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capacitors Preventing sparking Answered

im trying to build a sollenoid motor like this one

http://www.youtube.com/watch?v=e3tcdiO2HCc&feature=channel

and i need to no how to prevent sparking on the switch so that im not constantly having to replace it. ive heard somewhere that a capacitor will prevent a spark on the switch but will it? and how big of one will i need. thanks

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Æ (author)2011-08-05

Yes, you can add a capacitor across contact terminals, it's called a snubber. Same as the "condenser" on a an old fashioned car distributor with breaker points. Absorbs the arc/spark. A MOV can be used too, because it looks (measures) like a capacitor. You have to determine the amount of capacitance empirically. Add small amounts, start with .1uF and add additional amounts until the spark has subsided.

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aeronut01 (author)2010-05-23

Has anyone mentioned trying a varistor?  The website   www.phonda.com.tw/varistor.htm clearly describes its function.  Basically, its a resistor that varies from almost non-conductive to very conductive depending on the voltage fed into it.  You wire it in parallel to the switch and the next time a spark heads to the switch, the varistor should absorb the spike in electricity.  BTW, a varistor is also called a "metal oxide varistor" or "MOV".  If that doesn't work, try a ZNR (Zinc Resistor), but the MOV should work just fine.

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lemonie (author)2009-02-12

You could use a solid-state switch, something with silicon in it? L

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Plasmana (author)lemonie2009-02-16

Well, the semiconductor will burn out from the voltage spikes. it will still require some form of protection.

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11010010110 (author)2009-02-11

its parallel to the switch. i guess 0.1 uF 600 V is about ok but not sure

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NachoMahma (author)110100101102009-02-11

. The condenser from an old (points) automotive ignition should work. . Or get a switch with a higher interrupting current (AIC) rating.

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budsiskos (author)NachoMahma2009-02-11
i was planing on making my own switch out of a hacksaw blade so it would be easier to trigger. like the switch shown in this video :53 seconds in



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11010010110 (author)budsiskos2009-02-11

a massive switch won't mind sparking but you should use appropriate materials (so it won't heat cause of high resistance) and isolate well yourself from the switch insides

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budsiskos (author)110100101102009-02-11

like gold and copper? its also only using 24 volts

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11010010110 (author)budsiskos2009-02-11

no need to go that far aluminium for example is good conductor but idk if it stands sparks well. iron is not as good so i think it should make more sparks as for heating - use large parts of whatever material. resistance goes down when thickness of parts goes up

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budsiskos (author)110100101102009-02-11

i think youve got that switched around. iron is an ok conductor, not the best in the world but it works. alluminum on the other hand is not a good conductor at all im just going to cut out two 2X0.25 inch strips and use pliers to bent them to make contacts. a cam on the crankshaft will trigger the switch.

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tech-king (author)budsiskos2009-02-15

aluminum is a good conductor, but it fast increases in resistance as it heats up. the ideal material for parts subjected to sparks, arc, thermal shock and heat is tungsten. its also very hard to work with. steel and aluminum pit from arcing, which in turn causes corona loss problems and spark trigger misfires.

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budsiskos (author)tech-king2009-02-15

tungston would be ideal in a vacuum like it is in a light bulb but if exposed to air the spark will cause it to ignite.

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budsiskos (author)110100101102009-02-11

wouldn't putting it in series be better?

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11010010110 (author)budsiskos2009-02-11
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Goodhart (author)2009-02-11

On the solenoid, do you have a diode to suppress the spike kick back you get when the induction field created by the voltage from the coil of the solenoid, collapses?

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budsiskos (author)Goodhart2009-02-11

no, i never thought about that, ime using a store baught solenouid and didnt even think about it. but isnt a coil used to supress kick back on most devices anyway.

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budsiskos (author)budsiskos2009-02-11

well the transformer ill be using to provide power already has diodes so would that work?

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Goodhart (author)budsiskos2009-02-11

That'll work for the transformer. Anytime I incorporate a relay or a solenoid or anything with a coil, I double check to make sure there is a diode across that coil. Such feedback can do damage to equipment, and also cause a heck of a flash back at the switch when it is opened.

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NachoMahma (author)Goodhart2009-02-11

. A capacitor accomplishes the same thing as a diode. Caps are usually rated for higher voltages.

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Goodhart (author)NachoMahma2009-02-11

Higher then say the 1n4007 ? ;-)

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11010010110 (author)Goodhart2009-02-12

a capacitor gets the shock. a diode shorts it out so no need to use diode of high voltage but - capacitor can be used on ac and diode no

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tech-king (author)110100101102009-02-15

caps can ONLY be used on ac for this application. unless you mean from power to ground to filter the spike?

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11010010110 (author)tech-king2009-02-15

caps can be used on dc too the spike herre is across the switch a cap in parallel to the switch takes the spike and does not pass dc when the switch is open

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Goodhart (author)110100101102009-02-12

True, the voltage rating of the diode is it's reverse breakdown voltage limit

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budsiskos (author)Goodhart2009-02-12

ok, youve lost me, will the transformer work to prevent the arcing or not?

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Goodhart (author)budsiskos2009-02-12

Hmm? The transformer? That generates an electro-magnetic field, and when the switch cuts the current, the field collapses causing a reverse voltage spike that is greater then the input was. This can cause back flash (spark) that can damage equipment and ruin the switch. We were discussing whether a diode or a capacitor is best to use to suppress that particular arc. I have to agree that a cap would serve well in this case.

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