Thanks for the insight Strantor. I appreciate you walking a beginner like me through this. I follow the logic of governor and load control. The (bad) assumption I am making in this situation is that energy is plentiful.

I have been doing some (not a lot) of research on VFDs and am struggling to understand why I can't use one to control speed on an AC generator but adjusting frequency of load. Would you be able to point me to any resources that could help me better understand?

Additionally - Would you be able to give me an examples of controllers in the BLDC and PMAC scenarios. Can the same controller be used in both scenarios? Are there different types of phase angle fired load banks or alternatives?

Thanks in advance!

Controllers for BLDC, PMAC, servo, would all be the same in the scenario I proposed earlier. No "controller" like you're probably thinking (magical generator speed control box); just a phase angle fired power controller and a load bank. Since these motors have permanent magnets they will generate electricity with simple mechanical power input.. The idea is that we burn off (totally waste) however much electrical power is required to mechanically slow the generator down to the desired speed for any given condition. It's a really crappy plan but it's the only way to meet the goal of "electronically" controlling the speed of the generator when you've taken all the proper options off the table.

 

@Dawsonh4

Wanna know why brushed alternators are so popular for this purpose?

The magnetic field in the rotor isn't from permanent magnets OR induction. It's controlled by the voltage that you apply to the brushes. If the wind picks up and the alternator starts outputting too high voltage, you decrease the rotor voltage and the output voltage goes down. If wind dies down and the alternator isn't outputting enough, you increase the voltage to the brushes and output voltage comes back up where you want it. With an extremely simple circuit this adjustment becomes automatic, and so fast to respond that output never perceptibly changes from what you set it at. You set the output voltage you want, and the alternator will you give you that voltage no matter how fast you spin it (except zero RPM of course, and very low RPM). VERY SIMPLE. VERY GOOD. With an alternator you don't need to control the speed at all. Let the wind do what it wants, no need to fight it.

That's why alternator technology is used in cars, where engine RPM might be anywhere between 500 and 9000 RPM. Can you imagine how ridiculous it would be to limit a car's RPM to a very specific value just to charge the battery?

Alternators aren't as efficient as other kinds of generators but they're damned simple to implement and WAY more efficient than burning off unused energy in a load bank. AND they circumvent your perceived need to limit generator RPM without using any conventional means.

 

Thanks again Strantor! The information you provided is very helpful. I am happy to hit the "I believe" button. I do believe that the brilliant minds putting together these large generators have thought of the best ways to do thing. However, the electronic solution I am looking for is a result of not being able to control the flow through pipe. I can get into the long explanation as why, but I think it will just distract. I appreciate you accepting that and still helping find answers.

I am happy you brought up brushed alternators. The car examples really resonates with me. My question there is - what happens when the battery is fully charged and the car is still running?

As for the controller. You refer to the phase angle fired power controller which I am researching more now. I stumbled across this ODrive (link) contoller. Is this a phase angle fired power controller or is it something similar?

 

I am happy you brought up brushed alternators. The car examples really resonates with me. My question there is - what happens when the battery is fully charged and the car is still running?

When the battery is fully charged then battery voltage equals alternator voltage and no current flows either direction. The alternator just keeps spinning along at whatever speed the engine (or wind) wants to go, but isn't doing any work.

Further on the topic, note that alternators don't all output 12VDC like the one in your car. If you want AC output 120V, 240V, etc you can get alternators for that or you can modify a car alternator too, to get much higher voltages either AC or DC.

As for the controller. You refer to the phase angle fired power controller which I am researching more now. I stumbled across this ODrive (link) contoller. Is this a phase angle fired power controller or is it something similar?

No, not similar. You're still looking at motor controllers. A phase angle fired power controller is not a motor controller. It's a heater controller. It would only regulate the motor(generator) speed by extension; the more power that it dumps into the load bank, the slower the motor will go. But it does not directly control the motor(generator) speed. Such control is not possible as I have explained. Here is an example:

https://www.hbcontrols.com/product-page/lpc-50da

 

I am happy you brought up brushed alternators. The car examples really resonates with me. My question there is - what happens when the battery is fully charged and the car is still running?

You're under the false idea that many people have about cars and trucks. After the battery is fully charged every electrical item in the vehicle is using the alternator only to power them. The battery is charged pretty fast after the engine is started, and then is just along for the ride, waiting to star the motor again, or power items when the motor isn't running.

 

No, not similar. You're still looking at motor controllers. A phase angle fired power controller is not a motor controller. It's a heater controller. It would only regulate the motor(generator) speed by extension; the more power that it dumps into the load bank, the slower the motor will go. But it does not directly control the motor(generator) speed. Such control is not possible as I have explained. Here is an example:

Thanks! Admittedly I still am struggling to understand the differences. I will read up more.

 

Thanks! Admittedly I still am struggling to understand the differences. I will read up more.

Ok. If I may speculate, I think you are still looking for (and viewing the power controller solution as) a magical "generator speed controller." So such thing exists. I would encourage you to stop looking for that thing and to stop thinking you've found it when you stumble across this new product or that.

In the simplest way I can think of to explain, the generator is like a see-saw. When it is perfectly balanced, that represents the generator running at your ideal speed. On one side of the see-saw is the mechanical input power and on the other side is the electrical output power.

The way that nearly all generators work is, you pile your electrical loads on one side, and then you add mechanical input power (via variable pitch blades or control valves or whatever) until the scale balances. You only use as much mechanical power as necessary to feed your electrical loads.

This power controller solution I have proposed is the opposite. You will be dumping the maximum available mechanical input power onto one end of the see-saw, and then piling on a variable false load onto the other side to make it balance. Very ass-backwards.

There is no such thing as a magical see-saw level controller. That's what you seem to be after. Physics does not allow this to exist. The see saw level is controlled the weights placed on it, not some electronic device.

 

How do you know when a generator is an alternator?

Is this an alternator? https://www.wanco.com/product/compact-belt-drive-generators/

 

How do you know when a generator is an alternator?

Is this an alternator? https://www.wanco.com/product/compact-belt-drive-generators/

Yes it is an alternator. If you scroll down in that link to the specifications you will see the output is AC. Alternator make AC, generators make DC. Except for one application, vehicles. The vehicle makes AC and internally has a rectifier that turns it to DC.

Instead of all the back and forth and guessing why not just say what you want and need? As far as the output of the project.

 

How do you know when a generator is an alternator?

Is this an alternator? https://www.wanco.com/product/compact-belt-drive-generators/

Yes it is an alternator. If you scroll down in that link to the specifications you will see the output is AC. Alternator make AC, generators make DC. Except for one application, vehicles. The vehicle makes AC and internally has a rectifier that turns it to DC.

Instead of all the back and forth and guessing why not just say what you want and need? As far as the output of the project.

There there is more than one school of thought about what is an "alternator" and what is a "generator."

Per the textbook definition @shortbus is correct, but no, the linked units are not what I meant by "alternator." I meant something with brushes and a controllable field. Like this:

https://www.fabcopower.com/generat/bgen.htm

 

Thanks.

Back to your alternator explanation. Would that Wanco generator over heat or have other issues if there was not load connected and it was being powered by a prime mover?

 

Per the textbook definition @shortbus is correct, but no, the linked units are not what I meant by "alternator." I meant something with brushes and a controllable field. Like this:

A standard car alternator will put out AC if you bypass the rectifiers. And they have brushes and slip rings to control the rotor magnetism and output voltage.

But were still guessing at what he needs voltage wise AC/Hz, DC, or amperage. He, to me, sounds like wants to control something without controlling the prime mover power. In normal generators/alternators adding more load speeds up the prime mover not slow down.

 

Would that Wanco generator over heat or have other issues if there was not load connected and it was being powered by a prime mover?

No. Is that the concern that has generated this whole line of questioning? I know of no generator technology where not having a load and being while being spun by a prime mover is a problem. I had a feeling this thread was a case of not asking the right questions, but never did I suspect this was the right question. I agree with @shortbus you really need to come out with all the details because I feel like you're barking up a tree that I can't even see.

 

Its not. Just a side questions. Thanks for the answer.

As for be clear on the goal I will try to explain.

I am looking to adjust the speed of a generator that is being rotated by air through a pipe. The generator will "scavenge" energy from the air flow and charge batteries. The primary purpose of air flow is for other uses that supersede energy generation. If the end use of the air flow is in high demand the generator must spin as free as possible. The air flow speed/pressure fluctuates quite a bit both from supply and demand sides. I understand a smart valve system with bypass could also be put in place, but I wanted to explore the option of controlling generator speed.

 

https://www.thecabindepot.ca/produc...05857&pr_ref_pid=1995789500513&pr_seq=uniform

 

I am looking to adjust the speed of a generator that is being rotated by air through a pipe

Why?

The generator will "scavenge" energy from the air flow and charge batteries

Then an automotive alternator should do the job.

If the end use of the air flow is in high demand the generator must spin as free as possible.

Ok then, just stop drawing electrical power from it and it will cease being (much of) a loss in the air system.

I wanted to explore the option of controlling generator speed.

Again, why? I don't see why this is your primary design goal, or any goal at all. Speed of a generator usually determines AC frequency but you're charging batteries, so frequency shouldn't matter, just voltage. Also this perceived need to control generator speed is at odds with your goal to be flexible for higher priority loads on the air system.

What kind of air system is this? Compressed air? Air conditioner ventilation? How big is the pipe? Volume? Pressure?

 

It is compressed air. The volume can vary considerably from 1 mcf/d to 20. Pressure can also vary 200 - 1000 psi.

I found this and need to dig into it a bit more

 

It is compressed air. The volume can vary considerably from per minute to 20. Pressure can also vary 200 - 1000 psi.

That is a very very strange air compressor. Feet per day is not the way any compressor I've ever seen is rated. It's usually in feet per minute not days.

 

That is a very very strange air compressor. Feet per day is not the way any compressor I've ever seen is rated. It's usually in feet per minute not days.

https://www.lawinsider.com/dictionary/mcfd
"Mcf/d means thousand cubic feet per day" (in oil & gas terms).

I suspected this was about trying to scavenge energy from a building's HVAC ducts but now it smells more like this is to be inserted in a natural gas pipeline.

I am bowing out, not because of this suspicion (I would have no problem discussing this in regards to a natural gas pipeline - actually seems like a good idea to me) but because it seems all the effort I'm putting in here is being willfully disregarded. Case in point:

@Dawsonh4 is STILL looking for a magical generator speed control box. It is obvious to me now that he will not be convinced. Some lessons we must learn first hand. I know, I've been there (I'm there a lot). But I can't help further until the lesson has been learned. So please, go make your invention and when it doesn't work, don't go asking why until you come back and re-read this thread first. It will all make much more sense the 2nd time around once you can read it with some context.

 

Strantor - thanks for your help. I have learned a bunch from your posts on this thread and I will continue to learn more about the topic.