Regenerative Breaking

Lyn, you forgot to mention that he should hire a patent attorney first, follow your steps, then immediately abandon the project. We have protocol here.

True,

The object doesn't have to work to be patented.

Electrical resistance heat is energy intensive and requires a lot of current......Even if your setup would work you would need a very large turbine....

Here's an appropriate setup...

http://wind-water-power.com/id55.html

Just use permanent magnet motor for the generator. You will be loads ahead in both cost and efficiency.

That will be $58,000. PM me for my mailing address.

I need to tell my wife that love her. I go to the florist and buy some flowers. I send the flowers to my daughter, with a note asking her to tell her mother that I love her.

why is this illogical?

I am glad to see http://cr4.globalspec.com/blogentry/20254#newcomments did not have a dampening effect on the the type of comments I enjoy the most here at CR4.

anyway I think the OP will be well on his way to success in his regenerative 'breaking' endeavor... well at least eventual success with the latter part.

If all you want is heat, why not use a Prony Brake

or other means of frictionally burdening the spinning rotor = 100% efficient heat

Your idea seems mighty complicated just to provide heat. How about this, instead:

Use a wind turbine to turn an automotive alternator. Connect the alternator to a heating element. You will not always get the same voltage or current from the alternator, but you will get heat and will spend, probably, under $100 plus the cost of the turbine.

Regenerative braking is nothing new. Subways, elevators, trolleys have been using it since before 1920. New electrics use it to brake and recharge the batteries. Use an alternator, bypass the diodes to keep it as AC output, an old water tank and a couple of Calrod heaters for 120V hot water heaters will act as enough resistance to heat water. VFD not needed. Whatever voltage output is generated will be converted to heat. Just make sure the Calrod wattage at full voltage exceeds the alternator output to prevent meltdown of the alternator.

" Use an alternator, bypass the diodes to keep it as AC output"

There is a lot more to using an automotive or industrial equipment alternator for that matter than just hook it up and go unless its been converted over to a PM rotor which in itself adds quite a bit to the initial cost.

Typical alternators only work above a certain RPM which is usually in the few thousand RPM and higher range which eliminates all possibility of being a direct drive unit. Second the rotors take a DC current to work as well and do not handle over voltage at all which mens they Need some specific voltage regulation circuitry to work with an unregulated output voltage setup.

Basically this means that to use a alternator you have to provide a stable DC excitation power source plus a method of getting it spun up fast enough to do any good output wise.

To be honest if basic cheap electric power from a direct drive generator is the goal using a common low RPM PM type DC motor is your best choice and even then if you want a lot of power it still wont be all that cheap.

There are low RPM self exciting alternators but they are not going to be cheap or easy to find.

OK, a GA for two things: First, for earlier describing the means by which controlled-frequency power is generated from a given generator mechanical configuration run at a range of speeds through the use of controlled excitation of the rotor. I kind of figured this is what happened in windmills when contemplating the how-does-it-work question posed by my dad (EE prof at 85 yrs old!).

Second, for bringing this thread full-circle back to the original question around the use of a 3 phase motor as a generator.

The VFD in deceleration mode is exactly a system by which energy can be extracted from a motor-used-as-generator device over a wide range of speeds. Yes, one needs some circuitry to do the steps of: pulsing the stator coils to excite the rotor magnetic in order to induce emf in the stator from which energy may be extracted. One thinks that it might be easiest to pull the energy from the output with a PFC-esq circuit, to convert the AC energy to a DC bus which can then be inverted for use. That said, maybe it is possible to use the windmill generator scheme jumping through some hoops with the excitation control to get directly useful AC energy that can be put back onto the power lines, etc.

Anyway, I confess to being out of gas here on knowing enough about the construction and operation of AC induction motors, the scheme that VFD's use for field excitation and energy extraction when in deceleration (energy harvesting?) mode, and finally how efficient this whole process might be.

To the original poster's situation and question: Surplus (or new) 3 phase motors, readily available everywhere, might be pressed into such service at many levels (DIY included) generating some power. Depending on....

Utilization of available VFD hardware, or some originally designed system, to pull this off. VFD's seem to have the right pieces but are probably in need of custom programming to pull this off gracefully.

Begs the question: What is the minimalist set of hardware necessary to turn 3 phase motors into generators?

Hughv

(still looking for a defining quotation for my tag line....)

Perhaps it's my bad but then I did read this:

Vehicle-mounted generators

"Early motor vehicles until about the 1960s tended to use DC generators with electromechanical regulators. These have now been replaced by alternators with built-in rectifier circuits, which are less costly and lighter for equivalent output. Moreover, the power output of a DC generator is proportional to rotational speed, whereas the power output of an alternator is independent of rotational speed. As a result, the charging output of an alternator at engine idle speed can be much greater than that of a DC generator. Automotive alternators power the electrical systems on the vehicle and recharge the battery after starting. Rated output will typically be in the range 50-100 A at 12 V, depending on the designed electrical load within the vehicle. Vehicle alternators do not use permanent magnets and are typically only 50-60% efficient over a wide speed range."

I really was just chaffing at the bit to correct the OP "breaking" to "braking" since each time a reply was posted it popped up. I noticed a few others were too.

Using banks of resistors which basically gave off a lot of heat, were pretty standard for elevator regenerative braking. Using the middle stage of didn't make any sense either since it would just introduce another source of loss. Using whatever output was generated directly to some submerged heaters could be a limited source of hot water unless the wind is strong and constant.

'....the power output of an alternator is independent of rotational speed.'

...

...Can't trust every sentence conjured to fill Wikipedia.

But it certainly would be interesting if it were true. We could do away with all that tedious rotation without affecting power output. I'm sure we would look back and laugh at how foolish we had been hurrying around busy making everything spin.

(by the way, 'chafing at the bit' is the idiom not that different from 'raring to go'. 'Chaffing' is to tease playfully, a more friendly version of ribbing.)

I, since the bit is in the horse's mouth, am chomping at the bit to reply.... in an automitive alternator, the regulator controls the field current to control the output. higher torque with higher output power at a given speed to be sure, but within some speed range indeed the output is controlled independent of shaft rotation rate.

Well put!

Therefore GA.

Do not forget that many here do not understand how such an alternator really works.....though there are websites with good detail to be found using Google....

The best one I found (there are many that do not describe the voltage control correctly or fully) was here for those (other than you of course!) who do not understand the action correctly:-

http://www.familycar.com/Classroom/charging.htm

There may even be better sites, I doid not look further....

As you point out the alternator changes the field current to increase output at lower speeds hence maintaining a strong output even at reduced speeds. That is another problem with the OP's initial post about using an induction motor, it has no slip rings to feed a magnetic field. The motor's magnetic field's current is "induced" therefore the name "Induction" motor whereas an AC generator has slip rings to supply the current to the magnetic field.

An induction motor can be run as an induction generator but generally must be feeding into an utility system or grid. It's been many years since I looked into that but I vaguely remember some "no-break" back-up systems that utilized a motor driving a flywheel with a clutch connected diesel as stand-by. If the main power failed the flywheel drove the motor as a generator until the diesel came up to speed and it utilized something called an "over-running clutch" to drive the flywheel and motor. It may have had some sort of modification to excite the field.

There were other cases where an induction motor could become an induction generator by I think that in all cases you needed to be connected to a larger grid. that also acted as a governing system to keep the frequency at the proper cycles otherwise it could overspeed and generate excessive current and burn up.

To cause an induction motor to generate it must be connected to a LEADING power factor load, hence my comment about CAPACITORS in my previous post number 16.

It is probably easier to use a single phase motor if on hand.

Automotive alternators are a 1950's solution to problems of that era. They have about 25% efficiency, their field power at low speeds makes their efficiency abysmal when wind turbines' output is least. However they have high leakage inductance so induced voltage is proportional to speed and the reactance rises to match so short circuit currenr is limited indepandent of speed.

Connect a capacitor of something like the impedance of the load or 'motor voltage on current' across motor terminals, or in series with the heater.

The motor will self-excite and provide the heat you need in the resistive heater.

Your problem will then be either:- Governing the turbine to alternator speed needs or; controlling the heater power to requirements by switching.

Excessive speed may best be controlled with a classic windmill tail.

Good luck.

Gee whiz, you guys (gals?) can be brutal (while being somewhat funny, too!).

I have several power tools which have 3 ph induction motors and VFDs in my shop. When I have programmed deceleration surely some or most of the rotational energy is transferred to the drive and stored in the DC bus capacitors and/or whatever energy dissipation scheme is in there (resistors, back to the line, etc.) I don't use braking resistors since energy from the rotational inertia of the grinding wheels (in my case) is handled OK.

That said, some interesting points we might ponder:

1. Barring the question of the programming of the drive to continuously load the motor-as-generator, is the use of a 3 phase induction motors in such a system a reasonable idea from an efficiency standpoint? Indeed, how efficient is the transfer of energy from the deceleration of the rotating load to the drive/braking resistor? How much is 'wasted' in the motor windings?

2. What is the type of generator used in commercial wind turbines? PM Brushless DC motors? Electrically excited magnets (like the car's alternator)? What are the similarities and differences between this proposed method and the mainstream wind turbines' generator and controller?

3. I acknowledge here that the need and difficulty of building a custom VFD or at least outfitting one with custom programming makes a one-off of this idea prohibitively expensive/complex. However, the availability of low cost 3 phase induction motors makes this a potentially attractive idea for small and inexpensive wind turbine projects, especially when all one wants is heat out. It also might be a means to optimize the energy extracted from the turbine under varying wind conditions.

So, I offer that this idea might not be such a sophomoric, convoluted and circuitous means to solve the problem as it might seem at first, and these are interesting points to consider.

Hugh

Its not that it wouldn't work it just that its an overly expensive and complex way to do a simple conversion of wind energy to heat.

In a rational world the whole point of using AE is to be able to produce the needed power as cheaply ,reliably, and efficiently as possible.

Relating to commercial wind turbine generators the vast majority are three phase synchronous generators with a special three phase rotor system that is excited by a rather unique VFD of sorts which allows the rotors effective mechanical speed to be ran faster or slower than the stators constant magnetic field speed so that it can work at sub synchronous or super synchronous speeds opposed to having a single fixed rotor speed dictated by the number of poles and the line frequency.

GA

Its a complete waste of money to do it the way the OP describes.

If he is only after heating, then a vertical windmill (accepts wind from any direction), driving paddles in a barrel of water, will soon get the water hot on a windy day......

No electronics, simple mechanics......Adding a heat pump to improve the "quality" of the heat!! Also efficiency is better as there are fewer losses....

See here for my post #11, fairly well down the list.-

http://cr4.globalspec.com/thread/60083#comment636617

Follow the links in that post for more infos....

'....Its a complete waste of money to do it the way the OP describes.

If he is only after heating, then....'

I (like many others) quickly came to the same conclusion. What if we all also overlooked an important detail in our hasty assessment?

Could the true intent (what the OP is really after) have been something other than 'heat'?....something spelled out more prominently in the posting? ...perhaps even in the title?

OP has chose the title of this thread to be 'Regenerative Breaking'. Perhaps that is really what he is after.....

....enough expensive, overly complicated, unnecessary equipment to initially generate and then re-generate a near continual self-reinforcing supply of breakage events.

So, why hasn't he just employed effective communication to describe the actual question?

Wait, that was another post somewhere else...

I really don't want to second guess what people want if they can not or will not communicate fully, or at least come back to clarify the end goal when questioned. I will respond to the posted question as best as I can, but given the information, his proposed method is truly a Rube Goldberg approach.

Therefore, it seems deserving of the feedback that has been provided.

Regenerative 'Breaking' (vs braking)

come one. That isn't funny to you in the least?

He was definitely asking for it.

And I agree with you that the responses were appropriate and what one should expect given the question.

I was just having a bit of fun.

Ah! Okay. Good point and a common misspelling.

What is the heat being used for? Heating a house? Some chemical process? What about a solar thermal heater? If you just want to heat water with wind, use a vertical shaft turbine direct coupled to some sort of insulated water stirring paddle with an inline pump shaft thermostatically controlled to circulate only when hot enough.

Coupling the turbine mechanically to a Joule Heat Apparatus would avoid the investment in fancy electronic whizz-bang gizmos.

http://en.wikipedia.org/wiki/James_Prescott_Joule

Interesting exercise. If it were me, I think I would want to find another use for that nice three phase current than dumping it into a entropy puddle of heat. But would it work? Sure. And it would be versatile and capable of being adapted to other purposes.

The phrase..."VFD pumps current to breaking resistor only during deceleration" is throwing me off. Such breaking resistors would be used to help govern the speed of the turbine...keep it from over speeding, or to bring it to a halt for maintenance. I don't think they are designed to actually BE the load. I don't think you should use the load to govern the turbine... loads can be too variable for that purpose.

Personally I think there are better things to use than electricity. A water pump. An air pump. A hydraulic pump. A slush box puts out enough heat to distill moonshine. Grindstones, wood chippers and sawmills have all been driven by wind over the years. (okay, I have never actually SEEN a sawmill mechanically driven by a wind turbine....but the concept is sound) But that is just me.

(but then you didn't come to CR4 to get a conventional answer right?)

With all due respect to the members CR4, Its been a refreshing and educating discussion. What i am trying to do is not a college project or nor some homework stuff. The place i work for is near to a sea coast and we have ample velocity of wind for most the time, we have some spare 3phase induction motors and VFDs lying with us.

I just wanted to give a try with them, the reason for converting it to heat is to attain maximum efficiency which i believe from the discussion is wrong. From above series of discussion, i see that it is not an efficient way of energy conversion, i guess i need to find some other way to put this to use.

It would be of great help if any one has tried this before.

Thanks and keep posting your comments.

Madhusudhan

It's simply a question of how much heat you need to produce. The math is simple.

You don't say why you need the heat. If it's for space heating, maybe solar water panels on the roof that run througn a heat exchanger inside the building would be better. Use windpower to run the circulation pump.

Specifically, what will you do with the heat produced?

Lyn it not that i only need heat energy, electrical energy would be ideal

If you are near the ocean, maybe a wave generator would be better. Waves never sleep.

Directory:Ocean Wave Energy - PESWiki

Make a Wave Powered Generator - Wave - Renewable Energy UK

2. How to Harness Wave Energy | eHow.com

1. Wave Generator, Ocean wave generator, Wave

Lashing up some junk is just not the way to go!

What is needed is fixed magnet generators, a rectifier, and an inverter, together with appropriately-designed and selected circuit protection devices. That's for off-grid. If the aim is to supply the grid then the inverter gets a bit more fancy, as it needs to synchronise with the frequency and match the voltage of what's already there.

Just connect a space heater to the output of the wind generator.

You may need to regulate the power from the wind generator, but it is just that simple.