I'm building a vintage two stroke race bike out of a 78' puch maxi. The original points setup is junk and I'm switching to a CDI.

I have an LED headlight that I'd love to use for aesthetic purposes.

The CDI has a output of 60w 12vac the LED headlight needs 5w/3w 12vdc. I have the understanding that a rectifier will solve the AC/DC problem, but should I be concerned with the wattage output of the CDI blowing my lights?

How do I solve this problem? I have a basic understanding of electricity, but when regulators/rectifiers, resistors, etc. come into conversation I am lost.

Below are the links to the two products I plan on using. Any and all input will be appreciated. Thanks.




1 Answer 1


Looking over the (extremely little) information given ot the pages you linked; it looks like you'll want to get a combo regulator/rectifier & set it to 13.8V or less to protect from ac &/or overvoltage damage.

As for blowing the LED with overcurrent: Unfortunately, they don't specify whether the headlight module inclides its own current-limiting resistor(s)/supply, so while it is generally assumed that such a device 'should' have its own protection, there's not much way to know until you've used it for a few hours.

  • \$\begingroup\$ The description for the LED headlight given in that web link is useless. It doesn't explain why the unit has three wire connection. No information about its internal circuitry or any protection it may have. Without any such detail, u suggest you to look for well built external voltage regulator to maintain 12V output for the headlight for whatever input the CDI may produce. CDI output sometimes are not well regulated, it may shoot as high as 30V momentarily and your headlight may not like it. Building your own regulator is easy but got to make it rugged enough for your application. \$\endgroup\$ Feb 25, 2016 at 3:45
  • \$\begingroup\$ @soosaisteven as it's a headlight, there's a pretty good chance that 1 wire's ground, one is low-beam and the last one's high-beam. ;-) \$\endgroup\$ Feb 25, 2016 at 5:36
  • \$\begingroup\$ I think you are correct. One wire might be for the 3W low beam and the other wire might be for the 5W high beam. \$\endgroup\$ Feb 25, 2016 at 9:12
  • \$\begingroup\$ I plan on using a reg/rec, but I'm concerned with the wattage. I am thinking of using a (28.8Ω?) resistor for the headlight and taillight. Am I over thinking this? Sorry guys this may be elementary for you, I'm a carpenter by day and a hobbyist mechanic by night haha, So this is not my forte. I really appreciate the input though. \$\endgroup\$ Feb 25, 2016 at 22:42
  • \$\begingroup\$ @AaronApostol because it's being sold as a "headlight," it aould be highly irresponsible for the mfgr to have not put a current limiting resistor in there already. With that said, if you'd rather be "safe than sorry," adding a small resistance won't harm the light at all; at worst, it'll make it a bit dimmer than intended, but let it 'live' longer. \$\endgroup\$ Feb 25, 2016 at 23:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.