|Posted on Monday, March 03, 2014 - 06:26 am: ||
I sense many of the readers here do not understand how these alternators and voltage regulators work. If you do, I apologize, but in case you don't, please understand that motorcycle alternators, unlike automotive alternators, make maximum current all the time regardless of system requirements. This is because the excitation field comes from permanent magnets in the rotor. Excess power is simply dumped to ground through the voltage regulator and its heat sink. Whereas automotive alternators use an electromagnet powered through the rotor's slip rings. The voltage regulator in this case controls the excitation voltage, limiting the output current as the system demands. It should be clear now that the drag on the crankshaft is constant on motorcycles and very wasteful in comparison to the automotive type.
|Posted on Monday, March 03, 2014 - 11:31 pm: ||
You would love the Honda ST1100, ST1300, goldwings with their external alternators!
https://www.google.com/search?q=st1100+alternator& espv=210&es_sm=93&tbm=isch&tbo=u&source=univ&sa=X& ei=sVEVU4v7B8j0oATZooKoCg&ved=0CDYQsAQ&biw=1680&bi h=937
|Posted on Tuesday, March 04, 2014 - 08:58 am: ||
Good summary Stevel.
The permanent magnet stator will have a constant maximum current output, but the current output at any moment could vary.
Current will vary with engine speed and with electrical load. And electrical load is (as you note) largely dependent on the type of regulator used. Buells and many other bikes use shunt regulators, but they don't have too. They could also use series or switching regulators.
If your electrical load is low, the current from a permanent magnet generator will be low. If your RPM is low, your current output will also be low (relatively).
Permanent magnet generators have less potential output, but they are simpler and smaller.
|Posted on Tuesday, March 04, 2014 - 03:50 pm: ||
"Current will vary with engine speed and with electrical load.".
As stated is not correct, The coil current will not vary with load. You are correct in that it will vary with speed. In order to reduce the alternator power going to the load when not required, the excess power must be dumped or excessive voltage will occur. Yes, switching logic could be used, but I do not know of any in use for motorcycles yet.
The reason I started the thread is to point out that the alternator is always working at its max output regardless of load, so coil heating is inevitable and unlike automotive units, there is no air cooling. The only way to cool the coils is to oil cool them. In the case of the Buell, the drilled hole mod is super important for all 1125's. Even at that, I'm not certain there will be adequate oil flow with that mod. The source of that oil is waste oil from the crank end after flowing first through the starter Sprague. I know of several cases where this Sprague has failed, which should never happen if properly oiled. This does not give me confidence that the drilled hole is enough, especially in the light that the alternator in the Buell design is a shunt regulator and the coils are always working at max output current.
|Posted on Tuesday, March 04, 2014 - 06:30 pm: ||
Steve the CE605 regulator is a switching type
and is supposed to "disconnect" the ac system to regulate.
So far the folks with oil jets are not complaining with failures,
We have not seen that many sprague failures the hole was in the crank to start with, there was rumor that HD had nixed the oil hole in the rotor as too costly, given the rumored bad blood I can see the mod being nixed..
I have an '08 and KOW its still making juice..
|Posted on Tuesday, March 04, 2014 - 06:45 pm: ||
when I questioned the size of the hole in EBR rotor, I got this reply back from "anonymous":
It is very specifically sized for the right amount of mist to cool the stator best. Tons of testing to determine the optimum size for cooling and then durability testing after that. Also very hard to make a precision hole this size in a hardened part; it would be easier to make it bigger. Of course there is probably someone on the internet who knows better and will suggest you drill it out to a 1/4", so you can both flood the cavity and blow the main bearings.
The line to the whole thread is here: