# Solenoid control/function question

Discussion in 'The Projects Forum' started by gte, Jul 20, 2010.

1. ### gte Thread Starter Active Member

Sep 18, 2009
347
4
I'd like to understand the functions of solenoid control in a DC environment. Right now I have pulsed solenoid control, it's square wave, 0 to 10vDC and it cycles at about 312hz.

I believe the way the solenoid is controlled is duration of each cycle of high vs low.

I am wondering that if the analog value was calculated from the square wave value, would the solenoid function the same way sans a possible heat issue?

Theoretically, if the pulsed square wave calculated average for a certain position was 6.2v, could I send 6.2vDC analog and see the same movement?

Theoretically could I introduce analog voltage from the same power supply to the square wave signal and bias the square wave signal, would I therefore cause the same overall effect as if I were to increase the duration of each wave? Thanks for reading!

Jun 1, 2009
499
37
You need to be absolutely certain that the output voltage you calculate is exactly equal to the true RMS voltage the load receives. Square waves through a coil do not react linearly compared to a fixed DC voltage source.

In theory the device you're using was designed for it's operating frequency meaning at the frequency it uses PWM should be approximately equivalent to an analog voltage of a comparable value. It's highly device and application dependent. But by crude analogies what you've said should stand true, all things being equal. (All things are never equal)

gte likes this.
3. ### gte Thread Starter Active Member

Sep 18, 2009
347
4
Hi,

What do you think about biasing the square wave voltage with analog from the same power supply? Is that possible or do they have to be from different power supplies? If that is possible and I put 1 volt analog to the 0 to 10 square wave, this would bias my cycle to a 1-11v square wave signal? Is this possible with DC from the same power supply?

Jun 1, 2009
499
37
You would have to use a capacitor, probably a large one to buffer the square wave pulse without dulling it too much to isolate it from the applied DC voltage with a diode on the DC voltage side to prevent the pulse from discharing into the bias. At 312hz you wouldn't need a massive capacitor but it's a really ugly solution, and the DC voltage applied would have to be able to source the full current provided by the switched DC side, or the voltage would drop (IE The bias would disappear)

gte likes this.
5. ### gte Thread Starter Active Member

Sep 18, 2009
347
4
Thanks again.

I thought it might be a good way to preliminarily test without trying to setup an entire rig that mimics that signal ... or a good way to piggy back the preset signal to be the least intrusive as possible.

I guess the next step would be a pwm controller? Or a micro controller that switched a transistor? I think 312hz would be pretty nominal for most off of the shelf transistors?

6. ### gte Thread Starter Active Member

Sep 18, 2009
347
4
^

Scratch that, I forgot it needs to be able to switch 2 amps/20 watts

7. ### Bernard AAC Fanatic!

Aug 7, 2008
4,922
541
312 HZ is no problem for a transistor, or the 20 W, but may need a reasonably[?] high oparating voltage with a fast snubber, RC + zenor?? It might be possible to use a combination capacitive discharge and switched. Woulld supply high inrush current and reducod coil energey at termination to ease snubbing -- and all of this in 3ms?? Is this a rotary solenoid or low mass short throw?

gte likes this.
8. ### gte Thread Starter Active Member

Sep 18, 2009
347
4
Hi Bernard,

I believe it is low mass short throw, it does not appear to be rotary and it has a piston that moves against a spring and then goes back into a resting state when no voltage is cycling through it.

9. ### Bernard AAC Fanatic!

Aug 7, 2008
4,922
541
Might review post by timrobbins 6-7-10, reduced power relay drive.

gte likes this.