Please Help with this PWM Thing?

It sounds like the PWM card is bad and the output duty cycle is stuck at 100%. Have you verified this?

The pot on the output simply can not handle the power running through it and burned up. One of the reasons that the PWM card is used, because it is a good way to vary the average current to a motor or LEDs.

The right thing to do is to determine if the PWM card is at fault and either fix it or replace it.

Very curious, what is the solenoid on and in my field 33 hz would be high, I normally max at 8

Could you provide more deails on the complete application ?

Have you checked the input pot, and its wiring? This may be where the original problem is.

The pot you have added on the output must be able to take both the full power of what you are driving, and the frequency of the switching.

How are you measuring the output?

You need an oscilloscope to make sense of it, a DVM or analogue meter really just tells you that there is an output and with some thought may tell you something about the mark/space ratio.

Why are you driving a relay with PWM? Don't you just want on/off?

8 Hz is a slow PWM. Is it so that you can vary the position of the solenoid and say if controlling a liquid for example, allow less of more through? though I would guess it is quite "loud"......or did you mean 8KHz?

You have given us very little to work on and therefore the help may not be as good as you wish....

Andy, in my work we use pwm as a signal to operate relays and not to modulate. Individual relays operate only on the pulse count we assign. Modulation is accomplished either with a time on, variable resistance, current or voltage signal. I ask about modulation with a pwm signal out of curiosity because that is new to me and I am always open to learning even though I am 63 yo.

This is not a conventional usage of PWM, nor is the frequency.

Using it on relays will probably cause them damage as a relay is a device for on or off, not for such rapid switching....we have transistors MOSFETs for example, today that can switch DC loads far better and Triacs for AC loads.....

PWM is conventionally used to control the brightness of a Lamp or the speed of a motor. The PWM frequency will often be in the KHz range....there are many uses nowadays......

Please read through this link, it will give you a good over view. Search for the word relay in the whole article!!:-

http://en.wikipedia.org/wiki/Pulse-width_modulation

The question is complete nonsense. "33 Hz" does not describe "PWM" and we do not change the amplitude of a PWM signal, else its NO LONGER PWM, its AM.

And a pwm signal cannot be read with an ammeter. Ammeters expect sinusoidal current.

My suggestion is to block all internet connections to CR4 from India....

PS - serious and non sarcastic comment- in India, "engnieer" generaly means "mechanic" as is obvious from these posts.

Sadly, you are right on most points, though we have some Guys there that are true Engineers and useful to us all here.....this guy is not one of them......

this is the complete setup

http://imageshack.us/photo/my-images/269/solenoidl.jpg/

and this is the solenoid being driven (the forward and reverse coil in the above diagram)

http://imageshack.us/photo/my-images/215/solenoiddriverwiringdia.jpg/

I've checked the i/p potentiometers, they are working fine. and for measuring current, there is an analogue ammeter as u can see in the diagram.

My apologies for assuming that your 'solenoid' was a relay.

I think I see that your PWM drive is to a solenoid pump.

I hope I am not 'talking down' to you, but, where I have used a PWM drive to control a DC motor, the motor speed is varied by having a fixed frequency and varying the mark/space ratio. The amplitude of the waveform remains constant.

Thus the energy supplied to the motor or solenoid is a product of the 'on' time and the waveform voltage. No variable resistance in the output to the pump/solenoid is necessary.

You need to look at the loaded output from the solenoid driver card with an oscilloscope to see whats going on. Do you have access to a 'scope?

I don't go on such sites, no matter who says they are safe.....

I'm out of here, byeeeee......

Either replace the card or fix the card on a component level if you have the skill and tools.

I am almost 100% certain the problem is the card. Can you call the manufacture for the card? Usually they have a technical support department.