Driving Solenoid Valve (Re: Electronic Boost Control)

[orin at WOLFENET.com]

>      The valve is a 12V solenoid valve with a 3.2mm orifice. It is rated to 
>      handle 60 psi. It is called a 'pulse' valve and is designed to be a 
>      ble to handle PWM signals. I plan to drive it (using a MOSFET) from a 
>      MC68HC705B16 which has a PWM output, however the minimum frequency 
>      32768 times slower than the external clock speed, so for a 2.45MHz 
>      osc, my minimum PWM frequency is 75 Hz. Is this PWM frequency feasible 
>      for a mechanical solenoid valve driven by a 12V coil. I have tried to 
>      get specs from the manufacturer for the maximum frequency 
>      ofmoperation/ min switching time etc, but they do not have such 
>      ratings. Can anyone advise me if 75Hz duty cycled modulated PWM(which 
>      implies switching speeds much quicker since the duty cycle may become 
>      1%, so effective min switching frequency is about 7.5 kHz) is too 
>      quick for a sloenoid valve. If someone has used similar valves 
>      previously, I would appreciate it if I could find out what frequency 
>      they were clocked at?

Way too fast.  I'd say less than 10 Hz would be right.  I've wired an LED in
parallel with the wastegate frequency valve on my Audi 5000 turbo quattro
and I'd say the frequency is less than 10 Hz, probably closer to 5Hz.
This too is PWM, switching the output between manifold pressure (ie boost)
and just before the turbo (slight vacuum).  If you get too high in frequency,
the valve is going to float somewhere between closed and open due to its
inertia.

BTW: it may not like 100% duty cycle either; the Audi computer uses a
max of E6 out of FF on.

Orin.