Charging Lead Acid Batteries with variable voltage

[Dustin Smith]

I'm modifying a ceiling fan to become a wind turbine to generate electricity. How do set up my wind turbine to charge a 12V lead acid battery or two 6V lead acid batteries when my voltage could get well over 14V with moderate winds?

Ceiling fan coils connected in parallel:
120RPM = around 15V and 200mA
240RPM = around 26V and 350mA

 

[john monks]

I believe I would hook up the coils in a three phase fashion, hook up in a Y configuration, and use Schotkey diodes to get my DC and run that into a lead acid battery that is stationed outside. IF I didn't care much for the battery I might just let it overcharge. Otherwise I might consider designing a voltage regulator using power Mosfets, junction transistors, and a Zener. I would try to use the existing coils for simplicity. I would position neodymium magnets around the moving portion to facilitate three phase coming off the coils. Is this what you had in mind?

 

[Dustin Smith]

So you're saying I need to set up the magnets to create three phases with two coils? If that's what you mean, perhaps you could explain a little more detail in laymen terms for me?

 

[john monks]

f you only have two coils then you need to hook up a full wave rectifier with Schotkey diodes because you have single phase. That would be simple because you would not have to fool around with the wires at all, only hook on to the existing black and white power leads.

I'm a bit surprised that you only have two coils. Generally a ceiling fan has several coils and you will have to separate them and hook them up in a three phase fashion. The moving piece that is connected to the turbine will need to have magnets spaced around it glued so as to get three phase from the coils.

What is the make and model of the fan you are starting out with?

If you only have two coils you do not have three phase.

 

[Dustin Smith]

Maybe I should say I've got two sets of coils. The fan is quite old and I believe it may have been manufactured in England. I'm pretty sure I've got two phases when I spin it and create electrical current because of the way my magnets are set up. I'm happy with the two phases. I just need to focus on the charging system. So I'm going to look into the voltage regulator idea. Does that drop voltage only, or will it also drop amperage?

 

[john monks]

Voltage. You want to use every bit of amperage you can get for charging your battery. Otherwise you are wasting energy. So you do not want any current limiting. And you do not want a regulator that uses much current. So you probably want a voltage made with Mosfets and regulates up to about 14 volts or maybe slightly more so you don't wast energy.

I'm divided between use an old car battery that you can probably pick up for nothing or using a deep cycle batter used in gulf carts. I noticed that regular car batteries tend to have greater energy density than deep cycle batteries. Probably due to the thinner plates. Another thing is that for the same amp-hour rating a car battery has less internal resistance than a deep cycle battery. This also allows for a greater charge current than what you get with a deep cycle battery. The advantage that a deep cycle battery gives you is that they will last longer under harsh conditions. And the fact that old car batteries can be picked up for nothing makes that a very attractive alternative.