Use of relay or mosfet

[Kjetil]

I`m planning to use mosfet BUK555 to control my 5 rule 1100 pumps on my ROV. I read on an other thread that mosfet create heat. I was planning to use heatsink like these http://www.taydaelectronics.com/heatsin ... inium.html will these be enough in a 4" housing? Or should I use relay instead?

[reHosea]

The heat produced from a MOSFET will depend on the amperage load of your motor. If your amperage load is just a few amps I doubt that you will have much heat. MOSFET's are very effiecient and produce far less heat than a transistor. I use IRF5305 (55v 31amp) MOSFET's on my circuitboards. The motors (each with their own MOSFET controller) draw upwards to 10 amps each and there are usually four of them running all the time. I have homemade heatsinks that look smaller than the ones shown in your link, and they work fine. The nice thing about using MOSFET's over relays is that if you want to get elaborate when you design your circuit, you can design it to precisely control the speed of the motor. Whereas a relay is just on or off. I'm using Pulse Width Modulation (PWM) on the MOSFET to control the motor's speed and it works great with very little heat.

[Kjetil]

Thanks for a quick answer. I was just planning to use the mosfet as on/off.

I do have available PWM output on my arduino card. I can be good to have the possibility of having a speed control later. I just go for the mosfet then.