gary wrote:As a rule of thumb, if you are using the LR form of controller, you need about 10 times the steppers rated voltage. A lot of these steppers are rated at 2 volts or less (BTW when I say rated it has nothing to do with the breakdown voltage it is the voltage needed to bring the current up to the rated value), so a supply of around 20 volts is best but I am pretty sure I got up to 750 RPM on less than that.
BUT! above all remember that the rated current must not be exceeded (at least for any length of time) and so a series limiting resistor is mandatory - this form of controller is the least efficient (in terms of energy) of all the stepper controller methods, but it is also the easiest and cheapest by a country mile.
It is normal for a stepper to run warm, in fact very warm - the good ones are built to handle that.
Note also that with a bigger stepper the current will go up to a level where the ULN2003's are no longer viable (from memory they are about 1 amp - whereas the stepper I used required 2.5 amps). But don't forget when running in bipolar mode you just need 2 sine wave inputs (90 degrees out of phase).
To power it I used (to compare) a number of methods:
A power amplifier (very good but expensive, also reaching the required voltage can be a problem in some circumstances).
A push pull power transistor amplifier (good but was tricky to get going)
A class A amplifier pair using LM317s believe it or not (I never quite got this going at least to my satisfaction but is a plausible solution but requires hefty output capacitors).
I had intended to experiment until I had a cheap but effective controller that included ramping (essential) but got distracted and I will be more-or-less out of electronics design until I build my new shed which is a few months down the track I fear.
If someone else wants to pick the ball up on that all that is required is two power sine wave generators (and they can be pretty rough sine waves) with a common variable frequency - I was using a PC to generate the sine waves but it should be fairly trivial to use a cheap PIC or other micro controller. I think a simple push-pull amplifier will be the best solution but others may have further ideas - my main criterion was it to be cheap and simple.
PWM rather than LR may also be explored.
Hi gary thanks for the very informative reply ...thats very helpful putting me on to the bipolar ideas i find very interesting and i want to try out some ideas here.
I had not noticed the stepper getting hot yet gary as i am just running the circuit + diver ic and stepper off the same 5v power supply.
I have noticed the 2003 driver ic getting very warm but driving this on a higher voltage i have killed 2 other 2003's so i have been keeping it at 5 volts /// i do have a better driver ic but i had more of these to test with ..
I was using a H bridge for the L293 for bipolar idea but i think i should of just used a jk flip flop to feed it from the sounds of it ...
I had not thought of using sine waves for steppers i wonder if it matters so much at higher speeds if its a square wave or sine wave but i am sure you are right that they run smoother on a sine wave....i am going to look into this .
Yes cheap and simple is the way to go gary its no point if the thing costs to much it defeats the purpose ....i like trying what i handy .
I just got my large 6 wire 70's stepper out for testing a Sagem 20pp50 51 04 what ever they mean...i think its a stepper due to the wires but i can not feel the steps or they are very fine.......
Good luck with the shed yes takes a lot of time up the building projects i will play around with your stepper ideas for sure .