# Stepper Motor wind turbine AC to DC - what diodes / or rectifier to use?

I'm building a small wind turbine from this tutorial. It uses Nema 17 stepper motor as the generator.

We need to convert the AC of the motor to DC. The setup is said to be able to produce up to 30V and 1 amp in high wind speeds.

I have 3 questions:

1. If we were to make our own rectifier from 4 diodes, what size/spec diodes would we use? It says in the comments they used schottky diodes here but I don't know what size they used or what would make sense in this application.

2. If we were to just use a rectifier, what should we use?

3. Is there any electrocution danger in this voltage / amps (30v/1 amp) that I need to be aware of? What level of amperage is dangerous?

Thank you!

If we were to make our own rectifier from 4 diodes, what size/spec diodes would we use? It says in the comments they used schottky diodes here but I don't know what size they used or what would make sense in this application.

Your diodes V rating should be high enough to withstand your generators/any other stuff you added to the system. For you, they should be at least 30VDC rated. Of course, for practical purposes, never go that low. Pick something with 50VDC~100VDC. Also, diode amper rating must be selected using the same principles. If you will draw 1 amps, get diode rated for at least 1 amps. I'd get 3 amps.

So something like 100 VDC, 3 Amp rated Schottky Diodes are okay for you.

If we were to just use a rectifier, what should we use?

Something powerful enough as described earlier. Remember, you draw current. If you plan on drawing 100 mW from a 1000 W source, you can! So the rectifier power specifications demand on your load, not the source. (Of course it should withstand source's voltage, though)

Is there any electrocution danger in this voltage / amps (30v/1 amp) that I need to be aware of? What level of amperage is dangerous?

There is a graph, of how many amps can kill you per time. It is something like 10 mA ~a couple seconds to 100 mA ~a couple microseconds. So dangerous limit starts at 10 mA but thats not enough. Why? What causes electrons to penetrate human body? Voltage! Dangerous voltages (the ones that hurt you) start from 50V. Any source rated above 50V and has amp rating more than 10mA has a chance of killing you depending on point of contact. Example: Getting electrocuted from your left hand-feet is worse than right hand-feet because your heart (generally) is on the left side. Amperage ratings differ from people to people etc. so this is not a simple question to answer. But like I said, let's assume that any source rated above 50V and 10 mA has enough power to kill a grown man.

In your case, your source is 30V which is not enough to penetrate your body but I would be cautious. Use plastic gloves at least. You can also work on an insulated ground elevated above from real ground as used in labs.

• Thank you, very helpful. So just to clarify, 1amp below 50v can't kill? Or it could? – Agent Zebra Dec 18 '16 at 6:35
• Technically, and just technically, it should be okay for you to work with sources below 50V with bare hands. However, try not to complete the circuit as much as you can. For example, prepare your circuit when the generator is idle, and don't touch stuff when it is rotating. Remember, just because it won't kill you doesn't mean it's not gonna hurt you. There are people with burnt hands because they accidentally discharged a capacitor! When dealing with high power, using gloves is always a good idea. – user132236 Dec 18 '16 at 14:29

At first use just a four diodes bridge rectifier, 60V reverse voltage. Take Shottky diodes with least possible forward voltage to reduce losses.

Later try using just one diode- this way the losses on rectifier are smaller, but the movement will be less smooth.

Don't worry about electrocution. Just don't touch anything when it works- who knows, maybe the voltage will be higher than you think.