im a newbie. how many volts does a micro ac generator produce?/(to charge battery)

[Dodge631]

hi i am brand new to electronics working. i wanted to build a simple hand crank generator that charges a small battery and need some pointers.

one, i got the d/c motor / a/c generator from one of those kids toys that have candy but a fan on top. those little cheapy things you see at checkout lines. the little one with the foam blades. how many volts does it produced(imagine just if hand cranked possibly with a little lever and knob)

but i don't know anything about diodes or electrical equations YET. i wanted to know how i would connect the little ac generator to a battery. would i need to change the current type? what kind of diode would i need for a low voltage generator such as that?

so i think u just connect the +wire from the generator to a diode to the battery and the - wire directly from the generator to the battery?

thanks in advance

 

[enjunear]

That little motor probably won't produce much voltage from a simple hand crank. You can generally think of a motor and generator as the same thing, just reciprocal of one another (equal, but opposite). If two AAA batteries (1.5V * 2 = 3V) turn the motor at several hundred RPMs, then you'd have to spin the motor at several hundred RPMs to get a few volts back out of it (a very rough, rudimentary analysis).

In order to charge a battery, you need to overcome the voltage on the battery so that current will flow into the battery. Think of it like pouring water from one glass into another. The level of the water in glass 1 (the source) must above the level of the water in glass 2 (load) in order for it to flow from the source to the load. More height of the water level = more potential energy = more voltage.

Most hand-crank generators have a step-up gearing mechanism so that 1 revolution of the crank yields several hundred revs of the generator. For a quick test, find a voltmeter and another motor. Connect the motor shafts together, and power up one of them so that it spins the "generator". Use the voltmeter to see if any appreciable voltage appears at the terminals of your generator. That's a quick way to see if your motor will perform as a generator.

 

[Dodge631]

thanks.
but lets just say for the sake of knowledge, how would i make it charge a battery without the batteries making it a motor? was my thesis in my first post at the end right?

 

[allenf]

Take a look hereit shoild help you

Electric motors and generators

About half way down.
If you feed into then its a motor and turns.the shaft if you turn the shaft then its a generator and feeds out (very very basic explaination )

 

[Dodge631]

yeah i knew that when u put power in its a motor and when u use it to make power its a generator. but i want to know how to connect the generator to a battery and have it charge the battery without the battery making the generator a motor. do i need diodes? or LEDs? i just want to make a simple design the uses a little generator to charge a battery

 

[allenf]

a fixed mag motor is a two-way system. Put in electricity and you get rotation... if you put in rotation you get electricity?
but try this

taken from
How to Build a Mechanically Powered Battery Charger for LED Lighting - Appropedia: The sustainability wiki

 

[enjunear]

thanks.
but lets just say for the sake of knowledge, how would i make it charge a battery without the batteries making it a motor? was my thesis in my first post at the end right?

From a theoretical standpoint, you are correct; you would need a diode so that the current can only flow from the generator, into the battery. If you look at allenf's image, you'll see the proper orientation for the diode (arrow points in the direction of desired current flow). Once the generator's voltage is greater than (Vbattery+Vdiode), current will begin to flow into the battery, charging it.

As for the LED, I'm not sure where you'd want to use that in a simple generator/battery charging system. An LED is just another form of diode; one that creates visible light (LED = Light Emitting Diode). I wouldn't recommend using it as your blocking diode; you'd be better off with a schottky-barrier diode, since they have forward voltage drop around 0.2-0.3V, compared to 0.7-0.8V on a regular silicon diode. That way, less power from your generator gets consumed by the diode, so more power goes into the battery.