brushless alternator?

I'll put my 2 cents in .. Brushless Alternators are like induction motors more or less. if you take an induction more and spin the rotor having a AC volt meter on the stator windings with no load, you will get electrical energy, just not a lot. Now, since there is energy is in the field, you take that little energy which is also being induced into the rotor area. with the coil on the rotor, you do receive some current which gets rectified to a shunt load, this causes a DC field to generate and once this happens, the DC field just adds too and sums up and thus gives more to the rotor etc, it's like it's own electro magnet (DC) there is normally a cap in there somewhere on the stator circuit that links the stator windows and causes current regulation depending on how much load you're drawing from the alternator. If this cap fails, you'll get very little current output, also, sometimes the core needs to be demagnetized. etc.. Ok, that was as simple of an explanation i could come up with.

Don't get all defensive now. Oil filled caps have been around since the, well, before I was born and they just don't die - and I've tried. Got a few in my unreg choke input filter HV supply from the 40's still going strong.

Some AC motor run caps look like oil filled types bur are dry and a lot less permanent, and lighter weight - like one sees in microwave ovens. I'm guessing you might have one of those. Crimped drawn metal, aluminum case, with a plastic insulator - no elastomer seal, no porcelain turret connectors and a quick connect, push on connector. Looks similar to the old oil dielectric caps, but a lot more capacity and a lot less rugged.

Cap could be all the problem . . . but a 50 uf cap would suggest it is just there for sine wave smoothing and not a necessary generator part

- but I don't know what your load looks like to the gen either. Try changing the cap with a new one - that may be all that's wrong.

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Sorry, I just get a bit irked by all the knee jerk reactions implying that I'm some sort of idiot, I've been around here for a long time and know how to properly test components.

It may well be a dry cap, I just assumed it was oil filled because it's metal, has a soldered closed hole in the end, and says "No PCBs" on it. I also noticed tonight that it says "Protected" on the end which I assume means it's internally fused. I'll cut it open later to find out what's inside. At any rate I ordered a new cap, it was only $1.75 from a surplus outfit and I needed some other stuff anyway. If installing that doesn't fix the problem I'll dig deeper.

You're so right. Why would you bother to see if you can find a manual that might explain exactly how it works.

They are paper or mylar film capacitors in metal, oil filled cans, and they do fail. I have a military TS-382 audio generator similar to the original Wein bridge HP 200 CD that is all oil filled or ceramic capacitors, and every one of the oil filled capacitors is leaky.

"Oil filled capacitors don't fail" is a myth.

It works like a squirrel cage motor. An ac induction motor. That's why it needs a little DC for the coil or else it won't generate. An alternator is an AC generator, see the diodes? Those convert ac to dc. Internal regulator? That's what keeps the battery from blowing up.

On Thu, 28 Dec 2006 06:53:08 +0000, James Sweet Has Frothed:

An alternator in a car is different. It has to have a battery to provide its field with DC. An AC generator has permanet magnets in the rotor and the current is induced in the field where the RPM of the rotor is responsible for how much voltage is produced.

James,

This is one brushless 3-stage method - there are others.

rotor = permanent magnet stator = static coils

Rotate the rotor and AC power is induced in stator coils. Output from stator coils is fed to second stage within the stator.

stator = coils fed from 1st stage rotor = coils

Output from 1st stage stator is rectified and fed to second stage stator coils - regulation can be imposed here. Rotate 2nd stage coils in 2nd stage magnetic field - AC power is produced in rotor and output is fed to 3rd stage.

rotor = coils fed from 2nd stage. stator = coils

Output from 2nd stage rotor is rectified within the rotor body and fed to 3rd stage rotor coils. Rotating electromagnets cause induction of output in 3rd stage stator coils

I have the service manual, it explains nothing of the theory of operation, it just has a list of the components, shows where they mount, part numbers, and torque specs for the bolts.

As I said before, this is not a permanent magnet generator, it has a wound rotor and is more similar to a car alternator than you think. Frequency is determined by the RPM, voltage is not, at least it is not adjusted or regulated by varying the RPM.

At any rate, after doing some more research I think I have a pretty good idea of how it works. It's the same principal as spinning an induction motor to generate power except the armature with copper windings and a rectifier are much more efficient for generating than the aluminum bars in a motor armature. The service manual doesn't have an internal schematic so I'm not sure how the capacitor connects but I can guess. It's a clever concept at any rate, I'm not sure why they don't all work this way but I've seen similar generators which had slip rings and a circuit board to regulate the output much like a car alternator uses.

That's most of what I found online, this is different though, it has only one stage, unless other parts are cleverly buried within the armature. It looks like a giant two pole DC motor armature except it has no commutation, the free ends of the winding connect to each other through a diode which is mounted to the rotating assembly. The only external component is a single capacitor.

I have had several oil filled caps used in ferroresonant transformers go bad....

Mark

The DENSO brushless alternator service manual gives a brief description of its operation. (I think the schematic fails to show connection dots for the + and - side diodes)

On Sat, 30 Dec 2006 13:36:00 +0000, Ross Herbert Has Frothed:

That link just shows how to install it.

Hmm, I won't get into it, but you're a little off.

On Sat, 30 Dec 2006 16:32:24 -0500, Jamie Has Frothed:

Which means I'm for the most part correct.

SNIP

Duh! wrong link. It should have been

It would have been helpful for you to have stated that to start with.