edolo wrote:
Have a couple of manual testers, but would like to build an LED
in-line unit to test spark on two, four, and six cylinder outboard
motors. Anyone have a design or know where such a unit can be obtain?
tks, alp


Wouldn't a neon glow lamp be a better choice than an LED?

James, sounds like a good idea ... & sample of glow in:
http://www.giangrandi.ch/electronics/neon/lamps.html
What resistance would you suggest?
Might be easy to enclose in a ballpoint pen case.
alp

On Sat, 23 Dec 2006 07:32:03 GMT, James Sweet
wrote:

edolo wrote:
Have a couple of manual testers, but would like to build an LED
in-line unit to test spark on two, four, and six cylinder outboard
motors. Anyone have a design or know where such a unit can be obtain?
tks, alp


Wouldn't a neon glow lamp be a better choice than an LED?

edolo wrote:
James, sounds like a good idea ... & sample of glow in:
http://www.giangrandi.ch/electronics/neon/lamps.html
What resistance would you suggest?
Might be easy to enclose in a ballpoint pen case.
alp



You shouldn't need a resistor, in fact you might not even need to
connect it directly, holding it near the plug wire it may pick up enough
energy to glow.

James Sweet wrote:
edolo wrote:

James, sounds like a good idea ... & sample of glow in:
http://www.giangrandi.ch/electronics/neon/lamps.html
What resistance would you suggest?
Might be easy to enclose in a ballpoint pen case.
alp



You shouldn't need a resistor, in fact you might not even need to
connect it directly, holding it near the plug wire it may pick up enough
energy to glow.

It is possible to get a faint indication from capacitive pickup with 20
or 30 turns of hookup wire round the outside of the plug lead to one
side of the bulb with the other well grounded to the block, but any
attempt at resistive pickup with a direct connection to the spark plug
wire will almost certainly shunt your spark and shut the engine down.
High voltage resistors that can standoff that sort of pulse voltage dont
come cheap new and are difficult to scavenge and any lesser resistor
*will* arc over.

I'd look at putting a fairly substantial neon bulb WITH NO RESISTOR in
series with the HT lead. The drop accross it will be low enough so the
spark is not noticably affected, the only question is can the neon
handle the peak current?

I dont think the ballpoint pen housing idea is going anywhere, too
narrow diameter. I've made low voltage probes from BIC pens before,
knocking out the actual ball from the brass tip and soldering in a brass
plated pin for a probe point, but the most I've ever fitted inside is a
small LED and resistor. No way I'd trust the casing for insulation at
tens of KV either. I cant think of any common household item to
canniblise for a casing so I guess I'd be using two pieces of clear
vinyl tubing one inside the other, or maybe vinyl tube over a glass tube.

For a radical idea, do the neon voltage test screwdrivers still have
seperate resistor and neon bulb capsules inside them? If so, remove the
resistor and the pocket clip and discard. Solder the connecter off the
end of an old spark plug lead into the hole in the brass top plug and
stretch the spring enough to make up for the missing resistor. Cut the
blade end down to a short stub and cut back the insulation. turn and
thread to match the top of a spark plug

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