12v dc using a 2a relay to trigger a 10a power

Thread Starter


Joined Aug 8, 2016
Hi I am a newbie to this site so I hope I am asking the right question and in the right area.

I need a dc 12v 10a power supply from the battery to be able to be switched on/off from the auxiliary power supply that is dc 12v 2a.

Can I do this with a relay and if so can some one help me a diagram.

NOTE: I am not an expert with electronics but can follow it, if not too complicate.




Joined Jun 4, 2014
Certainly you can do that. Is the switch going to be literally a toggle switch or is it to be switched by something else, perhaps a PIR, a thermostat, etc.


Joined Sep 24, 2015
The attached drawing shows how easy this is. Only, I did not include any safety fuses in my circuit. Be sure to protect your circuits with appropriate fuses. Depending on how much current your relay draws you'll want a fuse typically 1 1/2 to 2 times that rating. Suppose your relay draws half an amp. A 1 amp fuse should be used between your aux supply and the relay. Before or after the switch doesn't matter, but I prefer before the switch (between it and the aux supply).

As for the 10 amp circuit on the battery - be sure to use a fuse that will protect your load. Here, I'd opt for 1 1/2 times the normal load. If your load draws 3 amps then I'd use a 5 amp fuse. Again, between the battery and relay for optimal protection. And your relay contacts need to be rated to handle at least twice the current your load may draw.

Keep in mind that the relay is nothing more than an electro-mechanical switch. It needs to be big enough to handle the load. The relay could be rated to handle 1000 amps - but that'd just be way over-kill for your purpose. Still, I say this only to point out that the relay doesn't need to be "Close" to the rating of the load. 2 to 10 times rating is fine. Since this is a battery (I'll assume a car battery), car relays typically can handle switching up to 40 amps. There ARE bigger relays available, but 40 amps is way more than enough to control your load. Switching 10 amps will be easy and the relay will last a long time.

As for the Aux Supply, it must be capable of supplying enough current to cause the relay coil to switch on and off. I'm assuming you're using something like a wall wart (plug in power supply). If it's a "DC" supply then use a DC rated relay. If it's an "AC" supply then use an AC rated relay.

01 relay.png