More generator Q's

On 03/08/2011 10:39 PM, Ed Huntress wrote:


There is a class of AC induction motor, now rarely seen, that DOES have a wound rotor and a commutator much like on a DC motor. One difference is they often have a "bracelet" in the commutator that flies out and shorts all the segments together when the motor reaches a certain speed.
A variable resistor can be put in series with the brushes to regulate torque when starting. We have an ancient merry-go-round here that has such a motor, it takes about 3 minutes to come up to synchronous speed, which would fry a standard induction motor. The operator slowly cranks out the resistor as the motor speeds up.
These were also used on streetcars, and a variety of other things that took a long time to start moving. Now, of course, a VFD would be used.
Jon
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On Tue, 08 Mar 2011 23:24:34 -0500, Existential Angst wrote:

Generally speaking, older, bigger rotating machines have field windings that need DC excitation. You can regulate the voltage in a generator by regulating the current in the field winding. It's exactly the same idea as a car alternator.

Either with field windings, a motor designed to turn at exactly 1800 (or 3600) RPM to match line frequency, and a regulator connected to the field windings. More recent ones have inverters, and probably permanent generators AC generators whose output gets rectified then inverted.
As above, the bigger and older it is, the more likely it is to be a wound- field synchronous AC machine.

Well, yes, if the stars are aligned right. If you excite it with a voltage, and turn it faster than its synchronous speed*, then it'll dump current onto the line instead of sucking current from it. Older small- time co-generation schemes did this, because maintaining synchronization is _not_ trivial. Nowadays, it's mostly done with special inverters that sense the voltage on the line and synchronize the current to the voltage.

I dunno.
* Synchronous speed = 3600, 1800, 1200, etc., on down. So an induction machine that has a design speed of 3540RPM has a synchronous speed of 3600RPM, and a slip of 1Hz. Turn it up to 3660RPM, and it'll absorb something close to its rated power while putting almost that much power onto the line along with some inductive loading.
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Current? maybe but it will be 90 degrees out of phase with the voltage.
It is often stated as putting reactive power back into the supply.
------------------------ "Tim Wescott" wrote in message
Well, yes, if the stars are aligned right. If you excite it with a voltage, and turn it faster than its synchronous speed*, then it'll dump current onto the line instead of sucking current from it. Older small- time co-generation schemes did this, because maintaining synchronization is _not_ trivial. Nowadays, it's mostly done with special inverters that sense the voltage on the line and synchronize the current to the voltage.

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On 03/09/2011 05:47 AM, Josepi wrote: (top posting fixed)

> Current? maybe but it will be 90 degrees out of phase with the > voltage. > > It is often stated as putting reactive power back into the supply.
Nope, sorry, you're just plain wrong.
Using induction machines as generators is an established -- if slightly obscure -- practice. Real mechanical power is transformed to real electric power. There are some inductive VARs, but there's real VARs, too.
But don't argue with me. Argue with the world wide web:
http://en.wikipedia.org/wiki/Induction_generator http://www.aerostarwind.com/induction_generator.html http://www.daviddarling.info/encyclopedia/I/AE_induction_generator.html http://www.electrodynamics.net/documents/electrodynamics_power_gen2002.pdf
(and all the myriad other pages that come up when you search on "induction generator).
--

Tim Wescott
Wescott Design Services
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(moronic posting format fixed)
I would love to see an example of this where you turn asynchronous motor at 3660 poles per second on a 60Hz line and it puts ***real*** power back into the line and the O/C protection stays intact. That is a completely moronic statement in itself.
You may get some real power out of this machine but not very much. The power is mostly VAR power and this is done on large grid systems, in many areas. -----------------------------
"Tim Wescott" wrote in message
Nope, sorry, you're just plain wrong.
Using induction machines as generators is an established -- if slightly obscure -- practice. Real mechanical power is transformed to real electric power. There are some inductive VARs, but there's real VARs, too.
But don't argue with me. Argue with the world wide web:
http://en.wikipedia.org/wiki/Induction_generator http://www.aerostarwind.com/induction_generator.html http://www.daviddarling.info/encyclopedia/I/AE_induction_generator.html http://www.electrodynamics.net/documents/electrodynamics_power_gen2002.pdf
(and all the myriad other pages that come up when you search on "induction generator).
On 03/09/2011 05:47 AM, Josepi wrote: Current? maybe but it will be 90 degrees out of phase with the voltage.
It is often stated as putting reactive power back into the supply.
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Not sure about the 3660 poles per second part but pretty sure just about every windmill that is placed onto the grid does exactly this.
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Small wind turbine typically produce multiphase energy that is converted to DC and then runs a solid-state co-gen inverter system to grid tie and synchronise.
Here is another quote from another method used on larger units. The doubly fed generator bleeds a small bit of ac power off the utility grid and converts it to a signal that creates the wound rotors magnetic field at low wind speeds, when the generator is spinning at below its synchronous speed. Fast electronics control the spinning rotors magnetic field such that the generator puts out a 60-Hz signal even when it is turning slowly. (Above synchronous speed, the rotor of doubly fed generators produce power to the grid.)
------------------------------------------ "PrecisionmachinisT" wrote in message
Not sure about the 3660 poles per second part but pretty sure just about every windmill that is placed onto the grid does exactly this.
--


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A old-style non-PM DC generator usually relies on residual magnetism in the pole pieces to start the cycle. One of the to-do items after working on a VW generator was to connect the battery to the field windings the correct way round in order to get startup polarity correct. Just a quick zap to provide some residual magnetism.
A wound alternator needs some DC to start up, one reason you can't push start a car with an alternator and a totally dead battery. When I was a kid, my dad took me to visit one of the sites he was currently working on, was a rural diesel power plant that had had a crankcase explosion and was being rebuilt. Got the tour from the guys in charge, had a huge V-16 engine attached to this dinky gray cylinder about the size of a garbage can. I asked what that was, they said it was the alternator. Had a tray of batteries sitting on a cart, were the old squarish cells they used to use for doorbells, all connected in series. That was the starting DC for the alternator when they were going from blackout conditions, no juice anywhere.
An AC motor may work as a generator, but you'll have to provide some method for providing and controlling the field current.
Stan
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On 03/09/2011 04:26 PM, snipped-for-privacy@prolynx.com wrote:

That is not strictly true. I drove a 72 AMC (with a Motorola Alternator) for months without a battery in it. The alternator retains enough magnetism to self excite enough to fire the coil. This was a carburated straight 6. I lived and worked in a hilly area. If I killed it in traffic, I was hosed.
A newer fuel injected vehicle requires enough current to run the fuel pump and the computer in addition to the coil, so you be walking now.
BobH
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On a wound coil armature and a wound coil stator any residual magnetism can induce a current into one of the coils and excite the other one. With motion energy applied this can feed itself (self excite), as if the battery was there, once in motion.
Without two sets of windings this doesn't happen.
---------------
"BobH" wrote in message wrote:

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In basic motor and generator theory examples (many online) current passing thru a conductor located within in a magnetic field/influence, or a conductor moved thru a magnetic field are the basic principles. Finding descriptions of how automotive alternators shouldn't be difficult, and will likely explain a lot wrt generation.
Many generators utilize brushes, but induction motors can generate under the proper conditions, as in Winston's referred example.
IIRC, the automotive generators of old cars utilized poles within the stator/field windings, (and brushes).. the poles weren't permanent magnet material, but they would hold in a magnet-like state after being properly magnetized.. same/similar to Don's example. If you can refer to an older automotive service manual (pre-1970s), you'll likely find the procedure to stun? the pole pieces in those old generators.
A very weak/slow-motion motor example would be analog panel meters. In the moving coil type meter movements, the coil (armature) is supported on low friction pivot points (were jeweled bearings in days of old) within a magnetic field. When an appropriate small current flows, the meter needle deflects, and if the moving coil is rotated manually (not a normal procedure), a small current flows. Many new analog meters are packaged with a shorting wire across the terminals to dampen the needle movement during shipping.. an example of braking of the generator effect. Not all analog panel meters employ moving coils, though, and those which aren't, don't effectively generate any current flow.
Over the years, I've seen a lot of DIY websites showing various generating techniques from portable/emergency power to wind generation generators that were made in home shops with powerful magnets (surplus suppliers) and hand-wound coils on forms and later potted in epoxy or resin.
--
WB
.........


"Existential Angst" < snipped-for-privacy@optonline.net> wrote in message
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I will address only 3 of your questions:
Existential Angst wrote:

I have a couple of 6.5 KW Onan 120/240 volt 60hz generators. They both have wound rotors and stators. One takes the power off the rotor via slip rings and the other (newer) takes the power off the stator. In this case the field,(the rotor) has dc supplied to it via slip rings. Even though there is usually enough residual magnetism to get generation going, both sets "flash" the field with some of the starting battery juice to make sure the field current builds up quickly.

Yes. I bought the Nigel Smith book mentioned in another post on this thread. I focused on the setup called "C-2C", using a 3 phase motor to produce single phase ac power. It does work. I am using a 5 hp 3 phase electric motor which is being driven by a 12 hp Briggs gasoline engine that is running at about 2200 rpm and belted to produce 60 hz at that engine speed.

Yes, The Nigel Smith book is the one to get. Also, type "induction generator" into youtube and you won't see the light of day for about a week.
Pete Stanaitis ------------------
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FWIW,
I have had the Nigel Smith book for nearly a decade now-actually bought the thing--if there is a prolonged power outage here what I do is I run a 50 hp 3ph motor as a single phase induction generator off from my 23 hp kubota tractor PTO--which easily powers the entire house including starting a 5 ton heat pump compressor..
C2C connection gives you single phase off of a 3 phase motor, rpm ( 60 hz ) is via throttle governor and isnt particularily critical, 20% is probably okay but if in doubt use a ole telechron clock, and compare with a quartz unit..they bothe should read within a few seconds after a minute's time on line...if not, then adjust your throttle to suit.
--





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Nice.
How do you excite the windings ?
------------------------------------------- "PrecisionmachinisT" wrote in message
FWIW,
I have had the Nigel Smith book for nearly a decade now-actually bought the thing--if there is a prolonged power outage here what I do is I run a 50 hp 3ph motor as a single phase induction generator off from my 23 hp kubota tractor PTO--which easily powers the entire house including starting a 5 ton heat pump compressor..
C2C connection gives you single phase off of a 3 phase motor, rpm ( 60 hz ) is via throttle governor and isnt particularily critical, 20% is probably okay but if in doubt use a ole telechron clock, and compare with a quartz unit..they bothe should read within a few seconds after a minute's time on line...if not, then adjust your throttle to suit.
--





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2 Capacitors

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2 capacitors never gets me that excited.
Where are they used? Was there a second set of windings on the rotor, armature, stator, field laminations? Is there a circuit available online or of a work-alike?
--
"PrecisionmachinisT" wrote in message
news:_eidnR-VT7nSOuTQnZ2dnUVZ snipped-for-privacy@scnresearch.com...
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Josepi wrote:

Gently stroke them while saying romantic things.
Hope This Helps! Rich
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Did we change the subject to fluorescent bulbs now?
We always laughed about the ones that didn't want to start, in those terms.
-----------
"Rich Grise" wrote in message
Gently stroke them while saying romantic things.
Hope This Helps! Rich
Josepi wrote:

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Existential Angst wrote in rec.crafts.metalworking on Tue, 8 Mar 2011 23:24:34 -0500:

Should be spelled "All".

You would like the 'book' _alternator secrets_ . Covers automotive alternators mostly, but has a section on using induction motors as generators. I got my copy from lindsay publications. http://www.lindsaybks.com/index.html
From what I remember, you may need to hit the windings with some current to get things started. A car battery should do, just for a second.
--

Dan H.
northshore MA.
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Sounds like a guy from the old days" of car generators. This was common then.
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"dan" wrote in message news: snipped-for-privacy@news20.forteinc.com...
From what I remember, you may need to hit the windings with some
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