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On-bike battery charger

Old 03-15-03, 01:55 PM
  #1  
Cadillac
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On-bike battery charger

I like to ride long distances and sometimes end up riding late at night. So I switch on my Planet Bike 5000X light which gives me satisfactory light if I use Duracells or Energizers (4xAA) for 3 hours (20 minutes if I use no-name brands). I bring along replacement AAs just in case.

However, I would like a system that recharges my spare AA cells (obviously rechargable AAs) while I ride. On trips of more than one day, I would need only two sets of batteries (one set in the light and the other on the charger).

Some will recommend the hub dynamo, but I don't want to go that route. I'd like a generator that attaches to the rear wheel that would provide enough juice to recharge the batteries.

Most (All?) chargers work off household AC current and must rectify it to DC. Surely a DC generator wouldn't need a rectifier.:confused:

Any help?
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Old 03-15-03, 08:26 PM
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Originally posted by Cadillac
Some will recommend the hub dynamo, but I don't want to go that route. I'd like a generator that attaches to the rear wheel that would provide enough juice to recharge the batteries.
You might want to look at a solar panel mounted atop the rear rack. That's the way I'm going to go when I start doing multi-day rides. You can get a 9V 300ma solar cell for about 70 bucks (suitable for charging up to four batteries in series), which is far less than a really good quality tire-driven generator, let alone a dyno-hub; and there is *no* rolling resistance. In fact, it will charge the batteries while you're eating your lunch, if you park the bike in the sun. You would need to brew up a little current regulator so as not to overcharge the batteries.

Oh, the solar cell should also weight about the same as a really good tire-driven generator.

Of course, if you have a couple of really overcast days in a row you're going to be in the dark...

John
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Old 03-15-03, 09:16 PM
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There are a few well made bottle genarators that would work, you will need to build a circut to control the voltage. There are two that I know of that have a built in voltage regulator. Most of the tire drive dynos are noisey when in use.

On our tandem we use a SON Dyno hub for lighting, during daylight we use it to recharge batterys (AA) we use in a CD player and the amp for the speakers, we carry on the bike. I like the SON hub because its silent, and has much less drag then a tire driven dyno.

For infomation on regulators see: http://www.nscl.msu.edu/~daniel/regulator.html
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Old 03-15-03, 09:29 PM
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I did a little research on solar chargers.
http://www.canadiantire.ca/assortmen..._specification
has one for under $40 that will charge 10 cells at once.
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Old 03-15-03, 10:22 PM
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Originally posted by Cadillac
I did a little research on solar chargers.
http://www.canadiantire.ca/assortmen..._specification
has one for under $40 that will charge 10 cells at once.
"Charges in as little as four hours" probably only applies when it's being powered by AC or a strong DC source such as an automotive electrical system. Just looking at the unit I doubt that it does more than trickle charge at 20 or 30ma off solar power. You need about 50 square inches of solar cell to get 300ma ("4 hour rate" on 1200mah AA NiMh batteries) at a useful voltage. Actually, if you recharge the batteries in parallel you can do with a little less area as you can use a lower voltage. However, for best results you don't want to charge batteries of different sizes and or charge percentage in parallel off a single regulator.

You can build a simple current regulator using about four readily available (i.e. Radio Shack) components (actually, if you have enough "spare" voltage you can do it with two components).

For this application, where you're charging batteries out of circuit, probably two at a time, the best bet would be a nine volt (intended for recharging 6V lead-acid batteries with no regulation) solar cell driving a simple regulator circuit (a 7805 3-terminal voltage regulator chip and a resistor) to charge the two batteries in series. If you need to charge 4 batteries in circuit you'd need a slightly more sophisticated current regulator that drops less voltage, or a higher voltage source.

John
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Old 03-15-03, 10:28 PM
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Just noticed original poster is charging four batteries. For that, you'd need the slightly more sophisticated regulator (or two of the less sophisticated regulator, run in parallel and each charging two batteries.)

On thing you should note, though. If you switch to NiMh rechargable batteries you will get significantly longer life out of a charge than with alkaline cells. Alkaline cells will give you just slightly more light when the batteries are very fresh, but then it quickly drops to the same level you get from NiMh batteries and the NiMh batteries should last probably four times longer or maybe even more. That's why almost all digital cameras (and, of course, cell phones) use NiMh batteries. My little Sony digital camera will eat AA alkalines in almost no time, but just keeps on going with the NiMh batteries -- sorry, Energizer bunny, but your days are numbered 'cause the NiMh cougar is in town

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Old 03-16-03, 01:28 AM
  #7  
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I admit i didn't read all the posts thuroughly, so maybe i missed something. But why do you need to charge them on the bike? Why not just bring along some fully charged batteries you charged at home?
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Old 03-16-03, 09:46 AM
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If I go for a three-day & night ride, we are talking about 24 or more batteries. With a charger, I would have about 8 batteries. Also, there is the environmental thing. It doesn't seem right to toss "disposable" batteries.

Charging them at home also takes energy -- admittedly a small amount.

I may be wrong, but I think the day may come when all bicycles will have to have day-time running lights like motorcycles are required to do -- probably flashing ones like the new motorcycles.
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Old 03-16-03, 10:30 AM
  #9  
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Originally posted by Cadillac
If I go for a three-day & night ride, we are talking about 24 or more batteries. With a charger, I would have about 8 batteries. Also, there is the environmental thing. It doesn't seem right to toss "disposable" batteries.
Before you get too wrapped up in an on-bike charger I'd buy a set of NiMh batteries and a simple home charger and try the batteries out. I think you'll find that they last significantly longer than alkaline batteries. So much so that you may well be able to get by with 8 or 12 batteries for three-day rides even without an on-bike charger. In any case, you won't have lost anything because even if you decide you do need an on-bike charger, you'd still have to buy those same batteries.

A good generator is probably going to weigh at least as much as six or eight batteries. So right there you can carry 16 NiMh batteries for the same weight as 8 batteries and a charger and probably get much longer burn time than you would from 24 alkaline batteries.

I may be wrong, but I think the day may come when all bicycles will have to have day-time running lights like motorcycles are required to do -- probably flashing ones like the new motorcycles.
With LEDs you can build a high-brightness strobe that will run for many hours on four-AA NiMh batteries. The one in my current avatar has 20 LEDs and goes at least 16 hours on one charge with little change in brightness. A yellow one for the front would be more effective in daylight than even a pulsing bicycle headlight.

John
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Old 03-16-03, 01:42 PM
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Thanks for the input and quick responses. I now have an armload of information which will help. Now, if the weather will cooperate (it is currently snowing again), I'll get out there and ride.
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Old 03-16-03, 04:47 PM
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If you have a dynohub, a battery pack, a bridge rectifier and a diode, you can make a circuit that will charge the battery (NiCad or NiMh) and run the lights.
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Old 03-16-03, 06:46 PM
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Where do you cycle? A dynohub with a headlight that has good optics, such as the Bisi or the Lumotec will provide you with 3 W that are carefully aimed. To cycle on streets and roads, the lighting you get with such a dynohub is almost as good as what you get with a 10 W rechargeable when its battery is new.

The light output is better than what you get with the Cateye Microhalogen (which I believe is similar to yours). You could keep your battery headlight to supplement the dynohub in more technical sections... or to read roadside signs.

Regards,
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Old 03-16-03, 08:50 PM
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I would suggest you purchase a Cateye el300 headlight. http://www.cateye.com/detail_mod02.php?products_id=91

The literature says that you will have plenty of light for about 30hours with alkaline batteries after which the light will gradually dim until the batteries are drained.

I use this light and highly recommend it. Some people may find it doesn't put out enough light but it will be very similiar to the amount of light you're getting with the Planet Bike light. I use the cateye with 1800Mah NIMH batteries and I really can't say what the usable runtime is, definitely over 30hours though. I just recharge the batteries every week or so or when I notice the light starts to dim.

If you're concerned about our enviroment do purchase NIMH batteries. They will give you more runtime and do not use heavy metals.
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Old 03-16-03, 09:00 PM
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I've seen people create bike light batteries that they then stuff into their flatbars. Obviously this won't really work with drop bars but has anyone thought to stuff a battery into a seatpost? I've seen it done with bikepumps.
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Old 03-16-03, 11:22 PM
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Originally posted by Cadillac
If I go for a three-day & night ride, we are talking about 24 or more batteries. With a charger, I would have about 8 batteries.
I'd buy the 24AA batteries along the way, myself, or carry them all from the outset if they were nowhere to be found.

24 batteries are heavy, but you can throw them away as you use them up (though I recognize you have other complaints about disposable batteries). As heavy as they are with all 24 at the start of the ride, the additional drag is small compared to what you're willing to endure to charge batteries. If you do the math with even the most efficient hub generators, for example, you'll see that you're going to lose anywhere from 1/3 to almost 1/2 mph from the drag. You'll lose even more with a tire generator. (And for those who would deny the drag is this much from a generator, I urge you to calculate the time cost of a 6-10W energy drain for your riding. The low end of this range is the energy drain from an efficient hub generator. The high end would be less efficient, but still good, tire generators. Cheaper generators do worse still. If you think this drag is no big deal compared to the light you produce-- and some people think this-- that's fine, but you ought to say the same thing about the drag cost of the 24 batteries, too.)

If you just don't want to carry a bunch of batteries, I second what others have suggested: use a generator to make light directly. If you're going to saddle yourself with the drag of a generator you might as well use the power most efficiently. Converting your pedal power to battery charge and then to a light is just tossing energy away.
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Old 03-18-03, 09:14 AM
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Check out http://www.batteryspace.com . You can get 24 NiMH AA batteries for $24. 1800mAh so they will run much longer than alkaline batteries. Just charge them all before you leave and you'll have plenty of juice for the whole ride.
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Old 03-19-03, 09:46 AM
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Thanks for the link, those are good prices. I also noticed they're carrying the first 2000mah AA's I've seen. Even those are a good deal at $20 for 10 of them.

John
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