Pinned Coil On Plug conversions - COP

Ninja 300 coils arrived in the mail today, measured them at 1.3ohms each, accounting for resistance in the multimeter leads.

They are Denso 129700-5430 coils.

 

OK here are my Ninja 300 coils installed in my ZXR250. They fit, just, and only slightly touch the radiator fan shroud. Not enough to worry about. I plugged in my two looms and started it up - success.

Note radiator is dropped down in this picture. I also slid the seals on the coils down about 5mm

 

Wouldn't know, haven't ridden the bike... been in the 'naughty corner' for a while... not long left to go now... got caught and am paying the fun tax

 

Yeah I am happy with it in that regard. There are plenty of learners smashing their 300's so bikes for parts/wrecking are plentily available

 

@ShaneP made a great post about running coils in series, which brought up series vs parallel circuits and a revisit of running coil on plug units, and how to do it properly/best. Guess who just started revision of basic electrical at TAFE?

Technically I have already completed that unit when I did my Cert 2 in light auto, but revision is good. Bad for headaches though.

Series circuits

In a series circuit, the current is the same for all elements.
The total resistance of the circuit is equal to the sum of all resistors in the circuit.
In a series circuit, the voltage is addition of all the voltage elements.

Regarding voltage in a series circuit like the one I made for my coils, putting a voltmeter across each coil would read only 6 volts on each. Adding both of those gets 12 volts total. Resistances are added (1.5 + 1.5 = 3 ohms total), current remains the same (4 amps). ShaneP is correct.

Parallel circuits

In a parallel circuit the voltage is the same for all elements.
The current in each individual resistor is found by Ohm's Law
The total resistance of the circuit will be less than the resistance of an individual resistor.

We can cheat a bit for circuits with only two loads of equal resistance. The total resistance of the circuit will be half the resistance of one of the loads, but the maths is as follows.

Resistance 1 (coil #1, 1.5 ohms) multiplied by Resistance 2 (coil #2, 1.5 ohms) is divided by the sum of both resistances.

The sum of both resistances is 3 ohms.

1.5 x 1.5 is 2.25, dividing by 3 gives us... 0.75 ohms, or exactly half of the coils' primary resistance..

0.75 ohms multiplied by 12 volts is 9 amps. That's close to blowing the fuse (10A) and we are only firing two coils.

We have to add resistance to this circuit, but it's a parallel circuit. Where do we add the resistor to the circuit and what value does it have to be?

My head hurts, someone else can do some thinking for a bit, I need a break.

 

Surely it wouldn't be that much? Resistors for LED indicators are about 8ohms at 12 volts DC (about 21 watts). I think we would be running resistors between 4-6 ohms.