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Arcing switches and snubber caps

Raccoon1400

Raccoon1400

Super Member
Seems it is very common to find arcing power switches. What can be done to make switches last longer? Do the existing snubber caps go bad causing the arcing? Or is there a better part I should be using when I replace the switch? I can't recall a unit that was missing the snubber cap, even if the switch was badly toasted.
 
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Since those caps are designed to fail open, then the only real indication might be when the switch contacts fuse together.

Still, safety caps don't eliminate arcing, but simply reduce it. Given enough years of power cycling the switch is bound to suffer damage eventually.

The solution is thus (for me): When I'm working on a unit that seems to have a history of switch failures (according to what I know personally and what I've read here at AK and other places on the web), I'll go ahead and replace the cap.

Something else to consider is that while a simple safety cap helps to reduce arcing, there are much better solutions. One is the Cornell Dubilier QuenchArc device, a safety cap and series resistor in one package. The combo does the best job of killing the AC arc as quickly as possible. Only drawbacks are physical size and device cost. But if you are after the best method of prolonging switch contact life, short of simply using the power switch to activate a relay to energize the primary circuit, this is what you'd call 'best practice'.
 
Not sure, but if you get one of those large thicker ceramic looking caps like 4kv or higher, the larger plate area will give more instant shorting power (joules) then look up those resistor plus caps combos, part numbers, and get the value of the resistor then solder that in series.
 
EchoWars said:
Since those caps are designed to fail open, then the only real indication might be when the switch contacts fuse together.

Still, safety caps don't eliminate arcing, but simply reduce it. Given enough years of power cycling the switch is bound to suffer damage eventually.

The solution is thus (for me): When I'm working on a unit that seems to have a history of switch failures (according to what I know personally and what I've read here at AK and other places on the web), I'll go ahead and replace the cap.

Something else to consider is that while a simple safety cap helps to reduce arcing, there are much better solutions. One is the Cornell Dubilier QuenchArc device, a safety cap and series resistor in one package. The combo does the best job of killing the AC arc as quickly as possible. Only drawbacks are physical size and device cost. But if you are after the best method of prolonging switch contact life, short of simply using the power switch to activate a relay to energize the primary circuit, this is what you'd call 'best practice'.
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Thanks for the reply.
The quencharc device would be well worth it for some units, but expensive if I tried to stock them. I will keep them in mind for higher end projects.
What about using a cap, and adding a resistor myself? How well would that work? If so what components are best?
 
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sregor said:
as any one tried these? http://www.allelectronics.com/make-a-store/item/THM-15/NTC-THERMISTOR-10-OHM-6A/1.html They go in series with the AC switch.
I have a couple, but haven't put them in anything, yet. They have a cold resistance of 10 ohms which drops to .44 ohms at 3A, .15 ohms at 6 amps. Datasheet at http://www.ametherm.com/datasheets/sl1510006.htm.
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Those carbon blocks are really mainly good for really high power amps and they don't want to use a huge switch.I suppose they would be ok for smaller stuff but just seems impractical or not needed.
 
Raccoon1400 said:
What about using a cap, and adding a resistor myself? How well would that work? If so what components are best?
Click to expand...

You want an X-rated (safety agency listed) capacitor for AC line exposure. It should be metalized film or some other type with "self-healing" properties. Also, I believe carbon comp resistors are better suited than film resistors for this job. They don't concentrate overcurrent stress into small areas, so they can tolerate surges better.
 
sregor said:
as any one tried these? http://www.allelectronics.com/make-a-store/item/THM-15/NTC-THERMISTOR-10-OHM-6A/1.html They go in series with the AC switch.
I have a couple, but haven't put them in anything, yet. They have a cold resistance of 10 ohms which drops to .44 ohms at 3A, .15 ohms at 6 amps. Datasheet at http://www.ametherm.com/datasheets/sl1510006.htm.
Click to expand...

Thermistor are good as a soft start, but only for class A amplifier, that is amplifiers with constant current request.
 
About the snubber caps in my KA8100, there are to caps in parallel on each of the power button contacts, and one more cap in parallel on the connecting pins of the AC cable, what does that do?
something like this:
"But now I get recommendations to use a AC rated cap (125 or 250) - and I saw a 125vac cap across the power switch in the Kenwood 7100. And there is another like it across the unswitched power supply plugs in the back but it was across the line H~N"
 
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verde57 said:
About the snubber caps in my KA8100, there are to caps in parallel on each of the power button contacts, and one more cap in parallel on the connecting pins of the AC cable, what does that do?
something like this:
"But now I get recommendations to use a AC rated cap (125 or 250) - and I saw a 125vac cap across the power switch in the Kenwood 7100. And there is another like it across the unswitched power supply plugs in the back but it was across the line H~N"
Click to expand...

It guards against spikes, if it comes from plugging something in, to any other reason you get a transient spike while things get turned on or off.

The ones across the switch are protecting both contacts in the switch.
 
The cap across the line should *not* include a series resistor -- that would reduce its effectiveness as a noise filter.
 
Queenarch only from US, and Murata 10nF 250vac, only 10 pcs.
thats why I'm asking, looking for something cheaper around me.
 
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It doesn't matter as long as you get a value that covers the frequency range of a spike. .1 mfd .047 mfd and large overkill size an 1kv or higher.
I would have to check my parts for values they use, but this part is not all that critical.
rip a cheap terminal strip apart that says it has protection and use those.

The blue looking ones a thick disc looking thing, have the resistor I do believe, but just about any ceramic cap will be fine. with a high voltage rating.
 
Modern X/Y safety caps aren't terribly expensive at Mouser. If you're messing around with much gear, just order a bag of them.
 
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