pwm schematic help required please?

[Jools]

If you measure voltage across the middle and right hand pin on the POT this should go from zero to 5v (or what ever the voltage in is) The missing central wire from the pot is the variable part of the voltage that controls speed. I would think that this should be wired up to your wire four from previous posts.

On mine I simply took out the pot and wired the PWM 10v in to the right hand pot connector (wire 1) (So I took my power from the machine) . The left hand ground to ground (wire 4). and the wiper to wire three. This controls mine perfectly.

Page 8 from this BOB manual helped me http://cnc4pc.com/Tech_Docs/C11GS-R1_1_USER_MANUAL.pdf though your's might differ. Though it may be the same.

This is my BOB's wiring digram though it was the same to my machine not using a VFD as they show.

Jools

[Doddy]

The issue here is that the OP's spindle speed control looks to be a digital PWM input drive, not an analogue input voltage. I accept this is somewhat different to the standard option on many speed-controllers on a standard spindle inverter driver.

In using the BOB the OP has inadvertently adapted the PWM output from the PC to an analogue voltage.

The Speed Controller looks to use only a PWM input.

The easiest test now would be to try to source the PWM output from the PC (looks to be available on pin 'P1' output on most BOBs), and feed this to the pin-3 of the speed controller. Connect BOB ground to pin 4. If this works at all - if the speed range is inverted (low = high speed, high = low speed) then write to confirm.

Or, if the PWM output from the PC (into the PWM input on the BOB) then look to remap via Pins/Ports from Mach to a different output than '1', and try again.

The original Pot set-up looks (a) to be mis-wired, and (b) likely intended to be a potential divider to scale input - whether this was PWM or analogue to a lower voltage/current. If the value of R5 is 4k7 then this just isn't needed for the opto-isolated input for any supply up to 10V (If ~= 4mA on the opto-isolator LED at 10V input). BUT, unless you get a PWM signal into it I doubt from the quick look at the board that this will give anything other than On/Off. The OP needs a PWM source.

EDIT:

OP: On the image of your BOB - what's the label on the fourth pin from the left on the top edge of the board (after the Red/Red/Yellow cables)? - Is that P1?

[john swift]

looking at the second photo in post 8
the BOB looks like this BOB



John

[Doddy]

looking at the second photo in post 8
the BOB looks like this BOB
John

Thanks John, that's very clear and I think supports my advice above.

[Tel 27]

Thanks John, that's very clear and I think supports my advice above.

Thanks for the replies gents - good to have people at least trying to help me despite my limited electrical understanding!

Havent had much time to look at it for a couple of days, but having read the reply about measuring the output voltage with the meter set on ac, it does indeed read 0.2v ac when programmed s1000 via mach 3 (assume that means its a result of pwm "wave"?)



As you can see pwm is activated to output on p1

[Doddy]

Be bold :) Just wire it up. There's not much that you can do via ribbon #3(+) / #4(-) to cock it up. #3 to P1, #4 to gnd.

[Tel 27]

Be bold :) Just wire it up. There's not much that you can do via ribbon #3(+) / #4(-) to cock it up. #3 to P1, #4 to gnd.

Well, tried that, (pwm to wire 3) the spindle fires up and goes to 3500rpm (when s250 m4 is mdi input on mach3)

Altering the s value makes no difference to the spindle rpm, (i.e. s25 gives the same 3500rpm!) although the pwm output voltage does alter accordingly...

any more ideas?