Hi,
I'm trying to drive 12 valves from a single Arduino Micro using 12 Mosfets connected to 12 Arduino pins. I have an LED circuit to show when a port is turned on and I'm using diodes to protect against the solenoids. See diagram:
When I try to switch the MOSFETs I don't get any voltage on the outputs. Did I make a mistake in the diagram? The LEDs are switching correctly. Any help would be appreciated.
What is Vgs for the IRF520? By the way, I hope you're not expecting to see any voltage on the MOSFET drains without a load connected...
Also, you mentioned capacitors but their location and component value remain a big mystery.
Thanks for the reply. Sorry yes. I mixed up capacitors and diodes (I have changed original post). Vgs is 10V meaning 5V can't drive it? (Edit: V_GS(th) is 4 V, so should work, right?) I connected a solenoid lock to test them. I'm trying to drive 24V up to 1 A.
Please don't go back and edit posts except to fix formatting. It makes the replies seem strange. Yes, that's it. The MOSFET drive voltage is too low. Vgs(th) is just the beginning of conduction, you have a long way to go to turn the MOSFET fully on.
Thanks again. If you don't mind can you suggest a good alternative MOSFET for 5V signal driving 24V/1A? I guess this was the misunderstanding. I thought Vgs(th) was enough voltage.
Maybe this one: IRLB3034PbF found on a similar thread : Which Transistor to drive a 12V - 180W heater wire - #14 by Smajdalf
What voltage do you see on the MOSFET gate when the Micro's output is HIGH? I see 3 wires going to the valve, how are the valve coils connected to the MOSFET?
The third wire is earth since some of the valves need an earth connection for safety, but can be ignored for the most part. The valves are connected to +24v and -24v on the plug side.
What voltage do you see on the MOSFET gate when the Micro's output is HIGH?
Isn't the voltage 5V or am I misunderstanding the question?
A lower cost MOSFET like RFP30N06 should work with a 4.5V Vgs.
If the Micro is powered from USB, there is a reverse polarity diode in series that drops about 0.3V, so the output pin voltage will be about 4.7V. Post a drawing of how the valve coils are connected.
EDIT: OOPs, was thinking Pro Micro, NVM the 4.7V babble.
They would always be ON, the coil - wire goes to MOSFET drain.
Looks good to me! 
Alright. Thanks for the help everyone!
Except, the wires should be connected to the coil, not the fluid ports. 
...
It was 3 in the morning for me.
The RFP30N06 is not available to me. Would a IRLU 120N or a IRLU 024N work? I'm going through the digikey list here, sorted by price and looking up what is available, but unsure if there is another pitfall.
They would always be ON, the coil - wire goes to MOSFET drain.
Wait, is this true?
Other options would be an IRLZ 24N IR, an IRLB 8721 or an IRLZ 44N. Sorry for many edits, other post hit link limit.
I've used both IRLZ44N and IRLB8721 with 3 ~ 5 Amp loads successfully, the IRLB8721 may be obsolete by now.
You said "The valves are connected to +24v and -24v on the plug side."
The - side goes to MOSFET drain, NOT -24V.
Ok yes. I worded that imprecisley. I ordered the IRLZ24N before I read what you wrote, but hopefully it will work for my use case.
