DC motor/generator needed to charge 14-20v battery

[mook]

Hi all, I am working on a project at the moment that requires a DC motor to charge a 14-20v battery pack that is running a 5v audio player and a 6-16v amp with speaker. The battery pack has both 5v and 12v outputs that can output simultaneously. The motor will be connected to a shaft that is turned to generate power to charge the battery.

I already had short lived success using a 5v battery but inevitably my 12v motor destroyed the battery after a while. I could get 5v motor or use a voltage regulator to reduce the voltage from the 12v motor but I'm not sure id get the desired amount of power to play for approx 3 mins of audio unless you were to turn the crank for a long period.

Could someone please tell a good 16 - 20v motor with the right gear reduction/torque etc that wont require turning it all day to get the desired power?

Thank you

 

[Gryd3]

mook, you can't just supercharge a battery.
Depending on the battery chemistry, it will need to be charged over a long period of time.

 

[mook]

The battery only has to have enough charge to play for a couple of mins. With the 5v battery 10 cranks got 1.5 mins. Im hoping that with a slightly bigger battery and the right 20v motor i will require less turns to get a bit longer.

 

[Gryd3]

The battery only has to have enough charge to play for a couple of mins. With the 5v battery 10 cranks got 1.5 mins. Im hoping that with a slightly bigger battery and the right 20v motor i will require less turns to get a bit longer.

Regardless of the time you want to run, you still need to limit the current into the battery based on the battery chemistry.

Also, NiMH are sensitive to damage on overcharge when the charge rate is over C/10

This translates roughly into 10 hours for a 'full' charge. If the battery is rated at 2850mAh, then you can push no more than 285mA into the battery or you risk damage. Swapping the motor out could very well push too much into your batteries. If you want a quicker charge, look into using capacitors, or different battery chemistries. If your stuck with the batteries you have, charging multiples in parallel will allow your generator to charge more cells simultaneously which will reduce the current through each one individually. (This would allow a larger generator to be used, just be careful you don't put too much into the batteries short term!)

 

[Arouse1973]

Use a constant current charging method. This way the current is limited and not the voltage, so as long as the voltage is below the maximum input allowed for the constant current source then I don't see why this shouldn't work.
Adam

 

[Arouse1973]

Here is something I found that might work.
http://2.bp.blogspot.com/-PPcOoP2sA...8/s1600/simple+charger+controller+circuit.png
Adam