The magic Smoke out of a component

[dan3460]

This is the third time that I have build a two rail power supply and like an idiot put the lytic caps with the negative side to ground in the negative rail. I bring the power supply up using a variac, to make sure that I don't have a short, or smell. Get it to full power and then .....
"Bang" and some times "Bang bang bang", the magic smoke is gone, i'm having a heart attack because at that moment I was testing the voltages from the supply.
I always tell the kids that teach to check and recheck cables and components, to make sure that polarities are correct and there is no shorts.

[German_EE]

Yes, they do fail rather well. I remember plugging a control PCB into an elevator cabinet and one cap was the wrong way around. There was a loud bang and it shot across the room trailing its foil behind it. Fun times.

[JoeN]

I use a lab power supply that tells you how much current your circuit is using in mA.  It's pretty obvious that if your circuit that contains a low power microcontroller and a few other chips and should consume maybe 20mA is consuming 100mA, and that figure is rising, there is something seriously wrong, like what you are talking about.  That is what you will see, current way too high and rising, a rather obvious telltale sign.  Get a supply like that.  It's reassuring to be able to look at it any time you want to see how much current the board is eating.

[Deathwish]

any chance of a pic of the top and bottom of the board ?

[Cubdriver]

Yikes!!  Yeah, electrolytics don't like being reverse biased and will let you know of their displeasure in no uncertain terms!     That must have been a heart pausing moment (or four).  Hopefully they didn't make too much of a mess, and you have some spares without needing to order more.  My guess is that this is now an error you won't repeat any time soon - it seems once something like this happens you get a lot more neurotic about making sure the caps are connected correctly.

-Pat

[dan3460]

any chance of a pic of the top and bottom of the board ?

I don't have any of the ones I built anymore, but I have the test board (which was the first one to have caps backwards) on my bench. Will take a picture and post.