How do you control a 1/2 HP DC Motor using a microcontroller?

Discussion in 'General Electronics Chat' started by aegistalons, Jun 3, 2011.

  1. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    I am going to be using a 1/2 HP DC Motor for a project where I need to do position control. It requires 180VDC and a maximum of 5.2 Amps and can spin at 1800 RPM. I have worked with smaller DC motors, but not ones rated by HP. When I use the smaller DC motors, I am typically controlling it with PWM via a microcontroller, which is coupled to a H-Bridge that provides the real power to the motor.

    I would like to either buy an cheap off the shelf component that can do that, or build my own. I don't know where to start. All the H-Bridges that I have looked at on DigiKey are not rated for this amount of voltage and amps. I'm probably looking in the wrong section.

    Any help would greatly be appreciated.
     
  2. BillB3857

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  3. strantor

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  4. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    It seems that KB controls is a little expensive for this project. What would be required to make an H-Bridge for this powerful of a motor. Like I said, I'm used to just having the microcontroller connect to the H-Bridge and the H-Bridge drives the motor. I only need to control 1 motor bidirectionally. Is there something like a L298 that is more beefy and I can just design a simple circuit around it?

    Or, do you guys have a recommendation for a motor that is 1/2HP with relative high RPM (1800+) and draws 12V and relatively inexpensive? Here is the one I mentioned in the first post: http://www.automationdirect.com/adc...-_180_VDC_Armature_(0.33_-_2HP)/MTPM-P50-1M18

    Thanks for the help.
     
  5. strantor

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    A used car starter from the junkyard? I have heard that they go aout 6000rpm with no load (you don't want to run it with no load though), but they will draw alot of current, so you might need a way to limit that. should be able to pick one up for dirt cheap.
     
  6. shortbus

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    Why not build your own H-bridge using mosfets and mosfet drivers? You will still have to supply the 180VDC but that doesn't have to be a fussy power supply for a motor.
     
  7. pistnbroke

    Member

    May 9, 2011
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    starter for a small car 11000 rpm at 40 A
     
  8. strantor

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    What do you mean by that?

    Do you need to maintain a constant speed, with varying load?
    Do you need to maintain a constant torque, with varying speed?
    Do you need to maintain a setpoint, varying torque and speed (PID)?

    If the answer to any of these is yes, then you may yet need to consider getting an off-the-shelf DC drive. these scenarios require feedback loops and (I have never attempted it, but I assume...) would be pretty complicated to engineer. Who knows, you may be able to do it easily with your microcontroller and PWM, but you may also waste alot of time and then end up buying the drive in the end anyway.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    If you are doing position control, I assume (yes, I know what that means) that you will be using a bipolar velocity command that is generated by comparison of commanded position to actual position. In that case, you will need a stable velocity loop with tachometer feedback. Another approach would be to use Brushless DC motors and an appropriate controller. Most of them will accept step/direction commands.
     
  10. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    The DC motor will drive a pulley system that drives a trolley. I need to know at all times the trolley's position. I will mount either an optical encoder to the pulley or some some magnets combined with Hall Effect sensors to get feedback. As the pulley rotates, I will count steps that will corresponds to how far out the trolley is. So it will be a constant load, but I will vary the speed. As for the home position, that will be done with a switch that will get trigger that resets the count.

    @ShortBus - I think that may be the cheapest route right now, building my own H-bridge with MOSFETs and MOSFET drivers. The company I have in the link has motors that can be either at 90VDC (~5A) or 180VDC (~2.5A). Would it be easier if I selected the 90VDC one, simply for power supply reasons or it doesn't matter that much?
     
  11. shortbus

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    Like the other guys said with this type of motor exact positioning is going to be a real pain. At 1800rpm you will need to shut it down before it gets to position and allow for the coast down of the motor, or add a brake to the motor.

    Knowing what you are trying to do would get a lot more ideas to help you. Have you thought of using a stepper motor? They in move to a more precise movement and the 'NEMA' series of motors are VERY powerful.
     
  12. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    Would running a little bit in reverse work to help it brake, or would it damage the brushes inside? For this project, I don't need to have absolutely good position, within 6 inches to a foot will work. But, I don't want to have something go on the trolley for 15 ft when I told it to go 10 ft.

    I was also looking at potentially using a motor from an electric scooter. Found this website: http://www.partsforscooters.com and I'm specifically looking at this model: http://www.partsforscooters.com/Electric_motor_350w . It's also nice because it looks like it features a control system with it, but I think it's overkill for what I'm trying to do.

    What do you guys think is better? Getting a motor at 36V or 24V but requires lots of amps, or a motor at 90V or 180V and requires at most 5 amps? Also I'm still looking at DigiKey, and I don't know what kind of MOSFETs I need.
     
  13. beenthere

    Retired Moderator

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    Might you get further using an Acme nut? Lots less slop than pulley systems.

    Either way, you have no means of holding the motor in place once it has moved the trolley to the desired position. It's possible that if we knew what you were trying to do, and what degree of accuracy in positioning you need.
     
  14. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    I am modifying a design of a small trolley system that has the motor stationary and drives a pulley. The pulley moves the trolley back and forth on a horizontal rail system. The current system is designed with simply a switch in place and the user flips the switch and the motor goes one way and flips it the other way, and the motor goes the other. The system I want to implement is where the user enters a distance say in feet with an accuracy of about 6 inches. The motor will spin up and drive it the trolley and stop it around that area.

    Unfortunately, I don't have access to the motors that are used in the present systems so I need to choose another one. Once the trolley is moved into position, the motor can shut off and not worry about the trolley moving as there will be little to no load on it.

    Hope that answers some of the questions.

    Edit: I also found an interesting H-Bridge that could potential drive a 24V motor. http://www.robotpower.com/products/simple-h_info.html
    It can do 24V at 25A and it could work with this electric motor: http://www.partsforscooters.com/Electric_motor_500w

    What do you guys think?
     
    Last edited: Jun 7, 2011
  15. BillB3857

    Senior Member

    Feb 28, 2009
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    Get a garage door opener and have your position control operate forward/reverse relays. Plenty of power, reverse function already worked out, etc.
     
  16. aegistalons

    Thread Starter Member

    Feb 12, 2011
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    Hmm, a garage door opener? Those are slow but high on torque. For this project, I was thinking something that is fast and has a decent amount of torque. That's why I was thinking the electric scooter motor would work for this application as it would send the trolley down the rail quickly.

    If the 500W 24V motor is rated for 27.4A, it is ok running it at 20 or 25A. It would just not produce as my power, correct? Would it still get up to its max RPM, or does that depend on the torque curve of the motor?

    So does it seem reasonable to use the 500W 24V motor with the H-Bridge that I linked to earlier? Additionally, if I go with a 24V motor, what power supply do you guys recommend?
     
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