Re: Sam's High-Energy Double Car Ignition Coil Driver... Update

On Fri, 01 Jan 1999 18:36:23 -0700, you wrote:

>Original Poster: Sam Barros <sambarros-at-yahoo-dot-com> 

>>I would use a space heater or electric oven element instead of those
>>bright lights.
> If I use
>something, which has even less resistance than the lamps, I will get
>even more output. The only thing I know off that has a lower
>resistance than the lamps and still limits the amperage are wire
>resistances. I can get those in 100Watt ratings max. Do you (or
>anybody else reading this post) know the resistance of a 500-Watt
>Halogen lamp? 

It varies enormously with filament temperature. At 'normal' operation
you can calculate it easily. Assuming it's rated 240V, 500W : 
Current is 500/240 = 2.08A, R = V/I = 115R 
It may however be a quarter of this when cold. 

> So, what rating should the resistances be for maximum performance?
Just high enough to stop blowing the fuse/circuit breaker/user!

>I was considering ten 100Watt 100Ohm resistances in parallel (parallel
>is the correct arrangement for power handling, right?),

No difference - series or parallel will both distribute the power over
several devices. For series, the resistance is the sum of the
individual resistances, For parallel resistances of the same value,
divide the value by the number of resistors.
To increase the power rating without changing the resistance, you need
to use a series-parallel combination - e.g. 2 pairs of paralleled R's
in series quadruples the rating.

>It would
>definitely save me a lot of money experimenting, seeing that I have
>already gone over $200 on this research… How can I keep the
>resistances from overheating? If I use a 20Watt resistance, it gets
>very hot. If I use five 100Watts resistances they get very hot too!
>What can I do to prevent this and still obtain a good output?

Remember that a 20W resistor will produce the same amount of heat as a
100W one when carrying the same power - the only difference is how
well the heat is removed from the resistance element, which determines
the operating temperature. The easiest way to increase the power
handling is to use fan cooling. The commonly available 'gold' coloured
metal clad resistors are fairly cheap up to 100W, and can be bolted to
a substantial heatsink and fan-cooled for high powers - you can
probably at least double the rating with fan cooling. Be careful not
to push them too far, though. internal thermal resistance means that
if you push them too far, they can get too hot internally however much
cooling is used - I've seen the ends violently blow off these when
seriously abused!

Remember of course you don't need to buy ready-made resistors - a few
feet of iron wire, fan cooled, should be able to handle a few hundred
watts easily. 

> I did build a driver I saw on Snock’s homepage. It consisted of a
>light dimmer and a capacitor in series with the coil. When I turned
>the knob on the dimmer it made a buzzing sound and the resistance
>smoked… I could draw little sparks to a screwdriver by turning the
>switch on and off though but the sparks were very dim.

I tried this arrangement a while ago - I think it produced bright
sparks about 1.5" long. The dimmer setting makes little difference - a
variac is really needed to regulate output. I think the series cap was
about 4uF

> To end my message I just though the people in the list might be
>interested in knowing how my work is progressing…
> I replaced the 300Watts Halogen by a 500Watts one. There was no real
>difference in the output power but the coils produced a louder humming
>sound. Since they were only getting warm I put the 300Watts halo back,
>with the 500W one. Now I have 800Watts going trough the circuit… 

If you have 800W of lamps lighting brightly, you certainly DON'T have
anything like 800W into your circuit - the lamps are taking most of