Stepper motor controller help please

I recently acquired a programmable stepper motor controller. It was made by Richmill Manufacturing Company Ltd. around 1982. It is designed to drive a unipolar stepper motor. The guy I got it from said it worked fine when he put it away and then upon trying it about a year later it only works intermittently. I did discover one wire in the cable that goes to the motor does not have continuity. This wire is one of the two common wires that are the center taps of the motor windings. I do not have the motor. I do not have a schematic and so far have not been able to find one. I have not applied power to it yet. It has a 3.6 volt ni-cad battery that is used for memory backup and it needs to be replaced. I need advice about replacing electrolytics. Though none are bulging they are old and have not had power running through them for a long time. Should I just replace them as a preventative measure? I have heard about "re-forming" electrolytics. Should I even bother trying this? There are only about

10 ofthem so they would be cheap to replace. Another question is would it be safe to try to power up and run the control without connecting a stepper motor? Looking at the board it appears that 4 power transistors switch rectified 50 volts AC to the motor coils. I thought about just trying to turn the thing on and trying to program it and see if it at least thinks it is doing something. Since I don't have any large steppers I thought about connecting a 12 VDC 500 mA power supply in lieu of the rectified 50 VAC to the circuit board and using a small unipolar stepper to test the controller. Finally, what I would like to do is connect the controller to a circuit that would convert the unipolar switching signals to step and direction so that I can use a Geckodrive servo amp and a servo motor. This way I can run whatever size motor I want connected to an indexer that I am building. Thanks, Eric
Reply to
etpm
Loading thread data ...

powering it up with no motor should not be a problem.

We use some sort of burden load if we don't have a motor to test them. This is also where a 4 channel scope works well.

Jamie

Reply to
Jamie

Why not buy a modern USB stepper motor driver?

--
John Larkin         Highland Technology, Inc 

jlarkin at highlandtechnology dot com 
 Click to see the full signature
Reply to
John Larkin

Thanks for the reply Jamie. Do you think I should replace all the electrolytics just to be safe? If none are bulging and they test OK with my $90.00 DVM do you think it is safe to leave them in? Eric

Reply to
etpm

Greetings John, This controller is a programmable controller meant to be interfaced with a CNC machine tool. So the controller is programmed to make certain rotary moves when the CNC machine asks it to with an M code. After finishing the program it sends a signal back to the CNC that is is finished and the CNC continues with its program. I would rather not buy a NEMA size 34 stepper when I already have servos and servo amps slated for use in an indexer I'm building. So this programmable device came along which will save me the time of building one with an Arduino. If it works. Eric

Reply to
etpm

It depends on what kind of drive system it is. If you have a ESR meter you could check them for high R, which is common in aged caps and if the circuit depends on low ESR you could introduce unwanted noise in the output or maybe even fail under load.

Unless your meter has a ESR/D function on it, it would be hard to determine this. Of course many of us like to pump a square wave into a cap and measure the drop across a known R feeding the DUP (device under test), which would be the cap. The idea is to measure the initial charge point at the start of the square wave to calculate the level of volts detected and perform some math to determine the effective Series resistance in the cap. Caps do not have absolute 0 ohms at the initial state of charge of a fully drained cap.

If this is going to be for you're own personal use, I wouldn't bother replacing them if they appear to be ok via a standard cap test. If you have plans to sell it, I may consider doing so.

Jamie

Reply to
Jamie

My meter just measures capacitance. The reason I'm worried about the caps is that if one is bad could it destroy something like the EPROM which holds the operating system of the controller. But if that's not something I need to worry about I'll just power it up and see if it sends pulses to where and when I think it should. If that tests out OK then I need a circuit that will convert the unipolar stepping sequence into step and direction. I could probably figure out how to do this myself, and maybe I should for the learning experience. But I do have a job coming up that would benefit from using this programmable controller. Eric

Reply to
etpm

Just put the two on separate power and drive it with an isolated device.

You should be doing that anyway to make sure you don't get any high potential coming back into sensitive circuitry.

Jamie

Reply to
Jamie

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.