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# newbie running solenoid valve off arduino microcontroller with transistor

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#### erinbanwell

##### New Member
can anybody help me figure out what transistor would work to run a 12v 19a solenoid valve from an arduino pin?
any help is greatly appreciated.

You mean that you want to switch 19 AMPS at 12Vdc? Seems like a lot of current, but a logic level FET with a really low RDS(on) would do the job. You'd need a heatsink for that much current.

if you are really throwing down 19 Amps, I would suggest a MOSFET driver between the controller and the FET. You can then use the 5V (or whatever it is) control signal and drive the FET with 12V for lower Rds(on) and there will be no chance of damaging the controller pin.

if you are really throwing down 19 Amps, I would suggest a MOSFET driver between the controller and the FET. You can then use the 5V (or whatever it is) control signal and drive the FET with 12V for lower Rds(on) and there will be no chance of damaging the controller pin.

can you suggest a model of logic level FET and driver that would work for this?
thanks again.

it turns out the company rep gave me some bogus info and the solenoid is actually 12v at 1.58 amps. i realize this changes everything. can anyone tell me what values i would need on a transistor to make this work? or even better a specific model that would work in this circuit?
thanks

What the part number of the relay?

im not sure how to calculate what ratings i need for the logic level FET. Do i need an RDS equal to the power of my pin?
For low speed switching (Less than 1Khz):
You need a ID (drain current) spec greater than your load. Choose a FET with an ID rating of at least 2x the load current. The lower the RDS(on), the less power that will be wasted in the FET when it is on. ie: An RDS(on) of 0.05Ω at Vgs of 4.5V would cause 0.125 Watts to be wasted as heat for a draw of 1.58Amps. But if you used a FET with an RDS(on) of 1.0Ω at Vgs of 4.5V you would generate 2.5 Watts of heat for a draw of 1.58Amps which would mean that you'd need a heatsink.
Also spec the Vds to be at least twice the supply voltage for safety.
Usually what I do when purchacing parts is look of one that can be used for future projects even if it means grossly over specing the part. That way you can take advantage of volume pricing. Sometimes a higher spec part is cheaper due to volume production. I bought a bunch of IRLZ44's because they were the cheapest logic level FET from the supplier at the time. Tell us the supplier you will be using and we can recommend an all round general purpose FET for you.

Don't forget the freewheeling diode to clamp the inductive spike of the coil when the FET turns off. Spec it's voltage rating the same as the FET. You can usually spec the diode current rating lower due to the transient nature of the inductive spike. Just don't exceed the surge current rating of the diode.

Last edited:
right on! thanks for that explanation.

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