Zener diode for solenoid

I am new in electronics and this is old subject but still. :○ I started new Arduino project where I control 4 solenoid valves independently via Arduino 4 chanel 5 V Relay module. From the beginning I put flyback diode on each solenoid to eliminate EMF (1N4002). Everything works fine but when I speed up cycle things get messy (I need speed about 30 Hz). Solenoid coil can't discharge properly that quickly (it has delay). I read some forums and found solution: diode+zener.

What kind of zener diode should I use and how to properly mount it (any additional parts)?

I am also afraid of over-heating due to quite high current. How can I avoid it?

My valves are: 48 VAC, 3.8 VA and 24 VDC, 3.1 W.

Everything works fine but when I speed up cycle things get messy (I need speed about 30 Hz). Solenoid coil can't discharge properly that quickly (it has delay).

It's usually the physical inertia that limits the speed of a solenoid. In theory the inductance could be a factor too, but I'm pretty sure the big issue is the mass. 30Hz is slow for electronics but fast for a solenoid or relay.

I am also afraid of over-heating due to quite high current

Overheating of what?

AC and DC solenoid coils are quite different and using AC coils on DC will cause over-current. AC coils rely upon inductance to control the current they demand (Xl) which is dependent upon inductance and frequency whereas DC coils rely upon the coil resistance (R).

Perhaps you could further illustrate what it is you are trying to do, possibly with a drawing

As Doug has suggested, getting a DC solenoid to vibrate at 30Hz will be difficult due to mechanical inertia. Applying 30Hz to 48VAC solenoid rated at either 50 or 60Hz will almost certainly cause a 'heat' issue.

Note also that an AC solenoid does not vibrate at the excitation frequency (50 or 60Hz) as it is specifically design to avoid such vibration.

I don't think many relays or solenoids will work reliably at 30 Hz.

Why do you need such speeds? are you trying to 'PWM' a fluid flow?

It may be better to have a set of differently sized holes switched by solenoids - a sort of fluidic D-A.

Or I think you can get special proportional valves to do the job.

Allan

Switching solenoids on/off with relays will be double slow.

Adding a resistor in series with the 1N4002 flyback diode could speed up things somewhat.
Could be better/easier than adding a zener diode. Doubt if you can reach 30Hz though.
Leo..

Curious posting. I wonder if an H-bridge could be used to DRIVE the solenoid in the opposite direction?

Paul

An old friend of mine had a company near Cambridge which made super-fast solenoid valves - <<1mS.

I designed some electronics to drive them.

I’ll see if I can find out if they’re still going - he’s long retired.

They weren’t cheap.

And freely available are electrically controlled injectors as used in modern cars and lorries - both petrol and diesel engines … pretty quick. Ditto the driver chips.

Visit your local scrappie.

Allan