12 volt Bicycle Generator : discerning polarities for hooking up loads

One terminal is the case of the generator. It must be solidly connected to the bike frame so the frame can be used as part of the circuit.

Probably two separate windings, both with one end connected to the case as with the single output generator.

(snip)

Have you tried the AC setting on your meter? These are almost certainly AC generators. Just a magnet spinning inside a stationary coil.

Those bicycle generators are AC devices. Try switching your multimeter to AC Volts position and see what you see. Unlike a toy DC motor they do not have brushes or a commutator on rotating coils. They have fixed coils surrounding a rotating magnet so they produce alternating current as first the north pole then the south pole sweeps past the coil. And yes, the bike frame is one leg of the circuit. May find that clamp that holds the dynamo on the fork leg has a set screw that pierces the paintwork to make good contact with metal of frame. The H and T terminals on one of your generators may go to separate coils of different sizes so head has more power to it than tail. Or they may both go to same coil and two terms is just for convenience of hooking up. Try measuring resistance from each term to generator case using your digital multimeter. Then measure resistance between each terminal. If res between terms is just about zero they're connected internally to top of same coil. If they're connected to two separate coils the res will be the sum of term H to ground plus Term T to ground.

Here's a link to just one page of some interesting reading.

However, bicycle gens are low powered devices, rated at about three watts so the likelihood of doing any significant battery charging with one is slim.

PH

Thanks,

Switching the DMM to AC made a huge difference. I actually got real readings. Grounding the negative terminal of the light lead to the bottle generator case/clip proved effective.

Now this raises other questions for me.

Can I wire 3 or four of these generators up in series or paralell to increase the power? Let's say I had three of them. If these were DC power supply, I would just hook up negative to negative to negative and positive to positive to positive for a paralell connection or positive to negative x

3 for series connection.

Since these are AC devices, is series and paralell wirings possible, effective, or? If yes, then how so?

Since the H and T terminals are of the same polarity, I would rather use them both (all if wired to other generators) for one load (i.e. motor charging) instead of two different loads (lights) How must I go about ?

Thanks again in advance,

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No. Doing that would require that they all be run in precise synchronism, and that isn't practical.

Even if they were DC generators, connecting them in series would be problematical, because of the case being one of the terminals. You would have to mount at least two of them, isolated from the frame.

Possible in theory, but not practical.

How do you know that H and T are the same polarity? Do you get zero volts AC between them with the generator running?

Actually, I was able to get some voltage between the two, but not quite as much between either of them and the casing. I'll have to measure them again and write down the exacts.

Generally for AC bottle generators (alternator to be PC)are the H and T the same or opposite terminals?

Maybe I'll just have to open one of them up and see which one connects to the casing.

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If you are trying to make a DC supply from these generators, there is an easy way to make DC with two rectifiers (preferably Schottkys, for low forward drop) and two electrolytic capacitors. Connect a cathode to the output terminal, and the anode to the negative side of the capacitor. The positive side goes to ground (frame). Connect the anode of the other rectifier to the output terminal and the cathode to the positive side of the second capacitor. Connect the negative side of that capacitor to frame. This gives you two half wave rectified DC outputs in series for twice the voltage you would get from a bridge.

Parallel the outputs of another generator (or another terminal from this one) with another two similarly connected diodes feeding the same two capacitors.

Connect your loads across the ungrounded ends of the two capacitors.

"greenwanderer108" wrote in message news:Y6udnSK85tWIt8LeRVn snipped-for-privacy@giganews.com...

Don't forget that theres no such thing as free power.There must be some form of input energy to convert to another form of energy, and with some losses inherent in the conversion process. One of those bottle generators is a significant drag on a bicycle wheel, four of them is four times the drag. Not so bad if it's the wind or falling water spinning the wheel, a different matter if it's YOUR bursting lungs and burning leg muscles that's providing the input. One thing is sure, you won't get out in electricity what you put in as muscular power. You'll get even less efficiency if you store the electricity in a battery and then use it to drive an electric assist motor. In other words, if you pedal twenty miles with a bottle generator adding to the wind resistance, rolling resistance and transmission losses, you won't get another twenty miles of blissful and silent progress on electric motor power. If you're interested in electric assist, it will be much easier on your body to charge your battery at home from the wall socket. I'd even say that's also the way to go for night-time lighting. However, if you love to experiment, I'll say that when I was a kid I was never very impressed by the design or construction of those bottle generators. Why not look into using stepper motors salvaged from dead computer printers/photocopiers etc? Here's a link to get you started.

That link was in the first three I found by Googling "stepper motor generator.." Just for fun, I walked into my workshop and picked up a little old printer stepper that's been on the workbench for two years. It took me 30 seconds with a multimeter to establish that its five wires consist of one common and four coil wires. (read the article) After that, an AC voltmeter conected from common to one coil wire read 6volts with just a flick of the motor shaft with my fingers. I then started to look with more interest at three BIG steppers marked 24volts that are part of a junked 1980's DEC dot matrix printer. That will have to wait till later. If you can get hold of a junked printer or two, I daresay you'll find a supply of steppers that are far superior in tolerances and construction to any Taiwanese bicycle generator. Again, when I was a kid, a pal of mine had a truly horrible little gasoline bicycle motor made by Solex in France. Its crankhaft had a grooved unglazed porcelain roller directly attached to it (unglazed and grooved for grip) This motor was mounted over the front wheel and was held off the tyre by a lever arrangement. You got the bicycle up to speed, flicked the lever and the roller dropped onto the wheel. Iif you were lucky the motor started and off you went in a cloud of blue fumes and noise.From my memory of the roller size, the reduction from roller to wheel was around 15:1. Of, course, in wet weather there was considerable slippage. Anyhow, this could be your answer to driving a stepper as a generator. Mount it above the wheel, about where a centre-pull brake goes, with some form of friction-ful roller attached to the shaft and contacting the tyre. As you don't have the weight of a gasoline motor holding the roller in contact, use s big spring or bungee cord or tie half a brick to it. All of this supposes that you have a few hand tools and bits and pieces of scrap metal to make brackets and such like.

In the meantime, you need to establish if that bottle generator has two windings or just two terminals attached to one winding. Use the ohm-meter. If there are two windings, if you're lucky they will be opposite in phase. In which case you can connect the anode end of a diode to each terminal, twist the cathode ends of the diodes together (the ends with the ring printed on the diode body) and get full-wave rectified DC at the commoned up cathodes. 1N4004 diodes for 10c each will do for the expereiment. If there's only one winding in there, you will be stuck with one diode and half-wave rectification. That means 10VAC turns into about 4.5VDC. Not very efficient and only good if you have power to waste. (You only get to use half the waveform and you lose about 0.6V across the diode).

PH

If you rectify the output they can be run in parallel. prbably seriies too... but one of them is hard enough to turn...

put a layer of polythene cut from a soft-drink bottle between the clamp and the frame, and then rectify....

Bye. Jasen