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Old 06-16-06, 10:26 PM   #1
jordanb
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Dynamo/Generator technical questions

Ok, I called the guy at Sturmey-Archer "Sun Race" USA in California about this and he said he'd forward the question to the engineers but I've not gotten an answer on this yet, so I thought I'd see if someone else with experience with dynamo hubs can answer it.

I have on order a new X-FDD hub, this is the SA hub with a dynamo plus a 70mm drum break. It is, of course, NOT the old S-A Dynohub.

I am designing a lighting system using superbright (like 18000mcd) LEDs. All the information I could find on the hub says that it produces "6V, 3W". Ok, so a half an amp at six volts, presumably AC like the old hub. I've heard that the hub, unlike the old dynohub, was regulated to not exceed that rating. But I was talking to an engineer friend about the project and when I said that he asked "Do you just think that or do you know that it's power-regulated AC?" He said he found it unlikely that they'd do that because it takes a lot more components than either (1 rectifying it into DC and power regulating it or (2 leaving it in AC and not bothering to regulate at all.

So well, if they turn it into DC, it's easy, just dump it right into the system. If it's AC I need to rectify it myself and if (and only if) they don't regulate it at all I need to set up some sort of z-diode/resister pressure valve system. I, of course, don't want to build my circult with a rectifier and z-diode built in if I don't need it, but at the same time I don't want to turn the system into a chunk of expensive plastic if the hub isn't that friendly (18000 mcd LEDs aren't cheap!). Does anyone know about this hub?
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Old 06-16-06, 11:05 PM   #2
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Originally Posted by jordanb
Ok, I called the guy at Sturmey-Archer "Sun Race" USA in California about this and he said he'd forward the question to the engineers but I've not gotten an answer on this yet, so I thought I'd see if someone else with experience with dynamo hubs can answer it.

I have on order a new X-FDD hub, this is the SA hub with a dynamo plus a 70mm drum break. It is, of course, NOT the old S-A Dynohub.

I am designing a lighting system using superbright (like 18000mcd) LEDs. All the information I could find on the hub says that it produces "6V, 3W". Ok, so a half an amp at six volts, presumably AC like the old hub. I've heard that the hub, unlike the old dynohub, was regulated to not exceed that rating. But I was talking to an engineer friend about the project and when I said that he asked "Do you just think that or do you know that it's power-regulated AC?" He said he found it unlikely that they'd do that because it takes a lot more components than either (1 rectifying it into DC and power regulating it or (2 leaving it in AC and not bothering to regulate at all.

So well, if they turn it into DC, it's easy, just dump it right into the system. If it's AC I need to rectify it myself and if (and only if) they don't regulate it at all I need to set up some sort of z-diode/resister pressure valve system. I, of course, don't want to build my circult with a rectifier and z-diode built in if I don't need it, but at the same time I don't want to turn the system into a chunk of expensive plastic if the hub isn't that friendly (18000 mcd LEDs aren't cheap!). Does anyone know about this hub?
We have these in stock. I believe the generator ("dynamo") part is quite similar to the Shimano Nexi.

No generator hub is truly "regulated" in the sense of using active components...zener diodes and the like. The only bicycle generator I know of that includes true, active regulation is the Swiss LightSpin. All of the other systems put the regulating circuitry in the lamp.

All bicycle generators that I know of get _some_ regulation from the inductance of the armature.

Theoretically the voltage should be proportional to the speed, but as the speed increases the AC frequency also increases, so the armature acts as a choke, a low-pass filter, keeping the voltage from rising linearly with the speed.

LEDs are MUCH less voltage critical than incandescent light bulbs, so I don't believe you'll need any additional regulation with any bicycle generator system.

Sheldon "Sparks" Brown
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Old 06-16-06, 11:05 PM   #3
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Originally Posted by jordanb
Ok, I called the guy at Sturmey-Archer "Sun Race" USA in California about this and he said he'd forward the question to the engineers but I've not gotten an answer on this yet, so I thought I'd see if someone else with experience with dynamo hubs can answer it.

I have on order a new X-FDD hub, this is the SA hub with a dynamo plus a 70mm drum break. It is, of course, NOT the old S-A Dynohub.

I am designing a lighting system using superbright (like 18000mcd) LEDs. All the information I could find on the hub says that it produces "6V, 3W". Ok, so a half an amp at six volts, presumably AC like the old hub. I've heard that the hub, unlike the old dynohub, was regulated to not exceed that rating. But I was talking to an engineer friend about the project and when I said that he asked "Do you just think that or do you know that it's power-regulated AC?" He said he found it unlikely that they'd do that because it takes a lot more components than either (1 rectifying it into DC and power regulating it or (2 leaving it in AC and not bothering to regulate at all.

So well, if they turn it into DC, it's easy, just dump it right into the system. If it's AC I need to rectify it myself and if (and only if) they don't regulate it at all I need to set up some sort of z-diode/resister pressure valve system. I, of course, don't want to build my circult with a rectifier and z-diode built in if I don't need it, but at the same time I don't want to turn the system into a chunk of expensive plastic if the hub isn't that friendly (18000 mcd LEDs aren't cheap!). Does anyone know about this hub?
We have these in stock. I believe the generator ("dynamo") part is quite similar to the Shimano Nexi.

No generator hub is truly "regulated" in the sense of using active components...zener diodes and the like. The only bicycle generator I know of that includes true, active regulation is the Swiss LightSpin. All of the other systems put the regulating circuitry in the lamp.

All bicycle generators that I know of get _some_ regulation from the inductance of the armature.

Theoretically the voltage should be proportional to the speed, but as the speed increases the AC frequency also increases, so the armature acts as a choke, a low-pass filter, keeping the voltage from rising linearly with the speed.

LEDs are MUCH less voltage critical than incandescent light bulbs, so I don't believe you'll need any additional regulation with any bicycle generator system.

Sheldon "Sparks" Brown
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Old 06-17-06, 02:38 PM   #4
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Quote:
Originally Posted by jordanb
Ok, I called the guy at Sturmey-Archer "Sun Race" USA in California about this and he said he'd forward the question to the engineers but I've not gotten an answer on this yet, so I thought I'd see if someone else with experience with dynamo hubs can answer it.

I have on order a new X-FDD hub, this is the SA hub with a dynamo plus a 70mm drum break. It is, of course, NOT the old S-A Dynohub.

I am designing a lighting system using superbright (like 18000mcd) LEDs. All the information I could find on the hub says that it produces "6V, 3W". Ok, so a half an amp at six volts, presumably AC like the old hub. I've heard that the hub, unlike the old dynohub, was regulated to not exceed that rating. But I was talking to an engineer friend about the project and when I said that he asked "Do you just think that or do you know that it's power-regulated AC?" He said he found it unlikely that they'd do that because it takes a lot more components than either (1 rectifying it into DC and power regulating it or (2 leaving it in AC and not bothering to regulate at all.

So well, if they turn it into DC, it's easy, just dump it right into the system. If it's AC I need to rectify it myself and if (and only if) they don't regulate it at all I need to set up some sort of z-diode/resister pressure valve system. I, of course, don't want to build my circult with a rectifier and z-diode built in if I don't need it, but at the same time I don't want to turn the system into a chunk of expensive plastic if the hub isn't that friendly (18000 mcd LEDs aren't cheap!). Does anyone know about this hub?
We have these in stock. I believe the generator ("dynamo") part is quite similar to the Shimano Nexi.

No generator hub is truly "regulated" in the sense of using active components...zener diodes and the like. The only bicycle generator I know of that includes true, active regulation is the Swiss LightSpin. All of the other systems put the regulating circuitry in the lamp.

All bicycle generators that I know of get _some_ regulation from the inductance of the armature.

Theoretically the voltage should be proportional to the speed, but as the speed increases the AC frequency also increases, so the armature acts as a choke, a low-pass filter, keeping the voltage from rising linearly with the speed.

LEDs are MUCH less voltage critical than incandescent light bulbs, so I don't believe you'll need any additional regulation with any bicycle generator system.

Sheldon "Sparks" Brown
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Old 06-18-06, 12:17 PM   #5
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You don’t even need a full wave rectifier, which requires 4 diodes. Rechargeable batteries work best when using only one diode so you get pulses of positive going voltage into the positive side of the battery. The battery will filter out the ripple so the light will not flash at low speed. If using a Sealed Lead Acid (SLA) Battery you wont really need a regulation circuit as most of them now have a regulator built into the battery. The regulators are cheap and the battery manufactures starting adding them to prevent battery charging damage insuring long life and return sales.
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Old 12-05-06, 05:03 PM   #6
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How is this project going? I'm having a front wheel built up with this hub. I have a couple Luxeon's laying around from another un-completed project.

Anyone have an idea what frequencies are typical with these generators? This of course depends on speed and wheel diameter. Alternatively, how many voltage cycles do you get per wheel rotation?

I'm also interested in using the same hub with EL wire. There are a lot of cheap DC->AC converters available for that purpose; it seems the route of least effort would be to rectify the AC from the hub and then put that into one of these cheapo converters.

Here are some links I've accumulated so far...

Dynamo regulator circuits:
http://www.nscl.msu.edu/~daniel/sreg.htm
http://www.gobike.org/feat_lights.php

EL wire by the foot and regulators: (as cheap as $4 plus wire for about $1.50 a foot)
http://shopping.netsuite.com/s.nl/c....category.41/.f

As for rolling one's own EL driver, here's a $2 chip available on Digikey
http://www.micrel.com/_PDF/mic4826.pdf
http://www.digikey.com/scripts/DkSea...?KeywordSearch
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Old 12-06-06, 10:41 AM   #7
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You donít even need a full wave rectifier, which requires 4 diodes. Rechargeable batteries work best when using only one diode so you get pulses of positive going voltage into the positive side of the battery.
But doesn't that mean you're throwing away half of the electricity you make?

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Old 12-06-06, 10:42 AM   #8
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Originally Posted by awagner
How is this project going? I'm having a front wheel built up with this hub. I have a couple Luxeon's laying around from another un-completed project.

Anyone have an idea what frequencies are typical with these generators? This of course depends on speed and wheel diameter. Alternatively, how many voltage cycles do you get per wheel rotation?
My recollection is that Dynohubs had 20 pole magnets. Current generator hubs are probably similar, judging by the apparent flicker frequency at low speeds.

Sheldon "Generators" Brown
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Old 12-06-06, 11:34 AM   #9
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But doesn't that mean you're throwing away half of the electricity you make?

Sheldon "Full Wave" Brown
No, you technically make half the electricity and reduce your rolling resistance.
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Old 12-06-06, 11:52 AM   #10
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No, you technically make half the electricity and reduce your rolling resistance.
That would be so if there was zero drag from the generator when it isn't powering a light, but that's not the case.

Also, using half-wave would likely reduce the RMS voltage below 6 volts, making it tough to charge a 6 volt battery.

Sheldon "Full Wave Bridges Are Cheap As Dirt" Brown
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Old 12-06-06, 03:50 PM   #11
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Originally Posted by Sheldon Brown
That would be so if there was zero drag from the generator when it isn't powering a light, but that's not the case.

Also, using half-wave would likely reduce the RMS voltage below 6 volts, making it tough to charge a 6 volt battery.

Sheldon "Full Wave Bridges Are Cheap As Dirt" Brown
It is the peak voltage of the rectified waveform that determines how high you can charge the battery, not the RMS. A full bridge will actually have twice as much voltage drop from the diodes, and will not be able to charge a battery to as high a voltage as the half bridge (i.e. a single diode). That said, the full bridge will probably charge the battery faster, since the rectified waveform will peak twice as often.

I found some more sophisticated circuits for generator powered LED headlamps:
http://pilom.de/BicycleElectronics/DynamoCircuits.htm

The graph on the bottom is interesting. With his fancier circuits, you can get the lamp to fire up at significantly lower speeds than you can with a diode rectifier.
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Old 12-06-06, 05:31 PM   #12
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Originally Posted by Sheldon Brown
That would be so if there was zero drag from the generator when it isn't powering a light, but that's not the case.
I didn't say it would cut the rolling resistance in half, I just said there would be less. And I would be right. Hook a diode up to an A/C motor and spin it with your hand at a good pace.

Now, hook up a bridge rectifier and try to spin it. It will be more difficult.

Noah "I mess with this stuff for a living" Dunker
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Old 12-06-06, 06:24 PM   #13
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