Hello to you all,
This is my first post in this forum, as it seems to be very good in ideas!!
I have a problem at the moment, I want to control the speed of a Motor using a Microcontroller PIC. I said I can used an Opto-Coupler, but here is the problem:
When I connect this Motor to a 24volt Battery this Motor take 15Amp when the LOAD IS CONNECTED.
15Amp is tooooo much, so any ideas, how can I control the speed of such thing.??
Is this a 24v DC motor you’re using? How much current is the motor supposed to draw? If this is a good sized motor, 15A may not be out of line. Also know that motors draw more current when stalled (power applied but the shaft isn’t turning).
What you may need is something to limit the current and something to limit the speed. A microcontroller can generate a PWM (pulse width modulated) signal feeding a H-Bridge to control the speed and direction of the motor. The controller can also sense the current and adjust the PWM signal to ramp up the motor or stop it if a dead stall is detected.
Fortunately, there has been a lot of work done in the area, and a Goggle for “PWM H-Bridge motor” will be very fruitful.
Thanks riden for your reply!
The motor that I have draws about 2 Amp when there is no load on it, but when you put it on the ground to move an object it draws 15 Amp, and the object does move :D. So, it the motor have got to have a maximum current which equal 15 Amp to move.
Anyways, about the H-bridge, the best that I could fine was 5 Amp here in my country L6203, but I need something to go up to 15 Amp, so is it possible to put 3 H-bridge in shunt, such that the three of them sum up to 15 Amp??
If it draws 15A under load then it might spike 30A stalled. You might try www.roboticsconnection.com, they have some high-end H-bridge boards that might do the job. Just don’t expect to find anything cheap. That’s industrial-strength current and you’ll need an industrial-strength driver.
The newer 18F and 16-bit PICs have enhanced PWM that doesn’t need a separate H-bridge chip. You need MOSFET drivers, of course.
Leon
The PIC16F690 has the ECCP H-bridge also, pretty much identical to the 18’s. The 16F616 has a slightly downgraded version of it. They’re a pain to debug because you need a bondout module, but the functions are available.
I think the real problem is 30A worth of FETs per leg… that’s whopper current and will make some whopper smoke from any shoot-through. If the OP wants to DIY a design, all I can say is be careful!
Have you had a look at some of [Infineon’s chips? Something like their [BTN7971B may work well for your application…
If not, just look for anything automotive, usually helps when dealing with high currents…](Opn - Infineon Technologies)](Products - Infineon Technologies)
Wow, that IC is a boomer. It would certainly do the job, the OP can just rig the full bridge circuit shown in the application section and replace their uC with a PIC. Only problem is, I was unable to google a supplier. Who carries them, Monk?
FindChips doesn’t show any stocks at any of the usual suppliers, they are probably only available from Infineon distributors. You might be able to scrounge a couple of samples.
Leon
I’m sure i put that part number in Digikey last week… Not there any more. 
DigiKey lists a little brother, the BTN7930, which is rated 20A on the high side. Since it has built-in protection, it would probably do the job for the OP. They don’t show any stock, but they do show it available in qty 1 under p/n BTN7930BINCT-ND for $7.17US. I presume that means it can be had with a lead time.
Another option for the OP would be to take the easy way out and turn to [Pololu… :roll:
One board i found, relies on the OP’s motor spec’s being correct tho… - [Pololu High-Power Motor Driver 18v15
Myself, i’ve never been too keen with Pololu’s products. They hardy ever give datasheets and even scub out the IC numbers in the pictures!
Don’t know they manage to get patent’s on some of their products…
But i’m not stopping anyone from using them if they want to. 
Or yet another option is to learn how to design a reliable, discrete H-bridge!
There’s lots of website through Google that explain the designs alot better than i could.](Pololu High-Power Motor Driver 18v15)](http://www.pololu.com/)
I think most of Pololu’s patents are simple design-specific stuff that keep folks from knocking off the exact design. Not much different from copyrighting the PCB art, and not hard to design around.
The OP would need to be careful with that Pololu board anyway… I’m assuming this is a robotics app, and that board specifically discommends use with 24V battery systems.
As for discretes… like I said earlier, if he wants to try it, my best advice is to keep a fire extinguisher in a very handy place. 