there is a relay for direct current?

Hi, I need a relay 12v for 40 amperes for Arduino but I can only find relay from 250v to 10 amps! you can use a classic relay with Arduino? if you like?
I apologize but I'm not well versed in this field :frowning:

Cars use high current 12volt relays, e.g for the headlights/horn.
What is the load. Maybe a mosfet can be used.
Leo..

and how many amperes is able to withstand a mosfet?It is able to withstand the engine start?

How long is a piece of string? You can get MOSFETs of many sizes.

High current DC relays tend to be big and bulky and use loads of power, because breaking a
a high power DC arc is not easy.

You mention 40A - but then seem to imply an engine start might be different - is 40A the
actual worst case current or not?

XY problem!

I recommended from 'elettrauto who told me to get me a relay 12v of 40 amperes, but these do not exist for Arduino, so I think a mosfet from 40 amps is enough

How about a nice hefty 50A N-channel MOSFET (for a low-side switch)

Or you can research others

Will likely need a MOSFET driver to drive the base, make sure it turns on & off good & quick and not burn up.
Heatsinking will be required. Power dissipated by the MOSFET = I^2 x Rds, 40A x 40A x 0.096ohm = 153W!

Make sure you understand the specs of the part you are looking at.

But then how do you make the connections of these MOSFET? using a relay?

dandi98:
But then how do you make the connections of these MOSFET? using a relay?

No. You'd better stick to relays if you are saying that. It's also a sign that you should tell us what you want to do with it.

my goal would be to start the engine of the machine

dandi98:
my goal would be to start the engine of the machine

Vehicles already have a relay for this. It's referred to in auto lingo as a "solenoid".

my purpose in the end would be to start the machine with cables without keys, but instead of joining the cable between them do this with the relay

12V 40A (N.O.)/30A (N.C.) RELAY

WHAT machine ?

microcar 500cc diesel

There would normally be a solenoid or starter relay.
I don't think these require more than 5 amps.
You're not going to put a regular relay on the
motor it self.
Depending on the type of starter motor, you may
need an external relay.
These can be purchased from an autoparts store.
You then just need a relay to drive enough to power
the starter relay.
These are typically under 5 amps.
There is no 40 amps going through a starter switch
on a car.
A diesel starter motor draws more than 40 amps when starting.
Dwight

So it can also be used the classic relay used in projects Arduino?

PHOTO OF MY RELAY: Dropbox - Error

but these do not exist for Arduino

You can use any relay with the Arduino, but most relays cannot be driven directly from the arduino, which puts-out 5V at 40mA or less.

You can use a circuit [u]like this[/u]. It says it's for driving a solenoid, but it can also be used to drive a relay coil. Since you've got 12V, get a relay with a 12V coil (such as an automotive relay).

You CAN find solid-state relays that can be directly controlled by the Arduino, but make sure it's designed for DC (an AC solid state relay won't work with DC).

And, make sure it's rated for at least the amount of peak current you are switching, because although solid state relays are VERY reliable when operated within spec, they don't handle electrical "abuse" (over-current or over-voltage) as well as regular relays... It might be hard to find 40A DC solid-state relay. (Solid state relays are more expensive than mechanical relays, but you don't need a driver circuit.)

Hi Dandi,
What is the "Thing" you are trying to turn on.

Thank you so much you were very clear! Tomorrow I will propose this solution from 'elettrauto and I will update you on the news! :slight_smile:

Boardburner2:
Hi Dandi,
What is the "Thing" you are trying to turn on.

Google say it's a car: http://thestirrer.thebirminghampress.com/Images/aixam/aixamside2.JPG

// Per.