Ignition circuit wire size

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Llessur
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Ignition circuit wire size

#1 Post by Llessur » Thu Oct 25, 2018 7:08 am

What size wire should I use for the ignition circuit on my 2500S? I'm replacing the melted ballast wire with standard wire and a separate ballast resistor.

My local place only sells 10amp wire which looks pretty small in gauge.
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White

My 2500 blog: https://triumph2500blog.wordpress.com/

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Re: Ignition circuit wire size

#2 Post by Llessur » Fri Oct 26, 2018 3:54 am

Put a different way, bearing in mind electrics are not my strong point, is there a downside to using higher gauge wire in a circuit? Can it be too thick?
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White

My 2500 blog: https://triumph2500blog.wordpress.com/

Rod 2500S
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Re: Ignition circuit wire size

#3 Post by Rod 2500S » Fri Oct 26, 2018 6:19 am

gday, no it can only help as the voltage drop will be less the thicker the wire, but thick wire is fuggly. See if you can find some 15amp, most parts retailers stock it.
Or maybe scrounge some from a wreck, you only need a metre or so as the long run on the original resistive wire is no longer needed, the ballast resistor now does all the voltage dropping.
Cheers
Rod
PS if you really want to improve the spark fit a relay and take the load off the car's ignition switch. This will have two main benefits, higher voltage at the coil = fatter spark and a far happier ignition switch. Use a fused relay (see pic) and and trigger it from the ballasted "run" wire. The ignition switch will suppply 12 volts to start then when the engine starts the ballasted wire will trigger the relay which will supply a nice 12volts to the ballast resistor which then runs the coil.
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Re: Ignition circuit wire size

#4 Post by Alec » Sat Oct 27, 2018 9:11 am

Hello Llessur,

10 amps is more than ample, the coil only takes an amp, possibly less?
The distance is short anyway so the voltage drop will be tiny.

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Re: Ignition circuit wire size

#5 Post by Rod 2500S » Tue Oct 30, 2018 6:11 am

gday
The current through a standard ballasted coil is 3 amps, when starting and drops to about 2.5 when running.
The voltage drops are not just through the short wire run but from the battery, through the ignition switch and its associated fuses then to the coil. This is where most of the losses are, fitting a relay ups the voltage considerably at the coil giving a better spark.
Also the ignition switch supplies a lot of other systems and these also create current demand and stress on the switch. Removing load from the switch can only help - everything.
Cheers
Rod

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