Trimpot on Fire!

[thehallofshields]

Okay. Bizarre. I kept seeing smoke coming from my PNP Fuzz Face project. It turned out to be a 1k trimpot to ground (+9v) on the emitter of Q1. If it turn it to 1k. It lights up bright yellow and starts smoking! I'm using the standard 1-stop 9v powersupply that I always use and I've NEVER seen anything like this. Has anyone else?

[Sacorus]

I have burnt out a few in my time, mainly whilst on the breadboard!

[PRR]

Resistor in the *emitter* of *Q1* in a *FuzzFace* design should NEVER get hot.

1K is more often in the emitter of *Q2*. Even so, if you have 5K-10K of resistance in Q2 collector, it should never get hot. Like 0.002 Watts in a 0.1W trimmer.

Something is wired way-wrong.

Other than that..... yes, roasting trim-pots is a fine fun past-time. There's some other circuits where it is inevitable. Sometimes 5-Watt trimmers, which with 9 watts flowing can set fire to the board.

[GibsonGM]

^  Yup.   Did you get the pot on the collector by accident?

Remember: voltage * current = Power (Watts).   So, if you had a 1K trimmer and a 9V source....when you crank it to say 500 ohms, you have 18mA.    9 * .018 = .162W, which is enough to fry that sucker!   The lower you turn it, the higher the current flow, and the more the pot must dissipate as heat (smoke).    Kind of stinks having to monkey with the numbers, but it helps for learning, in the long run!

The blue smoke....it's FUN!  ;o) 

[duck_arse]

the smell is to remind you not to do it again.

[mistahead]

Congratulations on a near life experience!



Dedicated a few minutes this weekend to showing my daughter catastrophic diode failure in action - scary but I could do firecracker shows off a cheap roll, and it would cost less than real crackers hahaha!

[seedlings]

I burn them up sometimes.  Burn up power supplies, resistors... it's easy!

Even using pots well under their rating, you can still burn one up.  Say you drop 4V across a 1k pot.  That's within spec (4*4)/1000= 0.016 watts.  But, once you turn the pot down below 160 ohms, you'll dissipate more than the 0.1 watt rating.

CHAD

[PRR]

> once you turn the pot down below 160 ohms, you'll dissipate more than the 0.1 watt rating.

Correct.

But all the places in a FuzzFace where a 1K pot makes sense *also* have 3K to 33K of additional resistance in series with the pot and the 9V. Hence max-dissipation far under 0.1W.

[armdnrdy]

What has this site become! Now there's a thread about smokin' pot! 

[mistahead]

It helps Jimi's eyes since he tried the diode fire cracker stupid component trick hahahaha.

[seedlings]

But all the places in a FuzzFace where a 1K pot makes sense *also* have 3K to 33K of additional resistance in series with the pot and the 9V. Hence max-dissipation far under 0.1W.

Aahh, yes.. but what seems to me like a small wiring error belches smoke and vile.



CHAD

[mistahead]

THE SCIENCE IS LEAKING OUT!!!!!

[seedlings]

THE SCIENCE IS LEAKING OUT!!!!!

I probably need to pick up some of those flameproof pots.

CHAD

[deadastronaut]

put tiny sausages on and have a miniature BBQ...

[bluebunny]

put tiny sausages on and have a miniature BBQ...

   

[deadastronaut]

 

[seedlings]

I've never been to China.  I've always imagined stepping off the plane into a strong smell of electronic components, like when you open the bag of transistors.  This would mean that a barbecue in China should smell like an electrical fire.


CHAD

[gjcamann]

On the topic of haphazerd entertainment. Ever microwave a grape?
Take a grape from a supermarket, cut it in half, and set the two halves, flat sides down and make sure they're touching a little. Then microwave for 10 seconds. You won't believe the show!

[Kipper4]

This is giving me ideas for a pyro stompbox.

[Govmnt_Lacky]

Dont ANY of you know that all of your basic electronics theory is WRONG? 

ALL electronics works because of MAGIC SMOKE!! 

Once you let out the magic smoke... the electronics don't work anymore!

PROVE ME WRONG!!