Most of the charging issues people have with 'one-wire' setups, is simply insufficient self-excitation, combined with the loss of residual magnetism.
When an externally-regulated alternator starts, the regulator applies battery current to the field, which is revolving inside the stator, which then generates AC, which is sent (usually in three phases) to the rectifier bridge (six diodes in one convenient package), where it is turned into DC... and that DC is 'sampled' by the regulator to determine wether voltage is too low (where it then adds more field current) or too high (where it reduces field current) to get the proper output voltage. Of course, once the alternator is charging, the regulator can obtain field current from the alternator's output... so the battery, as an excitation source, is only needed for a second or so.
A 'one wire' setup doesn't use the battery as it's source of excitation... it relies on a simple little piece of physics- Magnetism... specifically, the fact that iron and steel pieces inside the alternator, once subjected to a strong magnetic field, will have a tendancy to retain that magnetic field for a good while.
Now, most of you have a magnetic screwdriver in your toolbox... and when you need to start a phillips screw from a long ways away, that's a really handy thing. What about when you got a screwdriver, and you WANT it to be magnetic? Well, you snap a magnet on it for a minute or two, then you drag the magnet down the shank, past the end of the bit, and off... and tah-dahh... you have a magnetic screwdriver. Another way to make that happen, is to wrap a dozen turns of hookup wire around the screwdriver shank, and connect it to a battery... as long as the battery is connected, that screwdriver will be an electromagnet. Disconnect the battery, and MOST of the magnetisim will vanish, but SOME will stick around. It's called 'residual'... not because it is residue... it's because it's RESIDENT. It will eventually fade, but you'll have stuff stickin' to it for a fair amount of time.
When an alternator rotor is energized, it's an electromagnet. Turn off that power, and MOST of the field will drop off, but a LITTLE BIT will stick around.
Next time you spin that alternator, without adding external battery power, it might not generate gobs of power, but it will probably generate JUST ENOUGH to bring up excitation current all on-it's-own... and THIS is what the 1-wire alternator depends on.
Now, if that residual magnetism is a little weak, spinning the alternator FASTER will cause it's slight magnetism to generate more output, and it'll kick on.
Residual magnetism doesn't stick around forever... it fades, and eventually, won't be strong enough to self-start a one-wire. Applying a little external DC to the field will bootstrap it back into operation.
Running the engine more often... will help maintain a strong residual field.
Making the alternator work against a really high load... helps build and maintain a strong residual field.
Connecting the windings of the alternator in WYE configuration (rather than Delta) will result in higher output VOLTAGE (albeit at lower current), and thus, cause the alternator to self-excite 'easier' (at a lower speed). A prevailing thought by many, is that an alternator of higher CURRENT RATING is more desireable than a lower current rating... but frequently, the higher current rating is gotten by using a lower-voltage winding count... and as a result, these alternators require much higher rotor speed to output sufficient voltage to maintain a battery charge. Unless the engine is spinning the alternator in that range, it really isn't charging... so while higher output looks good on paper, the a lower output alternator is charging the battery basically constantly, while the high-output is only 'in working range' part of the time.
When a guy has a tractor that he doesn't start often, and it isn't charging while he runs it... means that the battery-charge-economics is simply never making it out of the red. Start it up, and run it at a higher RPM, mebbie it'll start charging...
The alternators I use on my retrofitted equipment are frequently one-wire, and when I get them, I have my local shop set them up for me for extremely low starting-speed. He wires the outputs in Y, and uses finer wire, with more turns in the windings so the output voltage comes up higher, faster... they all self-excite BELOW idle speed, so when they're running at idle, I'm getting at LEAST 10A of charging. Bring it up off idle, it might jump to just 25A or so, but it's solid 25 all the time, not dropping out when I idle it down.
As an aside note, if you ever wind up with a generator... either engine- or PTO-driven, and it won't generate output, it is highly possible that the problem is simply no excitation... due to the residual magnetism being depleted.
If this is the case, it can easily be solved by connecting the generator to a resistive load (a milkhouse heater, or heat lamp works great)... start the engine, then smack a big magnet onto the exterior of the generator framework. This will simulate a 'residual' field. Now bump the throttle on the generator engine for a few moments, and once you release it, you'll hear the engine 'grunt' while the governor brings on fuel to match the new load. Now that it's running stable, leave it run, generating a chunk of power for an hour or two... it'll rebuild it's residual magnetism, so no magnet will be needed next time.
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steve(ill) wrote:
