brushless alternator.
brushless alternator.
(OP)
I have fabricated a brushless alternator using a 12volt stator and rectifier/regulator assembly scavenged from a 20HP air cooled gasoline engine. One stator is rated for 15 amps the other fo 30 amps. The magnets rotate around the perimetor of the stator. The stator has 18 poles and is wound for single phase. Output voltage on the 15amp stator is 23 volts AC 14.2DC at 500rpm. I would like to substitute rare earth magnets in place of the ceramic ones on the original application. The dilema is that they are not available in the radius that I am working with. Question 1. would a flat face rare earth magnet perform well in this application? I would like to increase the amperage output. Question 2. would it be better rewind the stator with more wire on the poles ot run it through a step down transformer to achieve that objective? Question 3. is there anything to be gained by rewiring the poles for two or three phase output? Finally what device or method do these style alternators use to regulate the voltage?--------Phil





RE: brushless alternator.
You do need to consider the rotor structure as you speed it up.
You might consider using a standard automotive alternator. Typical junkyard fare puts out more than a kilowatt at 15V, 80A. The rotor is specifically designed to spin very fast. (20,000RPM)
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: brushless alternator.
RE: brushless alternator.
This is one of those "It depends".
We have no idea of the design parameters of your equipment.
A few factors to consider.
Changing magnets;
If the radius is wrong you will have excessive air gaps that will negate any advantage of stronger magnets.
You need to consider not just the face of the magnet passing the stator but also the back face where the magnet contacts the iron supporting structure. The magnetic circuit does not like air gaps, be they behind or in front of the magnets.
If your magnetic circuit is near saturation, and it may be designed that way to economize on materials, you won't gain much from stronger magnets.
As far as rewinding, reconnecting, three phase, etc. I hesitate to make suggestions without seeing your setup.
I have seen a lot of alternators on small engines intended for battery charging that take a lot of design shortcuts. A recommendation that is valid for all conventional industrial alternators would not be appropriate for some of the small engine alternators I have seen.
Tell us a little about your application, what do you want to power?
If you give us the make and model of the 20HP engine, someone may Google up some drawings and be able to give you accurate information rather than guesses.
yours
RE: brushless alternator.
RE: brushless alternator.
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Be aware that the magnets do not act independantly.
The magnets and the supporting flywheel are an engineered unit. The flywheel serves as the return path for the flux.
You may consider using a section of the Koehler flywheel with magnets attached instead of buying new magnets.
That will save you from having to determine the magnetic properties of the material on which you are proposing to mount the magnets, and designing the new magnetic circuit.
Output; You can increase the output by rewinding the poles with heavier wire. When you do this, you will not be able to get as many turns of wire on the pole. As a result you will have to be turning at a higher RPM before you get a usefull output.
Your regulator appears to be a shunt regulator. You will probably destroy it if you rework your alternator for more output.
You can stack two stators to increase output, but then you have issues mounting a double row of magnets.
Check thread237-145132 for some of the issues involved in building and regulating alternators.
There is probably much less work involved in finding a way to mount an automotive type alternator than in designing and building a flywheel alternator. The result will also be much more predictable.
yours