Power Generating Cart

This article is about power generating carts.

The first cart is made from two motors, used to power a pair of LEDs. The LEDs are not ON at the same time. The second LED is connected in reverse and turns ON when the car moves in reverse.

I also made a bigger cart with more motors to power light bulbs. I was never able to generate enough power even for the 1.5 V miniature light bulb because most of the low cost motors had very poor power generating efficiency. My big cart only worked with LEDs, that need a lot less current than light bulbs. You can see on the photo that I attached 9 dual shaft motors onto a 30 cm ruler.

I am now saving money for more motors to attach to 40 cm ruler.

I needed at least 0.3 amps current. This is why I used so many motors. However, testing showed that I only needed one motor to generate 20 mA needed for my big LEDs (small LEDs only need 5 mA). This is how I was able to implement the smaller cart.

Do not connect the motors in parallel. You need to connect the motors in series. If one motors can generate 20 mA of current as shown in the testing video then 12 motors will be able to generate 240 mA (20 mA * 12 = 240 mA) of current. This is almost the required 300 mA for the 1.5 V light bulbs.

If you look closely at the photo you can see that some motors have a longer shaft. That means you can put motors with shorter shaft in between to save space on your ruler, thus eliminating the need for purchasing a longer ruler. Thus you might not need to use a 40 cm ruler.

You can use batteries to test your motors. However, you can also do this by spinning the wheels with your fingers as you see in my video, in the testing step of this article. If you apply power to motors then they should all spin in the same direction. Motor spinning in an opposite direction will offset the generated voltage magnitude when you drag your cart on the floor.

Components: dual shaft motors - 2 (for LEDs) to 12 (for 1.5 V light bulbs), general purpose diodes - 6 to 12. wires, 1 mm thickness metal wire, insulated wire, ruler or thick wooden/plastic rod.

Tools: wire stripper, voltmeter.

Optional components: solder, batteries.

Optional tools: soldering iron, electric/manual drill (to drill hole for motor holding fixtures).

I used three diode pairs to clip the voltage for each current direction.

Calculate the maximum input current if 6 V is applied (four AA, AAA, C or D batteries):

Is = (Vs - 3*Vd) / Rs

= (6 V - 3 * 0.7 V) / 10

= 3.9 V / 10 = 390 mA

This is a reasonably high current.

Calculate the power dissipation across each diodes:

PdMax = Vd * Id

= Vd * (Is - Iled)

= 0.7 V * (390 mA - 10 mA)

= 0.7 V * 380 mA

= 266 mW

This protection circuit is for LEDs that have 2 V (0.7 V * 3 = 2.1 V approximately 2 V) potential difference. You will need to use four diodes (instead of six shown in the circuit) for 1.5 V light bulbs (0.7 * 2 = 1.4 V approximately 1.5 V) or eight for 3 V light bulbs (0.7 * 4 = 2.8 V approximately 3 V) or two 1.5 V light bulbs connected in series. You can also use one general purpose diode connected in series with Zener diode for clip the voltage for each current direction.

I used low power Zener diodes because I had only two general purpose diodes.

Because Zener diodes were lower power I connected a few Zener diodes in parallel to reduce power dissipation for each diode and thus improve reliability. If one diode fails that the remaining two didoes can still protect the LED. This is know as redundancy method.

You can see that I only need to spin one dual shaft motor to turn the LED ON in my bigger cart and swing the voltmeter needle to as much as 3 V.

The low current output can be modelled as a high internal resistance of the this cart generator that allows high input resistance voltmeter to show 3 V and low resistance 1.5 V light bulbs to remain OFF even thought they only need 1.5 V to turn ON.