Both SHUNT and SERIES R/R's provide direct control over the single of three phase alternator windings. I'm not sure where this comment is coming from. Are unregulated PM alternators installed on XS650s?As you know, there is no control over the voltage or current output from a PMA
so with the fuse as shown the output from the PMA regulator would be at maximum in the event of a partial short and that could lead to overheated wiring or a fire as well.
A dead short would blow the battery fuse, but the PMA would continue to produce maximum power in the time it takes for the engine to stop running.
In fact, it could be worse because the PMA is in parallel with the battery so if the PMA was supplying 15 Amps then the short would have to draw 15 + 20 = 35 Amps to blow the fuse and it's possible that the engine would continue to run with the blown fuse and the PMA would continue to produce power unprotected by a fuse.
Also, in the case of the XS650, a shorted diode in the rectifier does not result in battery current going to ground as the alternator stator winding's are not grounded.
posplayr,
As you have likely noted, the conversion to a PMA type alternator is very popular with XS650 owners. As you know, there is no control over the voltage or current output from a PMA so with the fuse as shown the output from the PMA regulator would be at maximum in the event of a partial short and that could lead to overheated wiring or a fire as well. A dead short would blow the battery fuse, but the PMA would continue to produce maximum power in the time it takes for the engine to stop running. In fact, it could be worse because the PMA is in parallel with the battery so if the PMA was supplying 15 Amps then the short would have to draw 15 + 20 = 35 Amps to blow the fuse and it's possible that the engine would continue to run with the blown fuse and the PMA would continue to produce power unprotected by a fuse.
Also, in the case of the XS650, a shorted diode in the rectifier does not result in battery current going to ground as the alternator stator winding's are not grounded.
...The old field controlled alternators on the XS650 will surely start to shut down due to over voltage spikes if the battery is removed won't it?
posplayr,
I think that the thing you may not understand about PMA alternators is that the regulator is a shunt type regulator, meaning that it just shunts the excess current to ground. There is no control over the output of a PMA. In other words, if there is excessive voltage, the regulator just shunts the output of the PMA to ground to reduce the voltage. If there is a gross load (partial short) that causes the voltage to decline, the regulator has no effect, but the PMA continues to produce its maximum current.
As far as the conventional configuration of the rectifier and fuse, I am not advocating any particular configuration. Just pointing out the design deficiencies. You are advocating a better system , so you have to address these deficiencies.
In the scenario about needing 35 Amps to blow the fuse, the PMA does not have to produce 35 Amps. It is a parallel circuit, so the PMA produces 15 Amps and the battery provide the additional 20 Amps to blow the fuse, but the total Amps feeding the short is 35 Amps.
2.) The notion that SHUNT R/R's dump current "to ground" is an old wives tale that defies ohms law. Current flows in circuits and so current can't be dumped to ground. The stator legs are shorted completing a circuit. Although the potential of the short is nominally at ground there is no current leaving the R/R to get to ground. Ironically you mentioned before that PMA stators on the XS650 are not grounded (I agreed none of them are), so how do you figure the stator current gets to ground? Through the R/R(-) wire that is "grounded"?
Just to clarify for the interested readers:
This Hayabusa schematic uses a delta-type winding, but if you follow the current flow arrows you can see how the circuit is a closed-loop during output shunting, and ground is tied to part of the path:
Wow, that is a massive repository.
Would you happen to know about field excited alternators used in other motorcycle models?
The mechanical regulator type 70-79 XS650 alternators do not use freewheel diodes, as I've seen in automotive Delcos and one other motorcycle (can't remember which one). Not sure about the 80-up regulators.
I've seen some anomalies that could be attributed to the lack of a freewheel diode, and wondered if this should be implemented...
6.) Apparently the XS650 and it's alternator have some type of voltage kick back when shutting off as evidenced by the 20 amp fuses as well as some of the XS650 owners observations. The SSPB will suppress those negative going pulses.
Yes, we may have touched on that with the 15 vs 20 amp fuse discussion.
The question is: Would the addition of a freewheel/shunt diode be prudent and recommended for stock 70-79 mechanical regulator circuitry (in the rotor power lines)?
It's standard practice to add freewheel diodes to semiconductor controlled inductive circuits, to protect the semiconductor driver from inductive kickback.
This may improve regulator life and performance by reducing points arcing and flutter.
Some anomalies that might be attributed to a lack of freewheel (anti-kickback) diodes in the rotor (field) circuit:
- The rare backfire that occurs when ignition is turned off.
- Failures of semiconductor contraptions added to these early models.
My first el-cheapo digital voltmeter eventually failed (no reverse polarity protection)
My second digital voltmeter (with reverse polarity protection) works fine
A couple years ago a member here inadvertently wired her LED neutral light backwards, and reported that the light would glow for a couple seconds after switching 'off' the ignition.
I thought I'd ask before pursuing this....
posplayr,
Yes, there are different ways to regulate the output of a PMA and I agree that shunting to ground is an oversimplification, but the current is shunted coming from the winding's of the stator in the simplest type of regulator. However, this shunting action only occurs when the voltage equals the desired regulated value. When the voltage is less than the desired value, such as when the engine is at low RPM's or there is a high load condition, such as a short, the regulator does nothing and the PMA is free to produce its maximum current output, unregulated. That is the situation used to point out the 35 Amp scenario. A partial short will cause the voltage to decrease at the junction of the battery and output of the regulator thus eliminating the function of the regulator so both the battery and the PMA will supply current to the junction of the two sources in parallel. Your answer to this scenaroi assumes a normal operation with a fully charged battery and in that case the battery will not supply any current and the PMA will carry the entire load, but my hypothetical scenario was for a partial short that would cause the voltage to decrease below the float voltage of the battery so the battery would then contribute to the current demand of the short. Of course, it gets a little more dynamic than that, because as the battery supplies current to the short it will discharge to the point where its voltage is too low to cause any current flow to the short through the fuse so the entire scenario of the 35 Amp will be short lived but depending on the severity of the short circuit the flow of current from the battery could exceed 20 Amps before it discharges below the voltage at the junction of the PMA and battery.
In any event, I am not trying to shoot down your new product. I am all for any new product that will help keep the trusty XS650 on the road, but in my experience, I have found that there is a tendency to focus on the "gee whiz" aspects of a new product and lose sight of the front end, in this case, the source of power to your product. You say that many aspects of your product are found in other more modern motorcycles but that doesn't mean that those features are perfect and now is your chance to improve upon them. As a minimum, I would suggest a different scheme for the PMA setup as apposed to the stock conventional field excited type of alternator. The conventional alternator takes care of load anomalies intrinsically because it depends on the system supply of current to excite the field. The PMA, on the other hand, ignores high load conditions, such as a short circuit, and just continues to produce the Amps.
Both types of alternators can produce destructive high voltages for certain types of failures of the regulator. The PMA is more prone to this type of failure.
I would like to see some protection for this problem in your design. (Perhaps it is already there and I just failed to see it )
I've been considering putting a PMA on my XS, but the first thing to be connected to it will be a SH-775 SERIES reg-rec, as I (and many other GS owners) are now, through experience of them, utterly convinced of the efficacy of them.
In the meantime, the original mechanical r/r was sometime replaced by a PO and the EOM alternator soldiers on with a solid-state r/r of unknown origin, but it's doing its job well enough. With a clean up and brush inspection, it was all fine and I'll continue to run it until it gives trouble, but after that - PMA and Shindengen SH-775, for sure.