DC Permanent Magnetic Generator Help

  • Thread starter coolio3
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Main Question or Discussion Point

Hey guys,

I want to build a DC Permanent Magnetic Generator that will generate electricity which I want to pass through a Bridge Rectifier to produce DC electricity which I'll store in batteries or I want to pass it through a power inverter for domestic use.

Is this possible?

I was reading these instruction here: http://www.scoraigwind.com/pmgbooklet/itpmg.pdf

and they seem like they're pretty good. What do you guys think of them?

Could I use the generator he talks about in that and pass it through a Bridge Rectifier to produce DC electricity to store in batteries or pass it through a power inverter for domestic use?

Also, what would do you think the costs would be to make this unit?

and would the electricity it produces be free?

I'm very interested in doing something like this (and I know these might be noobie questions) so any help would be greatly appreciated.

Thanks a lot.
 

Answers and Replies

  • #2
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You can of course do this. The general question though is what will you be using to apply torque to the generator and spin it?

Even if the source of electricity is free, such as wind, the system is not free. That is because inevitably things will break, wear down, and need repair or replacement. If you take the total original cost of the system, and the average costs of repair/replacement overtime, that tells you how much it costs to maintain your system. You then need to figure out how much electricity you are producing. If the cost of $/kilowatt-hours is less than what the electric company is charging, you will save money. If its more, then it just makes sense to keep buying from them.
 
  • #3
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coolio3,

Welcome to PF!

The three phase axial flux design you referenced was engineered by Hugh Pigott for use in HAWTs (Horizontal Axis Wind Turbines), and is a good choice for DIY construction with basic tools. There are lots of variations on the basic design, google: "Axial Flux Alternator" for lots of information.

A three phase alternator requires a bit more complicated rectifier than a standard single phase bridge rectifier, but that is covered on page 38 of the article you posted a link to.

The total cost of the alternator depends greatly on what you have on hand and what you can get from a salvage yard versus what you have to "buy new". I would guess one could be built for $300 to $500.

and would the electricity it produces be free?
"Free"? hrmmm, that depends a lot on how you define "Free", and what the source of mechanical energy is. I am going to assume you do not understand what an alternator or generator is and explain it clearly to prevent confusion later on:

An Alternator converts mechanical energy into electrical energy and you ALWAYS GET LESS electrical energy out of the alternator than you put into it in mechanical energy.

So, if you are planning to install an HAWT, the energy it produces will come from the wind (which is still "free" in most countries), so your only costs will be construction, maintenance and any associate land use costs. If your HAWT cost you $10,000 to build, has a peak capacity of 5kW and produces ON AVERAGE at your location 1kWh, then (assuming electricity is $0.15/kWh) you will get 1kWh * $0.15 * 24 * 365 = $1314/year of electricity. If maintenance costs $200/year averaged over a 10 year period, then in about 9 years you will get your first truly "Free" energy.

If your mechanical energy source is a river, your cost of construction could be considerably lower than an HAWT, and the output could be potentially much higher and hence your "return on investment" might be much sooner.

If you are thinking you can turn the alternator with an electric motor powered from the grid, you will INCREASE your power bill by at least 40%.

If you are planning on using an ICE (Internal Combustion Engine) to turn your alternator, the fuel will cost you at least twice as much as purchasing the same electricity from the grid.

At the end of the day, no matter how expensive you think electricity is, it is the cheapest energy available unless you have access to a river, live in a high wind area or have some other source of readily available mechanical energy.

Most RE (Renewable Energy) sources cost between $5 and $25 per capacity Watt to install, and very few put out more than 25% of their rated capacity, so for a 10 year return on investment, your investment could not exceed: $0.15 * 1W/1000 * 24 * 365 * 10 * DF = $13.14 * DF/Watt, where DF = "De-rating Factor". For instance a solar PV installation might have a rating of 5kW, but if this rating is only achieved 6 hours a day, then the daily de-rating factor would be 6/24, or 0.25. So, $13.14 * 0.25 = $3.29/W. If you then add in 50 days a year when there is cloud cover, you would get 315/365 = 0.863, so $3.29 * 0.863 = $2.84. Solar PV actually costs about $10 per installed watt, so an un-subsidized installation could take as long as 60 years to "break even". Solar PV has an expected useful life of 20 to 40 years.

Anyway, I have digressed. I worry when people mention "free energy". The electricity you get from the grid is the closest thing to "free" you will get until some major discovery reduces the cost of grid supplied electricity.

Fish
 
  • #4
247
1
coolio3,

Welcome to PF!

The three phase axial flux design you referenced was engineered by Hugh Pigott for use in HAWTs (Horizontal Axis Wind Turbines), and is a good choice for DIY construction with basic tools. There are lots of variations on the basic design, google: "Axial Flux Alternator" for lots of information.

A three phase alternator requires a bit more complicated rectifier than a standard single phase bridge rectifier, but that is covered on page 38 of the article you posted a link to.

The total cost of the alternator depends greatly on what you have on hand and what you can get from a salvage yard versus what you have to "buy new". I would guess one could be built for $300 to $500.

and would the electricity it produces be free?
"Free"? hrmmm, that depends a lot on how you define "Free", and what the source of mechanical energy is. I am going to assume you do not understand what an alternator or generator is and explain it clearly to prevent confusion later on:

An Alternator converts mechanical energy into electrical energy and you ALWAYS GET LESS electrical energy out of the alternator than you put into it in mechanical energy.

So, if you are planning to install an HAWT, the energy it produces will come from the wind (which is still "free" in most countries), so your only costs will be construction, maintenance and any associate land use costs. If your HAWT cost you $10,000 to build, has a peak capacity of 5kW and produces ON AVERAGE at your location 1kWh, then (assuming electricity is $0.15/kWh) you will get 1kWh * $0.15 * 24 * 365 = $1314/year of electricity. If maintenance costs $200/year averaged over a 10 year period, then in about 9 years you will get your first truly "Free" energy.

If your mechanical energy source is a river, your cost of construction could be considerably lower than an HAWT, and the output could be potentially much higher and hence your "return on investment" might be much sooner.

If you are thinking you can turn the alternator with an electric motor powered from the grid, you will INCREASE your power bill by at least 40%.

If you are planning on using an ICE (Internal Combustion Engine) to turn your alternator, the fuel will cost you at least twice as much as purchasing the same electricity from the grid.

At the end of the day, no matter how expensive you think electricity is, it is the cheapest energy available unless you have access to a river, live in a high wind area or have some other source of readily available mechanical energy.

Most RE (Renewable Energy) sources cost between $5 and $25 per capacity Watt to install, and very few put out more than 25% of their rated capacity, so for a 10 year return on investment, your investment could not exceed: $0.15 * 1W/1000 * 24 * 365 * 10 * DF = $13.14 * DF/Watt, where DF = "De-rating Factor". For instance a solar PV installation might have a rating of 5kW, but if this rating is only achieved 6 hours a day, then the daily de-rating factor would be 6/24, or 0.25. So, $13.14 * 0.25 = $3.29/W. If you then add in 50 days a year when there is cloud cover, you would get 315/365 = 0.863, so $3.29 * 0.863 = $2.84. Solar PV actually costs about $10 per installed watt, so an un-subsidized installation could take as long as 60 years to "break even". Solar PV has an expected useful life of 20 to 40 years.

Anyway, I have digressed. I worry when people mention "free energy". The electricity you get from the grid is the closest thing to "free" you will get until some major discovery reduces the cost of grid supplied electricity.

Fish
 

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