Using MESA 7i76e PWM to control 5-7kw DC motor.

Hello everyone, 

I'm working on 2 lathes (a Hardinge CHNC Super Precision & a Hardinge HXL Super Precision), retrofitting to LinuxCNC, each will have a Mesa 7i76e. I've done some bench testing now and proceeding to fitting the additional components into the control cabinet of the first lathe. Integrating the 7i76e is going very smoothly so far, and as I have learnt more about these cards I have arrived at the following question: 

Is it possible to create a section of code to run as a motor controller within Linux CNC using the 7i76e as the interface/PWM generator to control an array of MOSFETS (or similar) to drive the original 7kw, 90v DC motor that is on this lathe? I would like to impliment current control and figured it might be possible to read a current sensor signal using one of the analog inputs on the 7i76e and use that to perform current limiting. 

The motors have a DC tachometer and the spindle has a TTL(I think) encoder. The original 90V DC power supply is intact. I will need to make a custom 100V x 70amp switching system and control architecture (MOSFET driver etc).

I am looking for suggestions toward the feasibility of this implimentation, any examples of this already implimented, where this code would run within LinuxCNC (still new to the platform), and electrical considerations to investigate. 

Any feedback will be much appreciated. 

Thanks, 

Bennett

 

You might be able to do something with just a PWM output.
PCW has been looking at a triac controller inside the Mesa firmware.

forum.linuxcnc.org/27-driver-boards/4608...ntrol?start=0#244833

Interesting. I wonder if I can get the PWM outputs for spindle control to to react to current sensor input and regulate accordingly. Much to learn. This triac control system looks promising but my limited knowledge on this matter has me unable to gauge it relevance.

Thanks for these notes! 

Awesome. Very cool about the BLDC HAL component. It would be cool to have a DC brushed one that works with current limiting, too, and it's looking like these components can be made without TOO much trouble...that could be my naivety speaking...

I think the analog inputs on the 7i76e are 8 bits, so a range of 256. Seems good enough for some simple current sensing - It just needs to reel itself back when the system is about to fry itself. This thing is going to run on 600v 3-phase with a dog-simple linear DC supply, so plenty of current to fry everything if left unchecked.

I will report back with some findings.