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James James is offline
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First recorded activity by BoatBanter: Jul 2006
Posts: 163
Default LED in-line spark tester

In the case of the neon lights the bulb and resistor is in parallel with the
spark plug.

There is not enough current to light an led in an ignition spark.

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news.wildblue.net wrote:
that's about the firing voltage of a spark plug.

Yes, it is, but that doesn't mean the LED has to handle that 50,000
volts. Think resistance.....

How much resistance would you need? Series, parallel?


Last time I checked (which may be very outdated info) an LED's forward
bias "on" was around 3.6 volts DC or something like that. You'd need a
voltage divider network to supply that to each LED or enough LED's in
series that the voltage drop across each was in that ballpark.

The series resistor is to limit current ... it depends on the rating of
the LED. It's been a long time since I played with them, so take it for
what it's worth .... which is nothing.




Enough resistance to allow the LED to light and be usable again, would
stop the spark at the plug.