12 years ago
jeeth

how can i design a speed controller for a 12v: 24amps dc motor. can i use an IGBT?

how can i design a speed controller for a 12v: 24amps dc motor. can i use an IGBT?
Top 4 Answers
12 years ago
jrrymiller
Favorite Answer
This is a fair design challenge. We have an electrified "Razor" scooter that has such a controller. Golf carts also must have a similar controller. Pulse width modulation is indeed the way to go. This sounds like a fun project.
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12 years ago
Ecko
A basic speed controller simply needs the PWM source, a switching device and something to control the motor back emf. Generally individual bipolar transistors are not rated at so much current, and power is lost in the switching, considering the beta may only be 10 or so. The IGBT is more suitable and available in bigger sizes. So are power MOSFETS, so it depends what you prefer. It may be necessary to have two or three devices in parallel for heat reasons. All three devices mentioned can easily perform this task. Consider the peak current during motor starting may be much higher, depending how you operate the system. To get regulated speed there needs to be a feedback control and a tachometer. This works much like the governor on a diesel engine. You need a three term controller (PID controller) for best operation. There can be inner and outer control loops to manage current and acceleration too, so it makes sense to buy a speed controller. If you only want to vary the speed manually like the throttle on a petrol engine, the circuit could be as simple as a 555 timer (or 2 of them) to generate adjustable PWM, with appropriate drivers for the gate circuits which are high capacitance. The switching speed only needs to be a few hundred Hz, but should be chosen so it doesn't cause mechanical resonances in windings etc. Be aware that the motor can get overheated if it has a fan and runs at low speed high torque. There are speed controllers for RC electric model planes that switch these sort of currents or more, using a variable width pulse to control the speed. The pulse varies from 1 to 2ms width for speed control, and needs to be repeated every 20ms or so. Maybe this suits your need.
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12 years ago
Anonymous
You *could*, but you'd probably be better off with an ordinary enhancement-mode power MOSFET -- you might find the voltage drop of an IGBT a bit excessive with just a 12V supply. I presume you're using some sort of PWM scheme, otherwise the transistor -- of whatever technology you use -- will be dissipating up to several hunderd watts of power. Lastly, don't forget that your catch diode will have to withstand the full motor current for a brief instant at a time. The current through an inductor cannot undergo a step-change; so if there is 24A flowing through the motor as the transistor opens, then there will be 24A ready to flow through the catch diode. This *will* blow a 1N4007 to smithereens.
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12 years ago
solo
The answers above are great. But Googling your question results in plenty of how-to's and examples, even with schematics too. Just to copy and paste a few of them that came up: http://hobby_elec.piclist.com/e_pic6_9.htm http://www.aaroncake.net/CIRCUITS/motorcon.asp http://homepages.which.net/~paul.hills/SpeedControl/SpeedControllersBody.html http://www.solorb.com/elect/solarcirc/pwm1/
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