"tron" question for Rodbolt

[fairdeal]

I can't find any good info, despite energetic Googling -
but I'm sure Rodbolt -between his Navy electronics and Yamaha school has the answer:

ok, we are told on an excited field alternator, the voltage regulator controls the amount of excitation. Seems fairly simple.

but

on our permanent magnet Yamaha alternators - where the voltage regulator is a "shunt" type -

when it is "limiting the alternator output" how exactly is the regulator doing that?

(obviously also creating heat as a consequence)

Is it using less of the waveform? (sending part of it directly to ground?)

and - for us Ohms law challenged -

how does con*****ing based on the voltage result in less amp output

[rodbolt17]

the Yamaha system uses the flywheel as a rotor.
the lighting coil as a stator.
by moving the magnets(rotor) faster it generates more A/C voltage.
can be in excess of 1000 V A/c on certain models.
larger Yamaha models use a 3 phase Y wound stator.
once the battery is charged ,about 14.8V max the excess current is shunted to ground.
this is why most 150 and larger EFI motors use a water cooled regulator.
a shunt is a technical term for a con*****ed short to ground in this case.

[fairdeal]

"once the battery is charged ,about 14.8V max the excess current is shunted to ground."

thanks!

yes, I understand that in general terms - what is beyond me is the underlying:


"how does the regulator know" that there IS "excess current" ?


is it just "if there weren't excess, the voltage could not rise to that point"?

[boscoe99]

"how does the regulator know" that there IS "excess current" ?

A Zener diode knows all about the excess voltage. The Zener diode is the key.

When the voltage rises beyond a certain value the diode causes some switches to close. Those switches shunt current to ground. When current is shunted to ground the voltage drops. Voltage drops and the zener opens the switches. Voltage rises and the zener closes the switches. Over and over again. This happens about a billion times a second.

Same sort of circuitry that varies the field current in an alternator. The diode can cause current to flow through a field or the diode can cause current to be shunted to ground.

[boscoe99]

A graphical look at how a PMG voltage regulator does its magic. See below.

Ever had your head lights on in the old automobile and then turned the blower motor up? Did the lights dim a bit? Adding a load (the blower motor) to the electrical system caused the voltage to decrease. Turn the blower motor off and the head lights may shine brighter. Load removed, voltage went up. Now think of the regulator doing that a billion times a second in order to keep the voltage constant. That is what it does. It is magic I say.

[boscoe99]

Technical Article: How a Motorcycle Charging System Works - ElectroSport

[rodbolt17]

to clear up the next question.
the switchs depicted above are Zener Diodes.
the pic shows switch's for clarity.
the Zener acts like a switch. it does not allow current flow until a particular voltage is met, then it "closes" and allows excess current to ground.

[boscoe99]

I suspect that the switches shown are actually transistors. Electronic switches if you will.

The Zener diode causes the electronic switches (the transistors) to open and close.

[rodbolt17]

I doubt it.
most transistors could not stand that kind of heat.
a simple zener is all that is required.
that zener will switch on and off just as fast or possibly u
seconds faster than a transistor.
and it does not require any base biasing circuits or resistors.

same as the 32Kv Zener used in the coil on plugs. it wont allow current until voltage builds to a minimum of 32 Kv.

[fairdeal]

Technical Article: How a Motorcycle Charging System Works - ElectroSport

Have read many similar, but hadn't seen that particular page;

What I like is its simple statement:

The regulator looks at the DC-voltage across the battery-terminals and short-circuits a certain amount of power that is produced by the stator to ground. This is regulated constantly, so the output-voltage of the regulator-rectifier (which ideally is the same as the voltage across the battery-terminals) stays at 14.4 Vdc all the time.

and later - specifically for the excited field type:

the regulator..senses the voltage in the system and when the voltage is lower than 14.4 Vdc it switches on the field...
When the voltage in the bike’s system reaches over 14.4 Vdc the regulator senses that and just switches the field off.
...When the voltage drops below app14.2 V, the regulator switches the field back on.
This is a constant process and the result of this is a constant voltage across the battery-terminals of 14.4 Vdc.


One can infer that the result is that "the battery is charged" -

presumably the reason for building that particular voltage set-point into the regulator.

But - to me - that explanation is vastly different than reading a statement like

"once the battery is charged, the current is reduced"

which one can find stated all over the internet....

[boscoe99]

"When the alternator output reaches the specific zener voltage, the diode controls a transistor in the circuit, which in turn controls the alternator field current."

Zener diodes cannot typically handle heavy electrical loads. Power transistors can. Just like a teeeney tiny switch and a tiny wire can send an input to a big honkin relay that can handle a massive amount of current.

The little zener diode sends a small signal to a big transistor telling the transistor to open or close.

[boscoe99]

But - to me - that explanation is vastly different than reading a statement like

"once the battery is charged, the current is reduced"

which one can find stated all over the internet....

The internet does not prevent folks from spewing crap. Now there is lots of truth on the internet. But lots of crap. See THT for case studies in crap. How are the unknowing to know what is crap and what is the truth?

Most outboard motor and automobile generation systems are referred to as constant voltage systems. The voltage is what the voltage is set by the engineer. As loads are applied and removed current flows more or less. As the current flow changes, the voltage changes. The regulator simply does what it does to keep the voltage at the specified value.

[fairdeal]

Now there is lots of truth on the internet. But lots of crap. See THT for case studies in crap.

Of course your eyes are rolling from battery thread nonsense.

IMO the "smart charger" marketers have had a large hand in sowing confusion;

exaggerating, oversimplifying on one hand while complicating on the other, conflating cause/effect, and generally "muddying the water"...

[boscoe99]

Of course your eyes are rolling from battery thread nonsense.

IMO the "smart charger" marketers have had a large hand in sowing confusion;

exaggerating, oversimplifying on one hand while complicating on the other, conflating cause/effect, and generally "muddying the water"...

They are. I sometimes wonder if I should continue to try or simply let folks wallow in their ignorance.

Yes, the smart charger folks have certainly muddied the waters.

[rodbolt17]

would be nice to see the actual circuit diagram.
not that we as field techs could do anything with it.
unlike the CIWS manuals15 not counting the classified one.
when you stacked them they were about waist high on me.
but the showed every component in every card except the weapons control computer which the US navy did not own. GD owned it and US navy personell had no access to it.