# Taking an unstable DC voltage, and stabilizing it

I have a DC motor generator (basically the motor spins, and it powers an LED at the moment), and the output current (mA range) and voltage is very unstable.

For an entire circuit to run on the motor-used-as-generator's power, is it possible to stabilize the voltage and current of the output. The output voltage must be 5V and I am not concerned with current, no matter how low.

My circuit is made of, literally, a motor and a wheel of magnets.

The motor generates spikes up to a miximum of 0.97V and lowest 0.3V. My plan is to attach multiple wheels, then have three of the three wheeled motors, have theses circuits attached to a op-amp, and then simply charge a battery my multimeter broke, so I can't test the three wheels or the current until I get a new one

The project is for a competition and we need to use minimum number of parts, under 100 individual components.

• Over what range does the voltage vary? Apr 24 '15 at 3:32
• I want to post an answer. I really do. But I need you to post your schematic. Or at least a list of parts. Otherwise it'll just be pure speculation. But I'm almost positive I know what you did. Apr 24 '15 at 3:52
• I posted an edit :) Sorry for the late reply, I went to bed right after posting this Apr 24 '15 at 12:39
• I changed your title to match what you ask in the body. A motor that's turned to generate electrical power is called a generator, and the thing you are seeking to stabilize the voltage is called a "voltage regulator". There are many kinds, differing in quality, cost, complexity, and so on. Apr 24 '15 at 12:43
• Oh ok! I'm kind of a noob when it comes to this, so I wasn't very familiar with many of the terms. Apr 24 '15 at 13:10

## 3 Answers

The absolute simplest possible solution is a capacitor (high value electrolytic, greater than 5V - probably at least 10V) across the output terminals.

However, there are two problems with that: it will attempt to drive the generator backwards somewhat, and it merely smooths the voltage rather than regulating it to a particular value.

To solve the first problem, add a series diode (possibly Schottky) from the generator to the capacitor.

To solve the second problem, I would add a DC-DC buck/boost converter module to the output. You may be able to get this counted as a single "part". In order to prevent the capacitor voltage increasing without limit if there is no load, for small values you can use a Zener across the capacitor (some value higher than 5V but lower than the capacitor's voltage limit). For large generators you will need to build a dump load, which is a resistor that gets switched in when the generator is producing more power than required. Or feather the propellor.

• This is exactly what I was looking for! Apr 24 '15 at 13:37

Use a bigger motor to generate about 10 VDC and add a 5 VDC voltage Regulator (L7805 voltage regulator).

• I didn't downvote you, but your answer is a little light on details. Also, you don't need a 10V source if you just use a buck-boost regulator, it should be able to handle voltage swings a couple of volts +- from 5V. Apr 30 '15 at 12:58

https://www.kitronik.co.uk/blog/l7805-voltage-regulator-datasheet/

7v is all you need to run the L7805 voltage regulator. I just used one just now in a project (wifi controlled led) and it works great and very, very simple to use. pin 1 input +7v to +32v, pin 2 ground, pin 3 is out put +5v.