harry dalek wrote:
Hi Gary i am using a 5 pin unipolar that looks like a 4 or 6 pin bipolar ,i do have a few of those about as well....have to say that is a simple circuit saves a lot of electronics .
Unipolars can be run as bipolars normally but a 5 wire unipolar has the centre taps tied together and as far as I am aware can only be run in unipolar mode, so yes that is a problem.
harry dalek wrote:Does it just work off 12volts bet the stepper gets hot ?
Harry the higher the voltage the better because it helps to overcome the inductance of the coils, however if the voltage used causes the maximum current to exceed the motor's rated current, the current must be limited somehow. There are a number of ways to do that but the easiest by far, and the way I do it, is to use a high wattage series carbon resistor, or, as I do in my CNC machine, a car light bulb (it's fun watching them light up).
The series resistor is calculated using ohms law - just measure the resistance of the coil and use ohms law to determine what series resistance is needed to limit the current I = V/(Rcoil + Rseries).
I would like to emphasise it is very good to have a higher than rated voltage - however if you have a transformer just the right voltage then give it a go and see.
harry dalek wrote:What governs the speed Gary the line frequency?
The speed is indeed determined by the frequency according to that formula I posted earlier in this thread.
harry dalek wrote:could you use say instead of just line Ac transformer a 555 timer at that frequency feeding a mosfet perhaps also turning that square wave to a sine wave before the trany sounds like a simple way to get speed control out of a stepper?
Well that's more-or-less what Steve and I have been discussing - using a 555 is fine provided it gets turned into a true AC sine wave (true as in bipolar swing - the shape can be a little rough but not too rough).
It's sounds simple until you realise you have to turn it into a bipolar sine wave (i.e. the voltage swings sinusoidally from +V to -V (NOT +V to 0V).
It sounds simple and I have done it in a few ways but it isn't all that simple and can be expensive. A single mosfet won't cut it - you are probably familiar with a H-Bridge motor driver? It's something like that but for sine waves rather than square waves.
The simplest way is to use a push-pull amplifier with a dual power supply.
OTOH f you have a high power stereo amplifier you can press into service your work is done. (Note that is just what Albert did for his Edikow - it is exactly the same principle).
I suggest you try and stick to just the transformer and cap for now if it is suitable.
Just an extra point though, because I can literally hear the gears in your head turning, if you are thinking in terms of high speed (e.g. 750 RPM) then a high driving voltage is essential and the speed needs to be ramped up to speed to avoid the resonances that occur in the motor. That becomes a bit tricky but I have done it and it works well.