Motorcycle CDI voltage

Thread Starter

homerdodd

Joined Feb 10, 2018
67
I have an older two stroke dirt bike. The CDI is discontinued, and only available online used for over $400. I found a circuit online for building your own CDI and have attached a picture. However, it calls for 200VAC input, and my stator only produces 50-70 VAC. Just wondering if this is enough to power the circuit. Will the rectifier still convert to 12 VDC output with only 60 VAC in? Can you recommend any changes to the rectifier other circuit changes, given the lower voltage of my stator? Thanks !

motorcycle CDI.jpgother circuit changes, given the lower voltage of my stator? Thanks !
 

debe

Joined Sep 21, 2010
1,252
This is a CDI unit from Silicon Chip in Australia & was avalable as a Kit from Jaycar. Probably not avalable any more. But i have built several of them & the basic kit works great. You will find that the voltages on your engine will work.CDI.4.jpg
 

Thread Starter

homerdodd

Joined Feb 10, 2018
67
This is a CDI unit from Silicon Chip in Australia & was avalable as a Kit from Jaycar. Probably not avalable any more. But i have built several of them & the basic kit works great. You will find that the voltages on your engine will work.View attachment 241284
I'll try this one instead. I understand that timing advance in a CDI is controlled by resistors at the input of the trigger coil, the more resistance, the more advance. so I could adjust as needed for my power band. Wondering if one of the resistors could be a variable for easy adjustment. Any thoughts on this? Thanks, much appreciated !
 

debe

Joined Sep 21, 2010
1,252
For that to work the trigger coil would need to be in a position well before top dead center. The systems start in a retard position then advance. Other sytems use a step shaped trigger magnet for advance retard.
 

Thread Starter

homerdodd

Joined Feb 10, 2018
67
For that to work the trigger coil would need to be in a position well before top dead center. The systems start in a retard position then advance. Other systems use a step shaped trigger magnet for advance retard.

I just realized another issue. C1 on the left end of the circuit schematic, is supposed to be an X2 style non polarized capacitor. I realize that I have installed a polarized cap that was sold to me (must of been a mistake by the guy at the store). I'm thinking this would cause a no spark condition, you think?
 

LowQCab

Joined Nov 6, 2012
1,308
If the Capacitor failed, which it probably has, then yes,
it would prevent a Spark from being generated.

Another alternative Ignition System that will easily adapt is almost any
CDI-Box from a 50cc Chinese-Scooter.
They're dirt-cheap and very simple.
You can get Schematics online.

Replace the Coil while you're at it, it might even be your real problem,
they do fail,
especially if the Engine has been kicked-over with the Spark-Plug-Wire disconnected,
or run with a defective Spark-Plug-Connector-Cap.
.
.
.
 

Thread Starter

homerdodd

Joined Feb 10, 2018
67
If the Capacitor failed, which it probably has, then yes,
it would prevent a Spark from being generated.

Another alternative Ignition System that will easily adapt is almost any
CDI-Box from a 50cc Chinese-Scooter.
They're dirt-cheap and very simple.
You can get Schematics online.

Replace the Coil while you're at it, it might even be your real problem,
they do fail,
especially if the Engine has been kicked-over with the Spark-Plug-Wire disconnected,
or run with a defective Spark-Plug-Connector-Cap.
.
.
.
I have considered this. The only problem is the timing advance. It may be quite a bit more advanced on a scooter than my 250cc dirt bike (RM250). However, I think I could test ride it, and then adjust the timing plate slight before or after TDC ; this could retard if too advanced, and vice versa.
 

LowQCab

Joined Nov 6, 2012
1,308
Or you could jump-off the deep-end and just by a "ZeelTronics" Computer designed for your Bike.
They run about ~$400.oo, but they sure are nice.
You can create any Advance-Curve you like,
plus control the Power-Valve, etc..
.
.
.
 
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