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# Which MOSFET for Solenoid Circuit?

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#### Bamblic

##### New Member
Hello! I'm new to the forum and struggling with an electronics project. I created a circuit that hopefully should turn activate a solenoid using a MOSFET when a switch is closed and turn the solenoid back off when the switch is open. My problem is that having very little experience with electronics I have absolutely no idea exactly which type of MOSFET will do the job apart from it being an N channel type. All I know is the circuit will be powered by 6V and the solenoid has a power consumption of 15W. I've provided a link to the solenoid that will be used : https://uk.rs-online.com/web/p/linear-solenoids/1770137/

I was hoping someone with a better understanding of electronics would be able to recommend a specific MOSFET that would work. I've also attached a picture of my circuit. Thank you in advance for any help it will be greatly appreciated!

With power consumption of 15W at 6V the current the MOSFET has to carry is 15W/6V = 2.5A.
So you need a logic-level type N-MOSFET with a voltage rating of at least 12V and an on resistance of no more than 0.1 ohm.
A logic-level type MOSFET has a Vgs(th) of 2Vmax or less.

Where would you buy the MOSFET?

I would put the fuse at the + of the battery.
Where do you get your MOSFETs from?

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Is there a reason you can't use the switch directly to power the solenoid?

Mike.

With power consumption of 15W at 6V the current the MOSFET has to carry is 15W/6V = 2.5A.
So you need a logic-level type N-MOSFET with a voltage rating of at least 12V and an on resistance of no more than 0.1 ohm.
A logic-level type MOSFET has a Vgs(th) of 2Vmax or less.

Where would you buy the MOSFET?
Thanks for the reply! I'll have to get the MOSFET from the universities supply of components. They said they'd probably have what I need but would need to know exactly what specs the MOSFET has the have. Worst case scenario I'll have to order one from RS online, the same place where the solenoid is coming from.

I just have no clue what to look for on the data sheet, like what threshold voltage means and which range would be suitable?

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Is there a reason you can't use the switch directly to power the solenoid?

Mike.

Before coming up with that circuit I did a bit of research into how to turn on a solenoid using a switch. I learnt apparently the current the solenoid draws is capable of damaging switch if it isn't specifically rated for large currents and it was recommended to use a MOSFET instead. (I'll just be using a basic switch from the university so have no idea how much current it can handle). I don't know how true this is though, but opted to use a MOSFET anyway just incase it was.

3A is not a large current. If you google automotive rocker switch you'll find one that will handle the current with ease. If you still want to use a MOSFET then the IRL540 is very common and should do what you need.

Mike.

Pommie has a good choice for the MOSFET. With a low RDSon, it will dissipate only 1/2W of heat, meaning you may not even need a heatsink. However, if stuck finding that part, the IRL530 will also work, but it has a bit higher resistance (dissipate about 1W at 2.5A), or the IRL520 which will dissipate about 1.75W of heat. With those, I would put on a small heatsink, though it may not be necessary depending on how long you engage the selenoid.
PS: Heed Ron's suggestion, put the fuse at the V+ feed point, not on a ground path....

Before coming up with that circuit I did a bit of research into how to turn on a solenoid using a switch. I learnt apparently the current the solenoid draws is capable of damaging switch if it isn't specifically rated for large currents and it was recommended to use a MOSFET instead. (I'll just be using a basic switch from the university so have no idea how much current it can handle).
2.5A is not that much current, and with the diode across the solenoid, there will be little arcing of the contacts when the switch is opened to damage them, so doing it directly with a switch seems feasible..

There must be some part number for the switch so you can determine its capacity.
How large are the switches?

Pommie has a good choice for the MOSFET. With a low RDSon, it will dissipate only 1/2W of heat, meaning you may not even need a heatsink. However, if stuck finding that part, the IRL530 will also work, but it has a bit higher resistance (dissipate about 1W at 2.5A), or the IRL520 which will dissipate about 1.75W of heat. With those, I would put on a small heatsink, though it may not be necessary depending on how long you engage the selenoid.
PS: Heed Ron's suggestion, put the fuse at the V+ feed point, not on a ground path....

Thank you so much for the reccomendations! Hopefully the University will have at least one of those in stock.

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