ASK THE EXPERTS: Car Alternator for Wind Turbine?


I’m thinking about using an automobile alternator for a homebuilt wind generator. Will this work?

Ron Johnson • Albuquerque, New Mexico

Hello Ron, A car alternator is a bad choice for a wind generator. The efficiency in normal use is never more than about 60 percent. The bearings are too small to reliably support large blades (more than about 1.5 meters diameter). It is designed to be lightweight and robust, and to withstand running at very high rpm. At low rpm it produces nothing, and low rpm is where wind generators spend the majority of their time running.

If you use a car alternator in a wind turbine, the speed problem can be addressed in one of several unsatisfactory ways:

  • Use a small blade area so that the short blades can spin at high rpm. This means that you cannot catch much wind, and even so, you will need a high wind speed to get the necessary rpm. It will also take a lot of wind to produce high enough power to excite the magnetic field and actually have energy to spare.
  • Use gearing to increase the rpm. This involves extra cost, extra losses, extra unreliability, and overall ugly and clumsy engineering.
  • Rewind the coils to work at lower speed. This means more turns of thinner wire in each coil. This reduces the cut-in rpm, but also increases the losses in the coils themselves, limiting the power output and further reducing the already low efficiency.

A car alternator’s rotor needs to be powered to excite the magnetic field. The field has to be at a maximum to get output at the lowest speed. This represents a constant power loss of 30 to 40 watts during operation. You will also have to remove and bypass the internal regulator. The internal regulator in the alternator is not suitable for charging a deep-cycle battery via a long wire run.

While it is cheap and attractive at first look, the car alternator is more trouble than it is worth. It is better to build a purpose-built alternator for a wind turbine.

Hugh Piggott • Scoraig Wind Electric

Comments (20)

TJ2000's picture

I'm in the process of trying this right now; Perhaps someone could talk me out of it if they'd be more precise.

1) Voltage means nothing by itself - Which seems to be many peoples only conception of power. I know enough to know that 1V can produce as much energy as 1KV. Its entirely dependent on Amps ( Which no one seems to care about ).

2) I haven't tested the excited stage in operation but an inactive AC-Delco only consumes 500mA @ 12V = 6 Watts excitement energy not 30 or 40.

My thinking is - by having variable excitement stages one could harvest a wider wind range than conventional permanent magnet; i.e. feed 2V of excitement which will have limited drag, less activation energy, and still be producing +Wind energy at very low wind speeds. Maybe the internal circuitry doesn't allow this - but I'll be finding out soon enough. It would be nice if someone would ACTUALLY measure their voltage and their amperage of their setup so energy could actually be measured instead of just flopping out voltage concerns.

Hugh Piggott's picture

hi TJ,
There are a few problems with operating at only 1V output. One is that you will need an awful lot of amps and so there will be huge losses in the copper wires. It's not a practical voltage for power transmission. And the internal losses in the alternator will dwarf any output you might produce.
The inactive alternator consumes a small current that is used to help it to self excite, but once it is spinning it will generate the necessary current to excite the field fully and this will be much more than 6 watts. It would be nice if you could use a car alternator for a wind turbine obviously but unfortunately it has major handicaps that make it a blind alley for this application.
Have fun with your trials and let us know if you manage to produce a useful output (power) with reasonable efficiency at low rpm.

TJ2000's picture

Hi Hugh - Just want to clarify this for the reading audience, you state @ 1V "will need an awful lot of amps"
That concept isn't really how it works - Unless wiring is changed there is no way to increase Amps with 1V.

As for the other - here is what I've found
1) The alternator excitement reading of 500mV stated by me previously is due to the Alternators built in regulator being hooked up to a fully charged battery. The battery was charged high enough the excitement of the alternator was regulated to 500mV.
2) With regulator by-pass ( Or fully dead battery being the same )
Excitement of the Alternator consumes as follows:
- @ 10.68 Vdc 2.6 Amps = 27.7 Watts
- @ 11.68 Vdc 2.44 Amps = 28.5 Watts
- @ 14.2Vdc 3.5 Amps = 49.7 Watts ( Regulator would start cutting out if it wasn't bypassed )

Thus; You are correct by stating 30 to 40 Watts excitement energy. You are also correct about requiring a high RPM. I've tried 6Vdc excitement at ~1A only to receive less power than what was applied. I'm currently working on bringing the RPM up 6x windmill speed with gearing and will update this post with my findings.

Hugh Piggott's picture

I am sorry, TJ but I don't yet grasp your concept of voltage and current. So far as I know, the power delivered by a DC electrical circuit is equal to the voltage multiplied by the current. Using a circuit voltage of only one volt would require very high currents in amps to transmit useful power (100A for 100W). This was the point I was trying to make, but it appears that I am still not up to speed with your concept of electrical power.

I am glad that you have found data to support the fact that the field consumes significant power, because this is a big drawback, especially when wind speeds are low and losses can consume all the available power.

Of course you can use gearing to increase RPM but this leads to further issues including power losses, maintenance and reliability problems etc. These are the reasons why the car alternator is not a good choice although it clearly appears to be one at first glance. And this was the gist of my message.

Modern magnet technology is cheap and powerful, so it is relatively easy to build a much better alternator that is suitable for the application. Or use a brushless PM DC motor in some cases.


TJ2000's picture

Yes, you do have a very substantial point to your article. I absolutely agree with you, at this point, that it makes no sense to go to the parts store and buy a car alternator even at a $30 savings. Except; I think many who are trying to make this work have free alternators sitting around.

If you know of a place that sells Wind Turbine PMAs for under $50 with shipping; do drop a link. I've only been able to find them at $100 which is $100 more than a car alternator sitting on the shelf. With a homemade blade system costing about $40 w/ 3D printer; the PMA would be by far the most expensive piece to the puzzle and since many of us have up to 5 or 10 of these sitting around that's a total of $500 to $1000 saved versus purchasing PMAs. I believe that's the real driver in making these work for wind generation. Also along those lines if you know where one could get PM DC motors for the same $40 budget with decent output like an alternator; I'd find that very useful also.

It sounds like you have a decent grasp of what I was trying to point out - except you didn't mentioned that the amperage at 1V is entirely dependent on the load resistance and since load resistance of the alternators excitement coil is always constant there is no way to drive 100A at 1V on the application ( short of re-wiring as I had pointed out ). Guess that was my point - to just clarify the situation for other readers.

I'm also planning on cutting excitement power when wind speed is less than ideal and hopefully balance the magnetic load with wind speed. That was actually a big factor in deciding to give this problem a whirl. If some of the issues with using an alternator can be solved or bettered I think there would be a lot of interest in it.

Michael Welch's picture
The most expensive part of the system is getting it high up in the air -- high enough to get useful, non-turbulent air. With towers being expensive, I don't see the hesitancy to spend relative peanuts buying a PMA.

Of course, if we're just discussing doing a fun hobbyist experiment that's not going to make useful energy anyway, the combination of components doesn't matter at all.
TJ2000's picture

I disagree with, "The most expensive part of the system is getting it high up in the air" - That's entirely dependent on demographics. A person on top of a hill certainly isn't gonna spend more on a 1-1/2" pipe to clear the blades than anything else and spending $2k just to get an extra 2-m/s wind above a steel structure isn't a very wise investment anyways.

Goes back to my original comment; If someone is carelessly spending $4k to setup a wind generator they won't be worried about a $250 PMA - for the rest of us spending very carefully - a $150 PMA is the biggest expense.

Hugh Piggott's picture

Hi TJ,
I have been there and done that. I did it because it was cheap. I overcame the problems and made it work. I rewound the coils. I used gearing. The results were not good. I will say it again. While it is cheap and attractive at first look, the car alternator is more trouble than it is worth. It is better to build a purpose-built alternator for a wind turbine. You can join the rest of us who have tried. I hope you are more successful. But the evidence is that you are wasting effort and money when there is a better approach. I have helped thousands of people to build low cost wind turbines that actually work well. Using a car alternator was a blind alley that I went up on the road to finding the best solution. Come back when you have a solution to the intrinsic problems of the device. Meantime there is no point in telling me that it is low cost. Low cost but poor value for money I am afraid.
All the best.

Michael Welch's picture
We look forward to you reporting back on your success.
TJ2000's picture

Thanks Hugh & Michael - I do hear what you're both saying and promise to report back on my findings. So far "money wasted" is at $35 ( blades, gearing, structure ) - the pole & alternator costs, of course, aren't part of that since they were just "sitting around" the yard. The blades are 3' of vinyl siding attached to DIN rails hub-ed and geared with 3D printed parts. So far, in my perspective, I haven't had or heard of a legitimate reason to stop pursuing this design.

They say Edison failed 1000 times before a successful light bulb was created - I guess I'll either fail or succeed on another attempt at making a $50 500W wind turbine and will either publish the success or post here that it failed miserably :)

Michael Welch's picture
I totally get it -- but Edison didn't try the same exact experiment that thousands had tried before him.

Anyway, it's a fun project, and the reward can come from its undertaking.
jonenat's picture

On the speed and fan issues: I've seen old water windmills in my area, and they don't appear to turn slowly, even in low winds. Perhaps that type of windmill could work with a vehicle's alternator. Yes? No? Maybe so?
Alternately, I've seen yard ornament windmills and often wondered if one of them could generate enough power to spin a vehicle's alternator.
I'm not against people buying professionally made or purpose-built equipment. And I do believe in using the right tool for the job. But, what if the job needs to be portable, such as a camper or motorhome? I don't want to waste fuel just to read a book at night or watch movies on my projector. Also, I'm working on a house back home when I'm off college. I don't want to plug into the grid, nor do I want to buy a $300 specialty alternator/generator when I can get a car alternator at the local scrapyard for $30.

Hugh Piggott's picture

Hi Jonenat, I get that you don't accept what I am saying but bear in mind that I have learn this the hard way by trying it, so my hope is that by sharing I will save you time. Go ahead and try it yourself but as I have told you it is not the best approach in spite of seeming to be a good one. I know it looks cheap and suitable which is why I wrote this piece to warn you that it is not. There is a big difference between "not turning slowly" and reaching 1200 rpm or whatever speed you need to get power out of a car alternator. When you are generating with small turbines in moderate winds you really cannot spare the extra power to excite the field in an alternator. You can buy magnets and build an alternator at quite reasonable cost so as to get the benefit of what little power there is. That's all I wanted to tell you. Good luck and have fun!

baylensman's picture

What if a "generator" from an older vehicle or tractor that is designed to operate at a lower RPM and a lesser HP engine was used. Not to generate direct power but say to charge a set of back up batteries for when the grid shuts down. Maybe enough for lighting and fans?

Hugh Piggott's picture

hi Baylensman,
Back in the 1970s when I started doing this I did manage to find low rpm vehicle generators and built many machines based on them. I used jeep generators that weighed over 50 pounds each. I rewired the field coils so I could run them at lower rpm at 12V instead of the 24V they were designed to produce. It was a workable solution with recycled technology and it powered a couple of dozen homes for ten or twenty years. But when magnets got cheaper and I learned to build simple alternators with them I was very pleased and I never looked back.
The problems were twofold. The brushes and commutators needed frequent attention. but the worst problem was the power consumed by the field coils. Low winds were when we needed power the most. PV was too expensive for us in those days. And the field coils used up all the power in low winds.
Nowadays we can have all the power in low winds because the magnetism is permanent. It's easy to make an alternator using the axial flux approach. So I don't see any role for vehicle alternators or generators. They are too small, too inefficient, too fast-running.

goodall280's picture

you actually can add magnets to the alternator to make it a permanent voltage or you can build a turbine with a pully on the back with belt chain etc connecting to alternator. if your pully on turbine has say a 17" inch circumfrance and your alternator is a 1" your ratio is now 17:1 so lets say your turbine turns 3 times in one sec we times 17 by 3 then times by 60 to fig out what it would be in rpm which would be 3060 revolutions per min (rpm) your average alternator ranges from 500-1500 rpm and buy adding belts or chains you remove the strain on the bearings lets face it if the cant handle belts they wouldn't use it on a vehicle then all you would need is batteries and a powerful enough inverter many people are now using these types of power sources in camps where there are no power lines you can also make an easy to build power sourse with a old powerline wire spool for example and build a water turbine unit in a stream you can look some of these ideas that people have used on youtube

Ian Woofenden's picture
Most smaller residential wind turbines today are direct drive, because it reduces losses and costs -- KISS. As soon as you introduce gearing of any sort, you're introducing a loss. That might be acceptable if there's enough energy and money to play with, but the physics and the marketplace tells us that it's not the ideal scheme.

I'd suggest caution with leaning too heavily on YouTube videos, which may come from serious and long-term users, or maybe just from hobbyists or experimenters. Wind electricity isn't easy to implement, even when you have good knowledge.

Ian Woofenden, Home Power senior editor.
Michael Welch's picture
Some of that is true and doable. Belts work for car engines because of the large amount of power available from an internal combustion engine to overcome their high resistance. But if you want something that actually works and lasts, explore other options. Building your own turbine is doable, though. Check out "Wind Turbine Workshop," a book by Hugh Piggott.
hhanafi's picture

Hi, I think if you use a verical turbine you may avoid the bearing problem. The rpm problem may be solved by using a 1:2 or more belt assembly. Again this is only a rough thought that needs more research.


Ian Woofenden's picture

Vertical-axis wind turbines (VAWTs) have not shown themselves to be reliable in the marketplace or in the wind. Many uninformed people seem to think they are an answer to wind energy problems, but generations of real-world wind energy designers and users know otherwise. VAWTs' successes are generally for venture capital seekers and salespeople, not for the end users who want clean and reliable energy.

There's a grain of truth in the comment above, since VAWTs tend to run at lower rpm. But they also have significantly lower efficiency and reliability, so are not a good tradeoff if your interest is in reliable energy generation.

Ian Woofenden, Home Power senior editor

Show or Hide All Comments