ssr problems

[Peter Bowles]

Hoping someone can help me with this.

I've just had the electrician in to do the last hook up on a new kiln. Its 3 phase with 45amps / phase. Each phase is controlled by a 60A ssr.

When we tested it with a 9vdc input the draw was fine, it all switched on and off - until we left the input on for a minute and then the phase stayed on when we disconnected the input. Weird. And then the whole front of the ssr blew its face off pretty dramatically after another minute.

Anyone have any pointers to whats going on. I'll admit they were not the most expensive units so they may just be crap - or we may have something catastrophically wrong. Any thoughts would be much appreciated.

Peter

[Dave Bross]

They always fail in the "on" mode but the explosion is unique. Be sure that particular element isn't shorted to ground anywhere and the ssr pulling too many amps. It's unlikely but best to check.

I'm guessing you just got a bad one. Only one way to know that.....hang another one on there and see what happens.

[Peter Bowles]

Thanks Dave

I think I've got a bad set as the same thing happened when we tested it on one of the other phases with the same total and immediate catastrophe. Pretty radical I thought. I think I've just learnt a serious lesson in quality components.

I'm thankful that I've installed a separate controller and tc as an over temp control to the main contactor should they fail on.

Can anyone recommend quality 60A ssrs?

Thanks

Pete

[Dave Bross]

Used ones have always worked really well for me. I don't know how practical this is from where you are but a lot of surplus dealers sell them inexpensively on Ebay. If you have electronic surplus places there or places that break down and resell the parts from stuff like office machines and other electronics they usually have them.

Some more thoughts, check the actual amp load on them just to be sure. I've had some of my more entertaining mathematical errors pointed out in a flash and a cloud of smoke. Don't run them over 80% of capacity, or less if you can. You do have them mounted on heat sinks to dissipate the heat don't you?

[Peter Bowles]

Aaaaah, as a matter of fact I hadn’t had them mounted on heat sinks. I've never used ssrs before and didn’t know how critical this is for them - particularly on larger current draws.

So, I've just ordered some more with appropriate sinks and all the right conductive pads for them. I'll mount them in their own enclosure with plenty of air around them and even might put a small fan in the enclosure to ensure good air circulation just for extra peace of mind.

Thanks for the heads up on the heat sink - sometimes not knowing what I need to know has its implications. It still surprises me that they failed so radically just by overheating.

So, my thanks again


Peter

[Garner Britt]

Peter,

The heat sink are important and your plan of a separate enclosure and fan is a good one.

Before you blow three more of them up check and recheck your wiring. The only time I've had SSR's "blow their faces off" was due to bone headed wiring, something crossed.

good luck

garner

[Peter Bowles]

Thanks Garner

Did yours work for a spell before they blew or did they go as soon as there was power onto them?

[Garner Britt]

Peter,

It's a move I made that I'm trying to forget but as I remember, I was having power issues with my wire melter which uses 2 50 amp SSRs to control both legs of my 240 volt single phase power. After the SSRs, I use mechanical relays and a limit switch to shut power off when gathering. It seemed one of the mechanicals had gone bad. I shut the power off and swapped in a spare mechanical, crossed a wire or two in the process. When I powered it back up, POW!!! As they say, "I let the smoke out" of both SSRs.

Also, if you are not aware, SSR's "leak" a small amount of voltage at near full current even with the "coil" de-energized. Enough for a good jolt, Hence the separate safety system I built into the melter...

garner