Pots damaged due to solder heat

[ClenchedTeeth]

I recently managed to ruin 3 24mm alpha pots by removing the lugs and soldering directly to the rivets. The rivets provide a nice hole for wires to go through, so I thought it would be neater and more compact to do it that way. This turns out to have broken the connection between the lug and the trace (confirmed by taking one of the pots apart and checking for continuity). I presume this is because the heat is applied closer to the trace. Does this sound normal to anyone? Is this bad practice on my part, or poor quality pots? I thought alphas were quite good quality. Should I be using heatsink pegs? The pots were all different values, so I find it hard to believe they were a bad batch or something.

[ClinchFX]

Nobody seems to have answered yet, so I'll bite.

To put it nicely, you have voided any warranty that may have existed on these pots   Yes, it is bad practice to remove the lugs and try to connect to the rivets.

The lugs are there to provide a means of connecting to the resistive element of the pot.  The rivets are there to hold the lugs in contact with the resistive element.  The rivets don't necessarily connect directly to the resistive element.

It amazes me the things that folks will do for the sake of neatness.  I believe in neatness but, very often, uninformed practices that create neat looking wiring are, electrically speaking, the complete opposite of neatness.

Peter.

[GibsonGM]

I've done the rivet trick out of desperation, when a lug has broken off (when using recycled parts).  It's worked most of the time, but will be less trouble to use the original lugs in practice...they're made that way for a reason ;o) 

[ClenchedTeeth]

Ok, so now I know! I had always assumed that the lugs were there for soldering into a PCB, and weren't needed for a wire connection.
Thanks for clearing that up guys.

[B Tremblay]

Here's a tutorial for soldering to PC pin pots: http://www.olcircuits.com/documents/olc_soldering101_guide.pdf

[Minion]

I have soldered to the rivets before on quite a few occations and I have never had a Problem with ruining a Pot this way....I allways Tin both soldered contacts before hand and use a very hot iron so it actually only takes maybe of 1 -2 seconds of heat to fully solder the the wire to the Pots rivet....If you do this though don"t stick the wire through the rivet because it can come in contact with the outside of the Pot and cause a short ,I allways solder to the rivet it"s self as opposed to useing the Rivet as a Through Hole....

Cheers

[ClenchedTeeth]

Here's a tutorial for soldering to PC pin pots: http://www.olcircuits.com/documents/olc_soldering101_guide.pdf

This is at odds with the earlier advice - quoting that PDF: "I suggest cutting the pins off the pot. They're not needed for wire and it's a quick way to save space..."
It does warn against using the rivets, but purely because they might short out against the case, which is not the problem I had at all.

[ClinchFX]

Here's a tutorial for soldering to PC pin pots: http://www.olcircuits.com/documents/olc_soldering101_guide.pdf

This is at odds with the earlier advice - quoting that PDF: "I suggest cutting the pins off the pot. They're not needed for wire and it's a quick way to save space..."
It does warn against using the rivets, but purely because they might short out against the case, which is not the problem I had at all.

Sorry, I took you original post as meaning that you removed the complete lug and didn't just cut the pins off.  Cutting the pins off is OK, as long as you don't stress the PCB in the pot too much.  If the PCB flexes, it can break the resistive track.  I carefully bend the pins at a right angle and wrap the wire around them before soldering.

Peter.

[ClenchedTeeth]

Sorry, I took you original post as meaning that you removed the complete lug and didn't just cut the pins off.  Cutting the pins off is OK, as long as you don't stress the PCB in the pot too much.  If the PCB flexes, it can break the resistive track.  I carefully bend the pins at a right angle and wrap the wire around them before soldering.

Sorry, I should have used the right description. Yes, I cut the PINS off, and I was careful not to flex the pcb. I then soldered to the rivets.
I have since just bent the pins up at a right angle like you do, and I haven't had any problem with that. Fingers crossed. I think I will adopt that method from now on.
So, do you still think that it was the heat that did the damage? That's all I can think of. Applying heat directly to the rivet, (and maybe without the pin to act as a bit of a heatsink) caused it to get too hot near the trace and crack. I was, until now, under the impression that a pot could take all the heat my little soldering iron could give it, being a non-semiconductor.

[ClinchFX]

I wouldn't have thought the heat from a small iron would damage a pot.  Maybe heating the rivets takes the "spring" out of them and they lose tension?  I don't really have an answer.

With 40 years in electronics, soldering to the rivets is something I've never seen in manufactured equipment, so I guess there's a reason that it's not done.

Be aware that there's a lot of electronics "information" and advice on the net that is internet folklore with no basis in scientific fact.

Peter.