# Piggott Alternator

I’m going to construct a magnetic flux alternator using Piggott plans. The instructions have options for 12, 24 or 48 volts. The coil windings are adjusted by wire thickness and overall number of windings to produce the desired voltage system.
I think that I understand some aspects such as, 12 volt systems require heavy transportation cables to transport the electricity from the generator to the batteries. And 48 volt systems use thinner transport wires but more complicated battery storage systems. There seems to be other advantages to using higher voltages that makes the overall system more efficient.
But what, if anything do these options do to the resistance to the alternator? Is there a need for more or less rpm? What is the most efficient for the windmill to produce and transmit?

Thanks!
Dave

Re: Piggott Alternator

Other than more cells in series--there is not a big complication with 48 volts of batteries...

For small loads, you can get 12, 24, or 48 volt inverters pretty easily, and run most of you stuff at 120 VAC (or whatever is your local voltage)... Much better than trying to run long distances at high amperage and the low voltage of a 12 volt system.

Otherwise, if you are going to use a DC load (radio, etc.)--then pick your DC voltage to run at based on your load. Watch the DC equipment ratings... For example a car generally runs the battery between 12.5-14.2 volts. A deep cycle system can run the battery charging voltage upwards of 15-15.5 volts. Having DC converters, computer power adapters, and other 12 volt appliances for cars fail at those higher voltage is not unknown.

Personally, I recommend that you try and keep your battery to load current at ~100 amps or less... So, a 12 volt system would have a maximum of 1,000 watt inverter; a 24 volt would be 2,000 watts, and anything larger, try to go with a 48 volt battery bank.

To go any more than 100 amps, you will need very large cables fuses/switches, and pretty heavy duty batteries (or lots of them im parallel) to supply such high currents.

Also, remember to design your loads with conservation in mind... You can get some very large inverters that would drain your battery bank dry in a handful of hours, but could take weeks for your RE/Wind Turbine to recharge. Don't get any larger inverter than you will need. And don't plan on any loads larger than you can realistically recharge from your RE source. And lead acid batteries, don't like to sit below ~75% state of charge at all... You should plan on recharging back above 75% within one day. And don't run your flooded cell storage battery below 50% state of charge (and certainly don't let them sit below 50% for any length of time at all)--the batteries will sulfate and fail quickly.

I have not designed/built a wind turbine--but the basic physics should work out about the same if you wind a 12 volt at 20 amps (for example) or 48 volts at 5 amps (both would equal 240 watts).

Sending the power for any distance from the wind turbine to the battery bank/wind charge controller would be easier at 48 volts (less voltage drop, and/or smaller wires).

In any case, do you have any information on the output curves of the 12 volt vs 48 volt alternator (i.e., are they both equally efficient?).

Lastly, you will probably need an alternate power source too (solar, backup generator, water turbine, etc.)--so make sure which ever other source(s) you use, that they are compatible with the rest of your design/system and the amount of load you expect to support.

For more wind centric discussions, you might also try OtherPower.com too...

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 717Solar Expert ✭✭✭
Re: Piggott Alternator

Dave good luck with the axial flux machine i built hughs 10 ft design and it was a blast. it lives on a 70 ft tower. also we are testing the Classic it is a mppt charge controller and we have found it will give us 2-3 times the output from a hugh piggot machine and is very promising on solar to.
Re: Piggott Alternator

What Halfcrazy is talking about... An MPPT controller for a wind turbine, besides offering you more power because of better source/load matching--it allows you to design/build your wind turbine for >60 volt output (needed for charging a 48 volt battery bank) and allows you to simply switch the output switch on the MPPT controller for 12/24/48 volts without having to re-wind your alternator.

I do not know if this controller needs to programmed for each wind turbine's RPM vs IV output--but it would probably be worth contacting Halfcrazy or Midnight Solar directly.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 717Solar Expert ✭✭✭
Re: Piggott Alternator

To clarify a little, a typical axial flux is designed around a cut in voltage which would be average battery voltage. From there up in wind speed the blades are held back because alternator rpm can't increase because the batteries hold the voltage down.

The way an axial flux works is if you let it spin in the wind the voltage increases with rpms so by letting the turbine spin up with the wind speed, we see more voltage, ie more power.

So, for example my turbine which can put out 20 amps safely before heat is an issue in the stator will do about 1000 watts tied directly to my 48 volt battery bank (50 vdc times 20 amps = 1000 watts).

Now if we let the turbine spin according to the wind speed we may hit 150 vdc at that same 20 amps so then we get 150 * 20 = 3000 watts and still the same amount of heat in the stator as we saw previously at 1000 watts.

So basically we are going to let the turbine run in its most efficient power curve and we will be able to harvest a lot more power from the same size turbine which is huge in many ways

Before, if you wanted a 3kw turbine you had to build it bigger, meaning more money for the machine, a bigger tower and bigger wire to the house. Now we can build a typical 1kw machine and get 3+kw out of it.
Re: Piggott Alternator
BB. wrote: »
What Halfcrazy is talking about... An MPPT controller for a wind turbine, besides offering you more power because of better source/load matching--it allows you to design/build your wind turbine for >60 volt output (needed for charging a 48 volt battery bank) and allows you to simply switch the output switch on the MPPT controller for 12/24/48 volts without having to re-wind your alternator.

I do not know if this controller needs to programmed for each wind turbine's RPM vs IV output--but it would probably be worth contacting Halfcrazy or Midnight Solar directly.

-Bill

Thanks for the replys! My education continues...
As I understand it the stator coils determine the output voltage. Heavier wire and fewer turns provides lower voltage and requires higher rpm. Thinner wire with more turns provides greater voltage and requires lower rpm.
Please correct me if I'm wrong.
how would this MPPT controller allow say the heavier wire stator to charge at 24 or 48 volts? How would it affect the rpm requirements?
Forgive me for what may seem like simplistic questions but I'm "green" to this stuff and have been attempting to get educated before proceeding to cast coils into resin.
Re: Piggott Alternator

As a first estimate--I would believe you are correct, more coils of thinner wire, higher output voltage.

A properly configured and operating MPPT controller is able to measure the output voltage and current of the alternator and, using the equation P=I*V, adjust the current load up and down until it figures how to get the Pmax. (MPPT=Maximum Power Point Tracking).

I would guess there are several ways of doing this for a wind-turbine (that I can think of)--and, as far as I know, this is not a very common type of charge controller for windmills--yet.

The MPPT is a buck mode power supply that can converter high voltage / low current (from the alternator/solar panels) into low voltage / high current for the battery bank.

In a way, think of the MPPT as the DC version of a Variable AC Transfomer (Variac).

This is quite different to just connecting an alternator+recifier to the battery bank...

Whether this new Midnight Classic Controller is appropriate for a home made wind turbine--I have no clue.

You should really contact Halfcrazy (by PM) or the manufacturer for details.

Assuming the product works well--it could be a really nice way to increase the electrical power collected (big caveat, there are lots of other issues with wind turbines that a new controller will not address).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Posts: 717Solar Expert ✭✭✭
Re: Piggott Alternator

The combination of a Midnite solar Classic and Clipper will work excellent with the home brew turbines in fact i think it is the missing link. The furling system on the home brews has always been a grey area. And there is no real protection short of you physically turning off a stop switch.

With the Classic and Clipper we will be able to apply the brakes proportionately based on a few things. You will be able to choose a max RPM of the turbine as well as setting max power etc. I would recommend for now to stick with the design the Dans at Otherpower have worked out it works great and is very reliable. I would wire the stator for 48 volts also.

In the future I am shore that a few of us Otherpower regulars will design a better turbine for the Classic. It will most likely consist of a bigger more powerful alternator for the same size blade but that is a whole new experiment and can get expensive fast.

We do know the classic will really boost the power of these turbines. I have personally seen 3 times the power. And with the blades carved to there specs the turbine has a nice little sing to it around 600 rpms. You coul hear it but it wasn't loud enough to bother anybody , definitely quite then a lot of factory turbines.