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Joule Thief. I know how they work, but is a joule thief self-regulating and self-limiting? Is a varying input (DC) okay? Answered

Joule Thieves. I know how they work (my one works fine) , but is a joule thief self-regulating and self-limiting? Could I hook it up to a 12V source? Is a varying input voltage okay? -- Will the voltage/current across my white LED (should be 2.6VDC absolute max) be too high or surge? I would like to know if it would be suitable to use on my motorcycle to drive an additional LED or two for a headlight supplement. The voltage varies between 11.5VDC and 18.2VDC. I have a basic handmade circuit, with a hand-wound toroid and a generic transistor, usually running from a stable 1.1 to 1.6VDC, I have tried it with a 9V cell and it seems to work alright, but I want to be sure before modifying it/or my motorbike. Any help much appreciated! 8-)


Is that a yes or no? lol. The regulator on my bike does a pretty pants job of stabilizing the voltage and current for the lamps, I think it's a three-phase to single phase DC, it's an old regulator and it does it's job (I don't blow fuses and bulbs for a pasttime.) just seems a little unstable on the lights. They maintain brightness well, just the voltage is a little unstable, hence I wanted to know whether a JT would self-regulate at 50Mhz(ish). I recently installed an alarm circuit nabbing power direct from the battery, that's fine. Thanks for that lemonie, not quite what I was after, I was more interested in using a Joule Thief on my bike, purely for the "Cos I can" factor. lol I also recently built one so I was thinking of transferring that one, rather than make new circuits or modify existing ones. I was going to make a joule thief that can be removed from the top of my headlamp. I like overengineering things -- when i'm not too tired. That being said sometimes a simple solution is far better! :-)

You'd do better with a voltage regulator I think, the JT doesn't seem to be appropriate for this application. I have burned out 12V halogen-spots on a 50cc (unregulated) moped!


I like the "cos I can " attitude, very similar to "because it's something I want to do"

Yeah, no kidding! A cheap regulator wouldn't have been missed if it was placed into the circuit to help stabilize the whole thing. Thanks, I blitzed it at 9V, seemed alright, then boosted that to 11-15V(ish) and it (the LED) finally gave up -- I can still smell it now, yuck. Interestingly the voltage across the cheap LED I used for the (extreme) testing seemed to drop the higher the JT input voltage was, I can only assume that the LED current is what massacred it. In a JT the current is "pulled" isn't it? -- Thanks to the transistor? (Which I didn't think was possible, due to all the electrical laws I have read about here there and everywhere...) I have seen simple alkaline chargers using a tranny in a different way, they claimed that the current was "pulled" through the cell(s) on charge and thus they retained some of the power passing through them. As for the link thanks, -- I'll 'ave a shoofty. :-)