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Generator Hub and Batteries

Old 07-18-08, 03:15 PM
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Generator Hub and Batteries

On sort of a whim (kind of naively, since I'm not too knowledgeable about things electric), I bought a Shimano Nexus generator hub (3N71). I needed a new wheel, so for a few extra bucks, I thought I would check it out 'for scientific purposes'. I do not yet have a decent light to run with it, though I have made a simple bridge rectifier.

What I do have is a 'typical' rechargeable 6V battery and matching halogens (2 x 3W). With the battery, these provide very good lighting on dark roads (for 1.5 hours or so), but the generator hub cannot adequately power them. After reading several threads, including this one:

https://www.bikeforums.net/showthread...or+hub+shimano

I'm thinking of just adding the battery into the circuit as shown therein and running like that. The hub won't generate enough power, but it should (?) contribute to the run-time of the battery, right? And then I can charge during the day, if I want. I think Sheldon Brown ran something like this (see https://www.sheldonbrown.com/dynohubs.html).

My questions are the following:

1) Is this correct? Can I charge in the day and extend the charge during the night with the hub?
2) Is this a reasonable idea? Will I run the risk of damaging the battery?
3) Can/should I remove the capacitor from my rectifier?

If anyone wants more specifics, let me know.
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Old 07-18-08, 04:26 PM
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Here is a link to everything you need to know about building very bright LED lights for use with your dynamo hub.
https://pilom.com/BicycleElectronics/...lectronics.htm
Here is a link for the brightest star mounted LED suitable for using with a dynamo and bridge rectifier.
https://www.dealextreme.com/details.dx/sku.2394
If you copy the single LED and elliptical optic on Martins site here is where you get it for use with the Cree LED.
https://www.luxeonstar.com/fraen-elli...leds-p-306.php
A single LED light will be much brighter than your halogen lights and you will not need any batteries.

Here is the updated circuit I use which includes a USB connector for powering and/or recharging USB devices like a cell phone or GPS unit.

The 4 Ni-MH batteries must be solder tab type with no possability of an open or poor connection which would allow unfiltered and unregulated power into the USB device possibility damaging it. My original circuit used batteries to filter and regulate a single 1-watt LED that was not rated for more than 350mA. The new power LED's can take 1,000mA so a standard dynamo in incapable of producing more current than the LED can handle.

Last edited by n4zou; 07-18-08 at 04:35 PM.
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Old 07-19-08, 02:06 AM
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If your problem is not enough light replace those two halogens with two LEDs and don't worry about batteries at all. Should boost your light output 3-4 times. Or you can go with more LEDs for stupidly bright lights.

You shouldn't need the bridge rectifier for the halogens either.
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Old 07-19-08, 11:26 AM
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Originally Posted by znomit

You shouldn't need the bridge rectifier for the halogens either.
+1
Filament bulbs don't care if you feed then AC or DC current.
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Old 07-19-08, 01:41 PM
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Originally Posted by n4zou
+1
Filament bulbs don't care if you feed then AC or DC current.
OK, this is mildly comical because, despite the fact that I don't know much about electricity, I thought this was the case. When the first person I asked at work told me I needed a rectifier, I tried to explain that I didn't (on the grounds that a resistance element doesn't 'care' which way the electrons are flowing). When the second person told me, I figured I must have been wrong. Nevertheless, it was easier to give in and fun to learn how to make one and how it works.

I'm not necessarily trying to make the halogens work. When I bought the hub I naively thought 6V hub + 6V lamps = I'm set. I have since realized that LEDs are probably the way to go. BUT, if I still wanted to put a battery in the loop (even if I don't need it -- remember, I'm also experimenting), would a 6V Lead Acid battery work (basically this: https://www.amazon.com/SIGMA-EVO-Halo...6559&sr=1-22)? Or should I go with the 4.8V of NiMH like n4zou shows. Does it matter if maybe, someday, I want to stick a USB connector on there (primarily for charging a cell phone**)?

Thanks all for the advice and links. I'll start digging through stuff before it gets dark.



**in case your battery is running low when you're in the middle of France and it's getting dark and you need to call your wife to figure out when and where the nearest train is. Not that that would happen to me. No sirree. I'm far too well prepared...

Last edited by Pedaleur; 07-19-08 at 01:47 PM.
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Old 07-19-08, 09:38 PM
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Standard bicycle dynamo lights use a filament just like any other kind of filament type bulb. They just happen to be designed for 3 watts of AC current. This takes the form of a headlight bulb with a 2.4 watt filament and a taillight bulb with a .6 watt filament. This provides a balanced load so the dynamo generally will not produce more than about 6 volts at "normal" bicycle speed. 3 watt bulbs are used in the headlight when no taillight will be used. If you try to use a 2.4 watt 6 volt bulb without a .6 watt taillight the dynamo will produce more than 6 volts so the bulbs life will be shortened. Just any old 6 volt light will not work. The reason LED's have become so popular for use with dynamo light systems is due to there use of current for light production other than voltage like that for a filament bulb. A typical dynamo will produce about 500mA and due to it's design can't produce much more even with higher speeds. Voltage however is variable increasing with speed. Most bicycle dynamos can produce 12 volts when using a 6 watt bulb but those have become almost impossible to find. LED's produce light from the current flowing through them and not voltage like filament bulbs. When using LED's in a dynamo circuit voltage is no longer a problem as current determines light output and not voltage. Most power LED's are rated for voltage but only when used with batteries. The dynamo is limited in current production so as long as the current is below the maximum for the LED being used it can't be burned out even if voltage is higher than stated in the specifications. If light producing LED's could stand reverse current as they do forward current a bridge rectifier would not be needed.
You can add a battery to the circuit so the dynamo light remains lit at stops but this adds complication. Now you must use a voltage regulation circuit with the lights or LED's as voltage become a problem once again. It's so much easier to simply allow the LED headlight to quit at stop's and add a blinkie so that others can see you when your stopped than go through all the harassment of batteries and regulation circuits for your headlight and you'll have a lot more light when you do start moving again. My dynamo LED headlight provides enough light at walking speed as I'm pushing it up a steep hill to allow me to see where I'm going so a battery is never needed. Of course I always carry a small flashlight just in case I ever need to fix a flat or other repair when it's dark.

Last edited by n4zou; 07-19-08 at 09:42 PM.
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Old 07-21-08, 05:11 PM
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One thought about A/C through a filament bulb. 60 cycles coming out of the wall works well, as our brains are not quick enough to pick it up, but a hub dynamo ain't gonna be making 60 cycles unless you are going ....... uhhhhh pi X uhhhh something x uhhhh....well, let's just say you gotta be going real fast. A friction sidewall powered one will spin pretty fast though.

My point is, you may look like a strobe light going down the road. This will probably annoy you and surely annoy the oncoming cager to the point of maybe aiming for you.

On the plus side there is some entertainment value in causing folks with epilepsy to go into a seizure and flop around on the ground. Not so much of course if that epileptic is driving the tahoe headed straight at you!

Perhaps I am completely wrong in this regard, but, I figured I'd throw my 2 cents in anyhow.

I think I am leaning heavily towards the dyno idea. Anybody out there got a dyno hubbed wheel they want to part with for a reasonable cost?
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Old 07-21-08, 05:27 PM
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Originally Posted by trekker pete
One thought about A/C through a filament bulb. 60 cycles coming out of the wall works well, as our brains are not quick enough to pick it up, but a hub dynamo ain't gonna be making 60 cycles unless you are
My point is, you may look like a strobe light going down the road.

Perhaps I am completely wrong in this regard, but, I figured I'd throw my 2 cents in anyhow.
The incandescent filament doesn't have time to cool down between cycles.
Older flourescent bulbs do flash at 60Hz and you can notice it(set your monitor to 60Hz refresh and see ... new CF bulbs go at a much higher frequency).
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Old 07-21-08, 05:52 PM
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Thanks for clarifying that for me, zoom. So much for terrorizing epileptics.
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Old 07-21-08, 07:05 PM
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For that, you need one of these:
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Old 07-21-08, 07:29 PM
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Hubs rotate at a much lower frequency than bottles, and though they have more poles to somewhat compensate, they still end up delivering a much lower frequency. At 15 km/h, the B&M Dymotec6 bottle dynamo (8 poles) outputs 168 Hz AC while the Shimano DH-3D71 hub dynamo (28 poles) outputs only 28 Hz at the same speed. At 8 km/h, a 28 pole hub is down to 15 Hz, which causes visible flicker of the light.
https://pilom.com/BicycleElectronics/HubDynamo.htm
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Old 07-21-08, 10:03 PM
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Originally Posted by n4zou
Hubs rotate at a much lower frequency than bottles, and though they have more poles to somewhat compensate, they still end up delivering a much lower frequency. At 15 km/h, the B&M Dymotec6 bottle dynamo (8 poles) outputs 168 Hz AC while the Shimano DH-3D71 hub dynamo (28 poles) outputs only 28 Hz at the same speed. At 8 km/h, a 28 pole hub is down to 15 Hz, which causes visible flicker of the light.
https://pilom.com/BicycleElectronics/HubDynamo.htm
Okay my burning question (no pun intended) is how does a dyno hub powered lights compare to something like the Nightrider Digital Evolution? Which is brighter??
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Old 07-21-08, 11:05 PM
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You get around 150lm/led ... about 6w halogen equivalent. So a three LED will be like a 20w halogen, brighter than the nightrider and more importantly will run all night every night.
You want brighter just put more LEDs in.
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Old 07-22-08, 12:03 AM
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Originally Posted by znomit
You get around 150lm/led ... about 6w halogen equivalent. So a three LED will be like a 20w halogen, brighter than the nightrider and more importantly will run all night every night.
You want brighter just put more LEDs in.

Okay, when I was in school the teachers labeled me "a little slow" so help me out with the electronics side of it. If I'm understanding you correctly you're saying that the LED based lights are more efficient on their usage of current/wattage compared to halogen and three 1Watt LEDs put out double the light of a 10w halogen? Am I correct?

Last edited by Sirrus Rider; 07-22-08 at 12:07 AM. Reason: word usage
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Old 07-22-08, 12:25 AM
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A dynamo puts out 500mA constant current. The voltage goes up when you put more LEDs in. Kinda magic.
Word is it tops out around 12W which is an awful lot of light (over 1000lm).
See www.pilom.com for circuits and speed/power curves.
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Old 07-22-08, 07:23 AM
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While we are talking genies and batteries, I was wondering if any of the hub genies out there can provide enough torque to provide noticeable assistance. I'm not looking for a 30 mph ebike. Just a little extra something to help on short hills. You might also be able to reclaim some of that precious kinetic energy through regen on the down hills. Maybe a really big ass capacitor might serve well in this application as you can charge/discharge at pretty high currents for short periods.
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Old 07-22-08, 08:40 AM
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Originally Posted by trekker pete
While we are talking genies and batteries, I was wondering if any of the hub genies out there can provide enough torque to provide noticeable assistance. I'm not looking for a 30 mph ebike. Just a little extra something to help on short hills. You might also be able to reclaim some of that precious kinetic energy through regen on the down hills. Maybe a really big ass capacitor might serve well in this application as you can charge/discharge at pretty high currents for short periods.
It takes about 2.5 hours to recharge 4 AA Ni-MH batteries with a bicycle dynamo. Your not going to get any help going up a hill with a tiny little motor which could be powered with 4 little AA batteries. A modern bottle dynamo requires about 8-watts of your energy to produce 3-watts of light. A hub dynamo is a little better using about 6-watts. I hear some people complain about even this very small additional drag. I can't imagine the pedal power required when adding a larger generator to provide enough current to recharge batteries large enough to power even a very small 250-watt hub motor for any length of time.
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Old 07-25-08, 07:26 PM
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As a relative newbie I hope it's ok to post on this thread, I realise I shouldn't post on dead ones but the last post was only 3 days ago, so I hope it's ok ?



I've recently bought a shimano hub dynamo and have been looking at different types of front light without any real success.

I'd rather use LEDs than halogen and I would really like a decent light output.

Is there a definitive design of headlight that will work with my hub ?

My hub is a HB-NX30.

TIA for any advice.
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Old 07-25-08, 11:22 PM
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All the 6-V 2,4 W headlights will work, whether they are LED or halogen. That being said, you have two or three practical possibilities:

1. Lumotec IQ Fly

It uses LEDs and is designed to throw the light on the road. It is about 4 times brighter than the round (standard) Lumotec and about 3 times brighter than the famous Schmidt E-6. The beam is designed to throw most light on the road with a wee bit spill light on the sides but not all around. Not only is it very visible to others, it also does a very nice job to lit your way, even on wet asphalt. Unless you do lots of riding on totally dark roads, you won't need more. And at 90-100 $, the price is interesting.

My only (minor) beef: there is some spill light towards the top and I don't like that. A bit of electrical tape on the upper part of the window solved the problem.


2-3. Schmidt E-delux and Supernova E-3

Both these lights are twice more expensive and both produce almost twice the light.
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Old 07-26-08, 06:28 AM
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Originally Posted by Unknown Cyclist

Is there a definitive design of headlight that will work with my hub ?
If you can solder wire to circuit boards and drill holes you can make your own.
Martins site shows you how.
https://pilom.com/BicycleElectronics/...lectronics.htm
Be sure and look at his single and triple LED headlights.
He does not provide links to LED's and optics because there making huge jumps in light output every few months. Last year light output for a single power LED was 45 Lumen. SSC introduced the new P7 C-BIN just a couple of months ago with 900 Lumen output. The P7 is not suitable for use with a bicycle dynamo. The Cree XR-E is with near 200 Lumen produced at 500mA each. Here is the link for the Cree XR-E LED.
https://www.dealextreme.com/details.dx/sku.2394
Best optics available here and is the same used by Martin.
https://www.luxeonstar.com/fraen-lens...ika1fqislq6a01
Make sure you order optics for lambertian type LED's as thats the style sold by DX. Also make sure you get the holder as well.
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Old 07-28-08, 05:12 AM
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Hi Scott.

Originally Posted by n4zou
Be sure and look at his single and triple LED headlights.............
Will the triple LED headlight run from a dynohub without a voltage doubler ?

Is Dealextreme the only place to get the LEDs from ?

I'm in the UK and Dealextreme don't have £ on their website.

I've had problems with customs and items from the US already, the collection fee for import duty can be a lot more than than the fee itself, making some items very expensive.



I've searched the luxeon site and I can't find the triple collimator pictured on the pilom site ?

If I can get all the parts I'll certainly have a go at making one.

TIA !
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Old 07-28-08, 08:54 AM
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I run triple leds all the time with my hub and rarely use the voltage doubler. It takes longer to bend down and flip the switch than it takes to get up to speed. The differences with 3 leds are not that great.
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Old 07-28-08, 09:16 AM
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Originally Posted by snowranger
I run triple leds all the time with my hub and rarely use the voltage doubler. It takes longer to bend down and flip the switch than it takes to get up to speed. The differences with 3 leds are not that great.
Hi,

What do you mean by 'the differences' ?

Cheers...
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Old 07-28-08, 10:36 AM
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Originally Posted by Unknown Cyclist
Hi Scott. Will the triple LED headlight run from a dynohub without a voltage doubler ?
Yes! The voltage doubler is only for very low speed operation with older generation LED's. I do not use a voltage doubler or even the two capacitors used to bump up light output a lower speeds with my two LED setup. I use just the bridge rectifier and a capacitor to prevent flashing.
Originally Posted by Unknown Cyclist
Is Dealextreme the only place to get the LEDs from ?

I'm in the UK and Dealextreme don't have £ on their website.

I've had problems with customs and items from the US already, the collection fee for import duty can be a lot more than than the fee itself, making some items very expensive.

That is a problem! https://www.luxeonstar.com/ allows you to select your currency and will ship to you. Unfortunately your going to be paying full retail prices and import fees. It may not be worth the costs to build your own LED lights.

Originally Posted by Unknown Cyclist
I've searched the luxeon site and I can't find the triple collimator pictured on the pilom site ?
https://www.luxeonstar.com/fraen-narr...leds-p-341.php
These optics fit in MR-16 halogen lamp fixtures.
Originally Posted by Unknown Cyclist
If I can get all the parts I'll certainly have a go at making one.

TIA !

Last edited by n4zou; 07-28-08 at 10:41 AM.
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Old 07-28-08, 11:09 AM
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Originally Posted by Unknown Cyclist
Hi,

What do you mean by 'the differences' ?

Cheers...
The voltage doubler boosts the output at low speeds. You'd ideally switch to rectifier mode at a certain point. The difference between rectifier and doubler is more pronounced with more LEDs.

See this graph from Pilom.

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