Magic Smoke!

[awerby]

I decided I wasn't getting the all the response I'd like to see out of the motors on my home-made router, so I replaced the 50 volt supply with an 80 volt one. Everything seemed to go okay; the steppers (powered by G201 drives) were zipping along nicely when jogged, and the one servo on the heavy-duty 4th axis (powered by a G320) was cranking along happily when BANG! - that magic smoke (that makes all electronic devices run) started pouring out of the control box.

It turned out to be a capacitor blowing up on the G320; I'd used a small 470mh cap plugged into the Gecko, and for some reason it took this opportunity to kick the bucket. I'm left wondering what went wrong, and how to fix it. The servo (an Ametek) was marked "40v nominal" so it could be that it just didn't like 80v (although the motor itself never got hot). I'm wondering if I need to swap out the motor for something else, or if substituting a bigger capacitor would solve the problem. One thought was that I might need a different current-limiting resistor. Or maybe this was just a coincidence, since the caps aren't exactly new, and I wondered if simply replacing it with another one would work. I'm also not sure if the drive is toasted or not - the fuse seemed unaffected. Any words of wisdom would be appreciated...

Andrew Werby
Juxtamorph.com

[Al_The_Man]

Originally Posted by awerby It turned out to be a capacitor blowing up on the G320; I'd used a small 470mh cap plugged into the Gecko, and for some reason it took this opportunity to kick the bucket. I'm left wondering what went wrong, and how to fix it.

Electrolytic Capacitors especially are very voltage conscious, it sounds like you exceeded the rating, go at least 10%-20% above the voltage you are using, if the cap is in circuit that receives back EMF from the motor, then 20% min. I would suggest.
Did you mean 470µf?
Al.

[awerby]

Yes, I meant microfarads, not milihenrys (duh). So if my 470 was good for 50v, how big a one do I need for 80v?

Andrew

Originally Posted by Al_The_Man Electrolytic Capacitors especially are very voltage conscious, it sounds like you exceeded the rating, go at least 10%-20% above the voltage you are using, if the cap is in circuit that receives back EMF from the motor, then 20% min. I would suggest. Did you mean 470µf? Al.

[Al_The_Man]

I would go with a 100v minimum.
Al.

[Huckmeat]

Originally Posted by awerby Yes, I meant microfarads, not milihenrys (duh). So if my 470 was good for 50v, how big a one do I need for 80v? Andrew

Be sure you are looking at the voltage rating, not just the size. There will be two numbers, one for size (i.e. 470uf, 10000uf, etc) and one for maximum voltage rating (i.e. 100V, 250V, etc).

[Mariss Freimanis]

When an aluminum electrolytic capacitor explodes, it spews corrosive electrolyte in all directions. If this capacitor was on or near the drive, some of the electrolyte probably blew inside the drive. The conductive and corrosive electrolyte will then rapidly destroy the circuits inside the drive.

Remove the drive and remove its cover. Rinse it with very hot water directly from the sink faucet. Then shake the drive to get most of the water off and place it in a small (1' by 1' by 1') cardboard box. Get a nozzle-type hairdryer, set it on "low" and place the nozzle end into the box. Close the box top around the nozzle and let it run for 15 minutes. Remove the drive and let it cool.

Reassemble the drive cover and place it back in service.

Mariss

[awerby]

When that cap blew, it blew straight up, and deposited most of its goo on the inside top of the enclosure. I guess that was a good thing, considering. But there were 4 drives in that box. Do I need to launder all 4 of them, just the one that blew and the one next to it, or just the one that blew? (I never knew you could do that to electronics!)

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[Mariss Freimanis]

Andrew,

You only need to wash the one that got slimed. If the stuff was on the inside top of the cover then it's on the component side of the printed circuit board.

Up until a few years ago we used water soluble flux solder paste. Every assembled drive had to go through a water wash, rinse and dry cycle before post assembly testing. Virtually all electronics (cell phones, computers, TVs) in the world used water soluble flux then. All had to be washed prior to testing.

Today most electronics manufacturers use no-clean flux. It has very little residue and what little there is has a crystal-clear and non-tacky characteristic. This is a boon because it eliminated an expensive and time consuming process from the production cycle.

If you want to get the board really clean (that just manufactured look), use a toothbrush with with a couple drops of dish-washing detergent. Scrub the board vigorously with the toothbrush, rinse the drive with very hot water directly under the faucet, shake it dry and use the hairdryer in the cardboard box trick. It's what we do now with returned drives contaminated with plasma dust before we can test them. We used to have an industrial board washer but we got rid of it once we switched to no-clean flux solder paste.

Mariss