spst relay controlled by pwm

Forum 2005-2010 (read only) General Frequently-Asked Questions
1

Hi,

I have just received my relays (Relay SPST-NO Sealed - 30A - COM-00101 - SparkFun Electronics) and I am reading up. I have found a link that indicates that I can use this to control my 200W 12vdc motor using pwm from the arduiono (AspenCore | Electronics Industry Media & SaaS Group). Now my question is will the relay heat up? I don't feel comfortable testign all this on a breadboard, and I would like to make a PCB with sufficient traces before I give it a go. All this goes into a small blastic box and I am worried the relay will heat up from the switching. Any ideas?

Joachim

2

I have found a link that indicates that I can use this to control my 200W 12vdc motor using pwm from the arduiono

No you have a mechanical relay here and you can't use PWM to control this.

PWM controls average power by rapid turning on and off of a drive but mechanical relays switch over far too slowly for this technique to work.

3

Thank you GrumpyMike!

And can I assume that analogue switches are not made in high power versions? That means I'm back to MOSFETS and will have to take care of the heat some way? Or are there other options out there that can fit in a small box and not generate too much heat?

Joachim

4

By analogue switches do you mean solid state relays?

Most of these work with AC but you can get some that work with DC. Basically these are just mosfets.

I think what you are after for a motor is a H bridge but 200W is a lot of power so fitting it into a small box will not be easy.

However with PWM the power dissipation is no greater controlling the motor than just turning it on an off with a solid state device. It is only when you use a FET in the liner region, that is where things start to get seriously hot.