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Old 27th March 2007, 12:02 AM   #1
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Default on/off spark

Could someone explain why I might want to put a cap across my on/off switch? I realize it would probably quench a spark, but so what. If I need/should have one, then what would be an appropriate value/type? Thanks for any inputs.
-Bob
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Old 27th March 2007, 12:09 AM   #2
BWRX is offline BWRX  United States
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Sparking or arcing degrades the quality of the switch contacts. When you say switch are you referring to a mains switch such as one you would put in series with the primary of a transformer?
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Old 27th March 2007, 12:21 AM   #3
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Exactly -- in series with primary, 120VAC. Would you know what is a good selection for something like this?
-BG
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Old 27th March 2007, 12:25 AM   #4
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Sparking in the power switch will eventually destroy the contacts and the switch will fail. This is a bigger problem with toroidal power transformers than EI core transformers due to comparitively higher in-rush current. Amps and any other equipment that use big toroidal power transformers often have thermal in-rush current limiters, timer resistor/relay circuits, or big triacs to switch the power. Big in-rush current can also trip circuit breakers which can be really annoying.

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Old 27th March 2007, 01:06 AM   #5
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Thanks for your comments. I am using 2-800VA to provide for 8-LM4780's (parallel output). Some people think I am sick. I have a 120vac DPDT 10A relay across a 30ohm 25W, relay coil (one each toro) will not energize until the toroids have surged through the resistors, one for each toroid. Now that you guys have got me thinking, I may not need a cap across as the surge should be over before the relay closes.

Why 8, you ask? I wanted 8 for speaker design, wanted to be able to drive 4 ohms and thought it would be worth it to do a decent job and I could always use it for a home theater. The 2 ch proto I built sounded better than my $2700 Yamaha DSP.
-BG
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