90VDC, 1/2A Programmable Motor Controller: Any Leads?

Phil Pilgrim (PhiPi)

Today I was called to service a painting machine I built 18 years ago and that quit working. It uses a Z8 microcontroller whose firmware is (was?) contained in a DS1225 NVRAM, date code 1988. Yikes! (I guess the lesson is, if you sell a system with NVRAM, change your phone number before the battery dies. )

Anyway, the triac motor controllers I built for the unit never were that great, so I'm thinking about stripping out the electronics altogether and starting over. The machine uses two 90VDC 1/30HP gearmotors for which I need programmable speed (open loop) and direction controls. Parallax doesn't offer anything that will operate at that voltage. Can anyone recommend a programmable 90VDC motor controller — preferrably with built-in optical isolation — that would play nice with a Stamp or Propeller?

Thanks,
Phil

T Chap

Phil

You know way more than me about this, but just out of curiosity, why not a PWM'd SSR and relay for direction?

Phil Pilgrim (PhiPi)

That's basically what I'm using now. I have a PIC that operates as a coprocessor and monitors the 60Hz for zero crossings. It switches a triac on after positive crossings to make the motor go one way; after negative crossings, the other. How long after each crossing it fires the triac determines motor speed. But a DC motor doesn't run very smoothly with this kind of control, since the pulse frequency is only 60Hz. Packaged SSRs would have the same problem, since they can only turn off at zero crossings. More modern controllers use switching techniques with much higher frequencies and, with the aid of the motor inductance, produce a constant drive voltage.

I'd prefer not to build a motor controller from scratch, since my customer is desperate to be back on line ASAP. I'm sure there are controllers out there that will do what I want, but all the ones I've seen so far use knobs for speed and switches for direction — not digital inputs. Eventually this machine may end up in China. So the less on it that's home-built, the better for me! (I do draw the line at using PLCs, however, since my ladder logic programming skills are pretty sketchy.)

-Phil

T Chap

Thanks for the explanation. I have not been happy with performance using an SSR on a 10k 1/5HP CNC spindle. It is fine above 3k, below it is very unstable, so I just run everything higher. I have no control over the PWM, it is generated off the PC(Mach3). So, who knows if a Prop based system would improve it, since I would have more control of the parameters. I am anxious to see what you turn up.

You would certainly get some good ideas on cnczone.com.

stamptrol

Phil,

I've built a couple of neat little SCR variable speed drives for some 90VDC, 1 HP motors. Gives great speed control and should be adaptable . Don't have the circuit with me at the moment but will dig it out tonight.

The SCR's are great for high voltage stuff but you may need a relay for forward - reverse to keep the circuitry reasonably simple.
··· Update:· Phil, I had a look at the drives suggested by Jeff.......for the price, I wouldn't consider rolling your own. A couple hours of labour and you can by one of these drives. Tom


Cheers,

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Tom Sisk

http://www.siskconsult.com


Post Edited (stamptrol) : 1/25/2007 8:17:39 PM GMT

Unsoundcode

Hi Phil, we use Extron drives a lot I think they are priced reasonable. http://www.extroncompany.com

Jeff T.