Inductive kick is a cruel master...

Well since we didn’t use penumatics for any of our robots, we now have 3 years of pneumatics kits. We were going to make a compressor setup just for blowing out our robot in the pits.

Well I rigged up the pressure switch to a spike directly. (12v to the common on the switch, NC to FWD on the spike) Well it worked fine with one compressor, but when someone else decided to hook another up in parallel (20 amps on the spike, 10 amps max on the compressor, should be fine… right)

It was running fine and cycling like it should. But one time it kicked off, and I think I saw an arc between the m+ and m- terminals. There was no arc damage on the connector though. But the next time I tried to power it up, the spike didn’t even blink. I was thinking about opening it up, but there was no smoke, so it would just look like normal FETs except they are dead. I guess when the spike kicked off, the inductive “kick” from the two compressors made a rather large and nasty voltage spike.

No big deal, we have bunches of spikes from previous years around, just thought I would share, some of the rules may seem stupid and overly cautious, but they are there for a reason.


Some compressors produce this high voltage more then others. This is why in the rules, you are allowed to replace the 20 amp fuse on the spike powering the compressor with a 20 amp breaker.

I suspect that your spike is fine and the fuse is blown.

-Andy A.

The arc you saw could have been the plastic fuse blowing.

There are no FET’s in the spike’s, its a couple solenoids that trigger between GND and +12 to the M- and M+ terminals. Its unlikely, but you could have caused the solenoid to weld itself in one posistion.

Please remember that although the compressor is rated for 10 amps run it is actually much higher on start, especially with a pressure in the system. I would check the fuse before tossing. It is unfortunate that fuses go incandescent for just a short period of time before they fail. In that moment they are so pretty.

The spikes are H-bridge based and have at least four power FETs inside.

Edit: Okay, Al Skierkiewicz just PM’d me and said, very politely, that I didn’t know what I was talking about because the spike he pulled apart had relays in it. Sorry for further spreading bad information. I’m going back to my nice padded virtual corner of the programming forum and take a nap <grin>.


It’s so true… sob

We’ve had that happen too. It happened when the battery was somewhat low, and the compressor, when it ran, shook quite violently. I don’t know if that is what happened to your 'bot, but it’s something to look out for. And yes, I did see that beautiful spark of pure light eminating from that blown fuse.

PS: Kevin, naps make everything better…