Universal Motor Control

Hi,
I have a 110v 5amp universal drill motor. I wish to design a motor controller which will allow speed and direction control, and interface at
TTL to a PIC uC. I can run the motors in AC or DC. The motor is a series or universal type which requires the polarity to be switched at the coils in order to change direction. There are 4 wires going to the motor, 2 for the stator and 2 for the rotor coils. Shorting either side of the coils will change the motor's direction.
I have looked at crydom.com solid state relays to switch coil polarities, but it would required 6 relays for each motor. ( running on DC and PWM the relay ) I also have looked at using igbt/mosfet combo, but I would still need to find a way to change polarity at the coils...
Can anyone point me to any designs/schematics/appnotes available somwhere on the web to accomplish this?
Cheers, Steve
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Well, besides 110v DC or AC being exceeding dangerous, nowadays they hold people liable for damages or injuries related to this too. It makes it difficult for people to want to offer advice as to how to do this. Lawyers are expensive. I am not responsible if you injure or kill yourself in this endeavour, or cause any damages.
Are you wanting to run the motor off of single phase AC or as a DC motor? Are you wanting to use the motor as a series wound motor or a shunt wound motor? This motor isn't a compound wound motor is it?
If you are wanting to run the motor as a simple DC motor then a circuit like this would work OK http://electronickits.com/kit/complete/motor/ck1400.htm Depending on the MOSFET supplied, you might have to change it out for a higher voltage rated transistor.
Changing directions on a 110v DC motor under power is a spectacular undertaking. makes for a spectacular parts explosion, smoke, or fireworks too. For safety reasons, you would have to slow the motor down, stop the motor, then reverse direction and power it back up. Otherwise the reaction is like trying to jam your car into reverse at 60 mph, and you succeed. Thus you need to program the MCU to never allow this condition to occur.
I am planning to use some www.irf.com IR2104 half bridge motor controllers to drive N-channel MOSFETS at 130vdc for some motors I have. But I haven't got around to it yet. But I have used the chips to build H bridge motor controllers to run motors up to 48v and 120amps so far. The IR2104's are rated up to 600 volts so they should work OK. The IR2104's higher voltage cousin is rated up to 1200v. The IR2104's drive the IGBT modules quite well too. I would use high speed optocouplers from the MCU to the motor controller also. You need high speed optocouplers as the regular ones are too slow at higher PWM frequencies. The main disadvantage that the IR2104 has is that you cannot go to 100% duty cycle as the PWM pulses are used in the charge pump circuit for the MOSFET gate voltage. Thus you can't go over 90% - 95% duty cycle. But I haven't found that to be a problem for my purposes. www.IRF.com happens to have a lot of nice MOSFETS to choose from too. I would choose MOSFETS rated at 15-20 amps and atleast 200v max, preferable 250v. Plus you also want the ones with the lowest RDS rating you can get too (helps to keep the heat down). Also choosing MOSFETS that have the insulated mounting hole and backplate makes it a lot safer too. Also, you build and test the controller using lower voltages and work your way up to 110vDC carefully.
One thing to note is you have to use new parts from reputable dealers or distributors, not the surplus market. Especially the capacitors have to be new fresh parts, not parts that have sat on the shelf for years. I have run into surplus parts that have turned out to be rejects that, instead of being melted down, have wound up back in the supply channel. I have also ran into parts that have been relabeled as different parts. So it's a buyer beware scenario out there nowadays. So when your building a high power motor controller, you definitely need to know the parts are good.

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ACIT wrote:

Reliable speed and direction control needs more than switching field coil polarity. This site might help: http://truetex.com/servomod.htm It describes use of an encoder on the motor shaft to make any permanent magnet dc motor into a servo motor. Your universal motor can be used in the same way only difference being you have electromagnetic field coils rather than permanent magnet fields. The Renco brand encoders are excellent, inexpensive, and can provide you with signals for position control, speed control, torque control, and direction verification. Depending on your application you might also wanted a gated index signal that would allow you to register the motor shaft position at start up.
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ACIT wrote:

When I built a low weight RC model airplane engine powered DC generator using a permanent magnet dc motor I came across web sites that had useful circuits on them that might also be useful to your effort to adapt an electric drill motor to a servo application. (an excellent project because mass produced electric drills have the step down gearing for low speed high torque applications like powering robot drive wheels, and they are relativily cheap). This site: http://www.discovercircuits.com/P/pwm.htm has many PWM circuits that you might want to try. By the way if you use the universal motor in the shunt wound configuration but keep the field coils on a separate circuit, and use DC for the rotor, you can operate it like any PMDC motor. Increase the field coil current to increase magnetic flux, and use any simple PWM circuit to power the rotor for servo operation.
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ACIT wrote:

This reply is in addition to my other replies. You didn't ask about them but rotary encoders are the way to get reliable signals for speed, torque, and direction control.
Since I work at a company that also makes encoders I might as well inform you how to make cheap encoders, rather than buy expensive ones.. Here are some web sites that have the parts, and articles about how to do it: http://www.tecel.com/parts/coderdisk.html http://www.usdigital.com/products/em1-heds/ The first site sells cheap code disks with low resolution, and simple slot sensors. Adequate for motor speed control, torque control, direction sensing, and position sensing when you use the optical sensor output to also count a binary counter. You want to use the quadrature output design. The 2 parts- the code disk and sensor- can be bought for $10, and will provide the necessary signals for a servo controller. The code disk will need to attach to the motor shaft, so you will need to drill your own center hole in the code disk and glue it onto a hub with a center hole the shaft diameter. Then either glue the hub to the shaft or use a set screw. The second company makes code disks of higher resolution and modular read head assemblies. From them you can build your own rotary encoders for less than $25. This design also outputs an index with the quadrature signals thus allow you to register motor position before counting up or down with a binary counter. If you want to do even less expensive go to these web sites: http://academic1.bellevue.edu/robots/tanner / http://www.geology.smu.edu/~dpa-www/robo/Encoder/pitt_html/encoders.html Here you make your own code disks out of paper, and use inexpensive optical sensors. Digikey has even cheaper slot sensors that can be used. There are many variations of these designs. In the commercial field high resolution code disks putting out quadrant signals can be divided down as well as counted allowing varying resolutions depending on your application. The circuits for the incremental are the simplest you will find in encoders and should pose little problem when building the servo.
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