Because LEDs run on DC not AC like filiment bulds so you'd be wasting half a cycle (dont forget it's a Bi-cycle) to only rectifcy half the wave.
But I still see little point in it.
be fun to put a wind turbine on the back and a solar panel.
But I;m not sure how effcient a dynmo is I've heard most aren't I don't remmeber pro cyclist using them in compitition or for anything.
Hub dynamos aren't noticable in normal use.
There is a weight penalty, and a small power penalty (under a watt) when off and obviously a few watts when on. Racers don't use any lights, so why take that hit?
However they are popular for the long distance audax rides which aren't races, but do include eg paris-brest-paris which is 1200km in 4 days.
Too inefficient, the forward volt drop is well over 1V can be as high as 3V I believe.
FETs might make it viable energy-wise, they can rectify with minimal loss.
NT
A commutator (and brushes) is just a mechanical rectifier. Nobodies going to bother with such a thing when electronic diodes are available. The traditional "dynamos" were all in fact alternators. Just a permanent magnet rotating inside a coil.
The only reason you might need DC for is to charge a battery. Or a capacitor these days. Or maybe for LEDs. But that can be got round. I'd have thought LEDs drew so little current that (rechargeable) batteries would not be a problem. My LED torch batteries seem to last almost forever.
I would put moving magnets inside fixed coils and have no commutators.
Yup. Although the bottle type tended to give a brighter light in the days when I cycled. But a friction drive is horribly inefficient.
The generators on bike lights are slightly more complicated. They're designed to current limit, which means you get 0.5A or so at most speeds
- but if you increase the resistance, you get more than 6v. So 3V volt drop isn't necessarily that big a deal - though I'd try a bit harder.
What TNP is describing is close to what people use in real life - though the battery backup isn't needed, it's just a capacitor.
Sturmey hub vs other bottle? Yes, the sturmey hub wasn't very powerful - the wheel turns quite slowly, so the magnets required weren't available (or at least not at a sane price) back then. The modern hub dynamos give rather more.
These days the line between a battery and a supercapacitor is increasingly blurred.
That certainly makes sense. Modern low voltage DC motors have also been improved out of all recognition by better magnets.
Shimano Nexus with a bloody big lump of iron into a bracket on the frame to stop it rotating.
I did look glancingly at the Shimano price for a combined dynamo and brake, if I remember correctly, but I also seem to remember having to go and lie down somewhere quiet for a bit afterwards.
Cheers
Dave R
I had one on my bike in the early to mid sixties (which also had a hub dynamo). Alloy tube which held about three U2 batteries (whatever they are called now). The headlight had a 3 position switch underneath; on, off, battery.
Cheers
Dave R
But not recharging the battery.
There is no such thing as a DC motor. I've told you before.
does that mean that those hand held fans run from a battery need an inverter to work? I think not. And I'm sure the starter motot in my car runs on DC.
I use cheap but bright LEDs, screwed to the frame. Used all through last winter more or less daily (so 2 hours/week) on the same set of AAA batteries.
I do have one of those super-bright LED front lamps for the rare occasions I'm cycling on unlit roads.
So what type of voltage do you apply to a "low voltage DC motor"?
Every so often Harry like to show prowess in his greater misunderstanding. I'm surprised he didn't join the argument about centrifugal and centripetal forces.
The general definition of a DC motor is one that you apply DC to. Of course there is also the unipolar motor!
Yes there is. You are probably confusing something you read with reality.
Cheers
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