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Tool Talk Discussion Forum

question for the electronic buffs

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you

10-15-2006 00:20:32




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my dodge manuel shows a diagram to make a coil tester using a 0.33 MF capacitor and a couple of jumper wires.Now my question is would this be a 12volt capacitor,as it 's not specifide.I looked on the net but have not seen anything with 12 volts. i have seen lots of .33mf in 16,600 etc.I wonder would a basic condenser do the same job for me? thanks, you




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you

10-15-2006 14:45:42




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 THANKS FOLKS in reply to you, 10-15-2006 00:20:32  
I am much wiser now. thanks again you



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tech4

10-15-2006 06:13:36




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 Re: question for the electronic buffs in reply to you, 10-15-2006 00:20:32  
The others are correct. You will have a spike of several hundred volts on the primary (points side) of the coil (I have seen 400 volts on a scope) The primary purpose of the capacitor or condenser as called in the old days was to smooth that voltage spike and not burn the points. You will get a weaker spark without the capacitor but none the less a spark. The voltage rating of a capacitor is the highest voltage before danger of breakdown of the capacitor. You can always use a higher voltage capacitor but never a lower voltage rating as long as the capacitance value (Farads, Micro Farads,Nano Farads, Pica Farads) is correct.

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John T

10-15-2006 05:38:47




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 Re: question for the electronic buffs in reply to you, 10-15-2006 00:20:32  
About any discrete capacitor (other then possibly some real low power solid state/computer stuff) having wire leads laying around ought to be wayyyyy yyyyy higher then any 12 volts regarding its voltage withstand rating which is more like the 200 to 600 volts Bob was talking about. The microfarad rating is most important cuz if its too small theres like nooooo o affect at all (concerning a coil ignition, but she will still spark wiith no or an extereme low MFD capacitor) but if its too big the coil would never fire at all.

Actually I never worry about or use a capacitor to bench test a coil, it still fires WITH NONE AT ALL its just a weaker spark. I set it and a 12 volt battery up on the bench and use a spark plug and high tension coil lead to test for spark. Anytime the coil conducts current through its primary winding (lil + and - terminals) and then you disconenct the current source (battery leads) a high voltage spark will jump a 1/8 inch gap in a circuit between its high voltage output tower and ground (batterys - circuit).

NOTE a coil can pass this test but still fail due to breakdown once shes warmed up n cycling often HOWEVER if she fails this test its baddddd ddddd d

John T

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Bob

10-15-2006 01:17:00




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 Re: question for the electronic buffs in reply to you, 10-15-2006 00:20:32  
Simply use a condensor that would be used in a breaker points ignition system.

They are rated somewhere in the 300 to 600 Volt range, to deal with the voltage spikes produced by the coil's primary winding, when the breaker points open.



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