Charging 12vdc battery with Bike Generator Hub

[Justinwat]

I am powering a bike stereo I built with a LiFePO4 12.8V 6.8Ah battery. (http://www.batteryspace.com/lifepo42...2terminal.aspx)

I would like to buy a bike generator hub to slowly charge the battery while I ride to get more power and time from it. http://www.sheldonbrown.com/harris/l...g/shimano.html or the DC equivalent: http://www.bikewagon.com/Wheel-Goods...-p7819760.html

Questions:
What would the output of the generator hub need to run through before connecting to the battery? The charger I have for it obviously uses 120VAC power, is there a charger that I could buy or make that could work with 6VDC?

Is this worth it? Can a 6V generator provide enough power for a worth while trickle charge?

Would this damage the battery? The battery itself is pretty smart and I don't know if it was made to be charged this way.

Thank you all so much for reading this. Many of you have helped me in the past with other 12V project problems and I really really appreciate it.

[R!f@@]

sorry buddy, In order to charge a 12V SLA, you need at least 15V minimum @ at least 5 amps to get a decent power to charge ur battery.

If you plan to use a 6v hub then the hub should be at least capable of supplying more than 10 amps. but for this you need to built a dc to dc converter.

[rjenkins]

The best hub dynamos (like Schmidt) are rated about 6V 3W.

You can use a voltage doubler rectifier to get over 12V; basically two half wave rectifiers for opposite polarities.

The actual voltage will depend on the load, as alternators tend to give higher voltages at low currents. You are still limited to the 3W rating, or whatever the device is made for.

You could trickle charge the battery, but forget going via 120V it would have to be something suitable for around 12V or 6V input.

[Justinwat]

Thanks guys!

So if I was able to get the voltage higher does anybody know of a charger that could be bought or altered to work with this kind of power supply?

[R!f@@]

first thing is to get a voltage and from that we can find the charger

[retched]

If you had a trike, and used 3 hubs, you may be able to keep the battery charged.

If you used a lead-acid battery there would be a way. but in order to use Li-poly, you will need a smart charger IC that will also draw some of the power from the hubs.

It might take you 24 hours for a charge, if you didn't use the radio.

A stronger dynamo would be the way to go. Opposed to the hub, if you mounted one to behind the seat, and ran a chain to the dynamo, you could produce the power...slowly.

[Justinwat]

So they do make 12v Dynamos. If this can generate enough power to work with a charger how would I make it work with a smart charger? http://www.peterwhitecycles.com/dymotec.asp

I have a 400 watt DC to AC inverter in the stereo for an outlet on the side and I use the built in USB to charge my iPod while riding. I don't know if this would help the situation.

(forgive me I don't know many of the technical terms for electronic components, just of their existence.) If I had something that only allowed a full 12v at a higher amp from the Dynamo to pass through to the inverter and then had my smart charger hooked up to the AC output and that to the battery would that work? Would the inverter itself eat up too much power for it to be worth it?

Can anyone think of a way to use straight 12VDC with a charger that will work with this battery?

Thanks again!

[SgtWookie]

One horsepower = 550 foot-pounds per second = 745.7 Watts

If your 400W inverter is 90% efficient, it takes 444 Watts from the battery.

An average healthy human can produce 1/10 horsepower indefinitely.

How long do you think you can continue to lift 55 lbs per foot in 1 second?

That's just to power a generator that won't come close to keeping up with your inverter. You'll still need to provide additional power to move yourself on the bike.

[retched]

You may want to look up simple windmill charger circuits. There are many online that use a dynamo. You can simply build the "windmill" with the bike wheel as the propeller. That will give you a small charge that will keep the battery topped off. You will need HUGE legs to power the 400w inverter. So you should stick with DC all the way.

[R!f@@]

Originally Posted by retched

You may want to look up simple windmill charger circuits. There are many online that use a dynamo. You can simply build the "windmill" with the bike wheel as the propeller. That will give you a small charge that will keep the battery topped off. You will need HUGE legs to power the 400w inverter. So you should stick with DC all the way.

And start dead lifting as well