Also when interfacing the throttle (variable resistor) would I be better using a resistor/capacitor discharge time or using the analog to digital converter?
Running them with 12 volts is probably a good idea, but to do it since they are emitter followers you need to level shift the input to the driver up to 12 volts - like below: This will invert the signal so you will need to turn the micro upside down.
The gate resistor is a good idea as well.
Assuming the heat sink came of a 1 or 200 watt cpu, you should be able to run your fets at full power.
Don't forget about the diode. He can get pretty hot as well.
Edit: I think I would use the a to d converter to read the pot.
I would use a ready made current sensor module, like this +75A/-75A one from Pololu;Thanks, I may design a current limiter if I get my hands on a more powerful motor or decide to over-volt this one. What resistor would I use for a motor that draws ~40 amps?
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I would use a ready made current sensor module, like this +75A/-75A one from Pololu;
They have more choices on this page;
http://www.pololu.com/search?query=current+sensor&x=0&y=0
A really good technique with vehicle DC motoro control is to adjust both PWM and the current limit as the throttle is turned.
So low throttle settings have low PWM duty (low motor voltage) and also have low current limit. As the throttle is increased the PWM duty increases and also the max current. That gives a very natural safe throttle feel, more like a small gasoine powered engine.
If you don't reduce the current limit with reduced throttle you can get enormous torques at very low RPMs, which is great for locomotives but can be un-natural and jerky on a light vehicle like a scooter.
The driver is an emitter follower, so it's output voltage follows it's input voltage, minus a little, but it can supply more current to switch the FETs faster.
Since your thinking about changing FETs (good idea) and trying to reduce cost, why don't you think about loosing the micro and just running it with a simple 555 and one 12 volt regulator.
Sure, you could, but there is no reason to. The 555 can generate the PWM signal and can drive enough current to drive your FETs. The interface to the speed control pot is two wires. But you can't do anything else because it is all hardware.
http://schematiccircuit.com/pwm-dc-motor-driver-with-ic-ne555/
What's your budget?I'll consider it, but currently getting one of those sensors would literally double my budget. ...
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What's your budget?
That 75 Amp sensor module is $9.95 and the 31 Amp module is $3.95.
Surely you are not saying you budgeted only $10 to build an entire 50A DC motor controller?
Or is this some type of commercial design you are working on where every cent counts?
I have a couple 50v 10a diodes laying around, I also have a couple 15 amp 200 volt half wave rectifiers that I could use.I hate to sound like a nagging wife, but what diode did you get?
The diodes you listed are the same as the 1/2 wave rectifiers I was talking about. I have a dozen of them that I could use. 2 diodes in a 3 pin case similar to the mosfets.I was afraid of that.
The diode(s) should be rated for at least 1/2 the maximum motor current. So at least 25 to 30 amps. They should also be fast (not 1/2 wave rectifiers).
http://www.mouser.com/ds/2/115/SBR4045-92036.pdf
It will need to be mounted on a heat sink as well as the FETs, so be careful of isolation.
That's where I got mine, I had about a dozen computer power supplies that I scrapped a while back for capacitors, heat sinks, transistors, diodes, fans and transformers.You can get fast TO-220 diodes from PC PSUs, most PC PSUs have a couple of fast high current diodes in them you can strip out for free.
And sorry to hear about your cash problems.
by Duane Benson
by Jake Hertz
by Jake Hertz
by Jake Hertz