I am playing with five different voltage regulators. Two are wired to a three phase PM and three are wired to a single phase PMA. PMA's driven by electric motors. Switches are involved so that AC can be turned on and off to each of the regulators.

One of the two, and one of the three, are acting much differently than the others. I will call these regulators A. The other regulators I will call B.

Here is what I am seeing that I don't understand.

The A regulators are drawing considerable alternator current even when nothing is connected to them. If a bulb is attached to the regulator output leads, the bulbs will illuminate.

The B regulators draw no alternator current when nothing is connected to them. If a bulb is attached to the regulator output leads, the bulb does not illuminate.

Why in the world would a regulator be designed to allow current flow if and when no current was needed from the PMA?

 

Why in the world would a regulator be designed to allow current flow if and when no current was needed from the PMA?

Very common in the world.
It's to control the voltage.

The open circuit output voltage of PMAs is proportional to their speed and can go very high to damaging levels (including breakdown of the alternator winding insulation) if their outputs have no load, so a common-way to control the voltage is to short the output to ground (typically done in motorcycles which mostly have PMAs).
The PMA magnetics are designed to saturate and limit the short-circuit current, so the power dissipation is not excessive, being equal to the square of the short-circuit current times the alternator winding and external shorting switch (typically a MOSFET) resistance.

Since you have not given any information about the two regulators other then being labeled A and B, I don't know what regulator B is doing, or even if it is actually designed to control the output of a PMA.

 

I am guessing, based on experience, that the regulator that works is a shunt type that works like a Zener Diode shunt regulator. Less efficient and not as good regulation.. The other regulator is the series pass type, and itis current limited. Try to draw more current and it switches off.

 

Zener diode shunt regulators were very common on one brabd of British motorcycle a few years back. They would simply burn the excess power as heat. They did have a nasty habit of failing and lettingthe alternator voltage rise and burn out all the lights.

 

that the regulator that works is a shunt type that works like a Zener Diode shunt regulator.

Sort of.
But it likely rapidly switches the current on and off to ground to minimize the dissipation.

 

Sort of.
But it likely rapidly switches the current on and off to ground to minimize the dissipation.

NONE of the shunt regulators that I am aware of do any switching. That could be dealy for over-voltage sensitive electronics, and it would certainly add a whole lot of noise to the sound from any radio. On the one British motorcycle that uses a shunt Zener diode you can easily spot the large heat sink, placed where the air stream can sort of cool it. I suggested a series voltage regulator for one friend and it does work. It uses a power tab regulator to set the base voltage for the several parallel NPN power transistors. Each transistor has an emitter resistor to help in load sharing. The heat sinking does need to be adequate. BUT it keeps the battery from boiling, so it was certainlythe way to go.

IF the alternator delivered an AC voltage to an external rectifier then I would suggest a triac-type power control to set the output to the battery. That could work very well, but it is beyond the scope of this discussion.

 

From Google AI:
A motorcycle voltage regulator/rectifier converts AC from the stator to DC and limits voltage to ~14.4V to charge the battery. A typical DIY shunt regulator uses a 3-phase diode bridge (e.g., 6A10 diodes) and SCRs (thyristors) to short excess AC voltage to ground.

I would think an SCR counts as a switch.

 

It was a while back, but at that time the one brand of British motorcycles simply used a LARGE zener diode as a shunt regulator. Certainly some sort of switching circuit would be more efficient, but probably cost more. AND they may have changed the regulation scheme since 1985.

 

at that time the one brand of British motorcycles simply used a LARGE zener diode as a shunt regulator. Certainly some sort of switching circuit would be more efficient, but probably cost more. AND they may have changed the regulation scheme since 1985.

Yes, I'm familiar with that Zener approach.
But the regulators on my recent motorcycles are in a about a 5" x 5" module with fins for cooling.
And one failed due, I think, due to overheating, so I went with one that used MOSFETs instead of SCRs for the switches, for lower dissipation.

 

It was a while back, but at that time the one brand of British motorcycles simply used a LARGE zener diode as a shunt regulator. Certainly some sort of switching circuit would be more efficient, but probably cost more. AND they may have changed the regulation scheme since 1985.

Let me guess the brand: Lucas, the first and true Prince of Darkness. Sorry, Ozzy!
Lucas contributed more than any other company to destroy the British automobile and motorcycle industry’s reputation.

 

Let me guess the brand: Lucas, the first and true Prince of Darkness. Sorry, Ozzy!
Lucas contributed more than any other company to destroy the British automobile and motorcycle industry’s reputation.

I have also heard, from an ENGLISHMAN, that the reason they drink warm beer is because they have LUCAS refrigerators. However, I have not been able to verify thatas a fact.

 

I have also heard, from an ENGLISHMAN, that the reason they drink warm beer is because they have LUCAS refrigerators. However, I have not been able to verify thatas a fact.

Or the more likely, NO refrigerator at all. not when I grew up anyway!!

 

I am talking about 1975, MAX. REmark DEleted (THAT REMARK IS NOT intended to offend anyone.)