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I have a pressure system with eight solenoid valves on it and I'm controlling it from an Arduino. For each valve I have a solid state relay that an Arduino controls to switch on and off 12V from the supply. I've gotten this circuit to work properly with a single relay and solenoid:

enter image description here

Now I'm beginning to scale it and it all works but my setup is pretty messy. Here is a single SSR hooked up to a single valve and then the holders for all the other SSRs on the board:

enter image description here

So I was planning on using that terminal connector and then that small proto board mostly because this will be changing around a lot and I may be throwing some more pieces in so I don't want it to be 100% permanent but I do want it to be more durable and a little more elegant. Any thoughts on how I should wire this up? Or anything better than that terminal connector?

Here is a schematic of half of the full setup:

enter image description here

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  • \$\begingroup\$ The advice on the answers is good enough, my 2 cents: if possible use the chassis as return, so you would need only one wire from the control board to the solenoid valve. This should not be a problem unless you need the 12V floating from ground (it would be quite strange). Just make sure your PSU allows it, from the look of it it is a standard isolated supply so it should be ok. You will have one wire from PSU to control board, the other going to the chassis, 8 wires to the valves and 8 to the arduino, plus ground ofc but again, you can use the chassis. The beauty of high side switching ;) \$\endgroup\$ – Vladimir Cravero Apr 5 '17 at 21:05
  • \$\begingroup\$ @VladimirCravero. Interesting suggestion. Though I'd add, if you are going to do that make sure the chassis grounding system is SOLID and be careful not to create grounding loops. If it is done poorly it will be very sensitive to ESD, and noise. \$\endgroup\$ – Trevor_G Apr 6 '17 at 14:30
  • \$\begingroup\$ @Trevor yes, the grounding and the return paths must be solidly bolt to the chassis. The idea come to mind because in the picture you can see a grounding screw on the valve. I believe it is there because of the rubber suspensions. I would connect the return and the grounding screw to one of the mounting screws, hopefully it would be enough. \$\endgroup\$ – Vladimir Cravero Apr 6 '17 at 15:17
  • \$\begingroup\$ @VladimirCravero yes indeed. He would have to change his design a bit though to use high side switching. Not a big deal, but I have to point it out to complete your suggestion. :) \$\endgroup\$ – Trevor_G Apr 6 '17 at 15:21
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    \$\begingroup\$ @Trevor actually the schematics in the question differ, the top one has HS switching wile the bot one has LS... Who knows :) \$\endgroup\$ – Vladimir Cravero Apr 6 '17 at 16:25
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First I'd make the Relay board plug into the Adruino board as a piggyback assembly by adding a 2xWhatever header strip on the back.

Then on the relay board I would add suitable PCB connectors for each solenoid and a big one for the power supply.

The piggyback board should be a PCB eventually.

BTW those fly-back diodes should be closer to the SSR not the solenoid valves.

Actually, using I2C relay board(s) may be even better. Then the relay controllers can be localized close to the solenoids where it is needed with minimal connections to the Adruino and tighter power connections.

enter image description here

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  • \$\begingroup\$ Good point on the diodes as current switches from source to diode along same path. \$\endgroup\$ – Tony Stewart EE75 Apr 5 '17 at 20:38
  • \$\begingroup\$ Thanks for the suggestions! A couple quick questions: searching around for piggyback assembly doesn't yield consistent results, what is that exactly? Is the flyback diode wired incorrectly or just that it should closer to the SSR on the line? \$\endgroup\$ – clifgray Apr 6 '17 at 22:02
  • \$\begingroup\$ @clifgray Piggy back wold be a board the same sort of size at the Adruino, same mounting hole positions, with pins on the back that mate with the Adruino. \$\endgroup\$ – Trevor_G Apr 7 '17 at 0:45
  • \$\begingroup\$ @clifgray the diodes should be closer to the thing they are protecting (the ssr) because the long leads add a little inductance too. \$\endgroup\$ – Trevor_G Apr 7 '17 at 0:45
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Look at your car wiring and make the wire bundles similar.

You can use a single larger supply (e.g. ATX PC ) and a (cheap) quad 10A 5V optoisolated Relay card. (online everywhere)

Derate the VA on the supply because of mid-cycle surge currents or try not to switch more than one at once.

Use twisted current pair for each source and load for EMI control. enter image description here

But for source common supply another way is;

Determine load AWG cable for load power and upsize source power pair using -6 AWG smaller number gauge with an earth grounded drain wire wrapped around pair connected only at PSU source to absorb stray dI/dt from interference with high Z sensors cables.

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