exploding wirewound resistors

Damage to caps, or flashtubes?

On a sunny day (Tue, 19 Sep 2017 12:17:45 -0700) it happened John Larkin wrote in :

Yes that is nice stuff, but those cemented ones as I use are very sturdy, although indeed in old TV sets (tube age) where those were used in series with heaters or power supply for example, they were a common fault source. At least they are explosion protected (by the alu casing). When your PCB thing explodes the parts will fly all over the place? Just to be nit-picking..

On a sunny day (Tue, 19 Sep 2017 12:22:20 -0700) it happened John Larkin wrote in :

Probably both, I remember (eighties last century) working through those flash tube (BIG ONES) datasheets to get it right, was for a flash in top of a tower.

Yes, they work a lot better with steady power dissipation. Spikes of heat break them. The app where our big ones failed, they were acting as sort of a pre-regulator to a big power supply, bang-bang mode.

It's only 80 joules so I expect superficial wounds.

We got some TE 3-watt parts, 0.33R, SMW3 series. I kept increasing joules per shot. At 10.8J, the resistor went POP but kept working. The case has a small crack on top and little puffs of smoke came out every pulse.

It seems to have run out of smoke now. Still works.

I worked on a kilojoule flash once. It was a couple hundred pounds of oil caps and power supply on a cart. It was used to develop Kalvar film, which is (or was) diazo stuff embedded in plastic. A big light flash makes microbubbles, which scatters light.

Geez, I have done so much weird stuff.

On a sunny day (Tue, 19 Sep 2017 12:48:27 -0700) it happened John Larkin wrote in :

What had been bothering me is minuscule pieces of metal flying about and shorting other critical electronics, perhaps control circuits or some overload protection. I have many modules from ebay that when inspected with a magnifying glass, show minuscule pieces of solder stuck to the board, when that comes lose and starts traveling, then no telling what can happen. Since that day I inspect every board with a magnifying glass.

Jan Panteltje Low land Technology pick-a-second timing

There's also non-magic smoke.

Cheers

Phil Hobbs

It's fun and pays the bills.

On a sunny day (Wed, 20 Sep 2017 07:31:23 -0700) it happened John Larkin wrote in :

It is truely 'low land' here, and the French call it Pays Bas, last week I was driving to a city next to here and noticed the fields had water, and the irrigation canals next to it were nearly overflowing, water on the road too. The county fired up the old steam powered pumps to get the water level down.. rain rain rain. And I am writing soft with .2 s resolution for my drone.

No pico stuff. But,. the 'regulators' declared about 50 % of the country of limit for drones.... It is not fair. We need a revolution, this hinders inventivity and progress.

I'm conjecturing that the nichrome element is now nestled in a little coccoon of carbon, not much left to boil out.

I need a MELF wirewound, exposed wire on the outside and ceramic inside.

Den onsdag den 20. september 2017 kl. 17.23.27 UTC+2 skrev John Larkin:

Ah yes. And I have invested in weird things. Owned a couple of shares of Kalvar at one time. Oh well that is how one learns.

Dan

I emailed them about joule rating, or samples to test.

The coating looks organic. Maybe they would sell me uncoated ones.

Then you'd get damp ingress, corrosion etc. You need to go back to the 1920s for uncoated resistors.

NT

OK, I give up on surface mount. I blew the top off the 5-watt power-pad Vishay at 20 joules. The gianytish TE 5-watt part failed overnight at 0.05Hz and 21 joules per shot. It blew a tiny hole in the side and shot some goo out.

My production folks will grudgingly allow me to use an axial leaded part; I'll buy them some cookies or something. I tried a 0.1R 3W axial wirewound; it worked for a while at 40J but made a smellable event every shot; it failed open at 50J. I've ordered some vitreous enameled parts to try (and bigger electrolytics!) Maybe the glass coating will hold the molten nichrome in place, or at least conduct heat a little better than the smelly organic coating.

Why not use SMs in parallel?

NT

No. The higher the R the more vulnerable it is.

NT