Matching to the impedance of an alternator.

You seem to be the only one who still hasn't grasped that I'm not intending to shunt regulate the alternator (incorectly termed a "dynamo" in cycling jargon) with the SLA battery.

Reply to
Ian Field
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But you haven't only got 6V to start with.

Turning the pedals at a decent rate with the alternator unloaded, it can give you quite a belt.

The whole point of my question is to find out whether the alternator can deliver more power if I reduce the current draw so the voltage rises.

The alternator hit the market about 1937 when there were no solid state buck regulators - the bulb rating to regulate the alternator was probably determined by trial & error.

Reply to
Ian Field

That's the problem - my workshop is stripped out for refurb and my test gear packed away in tea chests at the back of the garage.

As I've already stated.

Reply to
Ian Field

Certainly not good with understanding alternators.

John

Reply to
John Larkin

A Sturmey-Archer _HUB_ dynamo is larger than those edge-of-wheel thingies I had as a kid, but is spinning at _wheel_ RPM (about 750 _revolutions_ per mile, 312.5RPM at 25MPH). I don't know how much we can extrapolate from Rick's data.

[Index: Sturmey-Archer hub] ...Jim Thompson
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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Brilliant! Always pedal the same speed. Why didn't I think of that? [1]

That would make cars a lot more efficient, always driving the same speed. You should investigate patenting the idea.

John

[1] the only gotcha being that copper losses will go up as the square of current. A small radiator, water-cooling the alternator, can fix that.
Reply to
John Larkin

I changed gears and went a little over 2000 RPM, driving direct. Voltage was still proportional to speed (until the dynamo came out of the chuck-I should have supported it better!)

If I can fix this one or find another cheapie I'll make it a friction drive...

Reply to
Rick

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

Yeah, I should have looked it up to see exactly what it is. The one I had was an edge of tire style

Reply to
Rick

[snip]

Thanks, anyway, Rick! Maybe re-run it with various loads? I have a fairly good idea on how to behavioral model the inductive current "limiting", but some real data might be enlightening. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

Because of the tiny rubwheel relative to the tyre diameter they spin a hell of a lot faster than a hub dynamo.

In the UK; a miller rubwheel delivers twice the current of a SA hub, but the drag is *HUGE* compared to a hub.

Reply to
Ian Field

Get a wheel off a "shopper" or foldaway cycle small enough to clear the lathe bedway, nip up the bearing cones so you can turn the wheel by clamping the spindle in the chuck, clamp the bottle dynamo in the toolstock and away you go.

The rubwheel speed will be slightly lower than what would be the road speed - the rpm will be more than for a more typical 26x1 3/8-590 wheel.

Reply to
Ian Field

It can. All you need is a simple switchmode current multiplier. I'm sure Jim will post it soon.

John

Reply to
John Larkin

Good stuff. The voltage does look low, given that Ian has noted that his unit will deliver a healthy shock open-circuit. It should increase almost linearly with speed.

John

Reply to
John Larkin

Simulation already posted. See...

Message-ID:

which refers you to...

formatting link

for which the netlist will be posted, once tested with the hub model. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

That's just a cartoon of the waveforms of a classic buck switcher. Note the negative input impedance.

If you let the voltage rise really high, the switcher won't pull much current, and its negative input impedance will be high, so things will be stable. But you may need a switcher that can handle a hundred volts input or more.

There are other ways to do it.

Seems to me the problem isn't fully defined anyhow. What are we trying to do? Increase, roughly double, a battery charging rate compared to what we'd get from a simple bridge rectifier?

Well, at least you're doing electronics.

John

Reply to
John Larkin

Nope. Not a cartoon. It's a fully functional switcher, but all done in behavioral code. No current limit at the moment, but I can add at will.

Of course. That point where it "wobbles" between positive and negative will be interesting to watch.

My behavioral model can handle thousands of volts ;-)

Depends on the definition of "it" :-)

"Other ways"? Show us.

Defined? Yes, Ian wants more current output. But we lack data from a real hub.

Apparently that's what Ian was after. Looks like everyone else is simply changing to LED lighting.

Snarky bait ignored :-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

would

-

Right. We need to define an outcome before we design electronics.

If all we want to do is double the battery charging current, just stick a 2:1 stepdown autotransformer ahead of the bridge rectifier. A little 60 Hz, few-watt power transformer with 120:240 primaries, or a center-tapped secondary, will work. That's easy to do, rugged, cheap. Putting electronics on a bicycle or motorcycle is a nuisance.

Electronically, more work, a buck switcher forced to run at 50% duty cycle does it.

Dealing with battery chemistry is another issue.

John

Reply to
John Larkin

--
Well, let's see...

Ian's dynamo is rated to put out 1.8 watts at 6V, so that's 300mA, and
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Reply to
John Fields

a

Ian has said that his alternator will deliver a healthy shock open-circuit, and since it usually drives about 6 volts worth of lamp, holding fairly constant current vs speed, the operating Xl component must be a lot bigger than the copper ohms. So series resonanting can seriously increase the current, certainly a lot more than 2:1. I don't see why anyone would design a thing like this with hugely thicker wire than necessary, so there is the potential for frying the windings.

There's no reason to try to get more current out of it, when we really want more power. Especially as series resonating only helps over a narrow speed range. To get more power, let the terminal voltage rise, then convert that to charge the battery.

John

Reply to
John Larkin

would

load

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posted

Yep. A buck switcher _alone_ won't do it. As soon as I hitched up the "dynamo" to the switcher via a bridge rectifier, I realized why. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

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