Hi Davy,
'Fraid you appear to be labouring under several electrical misapprehensions:-
My setup is non standard 12v negative earth
I tested the current between the positive power supply and the twin output coil
You're dealing with DC electrics; "earth" does not exist, except as a concept and a jargon word.
DC electrons don't understand "earth", so they 'flow' from battery -ve to battery +ve irrespective of whatever any human thinks.
The Tri-Spark (any e.i.) should always be
supplied from battery -ve and should
supply the coil(s); i.e. the e.i. (sorry
) output is
always to (first) coil -ve.
Anything I can do to reasonably reduce the voltage ... passing through the module is bound to have a positive effect on longevity.
Voltage doesn't "pass through" anything. Volts are simply the units of potential difference between two points in a circuit. If you measure between, say, battery -ve and the input into an e.i., you will see zero Volts; you must measure between battery
+ve and the input into an e.i. - because the e.i. input is connected to battery -ve - to see, say, the nominal 12V.
A ballast resistor is - as the name ought to suggest - a
resistance. If you put one in an electrical circuit, you increase the total resistance of the circuit.
Three electrical basics - p.d. (Volts), electron flow (Amps) and resistance (Ohms) - are linked by Ohm's Law (E=IR aka Volts = Amps x Ohms).
If the p.d. (Volts) between the battery terminals doesn't change but you increase the resistance (Ohms), Ohm's Law shows the current (Amps) falls.
If you fit a separate resistance between battery -ve and the e.i.'s input, the p.d. across that separate resistance will fall as a percentage of the circuit's total resistance:-
. if the coil is 3 Ohms and you add a 1.5-Ohm ("ballast") resistor, the circuit total resistance becomes 4.5 Ohms;
. the p.d. before the first resistance is battery Volts; e.g. 12V;
. the p.d. after the first resistance is 8V - 1.5 Ohms is 1/3rd of 4.5 Ohms;
. do you imagine supplying 8V to an e.i. designed for a nominal 12V is a good idea?
That is why any e.i. - which is just a glorified switch - must be on the -ve (supply) side of any coil(s) (resistances). Remember, when we go hunting for the causes of an ignition problem, one of the things we check is that the Volts across the battery terminals is the same as the Volts between the e.i. input and the other battery terminal? We investigate and fix any losses? So not very clever to
deliberately put a resistance - Volt drop - between battery -ve and the e.i.?
Mr Kelly's own twin lead coil which metered out at 3 ohms
If you put the 1.5-Ohm "ballast resistor" between the e.i. and the coil, again, the nominal 12V would be reduced into the coil; supplying a 12V-rated coil with 8V affects the HT output exponentially.
if the system voltage is allowed to get up around the 15volt mark (as mine was doing) then the current can easily rise to an unacceptable level.
Nope. As I've posted slightly differently above, Ohm's Law: if the resistance doesn't change, if the p.d. increases, the current decreases?
Finally, theoretically, you could put the resistor between coil +ve and battery +ve. But, as I say, because the circuit p.d. remains the same (nominal 12V), the current falls. Reducing the current increases the coil charge time; this might or might not be an issue at higher rpm.
12.7v @ idle and 13.4v @ 3000rpm and 13.7v at 5000rpm.
current between the positive power supply and the twin output coil and was amazed to see it drew only 0.5amps @ 1200rpm idle, 0.9amps at 3000rpm and 1.4amps @ 5000rpm.
Ohm's Law suggests a total ignition circuit resistance of around 4.5 Ohms (the values using your figures are 4.23 Ohms @ idle, 4.46 Ohms @ 3000, 4.56 Ohms @ 5000). One hopes this is due to the Tri-Spark's power-saving, the coil is being fully-charged, not high resistance elsewhere in the ignition circuit reducing coil charging ...
This all truly surprised me by how little current was going through the system.
I'm just going to go ahead and do the resistor for two reasons, 1/. it can't do any harm,
Given the foregoing, are you sure?
I know Tri-Spark for a triple only connects a coil long enough to charge it fully, the LT connection time isn't rpm-dependent.
If the Classic Twin version of Tri-Spark has that circuitry too, an additional separate "ballast resistor" would be unnecessary at best; at worst, ...? :whistle
I'm now in agreement with Mr Kelly that my original module did in fact see a voltage event
But, if I've enlightened you here, re-read post #16 and stop faffing around with additional resistances.
If Lucas and John Carpenter were right, the two things that'll apparently at least reduce the possibility of "a voltage event" mullering a Tri-Spark are:-
1. Assuming your bike's wired as per
http://www.trispark.com.au/images/Classic%20Twin%20Manual%202013.pdf, page 6, "
Negative Earth" diagram, detach the Black/Yellow wire from the pillar bolt and extend it out of the timing cover, ideally directly to battery -ve but - if the bike has one and you must - to the network of supply wires attached to battery -ve.
2. A Zener diode connected between the Tri-Spark's supply and battery +ve. I suspect this shouldn't be one similar to the charging regulator Zener beloved of Lucas but one that starts to conduct at higher Volts? If you have an electronics store that supplies the computer builders and similar, they'll suggest one, or you could run my suggestions past Steve?
Hth.
Regards,