Re: For those who believe in electricity

On 4/7/2025 12:14 PM, sms wrote:

On 4/7/2025 9:08 AM, Zen Cycle wrote:

On 4/7/2025 11:56 AM, sms wrote:

On 4/7/2025 8:16 AM, Zen Cycle wrote:

On 4/6/2025 10:22 PM, Frank Krygowski wrote:

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A battery puts out DC, it does not provide "half of a sine wave."
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An LED dynamo light would be rectifying the AC into DC, though there are ways around this if the light has multiple LEDs (two LEDs each conducting for half the cycle). If there is only a single LED it can still be powered by the AC from the dynamo but it would be wasteful as it would only be lit for half the cycle.
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For an inexpensive LED light I wouldn't spend too much time trying to repair it. If it were a high-end, LED light then that would be a different story.
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I also have a cheap dynamo light on one bike, the Planet Bike Blaze dynamo, the only dynamo light that I'm aware of that has a flash mode. It has a switch that I never use, it's always on flash mode, and it's powered by a hub dynamo. At night I have a more powerful light of course.
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A rectified AC wave form would work as long as the voltage is within spec of the LED. Pulsatile waveforms are exceeding common in LED driver systems. It's usually driven by a PWM for the intensity control for lighting and through a shift register for a matrix intended for information.
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It isn't wasteful, it's actually more efficient to drive with a lower duty cycle than straight DC.

 Correct that rectified AC would work but Frank was not using rectified AC, he was using DC.

I know, I was just saying...

 PWM DC is very different than AC.

"PWM DC"? PWM by definition isn't DC. PWM generators even at maximum drive aren't 100% duty cycle (yes, effectively DC considering the response of the LED, but still not exactly DC).

With pure AC, the LED would be conducting during only half the cycle.

That's not necessarily a problem, as long as the amplitude of the AC signal crosses the minimum voltage threshold but doesn't exceed the maximum, and as long as the frequency is above ~ 100 Hz most people don't see the flicker (though it can be annoying in poorly designed systems
https://www.scientificamerican.com/article/the-scientific-reason-you-dont-like-led-bulbs-mdash-and-the-simple-way-to-fix-them/)

With AC, it's done like this with two LEDs <https://www.heathcote-electronics.co.uk/images-leds/two-leds- wired-to-AC-power-supply.jpg>.

Yup, that's one way to do it.
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