New PWM Realy vs Transistors

[TACAMO]

hey, I just fried my PWM. I'm going to build a new one using a 555 IC. What would work better, having the 555 switching 4 High power 2N3055 transistors, or switching a high power relay.

[Philldpapill]

Your relay is going to wear out if you are switching it at any decent frequency - even 1Hz. Think about how many times it's going to engage/disengage per day. Then check the spec for the rated number of times it is good for in it's life time. Even 100,000 times is hardly anything at 1Hz. Just to give you an idea, there are 3600 seconds in an hour. If you were to switch it at that rate, it MIGHT last 28 hours until it fails(probably failing closed circuit so you couldn't stop the current flow).

Bad idea to use the relay. It's better to go with MOSFETs. They are solid state so nothing wears out. Those 2N3055 transistors are NPN bipolar transistors... Not the best kind to use for something like this, but they will work with low currents, and a good heat sink.

[TACAMO]

cool, Thanks. Scratch the relay. I went with 4 IRF510 MosFets(all radioshack had)

[Drafty-01]

Actually, I was just reading a local electronics distributors catalog and saw that they sold high current solid state relays - kind of works like a BIG mosfet, but can only switch once every second or two.

Just my 0.02 worth...

Cheers,
Martin.