# How can i charge a 1.2V battery with a lesser voltage?

#### onlyvinod56

Joined Oct 14, 2008
363
Hello,

I want to design a system in which a small DC motor acts like a generator and should charge one/two 1.2V AA batteries.

The shaft of the motor is linked with a platform which can be moved up and down. I want to keep this setup under the ground(test track). when a vehicle goes on this, the battery has to be charged.

The guess the voltage from this setup will be very small to charge a 1.2V battery.

How can i charge this?

#### steveb

Joined Jul 3, 2008
2,436
Hello,

I want to design a system in which a small DC motor acts like a generator and should charge one/two 1.2V AA batteries.

The shaft of the motor is linked with a platform which can be moved up and down. I want to keep this setup under the ground(test track). when a vehicle goes on this, the battery has to be charged.

The guess the voltage from this setup will be very small to charge a 1.2V battery.

How can i charge this?
You should use a DC/DC converter of some type. Since your specifications are very vague, it's difficult to recommend a particular topology and control approach.

Guessing that the voltage is very small to charge 1.2 V doesnt' tell us much. What is the actual voltage range expected, and what is the percentage of time that the motor is being driven to produce this voltage? Is it typically larger than 1.2 V? Is it typically smaller than 1.2V? Or, is it typically about equal to 1.2V? Or, all of the above depending on the conditions?

Joined Oct 31, 2010
1
for up and down to be converted to rotation u need to do reverse engg!! and thats to reverse mechanism of oscillatory to rotatry similar to the shaft mech of crankshaft to wheel. just a little modification

#### iONic

Joined Nov 16, 2007
1,650
You will need to generate a voltage of aprox. 1.5V and as much as 200mA depending on how long you want to spend charging the battery.

What mechanical activity do you plan on doing to make this motor spin fast enough to generate the needed current?

#### #12

Joined Nov 30, 2010
18,210
Quote:
"The guess the voltage from this setup will be very small to charge a 1.2V battery."

I suggest you start by not guessing. Measure the voltage.

#### onlyvinod56

Joined Oct 14, 2008
363
You should use a DC/DC converter of some type. Since your specifications are very vague, it's difficult to recommend a particular topology and control approach.
Iam thinking to use a small 12v geared DC motor. (Because already i have it).
The voltage generated from that is not sufficient to switch a transistor.(DC/DC converter)

#### onlyvinod56

Joined Oct 14, 2008
363
for up and down to be converted to rotation u need to do reverse engg!! and thats to reverse mechanism of oscillatory to rotatry similar to the shaft mech of crankshaft to wheel. just a little modification
I have designed a model in MAYA. Have a look at the attachment. The red color platform moves up and down when a vehicle passes over it. A metal strip fixed to the red platform vertically downwards. Small holes are made to the strip in which the tooth of a gear wheel are positioned. The up down movement makes the wheel to rotate clockwise and anti clockwise for a short period of time.

http://www.mediafire.com/?vkdeyba3l48fa16

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#### onlyvinod56

Joined Oct 14, 2008
363
You will need to generate a voltage of aprox. 1.5V and as much as 200mA depending on how long you want to spend charging the battery.

What mechanical activity do you plan on doing to make this motor spin fast enough to generate the needed current?
I dont think that my setup will generate that much voltage and current. What is joule thief? Can i use it to charge the battery?

#### steveb

Joined Jul 3, 2008
2,436
I dont think that my setup will generate that much voltage and current.
Well, how much is it then? We're not mind readers, and guessing doesn't help you. If you generate 1 mV and 1 pA, then forget it because you're not going to be able to charge your batteries by any method. If you generate 1V and 100 mA, then you at least have a chance, although it's a difficult design problem, and low efficiency will be obtained.

#### onlyvinod56

Joined Oct 14, 2008
363
Well, how much is it then? We're not mind readers, and guessing doesn't help you. If you generate 1 mV and 1 pA, then forget it because you're not going to be able to charge your batteries by any method. If you generate 1V and 100 mA, then you at least have a chance, although it's a difficult design problem, and low efficiency will be obtained.
Right now i didnt have the setup. But i tested it that the motor able to lit a bright blue LED. Sorry for this insufficient info.

http://www.mediafire.com/?vkdeyba3l48fa16
See the model. I can arrange total 10 generators(motors). Is it possible then?

#### t06afre

Joined May 11, 2009
5,934
What is the practical use for such a system

#### onlyvinod56

Joined Oct 14, 2008
363
What is the practical use for such a system
Its a high school project of my friend. He gave me the idea. I designed the 3D model with few motors in it. I want to show that system is useful to charge a battery and is used to lit the indicators on road somehow. Realtime application will have so many disadvantages i think.

#### steveb

Joined Jul 3, 2008
2,436
Right now i didnt have the setup. But i tested it that the motor able to lit a bright blue LED. Sorry for this insufficient info.

http://www.mediafire.com/?vkdeyba3l48fa16
See the model. I can arrange total 10 generators(motors). Is it possible then?
Personally, I don't download .doc files. If you post a pdf here, I'll look at it. However, the gist of what you are saying is that you can use more motors to generate more voltage. Also, you can light up a bright blue LED which does require some decent voltage. So, I would guess that it is possible, and it should be possible to use DC/DC converters which seems to me to be the best approach for things like this.

Still, more details are needed to work out a full design. A SEPIC converter topology, or an inverting buck/boost topology may be good because your input voltage is likely going up and down both above an below your 1.2 V charging voltage. The control approach is important because you want to load the generator in a way that captures the optimum power. However, you also want to regulate the charging voltage and current. This may require two stages and two control loops. SEPIC converters work very well in this type of load control mode where you are trying to maintain optimum power point tracking.

Bottom line is that you need a lot more information about your input power conditions, and you need a lot of design work to make a good system. So, it's likely doable, but certainly not easy.

#### iONic

Joined Nov 16, 2007
1,650
I dont think that my setup will generate that much voltage and current. What is joule thief? Can i use it to charge the battery?
A Joule Thief essentially bumps up the voltage to operate a 3V LED with a 1V - 1.5V battery.

When you said that you don't thing your motor will generate enough voltage or current to charge the battery you are in effect saying you do not enough power to charge the battery. You can boost the voltage at the expense of current or current at the expense of voltage, but the power remains the same or even less, still not enough to charge the battery. Some 12V CPU fans can run on 400mA, but you'll never be able to spin them yourself as fast as the do when their consuming 400mA unless you devise some bizzar geared up setup. Is there a reason you want to do this with a small motor as apposed to a small solar cell?

For those who don't want to DL the .doc file
View attachment Doc3.pdf

#### Bernard

Joined Aug 7, 2008
5,479
Is the vehicle a full sized car? How fast? How often?
Wild thought #1: Use hinged platform to drive an air pump to charge small air resivoir. High pressure air to turn turbine, direct coupled to motor. Air pump will be able to accept high power impulse
#2: Rack & pinion with one way clutch coupled by spring to a flywheel connected to motor. Might add a pneumatic shock absorber to allow a slight delay for platform to return to start position.[ this could be the air pump ].

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#### vrainom

Joined Sep 8, 2011
126
Have you seen those little hand led lamps that you need to press to recharge the batteries? I think it's similar to what you need, just needs some improving

#### iONic

Joined Nov 16, 2007
1,650
Have you seen those little hand led lamps that you need to press to recharge the batteries? I think it's similar to what you need, just needs some improving
Do you have the link for those lights?

#### vrainom

Joined Sep 8, 2011
126
Do you have the link for those lights?
Sorry that particular image I got it off google images. I live down in Mexico and have seen them in novelty stores for around 2 bucks.