7i76e Analog 10v Spindle output not working

If you only have 2.94V power the 7I76Es spindle interface will not work.

This probably means the motor control will not supply the several mA of current that the
spindle interface requires.

You can possibly use an ISOLATED power supply (like a wall wart) but you have to be very careful
because its all live. Also some potentiometer controlled motor circuits ( especially SCR circuits )
simple cannot be controlled by a variable voltage.

My understanding is that one the type of speed control in my mill the + and - on the potentiometer is at AC line voltage say - is 108 and + is 120 so whatever you do with these must be isolated. I accidentally grounded the E-Stop lead a while back and blew my speed control. I asked the guy that fixed it about controlling the speed from the Mesa 7i76. This is what he had to say:

Hi John - The key thing to look for is a variable output voltage (0-12 volts) that is optically isolated from ground. If your board can output that, then you will be OK. What gets everybody in trouble is trying to make a direct connection to P1-P2-P3 on the XMT board which will fry everything unless they have optical isolation. -Pete

John - I think you are looking for something along the lines of a C41 interface board. I'm not a CNC expert but you can speak CNC to this spindle control board and it will output a voltage that will control the XMT board in your machine - and it has a couple of relays you could use in conjunction with a reversing relay/switch for direction control

My mill has a potentiometer to control the speed so based in the description below it sounded like I could just swing the leads from the pot to the TB4 terminals. However I understand the issue with there not being enough mA which it why the voltage drops from 12.11 when connected to the 7i76

With the three wires from the controller still connected to the 7i76 TB4. Would I just take a wall wart and connect the negative wall wart lead to TB4-1 and positive to TB4-3?

Thanks
John

7i76
SPINDLE INTERFACE

The 7I76 provides one analog output for spindle control. The analog output is a isolated potentiometer replacement type device. It functions like a potentiometer with SPINDLE + being one end of the potentiometer, SPINDLEOUT being the wiper and SPINDLE- being the other end. The voltage on SPINDLEOUT can be set to any voltage between SPINDLE- and SPINDLE+. Polarity and voltage range must always be observed for proper operation. The voltage supplied between SPINDLE+ and SPINDLE- must be between 5VDC an 15VDC with SPINDLE + always being more positive than SPINDLE-.
Because the analog output is isolated, bipolar output is possible, for example with SPINDLE+ connected to 5V and SPINDLE- connected to -5V, a +-5V analog output range is created. In this case the spindle output must be offset so that 50% of full scale is output when a 0V output is required. Note that if bipolar output is used, the output will be forced to SPINDLE- at startup or when SPINENA is false.

Well I finally got the spindle speed control to work. Not perfect, it still needs some tuning but it looks like I'm getting about 500 rpms more than I get with the manual pot. I still have to get the all of this hal stuff straight in my head but I think t he key here was getting a 12 volt wall wart power supply hooked up to TB4 per PCW's suggestion.

At value 1 on hm2_5i25.0.7i76.0.0.spinout the spindle is still turning very slowly. If I click on the stop button hm2_5i25.0.7i76.0.0.spinout goes to 0 and the spindle stops. I think I read somewhere about someone else that had the same problem.

Thanks Guys
John

JohnnyCNC wrote: Well I finally got the spindle speed control to work. Not perfect, it still needs some tuning but it looks like I'm getting about 500 rpms more than I get with the manual pot. I still have to get the all of this hal stuff straight in my head but I think t he key here was getting a 12 volt wall wart power supply hooked up to TB4 per PCW's suggestion.

At value 1 on hm2_5i25.0.7i76.0.0.spinout the spindle is still turning very slowly. If I click on the stop button hm2_5i25.0.7i76.0.0.spinout goes to 0 and the spindle stops. I think I read somewhere about someone else that had the same problem.

Thanks Guys
John

Did you ever resolve this issue? I'm setting up a lathe with a DC motor and speed control. I also get 12 vdc across P1 and P2 when not connected but when I connect them to the isolated digital pot on the 7i76 I only get the spindle turning slowly with no control.

Yes. I used the Lincurve function where you can map the commanded speed to an actual observed speed. You can map up to 16 points along your speed range to the actual speed. If you find that say 1500 RPM commanded is actually running at 1350 you would map 1500 to 1400 and see where that lands your speed. If still off then adjusted again until you get the correct result. I later switched the motor to a DYN4 servo motor and switch to using the PID to control it.

linuxcnc.org/docs/html/man/man9/lincurve.9.html

John

Thanks for the reply, I ended up adding an extra isolated 12vdc power supply and then just adjusting the gain on the pots of the speed controller. I am curious though how you like the dyn4 servo as a spindle motor. Any complaints? I've planned on replace my spindle motor with something similar if the DC motor/controller ever gives in.