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Re: KV's and multimeters
From: Adam[SMTP:absmith-at-tiac-dot-net]
Sent: Thursday, November 20, 1997 12:54 AM
To: Tesla List
Subject: Re: KV's and multimeters
>Last night I finished the driver for the ignition coil useing a 555 timer.
>I was surprised when I hooked the thing up and it actually worked!
>The coil that used to put out only about 500 V now
>makes sparks about 1/4 in long. My question is: is there to figure out the
>voltage its putting out? My multimeter is a cheapie that only goes up to
>1000 V. Also why does it spark to everything..even when its not grounded?
You can find the voltage from this coil by using a simple resistive
voltage divider. You will need a high total resistance value (in the
megaohm range), since the ignition coil has a very high output impedance
and you do not want to put any kind of load on it. You do not want to
just use a few 1 MEG resistors however, since the spark is likely to jump
over them and right into your oscilloscope...ZAP! I would recommend
chaining together twenty 510K 1/2 watt resistors, with a 50K in series
for measurement. The 50K resistor would have one end at ground (the low
voltage common terminal) The voltage across this resistor will probably
be 50 volts or less, easily measured on a scope. If you need the voltage
in the 10 volt range, use a 10K resistor. You should also not use a
volt/multimeter- most do not give meaningful results at radio
frequencies, even if they are true RMS meters.
As for the spark jumping to different non-grounded objects, you have to
remember that you are dealing with AC, specifically RF. All the
conductive objects have a little bit of capacitance, and the coil is more
or less just throwing electrons on and off the object, very quickly.
Each object is its own little ground. The coil will throw a spark to
anything with capacitance, including the air itself.
-Adam
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absmith-at-tiac-dot-net
Epoch, Inc. Digital Music Project
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