On Thu, 11 Mar 2004 23:56:08 -0000, you wrote:
I made the circuit in the files with the LM358AN and the 100K multi
turn etc. to drive my VFD.
Can only get about 5.5 vDC and it is backwards.
When I lower the speed in MACH2 it goes up and visa versa ????
I can turn on and off with SSR-to VFD and change the speed (in
reverse)to about 1/2 desired speed.
Hi Jack - just insert or remove the tick in Active low for PWM out pin
- that should sort the reverse action. Tuning "may" increase the
voltage, but I found I had to supply 14V to get 10V out. You should
still be able to get the VFD to work full range on 0-5.5V by setting
it's low/high limit pots.
I could never get anything like a linear response from the PWM so gave
up and went to step out instead. Still not linear, but much better.
I think the reason is a linear change in pulse width does not
represent a linear change in RMS voltage. Commercial circuits are much
more complex than the LM358 one. The Robot guys often use a PIC and
lookup tables to get a PWM to VDC linear response, too complicated for
me ;)
--
Steve Blackmore
