Matching to the impedance of an alternator.

(Normally

loads to

of using

specified voltage.

few

etc.

Rick's numbers are, unfortunately, from a rim-driven unit. I'd expect (but I don't really know for sure) that the wire in a hub dynamo would be a larger gauge (maybe). ...Jim Thompson

Its a 20 pole magnet/armature, the wheel size is 26x1 3/8-590 and these days I never get anywhere near 30mph.

In my younger day I frequently endstopped a 40kph speedo with a good wind behind me.

I'm thinking maybe MC34063 - so the input will have to be clamped below 40V.

A discrete design does have some attractions - in which case a clamp voltage around 60 - 80V might be feasable.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

You clearly haven't read/understood anything!!!!!

I'm already using LEDs.

I'm not trying to get more current from the alternator - I'm trying to get more power by better load matching.

JL is correct - you're pretty much clueless!

While working the GM version of my regulator I was astonished to learn that bus alternators are "cooled" by the engine oil !! ...Jim Thompson

I think that Ian's goal is not to get the maximum possible current, but to get about twice what he'd get with just a bridge rectifier.

John

Is there a mechanical step-up ratio from wheel speed to alternator speed?

John

load

suspect

would

load

here -

the

pair

allowed

(experiment

Output

subliminally

posted

Why?

As I noted, if you run a buck at a fixed 50% duty cycle, the output current is twice the input current. So: alternator, bridge, cap, fixed-duty-cycle switcher. The alternator, being a roughly constant-current gadget in this regime, automatically doubles its output voltage.

Simple. But the autotransformer is simpler.

John

Here are some german links that could be interesting (the graphs and formulas at least). Note that they are concentrating on hub dynamos. The second link also seems to contain some measured data.

(Normally

loads to

using

voltage.

few

Typical MIT geeks, using advanced optics to peep at girls a mile away in the dorms. Nobody at Tulane did that. We just snuck up the back stairs and spent the night.

There was one girl assigned to each floor to guard the purity of the rest. What they actually did was, when a guy was on the way up, they'd yell "Man in the hall, Y'all" so nobody would be embarassed.

John

message=20

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loads to

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know

output

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at

really=20

bench=20

plot=20

Not mentioning traction issues between the dynamo and the tire.

?-)

These things normally run almost short-circuited. I suspect that you'd see *less* mechanical load with a short, as compared to the normal light bulbs. Somebody could verify that.

John

Very true, but mankind has been amplifying his power with that of draft animals, and teams thereof, for a very long time. Moreover electricity has not always been as cheap as it is today. Not to mention steam power, hydraulic power, and wind power have been used for centuries before electricity came on the scene.

?-)

Not really true. Power does get developed and pissed away in the = magnetic and copper losses internal to the alternator. No power delivered does = not mean no power generated; thus torque (roughly proportional to current) = for the shorted case is effectively maximum.

?-)

I doubt it, at normal operating speeds. Someone could try it. A graph of torque versus load resistance would be interesting.

Torque is not simply proportional to current in an alternator. Check this out: lots of current, zero torque:

The *phase* of the current matters.

John

Nope - the armature is nipped up by the bearing cone locknut on the spindle and the 20 pole magnet is bolted to the hub shell.

AFAICR the old bottle 'dynamos' have only 2 pole magnet, but the rubwheel is tiny compared to a typical tyre (maybe about 1" dia) but be that as it may its driven at slightly less than road speed - although that type of 'dynamo' produces twice the current, I havent used that type for years - one side of the coil is grounded to the frame making bridge rectification inconvenient and the mechanical drag is *HUGE*!