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Mad Modder speed control for DC motors...

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Dawai:
A H-bridge control with current feedback is what you need. I wasn't trying to be smart saying it is cheaper to buy a drive, but it really is..

with a H-bridge, you have 4 power transistors and a big heat sink to dissipate the "lost power" or braking heat.
it is a push pull arrangement with two transistors doing a forward current, and two doing a reverse flow.

A good universal transistor to learn & play with is a IR540 FET transistor. it takes logic voltage input and can source (bad memory) 27 amps or so. With the logic gate you can tie it directly into a output pin on something like a basic stamp or a arduino processor. From that point you PWM (pulse width modulate) the signal going out to vary the amount of power it passes. Last similar project I had about sixty - eighty dollars in parts.

Setting up a dc motor and drive, you turn the max pwr adjustment all the way down, back up just a tweak, put a pipe wrench on the motor shaft, put your dc current meter inline with the motor, turn on the drive and turn the drive up to "YOUR motor nameplate power out", this will take a minute or two, it will heat up pretty fast under full current, but not burst into flames.. a dc motor can stall out and still apply torque pretty well.  THIS way, the dc drive will not "over current" the motor and burn it out, but stall when it reaches the max load the motor can pull.

The current feedback circuitry inside a dc drive is basically a inline resistor with a voltage drop across it comparative to the amount of power being pushed through it, used to be all IC circuits, now days it is a micro-processor.  I installed one dc drive that I as there from 8pm to 4am trying to program it without a booklet telling how..

Last real big dc motor I had, I put on a water wheel in a creek, a old truck axle, tied it directly to a heater coil inside the house and a switch on the wall, it'd never really heat the heater up red, but it put out free heat.. and I like free.

Look to the HF router speed control.. cheap, sometimes on sale.. I have one here, it is tied into a pvc welder to control the heat. it has no true feedback thou. Motor speed would vary with load.

BaronJ:
Hi Guys,

These are links to useful application notes.  It deals with several motor configurations.

<https://www.fairchildsemi.com/an/AN/AN-7511.pdf>  and
<http://www.nxp.com/documents/application_note/APPCHP3.pdf>

Also see this thread: <http://madmodder.net/index.php/topic,8693.0.html>

HTH.

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