Wall Socket AC Power + Breadboard = Trouble?

Bryan · Joined: 23 Apr 2005 Posts: 73

I have a SSR that interfaces with my PIC (PIC controls the SSR control) which energizes an AC circuit to power a pump. I have gone through 3 relays now because occasionally the SSR will blow up as soon as AC power is supplied by the relay closing action. The relay literally blows up in a large spark and smoke cloud and remains in the "closed" state permanently afterward so it is obviously burned closed. I am wondering if this is because a breadboard has very very small conductors and AC from the wall socket delivers 20 amps so it may be arcing and shorting the relay. Maybe if I make a PC board with larger conduction traces it will be more stable? Anyone able to give a likely cause and solution?

newguy · Joined: 24 Jun 2004 Posts: 1909

You can find countless examples of "breadboarded" ac without problems - just think of any undergraduate EE lab.

I'd suspect that you have some sort of a short.

Remove the ac mains power from the SSR, and just verify that everything works without main power applied. Then verify your connections on the "hot side".

Should be something like Hot - SSR NO terminal. SSR COM terminal - load - Neutral.

You may also need an MOV between the SSR's NO and COM terminals, depending on the load you're driving, and whether or not it's inductive.

rnielsen · Joined: 23 Sep 2003 Posts: 852 Location: Utah

One thing you need to remember, a motor when first energized will act like a direct short until it starts to rotate, causing a high inrush current. Then the current will go down as the rpm goes up. If your SSR is not rated to handle this inrush current it will definately let out it's magic smoke. If you are using a SSR that is rated at what the pump's normal operating current is then it might not be able to handle it. You might need one that is specifically made to start motors, or even a motor starter of some kind.

Looking back at one of my lab classes, maaaaany moons ago, a student simply needed to hook up a 3-phase motor, with test leads, and make it rotate. Then, reverse two of the leads to make it rotate in the opposite direction. Well, his leads were way too small, gauge wise, and when he applied power... POOF! His leads dissapeared. This might be what's happening to you.

Ronald