Mini wind turbine to light an LED

[AS111]

Hi there,

I am trying to breadboard a circuit which uses a mini wind turbine to power a generator and charge a super-capacitor.
Once charged, a switch is pressed to discharge the super-capacitor and illuminate an LED.

I have searched all over the place and can't find a circuit diagram which when bread-boarded achieves this. Could anyone offer some help?

When attaching a multi-meter to the capacitor I can see it charging and discharging but never illuminating the LED - might this be because I am using a capacitor of the wrong spec for example? The super-capacitor I am using is a Goldcap RG series 1.5F 3.6V.

Any help would be really appreciated.

 

[Harald Kapp]

There are several potential issues here:

1. Does your generator deliver DC voltage/current? If so, o.k. If not you will have to add a rectifier to generate DC from the generator's AC to charge the capacitor and light the LED.
2. Is the LED correctly connected? An LED, other than a lamp, has a defined polarity: anode (long 'leg') to '+', cathode (short 'leg') to '-'.
3. Do you have a current limiting resistor in palce ? I'm afraid you don't, according to your description. See this ressource how to correctly operate an LED.
4. Last not least: is the voltage sufficient to drive the LED in question? Depending on color LEDs have a pass voltage from 1.6 V to > 3 V, If the voltage generated by the generator is less than the pass voltage of the LED, the setup is doomed to fail.

I hope these points help you localize the issue.

 

[Alec_t]

Welcome to EP.
What LED are you using? A white one needs about 3V to light, whereas a red one needs about 2V. A series resistor can control the LED current, but drops a small voltage.
Such low voltages create a challenge for a circuit to switch the LED on, which is probably why you haven't found one.

 

[Audioguru]

A while ago there was a thread where a guy used a computer fan on his bicycle to charge a battery to power night LEDs. The LEDs lighted only for a moment unless he rode the bike very fast all day to charge the battery.
If you fully charge your capacitor then how long does the LED light from it?

 

[AS111]

Thank you very much for all your replies, they are really really appreciated!

I believe the small amount of voltage created from the turbine will be an issue. However in the mean time I have tried using a power pack to provide a small voltage (roughly 2.5V) that successfully lights the LED when out of the circuit.

The issue I'm really having now is actually designing the circuit so that it charges the capacitor, stores the charge, then releases the charge to illuminate the LED once a switch is pressed - does anybody know how this circuit diagram should look?

I have copied the circuit at the bottom of this link whilst adding the LED after the resistor but had no success. I assume this is incorrect?

http://www.schoolphysics.co.uk/age1...ext/Capacitor_charge_and_discharge/index.html

The LED is just a small Red one.

Again any help in knowing what the circuit should look like would be really appreciated! Thanks again!

 

[AS111]

The generator is DC and the LED installed the right way round

 

[Audioguru]

Did you measure the voltage from the generator and the voltage of the charged capacitor? If it is 2.5V or more then the red LED should light if the resistor value is correct. What was your resistor value?
Here is a simple schematic providing about 10.3mA of current in the LED:

 

[Alec_t]

Here's a circuit which, if the turbine voltage is > ~4V, allows the cap to charge to ~3.2V then automatically turns on the LED to discharge the cap (partially). Be warned; with a 1.5 Farad cap the charge time, assuming the turbine puts out 5V, is nearly two hours!

 

[Audioguru]

I smell a home-made PUT!

 

[Alec_t]

I smell a home-made PUT!

Indeed you do. Might be simpler to source than the real McCoy.

 

[AS111]

GREAT SUCCESS. Have the LED lighting up from the discharging capacitor. Thanks for the circuit schematics!

I am having trouble with the capacitor holding the charge however - once the turbine turns and the switch is closed to the capacitor it charges, however as the turbine slows down the capacitor also discharges unless the switch is quickly opened once it reaches peak charge. Does anybody know how I can resolve this?

 

[Audioguru]

The schematic with the transistors shows no switch. It has a diode to prevent the capacitor from discharging into the slowly turning generator. The voltage from the generator must be higher than the diode voltage plus the LED voltage. Where did you connect your switch? Please post your schematic.