I need a switch on/off power of 18V 20Amp with a arduino. Not sure what to use.

I am using an Arduino to switch on/off power from a Ryobi 18V 20Amp Lithium drill battery to 2 RC car motors. I tried using a TIP120 Transistor but that went up in smoke. What can I use that can handle this current/power that I can switch on/off with an Arduino? Thanks!

It may be a 18V 20A battery, but what are the motors rated at?

These are the motors. When wired to the battery the motor run full tilt no problem. Just stuck on how to control on/off with the arduino and the power source being a 18v 20a battery... https://www.amazon.com/Redcat-Racing-Blackout-550-Motor/dp/B00O9MRKIK/ref=sr_1_4?ie=UTF8&qid=1480651088&sr=8-4&keywords=550+motor

Simplest "mechanical" method is to use a 'power' relay driven by a transistor. Finding an 18volt relay might be a problem but you could use a 12volt one and a series resistor who's value(R) is 1/3 that of the relay coil resistance and wattage at least 36/R but preferably 72/R

Solid state would be a MOSFET but you need to allow for stall current and back emf from the motors when selecting

You don't need a 18V relay, the arduino has to switch it. But yeah, to not heavily load the regulator you can use a transistor to switch a 12V relay + resistor.

But 20A DC relays starts to get more exotic... Don't forget the flyback diode.

But a transistor should also work. But you need a beefy one. Use a logic level mosfet with a low Ron and don't forget to mount it on a heatsink. And again, don't forget the diode.

And what is beefy, is that 20A the max current or the nominal current? If the latter, start current will probably a few times higher...

The battery being rated 20amps does not mean the motors draw 20amps. They might…I’m just saying that the motor pulls what it needs and the battery can only safely deliver UP TO 20 amps. If you can, meter the actual amp draw of the motor and don’t forget that spinning free it will draw only a fraction of what it draws loaded up (ie - pushing the car) and starting up or “locked rotor” it will draw the most.

Just on/off would not be typical and really awkward to control a car - the most common motor control for rc cars/robots/etc is called an H-bridge that you can control direction and speed with. You can make one with a bunch of transistors/heat sinks rated properly, but they can be had relatively cheap (compared to the old days) on ebay.

But don't expect them to be cheap in the 20A range....

Here's a bunch of 20A relays. Coil currents are 180-200mA, so you'll need a transistor to buffer the Arduino signal to turn the relay On/Off. http://www.digikey.com/product-search/en/relays/power-relays-over-2-amps/1049447?k=relay&k=&pkeyword=relay&pv72=1&FV=fff40010%2Cfff80367%2C1608000a&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25 Logic Level, Low Rds N-channel MOSFET would be good. AOI508, AOI510 for example.