Twin ballast resistor. Help please

[rammer]

hi
ive been helping a young guy down the street get his chinese quad to go again, broken frame seized brakes wouldnt start.........you name it ,it was munted
anyway i got it all fixed and running,but theres a twin ballast resistor on the side of the frame and its snapped in half,what does the ballast do and should i be replacing it for the poor bugger??it seems to start and run fine but obviously the ballast is there for a reason ??????
any advice would be appreciated
cheers
rammer

[crash harry]

I'm assuming you're talking about a ballast resistor in the ignition circuit?

Ballast resistor for the coil limits the current in the coil. The theory is that the ballast resistor is shorted out during starting which overdrives the coil and produces a bloody great spark to help the engine start, then during normal running the ballast is switched in to limit the coil current to keep the coil from overheating.

If there are two ballast resistors in parallel, then if one is missing the coil will not be getting as much current as it should so the spark will be weak. If you have had to short the ballast to get it to run then the coil may overheat.

Simplest advice is to replace the broken ballast resistor and all should be well. Also, check that the coil is a 9V coil not a 12V coil. 12V coils are designed to be used without a ballast. You're a bit far away so I can't lend a hand in person, but if I've done a crap job of explaining (probably) feel free to PM me and I'll see if I can help.

[pete376403]

The version I was taught during my apprenticeship is that during cranking, battery voltage will drop; if the coil is rated at the full 12 volts the spark will be weak, at a time when it really needs to be good and fat. When a ballast resistor is incorporated, the coil is nominally rated at a lower voltage. During cranking, the resistor is switched out, so the coil is getting all the voltage the battery can deliver. Once started, the battery voltage is back up to 12v, so the resistor is switched back into the circuit to prevent the coil getting over voltage.
So - two versions of the same story, one limiting current, the other limiting voltage.

[rammer]

thanks guys, i will track down a new ballast setup and fit it .cheers

[glegge]

is this bike injected? some injection systems have ballest resistors in them for the injectors as well, if not, it's most likley for the ignition, either way - replace it. funny, if the bike is running and the ballests have NOT been bypassed, then - yeah, well weird, i wonder what they are for...