Re: OT: Condenser Capacitance Value

Posted by MarkB_MI on April 20, 2007 at 17:52:03 from (216.234.125.152):

In Reply to: OT: Condenser Capacitance Value posted by VinnieNC on April 20, 2007 at 07:57:48:

Vinnie, an ignition condensor is matched to the inductance of the ignition coil. The ignition system is a crude tuned circuit. So the value of an ignition condensor is irrelevant to your problem.

As KT and KEB said, a better solution is an anti-kickback diode. KEB described the correct way to connect it; it must be connected in parallel to the load, not the relay. And it must have a very high current rating, as Gerald said. If your horn draws 3 amps, you might get away with a 1N400x, which is rated at 1 amp. If it draws 10 amps, I doubt it will last. (Of course, you'll never know if the diode is blown, unless you disconnect it and test it!) You can get 3 amp silicon rectifier diodes (e.g. 1N5402) with axial leads that are a better choice.

Really, if you have a sufficiently big relay, you don't need to worry about arcing. After all, your starter relay routinely handles several hundred amps, and you don't see capacitors or diodes hanging off it. Also, I think the current through a horn is basically ac (pulsed dc, to be correct); if you look on most switches and relays you'll find that they have much higher ac ratings than dc, because ac interrupts itself.

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