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Resistors in Ignition Circuits
grassracer - 27/7/09 at 05:48 PM

I'm busy wirirng a ZX6r for autograss use and have fitted a 100ohm resistor in the switched live to the cdi, theproblem I have is still no spark and when I test the circuit I have 12v before the resistor but only 0.6volts immediately after when I test with a multimeter....is this pointing to a problem with the resistors ( I've tried 2 just in case!) any help gratefully recieved

02GF74 - 27/7/09 at 06:16 PM

quote:
Originally posted by grassracer
have fitted a 100ohm resistor in the switched live to the cdi, theproblem I have is still no spark and when I test the circuit I have 12v before the resistor but only 0.6volts immediately after when I test with a multimeter....is this pointing to a problem with the resistors ( I've tried 2 just in case!) any help gratefully received


why is the resistor necessary?

dunno what you are trying to do but resistor appears to be working - it is dropping voltage; that gets converted to heat.

resistors fail if they are made to dissipate more heat than intended, usually accompanied by smoke - I have seen them glow red hot for a short time.

if yours has not gone up in smoke and is not getting too hot to touchm the porlbem lies eslewhere.

grassracer - 27/7/09 at 07:03 PM

The resistor is needed to drop 12v supply down to a 9v supply for the coils to operate so I'm led to believe

britishtrident - 27/7/09 at 07:42 PM

You need a much lower resistance ballast resistor ---- not sure exactltywhat is required for your coil but I suspect it will be in the range of 1 to 6 ohms

02GF74 - 27/7/09 at 07:59 PM

quote:
Originally posted by grassracer
The resistor is needed to drop 12v supply down to a 9v supply for the coils to operate so I'm led to believe


so like a ballast resistor?

without knowing you coil spec. 100 is way too high.

if you can measure resistance of coil, then the ballast would be 1/3 of that value that to drop 3 V, leaving 9 V across the coil.

The resistance of the coil would be around 1.5 ohm (not more than 3 ohm for sure) so resistor is very small value, closer to 1 ohm than 100 ohm.

Check the power rating -you'd been looking at quite a few watts or you'll see smoke.

yorkshire-engines - 27/7/09 at 10:04 PM

Hi some of the early carb engines (which you proberbly have ) dont need a resistor to work
the later need a 100 ohm 10 watt resistor between switched live and the grey wire to ecu the voltage drop is 12 to 10 volts
if you have a resistor that is dropping to .6v then its the wrong wattage try one from the kawa ignition lock any model

cheers malc