFETs
is lower Rds, and thus, higher efficiency, depending on the
load.

The current sense involves detecting the voltage drop across
the motor B+ supply wire. By choosing a suitable gauge, the
amount of current at which current limiting engages can be
adjusted. This feedback may cause a suboscillation, but the
loss of complete smoothness is worth the gain of current
limiting, I think.
You can add just about as many MOSFETs as you like in parallel to increase either the efficiency or the current capability, or both.

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Joseph
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Post by Joseph » Fri Feb 22, 2008 8:20 am

i had a stripped flywheel on one of my old cars. I had to place a resistive limiter in series with the starter power wire to limit starter power until the teeth engaged. Then, i had to engage a bypass switch around that resistor. It worked perfectly. I see no problem with the functionality of what you want to do.

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Post by chribec2 » Fri Feb 22, 2008 4:43 pm

:razz: Hi Roger. (time is 4:22 p.m. local)

If this engine is for display, don't forget to change the valve springs to something much lighter - just enough pressure to
keep the valve closed on the cam's base circle but light enough to be able to push the valve open with your finger. Removing
the sparkplugs and rings as mentioned before is also excellent. Using the starter, though, may not be a good idea for running
the engine. It's not made for long term operation due to heat build-up (most spec's I've seen say 30 sec's max every 5
min's) - something to think about. I remember seeing an engine displayed like that back in the stone-age when I was in high
school (skool ? !). It was outstanding! Good luck!

Phil Potter

:cool: The earth is - oh my gosh - round :shock:

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haklesup
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Post by haklesup » Fri Feb 22, 2008 9:37 pm

I bet you could find a stepper motor about the right size to replace the starter, then it would be easy to control speed and position precisely, even very very slow.

The PWM is the most reasonable way to control the speed of a starter motor. Reducing voltage or limiting current would otherwise reduce torque to unusable levels pretty quick. A gear motor would give you the best combination of torque, low speed and low current and could be variable with a PWM as well.

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Joseph
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Post by Joseph » Sat Feb 23, 2008 5:06 am

Joseph wrote:i had a stripped flywheel on one of my old cars. I had to place a resistive limiter in series with the starter power wire to limit starter power until the teeth engaged. Then, i had to engage a bypass switch around that resistor. It worked perfectly. I see no problem with the functionality of what you want to do.
Oops.

i had a stripped flywheel on one of my old cars. I had to place a resistive limiter in series with the starter power wire to limit starter power until the teeth engaged. Then, i had to engage a bypass STARTER RELAY around that resistor. It worked perfectly. I see no problem with the functionality of what you want to do.

The switch activated an extra starter relay that was in the circuit parallel with the resistor.

badtube
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dc motor controller

Post by badtube » Sun Feb 24, 2008 3:32 pm

SORRY GUYS. I had this all wrong. I am trying to do this for a friend and I miss understood.

He wants to use the starter motor off of an automobile engine like I said. But he wants the starter to be put on his off road vehicle winch. So he can very the speed of the winch.

sorry

any ideas?

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jwax
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Post by jwax » Sun Feb 24, 2008 4:32 pm

That's a different beast! If this is to vary speed under mechanical load, you're back to a large Curtis type of controller. 300 amps is not unreasonable. Check the specs on the winch.
Since a winch is "slow" to begin with, why would anybody want to slow it down even further?

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Bob Scott
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Post by Bob Scott » Sun Feb 24, 2008 5:00 pm

jwax wrote:That's a different beast! If this is to vary speed under mechanical load, you're back to a large Curtis type of controller. 300 amps is not unreasonable. Check the specs on the winch.
Since a winch is "slow" to begin with, why would anybody want to slow it down even further?
I'd like to take the winch hook from one of those off-road vehicles, feed it over the roof of the SUV to the back, down and under the truck and hook it on back to the winch. Wrapped around the truck. Then turn it on and see what happens. :shock:

Bob

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