If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
Ok, so I got this big, single phase [apparently induction] motor as a gift, but was told by my teacher that it cannot be used as a generator, but as I have found out: it can! but there are some issues, mainly with magnetizing the "squirrel cage" before starting to generate and not letting that energy go away by using a cap, and in some cases applyin g power to use as a motor before removing power to have it generate... after hooking it up to a multimeter and spinning it by hand, me and my friend got only around .0014V AC (expected to be low, since the thing is rated at around 1700 RPM). At home, I hooked it up to a drill and got around .117V AC, then I decided to try to magnetize the core by adding magnets, and after adding a couple to check for a difference (I was not going to leave them there for good) I noticed that there were brushings on the back of the armature, but no visible significant windings... after reading a little I found that it may be the "starter circuit" that gets the motor going in the desired direction by applying out-of-phase voltage. Well, after looking that up, I set the drill at a higher speed, and got a reading of 0.85 VAC! (magnets attached)...
HOWEVER: I cannot get a Amperage reading on my meter, not even in the micro range... so here is my question: could that starter circuit be shorting my output load capability? I do not know if I got it up to the rated speed (at which I was told by my teacher that the brushings would detach)... would the reason be something else? I also tried adding the load after starting, which I read was preferable in the homemade induction motor generator pages online, but no effect was noticed.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
With an induction motor being used as a generator, you must have the right capacitance in parallel with the output. You need to run the motor a bit above its intended rpm. Do not put a load on it until it reached full speed, or it will not generate anything. Also, if you do all that and it does not start generating, try either running it at slightly higher rpm, and once it is going reduce rpm until needed voltage is obtained, or turn it all off and connect the power leads to a DC source for a few seconds. Do not use 120 volts, just something like 12 will do.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
A DMM on the voltage range has an input resistance of about 10 Meg ohms. How much current does it take to develop 0.85V across that? How does that compare to the lowest current your meter can measure in its AC voltage range?
And yes, the secret to making an induction motor generate is putting capacitors across it. Accidents have happened this way when people used PFC capacitors that compensated the motor to exactly 1.0 PF. If the motor and PFC caps somehow get disconnected from the line, it tries to generate infinite power and bad things happen. In bigger motors the resulting braking torque can bend or snap the shaft.
(A cookie to the first 4hv member who can harness this effect to make a compulsator)
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
> Accidents have happened this way when people used PFC capacitors that compensated the motor to exactly 1.0 PF.
Yes, you always under-compensate induction motors with PFC capacitors. That puts the resonant frequency higher than the line frequency so that it does not get excited as the motor gradually spins down.
Improper over-compensation of a large induction motor results in an initially gentle drop in RPM when the power is removed followed by a sharp thud, fused components or bent metal when the RPM goes through the resonant frequency!
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
Steve McConner wrote ...
A DMM on the voltage range has an input resistance of about 10 Meg ohms. How much current does it take to develop 0.85V across that? How does that compare to the lowest current your meter can measure in its AC voltage range?
And yes, the secret to making an induction motor generate is putting capacitors across it. Accidents have happened this way when people used PFC capacitors that compensated the motor to exactly 1.0 PF. If the motor and PFC caps somehow get disconnected from the line, it tries to generate infinite power and bad things happen. In bigger motors the resulting braking torque can bend or snap the shaft.
(A cookie to the first 4hv member who can harness this effect to make a compulsator)
barely within the DMM Amp range, but nonetheless within the supposed range (I plan to get a much nicer one anyways)
and on the caps I noticed that it could be bad, but I never knew it could be that bad! thanks for all of the info...
but my main question still hasn't been answered, as I used the methods that do not require the induction motor to have a cap connected, but still have exceedingly low power: could these brushings be affecting my output power? why are they there iof it an induction motor? are they there to get the motor started in the proper direction?
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
As far as I know the slip rings are part of a centrifugal switch that opens the starting winding when it's up to speed, like your teacher said. The starting winding isn't continuous rated, and would burn out if it were left on all the time. (don't ask how I know this!)
To use an induction motor properly as a generator, you need a capacitive load, period. Sticking magnets to the rotor won't do much of anything, because the rotor needs a time-varying field induced in it. It's soft iron, too, so it doesn't hold magnetism. You can't flash it like a generator from an old Chevy or whatever.
Registered Member #902
Joined: Sun Jul 15 2007, 08:17PM
Location: North Texas
Posts: 1040
ok, i get that i need the caps to use it properly as a generator, but my question still is not being answered: for the voltage i am getting out, my current should be within the range of my meter, but it is not measuring any, though it is measuring voltage: is my DMM broken, or are these rings affecting it? I am NOT trying to get usable power at the moment, I really need to know if my DMM is functioning right before I get into figuring out what cap to attach and a system to properly add the load...
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
Induction Motor Generator Questions...
