Matching to the impedance of an alternator.

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

My workshop is stripped out for refurb ATM and most of my test gear is in tea chests at the back of the garage.

I'd sell my soul for a set of GH6 load curves!

wrote in

cells

what I

that

want

to be

The wide frequency range of a vehicle alternator will make that tricky. Maybe one cap that peaks things at lowish RPMs would help low-end power transfer. It will become a short at higher speeds, when plenty of voltage is available anyhow. Might be a reasonable cap for a bicycle-sized alternator.

John

--
Depends on frequency and inductance, and switching make-before-break
will get rid of the high-voltage problem.

Zero on-topic content, as usual.

Say something about alternators, unless you forgot it all.

John

Not if it's pure synchronous. It will just sit there and hum. It needs some induction or eddy-current component to generate net zero-speed torque.

Big polyphase synchronous motors are usually started in induction mode. Some have specific rotor windings and startup controllers for that.

But the point is that a PM alternator does NOT present a lot of torque load when its output is shorted, because it's not transferring power. The terminal current is high, but that's just quadrature current sloshing around, only heating the windings a little.

Hey, I had to take two full semisters of Electric Machinery, with labs, and my test average was in the low 60's. I got an "A", because class average was in the 20's. The prof's name was Weber, not the original Weber I think.

John

--
You'd certainly be getting the better end of the bargain!

[snip]

Something about alternators ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

An alternator's output current is usually limited by its internal inductance, which is why load current is fairly constant as speed changes. If you add a cap to series resonate out the inductance, the available current becomes the open-circuit voltage divided by the copper resistance. That could be huge, way more than the alternator was designed to deliver.

John

Yup, you forgot it all, if you ever understood it. Stay "puzzled"

John

You want simple? Dynamo output through a series capacitor (experiment to get the size right) into a full-wave bridge of Schottky diodes. Output of that into the battery. Battery through a switch into your light.

The design complexity ramps up for three reasons. First off, this is a design group, so solutions that involve minimal design are subliminally discouraged. Second, some of tha parts out there (why hasn't Jan posted a PIC solution) allow very complex solutions with low parts count. Finally, if this was to be a commercial product, extra design effort might pay off in better product performance.

As if we needed any more reminders you know much more about thinking up insults than you do about electronics.

BTW: I wouldn't give you the steam off my shit for yours.

I always do as minimalist as I can get away with.

'Fraid you're wrong there, John. I said *three phase* synchronous

*permanent magnet* motor. The permanent magnet rotor will follow the stator's rotating magnetic field at any frequency (rotation) right down to, and including, zero.

You just have to keep an eye on the volts-per-hertz.

It's the basis of most, if not all CNC axis servos, and other positioning systems, for about the last thirty years.

They aren't permanent magnet, but DC excited via slip rings. They will still start from rest. They usually are started with gradually increasing voltage, resistor bank, or autotransformer.

Torque is proportional to current, not power. Otherwise you couldn't lock a permanent magnet motor with DC.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Larkin keeps saying, "An alternator's output current is usually limited by its internal inductance".

Equating a bicycle hub "dynamo" to most meanings of the word "alternator" is absurd.

Hub _PM_ "dynamos" use inductive limiting as a cheap-ass way to "regulate". ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

That's similar to one of the thoughts I had... I thought that using power FET's as circuit-controlled rectifiers would buy some useful output by eliminating the diode losses. AND could do double duty as a regulating element. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

"Ian Field" wrote in news:031Oq.214$ snipped-for-privacy@newsfe14.ams:

having two LEDs in series means you need a higher battery voltage than what

4 AA NiMH can supply.

I did my bike light with each LED separately supplied; the DealExtreme regulator I chose had 3 325ma ICs paralleled to sink 975ma (their "1A" rating),I removed one IC(SOT pkg,tiny!),cut a run and used the two remaining ICs separately,but supplied from the same pack. the regulator PCB is the size of a dime.it's not a switching regulator,but I have no complaints about battery life. I figure it will run at least 3hrs,maybe more,andI don;t do that much night riding. It works great,the light doesn't even get warm. IIRC,the regulator PCB was only 2 USD,the Cree LEDs were 5.35 USD each,and aluminum reflectors I can't recall,but cheap. the housing is 1" square AL "tubing",two pieces side-by-side epoxied together,with the mating sides notched for heat sink and rear panel.I used another piece cut into a U channel that slides into the notch,mounted the switch and power jack on the end,and the inside butted against the L-shaped heatsink-LED mount.They screw down on the bottom of the unit.

I got the design from Googling DIY bike lights.It's 2" square,and the 4-AA battery pack is velcroed to the front bike frame,the vertical part. the headlight could easily be mounted on your helmet,the guy who created the design intended to do that,with the battery pack on his belt,I guess.

If you give me your email address,I'll send you a pic of my bikelight on my mountainbike. my email is the proper conversion of what's below my name here.

--
Jim Yanik
jyanik
at
localnet
dot com

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

OK, I chucked a two terminal bicycle dynamo I had laying around in a small lathe and measured the following on the "headlight" terminal with no load connected. A TEK 2236 scope was used. Vpp was calculated from the trace, frequency and Vrms recorded from the display

RPM Frequency Vpp Vrms Hz

200 13.3 4 .99 300 20 6 1.61 400 26.6 7.6 2.22 500 33,3 10 2.81 600 40 11.6 3.38 700 46.6 13.2 3.96 800 53.3 15.2 4.54 900 60 17.0 5.11 1000 66.6 19.5 5.68 1150 76.6 21.0 6.51

Then I measured the resistance and inductance of the headlight winding using a General Radio 1685 digital impedance bridge.

Resistance 8,83 ohms Inductance 7.8/14.2 mH at 120Hz, min/max depending on rotor position

a

This thread is about permanent-magnet bicycle alternators, which are mostly operated in inductance-limited mode, running at much less than open-circuit voltage.

I've worked with, and designed controls for, AC power generators, mostly shipboard, and they run closer to 90% of open-circuit voltage. But they are dumping power into a constant-voltage constant-frequency bus, and run at synchronous speed. That's not what we're talking about here.

In fact, megawatt-level power alternator outputs currents dumped into a system bus are dominantly controlled by internal inductance. It's interesting to manually run one up, synchronize, connect to the bus, and then ramp up the power. It takes a bit of practice.

You obviously don't know anything about any of this, which is why all you have done in this thread is whine.

Which point has already been made in this thread, a couple dozen times, by me and by others.

Idiot.

John

That's part of why I was "bwahahahaha_ing" so :-)

Larkin is so narcissistically ignorant. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
Cranky Old Git With Engineering Mind Faster Than a Speeding Prissy