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Old 10-01-2007, 15:14   #1
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Permanent magnet alternators

I have been advised to switch over to Permanent magnet alternators on my vessels.
I have started to do some research on these apparent long life alternators, and as usual instead of collecting a clear understanding of these devices that apparently out perform alternators 100% I have come up with more questions.
What is your knowledge on Permanent magnet alternators ?
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Old 10-01-2007, 15:57   #2
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AFAIk if it uses magnets, it's a generator not an alternator. On an alternator, if you interrupt the field current you can reduce the output. But on a generator (something with magnets instead of coils) you can't interrupt the magnetism, so you can only regulate it by shunting the output to a dummy load. That can mean changes to the whole system, plus, the generator will still be putting a heavier load on the motor even when you don't need full power--because it is still producing full power, and you're shunting it to a dummy load.

In my limited knowledge of them.
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Old 10-01-2007, 19:09   #3
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My KISS wind generator which is really an alternator uses rare earth magnets. Description follows, don't ask me what it means.

The power plant is a brushless alternator specifically designed to match the low speed characteristics of the rotor blades. The alternator produces 12 volts at only 200 rpm. The alternator incorporates epoxy coated neodymium magnets, a shaft seal and plastic sealed #6203 metric ball bearings, the most common bearing in the world. Note what the wind generator does not incorporate: commutators, brushes or slip rings. All of these features ensure maintenance of the wind generator will be infrequent, simple and inexpensive.
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Old 10-01-2007, 19:30   #4
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Alterators produce AC current (Alternating Current) then converts it to DC thru a rectifier.

Generators produce DC current (Direct Current), and that's the main difference.

With permanent mag's I would think it's a generator like on the old Harley's.
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Old 10-01-2007, 19:49   #5
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A good place to start your research:

Alternator - Wikipedia, the free encyclopedia

Bill
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Old 11-01-2007, 12:47   #6
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I have found the following information from this web site:
http://www.hydrogenappliances.com/powerpmas.html

It appears that this type of "alternator" has been around for a long time. The Alternator has fewer parts that wear out, and over all it produces much more power than a conventional alternator at much lower RPMS, as well it produces extreme heat with the production of the power. The Alternator requires a voltage regulator that regulates the voltage of the battery and not the voltage output of the PMA.
As previously stated that the engine would have a larger load, it appears that it is quit incorrect.
It appears to be a no-brainer expensive replacement for a conventional alternator to produce copious amounts of power. I have burnt out Alternators in the past by placing too much of a load on them, tis alternator is not bothered by load, it simply displaces more heat when loaded that is disipated with the cooling fan providing the correct amount of RPM.
I am aware that this alternator is typically used on wind generators and now is making it's way into Marine applications. This device truly sounds like it will be perfect for marine applications, however I am concerned about usng it.
This is a picture of the Alternator.
What do ou know about this product/conversion..
Thanks.
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Old 11-01-2007, 13:02   #7
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In practice the terms alternator and generator are bandied about and contradicted to each other even by the same makers. Take an "alternator" with a built-in regulator and diode frame...and companies sometimes call it a "generator" because if you treat it as one box, what's coming out is DC not AC.

I suspect the real meanings of "alternator" "generator" and "dynamo" are all hopelessly lost to common usage by now, even if some folks out there are really sure what they each mean.

Chris, I'd run scared from Thermodyne. They say "...standard automotive alternators are usually putting out 40 to 50 volts into the 12 volt battery in your car. ... It won't harm the battery AS long as the battery is not FULL it can take high levels of charging voltage no problem. "
Well, ignoring their opinion of "no harm"...the fact of the matter is, no automotive alternator puts out more than 14.4VDC past the regulator to the battery. Regulators are AFAIK all internal to the alternator case itself these days, so you never see more than 14.4VDC outside the alternator. Putting 40VDC into the battery would mean putting it on the power bus and that would immediately blow out hte headlights, ignition system, and everything else. If these folks know what they're doing...they didn't stop to read their own words. That kinda slip scares me when the folks making it are supposed to be selling technology.

Sounds like they are making the same core as the KISS machine, but neither really tells you how it has to be regulated or damped.
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Old 11-01-2007, 18:31   #8
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Quote:
Originally Posted by hellosailor
Putting 40VDC into the battery would mean putting it on the power bus and that would immediately blow out hte headlights, ignition system, and everything else. If these folks know what they're doing...they didn't stop to read their own words. That kinda slip scares me when the folks making it are supposed to be selling technology.

Sounds like they are making the same core as the KISS machine, but neither really tells you how it has to be regulated or damped.

I agree with you on the matter of excess voltage blowing out any 12v devices making a draw. Over all if there is a way to manage the alternators output, would it not make more sence to go with this device?
I am still doing some searching, now I am looking into the wind generators and how they regulate the voltage.
It would be amazing if someone had some experience with this topic as this may be a very expensive experiment.
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Old 11-01-2007, 19:21   #9
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Efficient utilization of an alternator output

In general, the only truly dc output rotating device that does not utilization commutation (which includes diodes) is a Hall effect generator. They were most commonly used by the locomotive industry to generate high currents to fuse railroad ties together. In general, all other devices generate ac which must be commutated by some means to dc, if that is what is desired.

Permanent magnet alternators can be either regulated by their rotational speed (not convenient with your engine, yet possible) or by an electronic regulator. To date the only affordable regulator would be a power dissipating shunt regulator. Not only is this very inefficient, it can inconveniently load the engine at a time when you need all the power that you can get and you cannot merely turn off the regulator as you can with an externally regulated external current fed field alternator.

An "ideal" regulator for a permanent magnet alternator would be a switch-mode device that extracts the energy from the windings during the entire conduction angle of the waveform. So far no such product exists yet it could be designed and it would be expensive due to several factors. Such a device would not require unnecessary power dissipation yet it would require toleration of a very wide range of voltages and currents to be useful.

Make no mistake about jumping to the invalid conclusion that a permanent magnet alternator is necessarily more reliable or desirable than is a standard high output alternator using a GOOD external regulator with temperature monitoring of the alternator. I believe as well that you have not considered a more expensive brushless external field current driven and regulated alternator. They are VERY rugged and reliable.

Large frame alternators (about 9 inch diameter instead of the usual 8 inch or so diameter ones) have HUGE bearings by comparison and have proven to be quite reliable compared to the usual run of the mill high-output alternators. Brushes are inexpensive, relatively easy to replace and infrequent in that they just do not wear rapidly.

Do not condemn the good existing external field current fed regulating alternators for the wrong reasons. Instead, condemn the thought of using permanent magnet alternators for valid reasons outlined here.
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Old 11-01-2007, 19:32   #10
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Does this make any sence, utilizing an element from a hot water heater toheat water, or other high draw device to regulate.
See link: Permanent Magnet Alternators PMA pmg Permanent wind turbine mill Magnet Alternator Permanent Magnet generator wind power PMG wind turbine wind turbines





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Old 11-01-2007, 22:09   #11
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Challenge your original ill-advice

Your original statement was regarding advice to switch to using permanent magnet alternators on your vessels. I interpret that to mean switching the engine alternators. This does NOT make any sense.

Let's understand one clear advantage that permanent magnet alternators have: At small input horsepower (like little wind for wind generators or little head pressure and flow rate for water generators or hand-cranked devices) such devices will have better efficiency than current-fed external field alternators can have. The obvious reason: field energy is almost a "total loss". For input horsepower approximately 1/3 hp and above it does not make any sense for a prime mover such as a gasolene or diesel engine to use one with all of the attendant disadvantages of power regulation for battery charging. For water heating or other total energy absorption applications with dedicated run times, sure, maybe.

It certainly make no practical or economic sense to use permanent magnet alternators to charge batteries when 50 Amps or more is required for initial charging when using an engine also used for long run times, like when you are trying to go somewhere for many many hours.
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Old 12-01-2007, 05:59   #12
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They have been around for years. The Daschews have used them forever.

Electrodyne Brushless Alternators
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Old 12-01-2007, 10:27   #13
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Chris-
You ask if it makes sense etc., well, sure it does. You can waste ("use") the dumped power to create some form of stored energy, but when you think about it, we normally use an alternator to create stored energy.

We normally store it in the battery, and then we stop wasting energy (we stop putting a load on the alternator) once the battery is full.
If you add some other energy storage device, whether that is a hot water tank, bigger batteries, pool of molten lead <G> or a hydrogen generator (rocket propelled boat anyone?<G>) it is really all the same thing. If you can't stop wasting energy on the "generator" you have to store it or dump it. For a wind generator that's no big deal, you aren't paying for the wind. But it still means there is an active process you have to monitor, and if you are on a small boat with a 10 gallon hot water tank...how long do you want to boil the water or heat the cabin with it?

It isn't that I'm against the idea, it is just that I'd rather see something like an airconditioning clutch that disengages the fan blades, or something that actively feathers the fan blades, so that once the generator was no longer needed--the waste and the load shedding stopped.

A friend of mine had problems like this on his motorcycle, also a vintage design with a "real" generator on it. At low speed he gets no power, which is the hallmark of a generator. At high speed...there's too much power and there's no way to stop that without dumping it. Which they designed by using a regulator with a resistor heat pack in it, so at high speed it heats up and then...kept failing on him, because of other design issues. In many ways it is simpler to use an alternator where you can electronically "starve" it and shut it, especially if you want one regulator for multiple sources, using one way to regulate. But I'm sure there are situations where the generator and dumping still pay off, i.e. on a commercial vehicle with a 250hp engine, maybe it is easier to run the lower-maintenance (no brushes) generator all the time and sure, you can use the huge metal chassis as a heat sink to dump power. No doubt you could put two electrodes under a boat to do the same thing, along with a warning placard "NO SMOKING, Hydrogen Generation Zone!"<G>

Oh DUH! That's it! Use the dumped energy to split water and collect the hydrogen to fill blimps. Then use the blimp to help lif the hull out of the water, lowering displacement and making the boat faster all the time. Silly me, I was missing the obvious way to make all that wasted power go to good use. And since hydrogen leaks out of everything very quickly...there's no such thing as too much hydrogen, these generators will be PERFECT for boatblimps. Or is that, blimpboats? 'scuse me, gotta go run file the patent now.<G>
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Old 12-01-2007, 11:11   #14
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A non-problem that doesn't need "fixing"

Gee-wiz, a HUGE point is being missed here! There's no reason to replace existing alternators with field windings with permanent magnet ones for engine applications!

Keep in mind that the REAL problem with using powerful high output permanent magnet alternators that match the 2.8 kilo-watt large frame field controlled ones is that they will unnecessarily waste huge amounts of heat in the stator windings when having a shunt regulator "truncate" the voltage peaks from exceeding 15 Volts or so when you cannot use the excess energy! This means that you will waste fuel and unnecessarily load the engine and wear the belts and bearings! Wake up!

If you want to make hot water use the engine cooling system to do so it will waste much less fuel. Permanent magnet alternators are much more inefficient when regulated than field-controlled alternators!
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Old 12-01-2007, 11:37   #15
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Although highly impractical... You could clutch the alternator.

I could only see using this style alt, if you were wanting to put it on the prop shaft for power generation underway... without the engine turning.

Or, if you wanted to have a welding rig on the boat. They will put out cleaner current than an ac rectified generator.

Have you guys ever had an alternator that did not have some risidual charge to stimulate at startup? I'm thinking about push starting a car with no battery... still fires up.
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