hello
can any dc solenoid be proportionally controlled by PWM or are there differences between PWM and 'regular' solenoids?

On/off solonoids have a different construction than proportional solonoids. I believe any proportinal dc solonoid can be controlled with PWM, but as far as I know a standard on/off solonoid will not be that controlable.

You can use PWM on any solenoid but whether it is controllable or not is another thing. You can control something without feedback and that hasn't been mentioned. A LVDT is used to provide the feedback. The controller must update quickly. The PWM frequency must be MUCH faster than the mechanical response otherwise the valve will appear to dither. If the PWM is fast enought the valve will not move and hold a constant spool openning.

A lot depends on the controller and LVDT electrical response relative to the speed of response of the solenoid and LVDT mass.

I am working on an excavator that has 2 solenoids on top of bank for each funtion. Putting 12v on either will make spool move forward or backwards. I built a PWM generator and applied to solenoid but it will only move spool at close to 100% duty cycle therefore I'm thinking these are not PWM solenoids ... but the broken panel I am trying to replace has PWM chips on it??? ... Is freqency setting on the PWM critical mine is set at about 32 Khz

thanks for the help

mark

quote:

Originally posted by glenville:Is freqency setting on the PWM critical mine is set at about 32 Khz

The frequency must be approximately right to operate in the linear region. Can you sweep the frequency?
32Khz is definitely fast enough maybe too fast.
You need to be in the linear region. See the graph between equations 26 and 27.
http://158.132.178.85/norbert/Papers/C012.pdf

I would have to study this before getting too deep and know more about the data for equation 11 use that to do a simulation using equations 8,9 and 10. Then can see the affects of making V a PWM signal. It would take about 4 hours of my time to work this out given the correct values for the constants.

I think it is cheaper to buy a new part(s).

This message has been edited. Last edited by: Peter Nachtwey,

great information thank you

certainly buying the original would be preferable but parts/schematics can't be sourced

if 12v dc or PWM 100%(or close to 100%) is applied to solenoid it opens full and the appropriate cylinder on the excavator moves at apparent full speed. There is another gadget associated with each pair of solenoids that may be a proportioal controller. It is black, round and has 4 wires(two have 5 wires). What I can't seem to comprehend is that if there is a proportional control with the black gadget why would the design bother incorporating the solenoid? and if the PWM chip on original equipment is for the black gadget why the 4 wires? I have had a hydraulics shop do a house call and 2 fairly experienced heavy equipment mechanics look at this and were not familiar with the black gadget. With the 4 or 5 wires ?linear stepper control ?liear actuator ... I'm really guessing here!

any help or input would be much appreciated

thanks again

mark

quote:

Originally posted by glenville:
great information thank you

I posted that to let you know that make a proportional PWM control of a ON-OFF solenoid is not simple. It wasn't really meant to be helpful except to steer you to some sort of off the shelf solution. Your description of wires and gadgets is not good enough. If you had a scope you can figure it out by tweaking the inputs and watching the outputs and then draw a schematic. That is a lot of work.

Can you buy another valve that can be controlled proportionally?

the machine I am working on has one valve bank controlling 8 functions. I will reprogram to be able to variably change frequency with a potentiometer (as suggested) while my joystick potentiometer alters the duty cycle. This will take a few days to program and test. To buy off the shelf componenets would require buying 8 bank proportional and the controller that interfaces with joysticks. The price is prohibitive.

I can repost after experiment with pictures and schematics(that I try and create) if worth while

again thanks for your input