# Questions of mechanical to electrical energy transfer

1. ## Questions of mechanical to electrical energy transfer

Hi,

I am looking for a converter to transfer the mechnical energy from bicycling pedal to the electrical energy. Here is the application:
1. the tire of the bicycle can move ahead around 1 meter per second, that is the input of the mechnical energy
2. I am trying to charge a battery that is 3V and 500mAhr capacity. That is where the output electrical energy goes

Would anyone give me an example including the following information?
(1) an off-the-self converter that I can directly buy online
(2) the spec of this converter, regaridng the power transfer efficiency, so I can calculate the time to charge this battery from empty to full when no other load connecting to the battery

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2. ## Re: Questions of mechanical to electrical energy transfer

Originally Posted by bhl3302
I am trying to charge a battery that is 3V and 500mAhr capacity.
This is similar to two AAA in series. Mine have instructions to charge at 72mA overnight.

There are store-bought generators which you mount close to the tire. It's on a spring-hinge. Inside is a generator (or maybe it's simply a small motor, because that also does the job). Typical output is 6 or 12V. Several Watts. It's liable to ruin your battery unless you slow it down somehow.

It's worth a try to experiment with a small motor, say from a cassette player. Just spin it and see how many volts and milli-Amps it puts out.

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3. ## Re: Questions of mechanical to electrical energy transfer

This is similar to two AAA in series. Mine have instructions to charge at 72mA overnight.

There are store-bought generators which you mount close to the tire. It's on a spring-hinge. Inside is a generator (or maybe it's simply a small motor, because that also does the job). Typical output is 6 or 12V. Several Watts. It's liable to ruin your battery unless you slow it down somehow.

It's worth a try to experiment with a small motor, say from a cassette player. Just spin it and see how many volts and milli-Amps it puts out.

1. Would you share what kind of store-bought generators you are talking about?
2. I assume the mechanical energy will be transffered to AC electrical enenrgy. Since you mentioned the typical output is 6V or 12V, that means there is an AC-DC converter inside?
3. You mentioned you have your two AAA in series charged 72mA overnight. I assume this is a CC charging thus if we neglect CV charging phase, the 500mAhr battery can be charged at around 7 hours. Is this correct?

Thank you!

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4. ## Re: Questions of mechanical to electrical energy transfer

Bicycle mount generator via internet search. Often a headlamp is included (for more money).
At left is the contact wheel which spins against the tire.

For comparison, cheap battery chargers produce about 10V, sent through a safety resistor, so as not to overheat the battery. Likewise your generator should have a safety resistor. The 10-hour figure is conventional, although there are 'smart' charges which use a higher charge rate, and sense when the battery is full. The goal is to avoid overcharging and overheating.

Learn about batteries at this website:

https://batteryuniversity.com

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5. ## Re: Questions of mechanical to electrical energy transfer

Follow Brad's advice but please bear in mind that nobody makes a 'dynamo' charger specifically for the voltage and current you need. I cases like this you generally have to add some electronics to convert the raw AC or DC from the generator to suit the load you impose upon it. For battery charging, you probably want a standard CC/CV charger circuit capable of being fed from whatever voltage the generator produces.

Brian.

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