AC Powered Motor Controller for DC Motor?

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muniorbust
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AC Powered Motor Controller for DC Motor?

I'm building a special treadmill that will keep a unicycle rider in the middle of it no matter his speed.
I'm starting with an existing treadmill, but I'll swap the motor out for a DC motor that can move in both directions.

I haven't purchased a motor or motor controller yet.
I'll be using a microcontroller and I'd like to output PWM to the motor controller.

Since the treadmill itself will be stationary, I'd prefer to use AC power and no batteries.

I figure my motor will draw similar currents to an electric powered bike.

So, how would you power a motor controller and DC electric "bike" motor from AC?

Thanks for any help!
Buzz

Spaceangel
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Re: AC Powered Motor Controller for DC Motor?

If the motor is DC either permanent magnet or series wound and controller is DC controller then all you need is a full wave bridge rectifier and maybe a small bank of capacitors. But be careful!!! 120 volts AC times the square root of two is 170 plus DC volts and a lot of capacitors in a PWM will go kaboom. On my wife's tread mill it is already a DC motor just like the ones in Surplus stores. I know that because Sears sent me a NEW controller and I installed it and it works fine. I fixed the old one and it is a light dimmer now. I would use one of those three phase mega Rectifiers and use the two AC terminals or a good 50 or maybe 35 Amp bridge rectifiers with at least 600 or 800 PIV or even better yet a 1200 PRV rectifier and go from there. A slight protection of L di/ dt and surges?

KB1UKU

muniorbust
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Re: AC Powered Motor Controller for DC Motor?

Thanks Spaceangel.

Let's say I were to buy a DC power supply instead of building my own.
Voltage, current, and peak current are important.
It sounds like peak reverse (inverse) voltage is important too.

Is buying a power supply for this application a reasonable path to follow?
Or is building one better? Safer? Cheaper?

I think I could build my own with some guidance, but I'll pass on it if I can buy one within reason.

colin9876
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Re: AC Powered Motor Controller for DC Motor?

How many volts is your DC motor? Lets say its 48v
Because of peak current draws it would be better to use 4 x 12v car batteries, and have them permanently connected to 12v power supplies.

You wouldnt have to even use new batteries, older ones would be ok as you are keeping them plugged in, and and use cheap car chargers.

muniorbust
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Re: AC Powered Motor Controller for DC Motor?

I haven't actually picked a motor yet. I've looked at robotmarketplace.com and saw a few that would be options.
Can you/anyone recommend another place to buy a motor likely to do the job?

So what is it about the peak current draw that makes batteries preferable over an AC/DC supply? I don't have much knowledge on power supplies.

colin9876
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Re: AC Powered Motor Controller for DC Motor?

I had a very early prototype of an electric unicycle, it was like a segway that self balanced (to a point)
when the motor changed from fwd to reverse it could pull high peak amps.

Why are you building this treadmill, is it for you to practice cycling?

I reckon you would need a fairly long ramp (>2meters) and a sensor to see where you are.
What computer / interface would you use to feed the sensor info back to the motor?

It sounds an interesting project, quite a challenge.
I think you would need at least a 500-1000w DC motor, so thats 20amps, perhaps drawing more when there are rapid changes in speed required.

Give me some answers to the above questions and I can give u some more thoughts!

muniorbust
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Re: AC Powered Motor Controller for DC Motor?

Yeah... I ride a mountain unicycle (muni) and it's cold and snowy here in Rochester, NY. I thought it would be cool to ride inside, and I'm a geek (software engineer) who likes to tinker. If my project works out, I could envision extending it. Maybe raising and lowering the front and back of the treadmill as I ride to simulate hills. Maybe all synchronized with a video. But that's way far away.

People have ridden unicycles on treadmills before, but it's very unnatural, since the treadmill is moving at a constant speed regardless of how fast you're pedaling. Ideally the treadmill will move at the riders exact speed, so he'll remain in the middle of the belt at all times.

I am using a microcontroller (Parallax Propeller) as the brains of my control. I have mounted 4 IR leds on the rim of my unicycle wheel. Using a Wii remote mounted about 6 to 10 feet to the side of the treadmill I can monitor the 4 leds at 100Hz. My microcontroller reads the IR "blob" positions from the wiimote and calculates the center of the wheel. I couldn't use a single IR led at the center of the wheel because my leg would cover it too often. I have implemented this part of my project, and with visual output to a monitor, it looks like it's working well.

So if I'm monitoring my wheel a 100Hz, I'd like to be adjusting my motor speed 100 times each second.
I've never controlled a motor before, but it looks like PWM is easily implemented on my microcontroller.
But, of course, I'll need a motor controller that inputs my PWM to handle the voltage and current required to drive the motor.

I weight about 170 lbs with my unicycle. I expect to normally be riding up to 10mph, but it's possible with a geared hub and bigger wheel to reach speeds just above 20mph... possibly someday.

I think it would also be cool to "idle"... the back and forth movement you see when a unicyclist is staying in one place.

I've done some calculations on required motor torque, but maybe the above info is enough for you for now.
Buzz

colin9876
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Re: AC Powered Motor Controller for DC Motor?

Wow sounds like you have some complicated stuff figured out.
the codeing on your microprocessor will be interesting.
Ok so if we call d length of the treadmill, x the distance you are along the treadmill, dx your speed,and you want to stay at d/2 then you want some kind of loop
if x>d/2 then dx=dx+constant (speed up) else dx=dx-constant ...etc..

Guess you will need some damping to stop it overshooting

Similar thing here
www.youtube.com/watch?v=pTawpTqxuiw

What size of motor did you calculate you would need? I think 500watts would do it if its geared ok, Im not sure how fast your top speed unicycling could be lol. I had a 500w motorbike that could do 20mph and had good torque
It will be a lot of work and experimenting to get it to work.
Good luck, keep us informed how you get on!

muniorbust
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Re: AC Powered Motor Controller for DC Motor?

I didn't calculate my motor needs in watts, but it oz-in.
I calculate 405 oz-in, but then doubled it to be sure.

mass (lbs) 200 (heavier than I need, but who knows who will ride it)
mass (kg) 90.718474
acceleration (m/s^2) 1.524 (estimated in my driveway)
force (n) 138.254954376
wheel radius (in) 0.815 (actually the treadmill roller. No gearing is represented in my calculations)
wheel radius (m) 0.020701
torque (newton-meters) 2.86201581053758
torque (in-lb) 25.3309743860289
torque (ft-lb) 2.11091453216907
torque (oz-in) 405.295589140771
double torque (oz-in) 810.591180475311

If you have any comments/suggestions about these calculations please speak up. I'm very much a novice at this.

The motor I am currently looking at is this Ampflow A28-150.
It draws 37Amps at peak efficiency.
At 24v that's 888W.

Would you go with a electric scooter/bike/go-kart motor instead?
Where's a good place to look at these online?
Ideally I could see some specs too, other than Watts.

Thanks
Buzz

memojazz
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Re: AC Powered Motor Controller for DC Motor?

hi..!!

I design y build AC motor controllers for EV systems
very similar to Azure Dynamics and UQM Technologies, but more cheap.
Live in Chile and ship to Europe & USA/Autralia.

Solutions for Cars, Trucks, Buses.

Note: Sell AC Controller, AC Motor (ACIM), LiFePo4 Batts.

Contac to me :

giturriaga1 [at] hotmail.com

Guillermo Iturriaga C.
Civil Electric Engineer
(56-9) 87311952
Santiago of Chile.

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