Permanent Magnet Alternators - PMA

Paul Sutton

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Thank you for the comments Xjwmx. Unfortunately we seem locked in circles, probably my fault/brain. I need to dig deeper and explain better so give me a couple of days/weeks. Off to sort out some fuel lines: F-4040 -A .
 

Grimly

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Neither one. Think of the SCRs as gating the generator away from the battery. Apparently there is some problem with simply opening the legs, which could be easily done, so instead they're grounded. The rectifier keeps it from grounding the battery.
Back-EMF, etc.
That was my point about the electronics of the day being too fragile to handle switching currents of the type we encounter here, and quite probably why, if they existed at all, only to be found in military applications where the taxpayer was footing the bill. Shunt (or short) regulation was a cheap and
simple way to handle it instead. Even though it seems crude now, it was actually a clever solution - for a while (my comment about warranty period applies). This situation continued for decades, until cheap and reliable high-current semiconductor devices were developed.
Thus, we have the consequent development of the series regulator...
The series regulator cuts it off entirely, saving the stator from working at full tilt all the time. The stator is happy, the regulator is happy, and the rider is happy.

Even at that, the first proper mass-production series reg/rec wasn't taken up by any of the Big4 bike makers, but by Polaris for their ATVs. It was a resounding success and grew from there. Polaris had a real problem with their PMAs and shunt r-rs, with damn near every one being warrantied, so they were happy to try the Shindengen SH-775. It certainly got them out of a jam.
 

xjwmx

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Unfortunately we seem locked in circles, probably my fault/brain.
It would probably help most if you asked very specific questions. Your idea about bi-directional SCR circuit, the bottom 3 diodes in the rect prevent anything below ground, as always. Also, we're discussing an approximation -- if something goes to ground, it might really be a diode drop away, approximately ground. Next level there would be the details like how to bias Q1, what values for the voltage divider on the gate of the SCRs, and so on. But as an approximation it's real simple.
 

Paul Sutton

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Here I am back sooner than expected. I have found my key reference to the topic:

https://www.apriliaforum.com/forums/showthread.php?240785-Facts-about-shunt-based-regulators

This is quite a monster to read but puts the views of electrical engineers against some of the common held views. You will find that a PMA has properties under shunted conditions which are counter-intuitive/unique. The following is a very rough indexing of the discussion:

Page 1: The case is set for demystifying the PMA. Some rebuttals are dealt with.
Page 2: Rebuttals are dealt with as common views start to conflict with fact.
Page 3: Electrical Engineer input starts and the counter-intuative properties of the PMA are examined under the condition of shunting where the 3 phase wires are essentially tied together.
Page 4: More detailed technical discussion regarding the current and load on the engine under the condition of shunting.

To get the maximum understanding will require a detailed reading of the full thread. I plan to read this again tomorow which will be my 3rd reading.

Best of luck.
 

xjwmx

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In that link, the "Time Bandit" character has enough rope to hang himself, including asking confusing questions like it is "on" 100% of the time.
All you really want to know is the current in the loop that is shunted. That will tell you everything, and it can be measured. If you don't want to do that, the parts list calls for a 25w SCR mounted on a heat sink. That says the current is pretty high... And it means that current is being "wasted" or whatever the quetion was :)
 

TwoManyXS1Bs

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...a detailed reading of the full thread...

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