Grid Tie and Induction Motors
 

Yes, I know it's nearly 3am on the east coast... but and idea struck me. So the idea is to feed small amounts of mechanical power into the power grid. Not necessarily run the meter backwards, but supplement power consumption.

I've researched grid tie inverters - which are very expensive. For those wondering, a grid tie inverter is feeds mains power back into the grid by syncing phase angle and phase (no dead shorts :) ) and applying slightly higher voltage. They are very efficient and really not within a college student experiment budget :p

So I was thinking... Rather than go from mechanical to DC to AC to grid - go from mechanical to AC to grid VIA an induction motor. As a proof of concept, use a DC motor + battery to turn an induction motor. Plugged into the grid, in theory, should apply current if spun fast enough with enough torque.

Oh, but the phase! you say? How do you prevent a dead short?"
I've thought of this -- before applying mechanical power - have the grid bring the induction motor up to speed. Then try to turn faster (apply a torque) with the DC motor, for example. In theory, the amount of extra power put into the grid will be related to the slip angle of the motor - which will also control the speed of the input (so you can't go over speed by too much).

Keep in mind that this whole battery business is just a proof of concept sort of thing - I'm not talking perpetual motion or any hohaa craziness. In the end, the final mechanical input will be around 200 watts. I expect this to be very low efficiency (likely 50%ish), 100W isn't an answer to the energy issues - but it's an experiment. It's also not going to come even close to driving the meter backwards, but it should run (as supplement) my laptop + two to three 13w CFL's :D

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I think the theory is feasible -- the inspiration comes from flywheel driven UPS systems. An induction motor is driven while mains power is on to keep a flywheel in motion. When the power goes out, the FW drives the motor and feeds to local grid.

I'm thinking of using a "low" rpm induction motor.... If I recall, ceiling fans are 16 pole? So that's 60Hz2*2/16=450rpm... Add ceiling fan motor to the list of things to hunt for :) Looking at the one above my head, it looks like it even has a nice bolt pattern for some sort of pulley shenanigans :D

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Can someone either throw some ice water on me and slap me for being an idiot -- or let me know if I've found a boat to Valhalla.

Oh, and my apologies for dancing around the "mechanical input" details.... There's a reason for this, I promise :) In any case, insight and information is appreciated :)

Why not use a "dead" box fan motor and gear the DC motor appropriately, too much slip already w/ a fractional hp motor?

Totally possible -- I'm just looking for a proof of concept at the moment :) All I need to see is the current flow change directions, even if it's small. I'm just looking for a "yeah, that works" or "No, you need to do {insert action} first" before I dive in :D

By all means, experiment, that's what circuit breakers are for :p . I don't quite understand what is going to keep it in synch. I suspect the slip angle will be more like different rotational speeds, but I definately would like to see a simple mechanical tie-in happen. Maybe I'm missing something here.

You start out in synch, yes, then you manually keep it in synch, at a resolution of 60 hz?

Think of what happens when you put an induction motor under load -- you start at the rated speed, and slow down a little... Say from 3600 to 3550 - this is related to the motor slip and the motor is always in a state of attempting to catch up to the field. If you apply too great a load that the motor slows down too much, the motor will just completely stop. This is why (generally speaking) you can hold a motor in place with a heavy load, apply power, and nothing happens - induction motors require some sort of excitation to get moving (today's design and motor controls allow for such starting though).


Now, to my understanding, it works in the opposite direction. If you apply a load in the same direction as the motor - the motor slips in the same direction of rotation - say from 3600 to 3650 rpm. But, because you are coupled to the grid, you're governed by the grid itself -- the grid itself keeps you from going over speed AND under speed. Go too fast, and you'll feel more resistance - go to slow and the motor will start drawing power from the grid.

Of course, this is what I think is going on - based on a physics II course I took 3 years ago and haven't touched since

Oh yeah, portable fan motors are easy peasy to find/fix. The manufacturers, instead of spending an extra quarter and using a thermal switch, use a thermal fuse, so if/when the fan binds because of the crappy lube getting contaminated, it'll blow and the fan won't work no more. So, free fan you can fix for a couple bucks or so, or even freerer if you just bypass the blown thermal fuse. :thumbup:

Cool, I didn't know that - but makes a lot of sense :thumbup:

This was done with some commercially available home sized wind generators back in the 1970s. I think that Enertech was one brand name.

Here's a bit of info:
https://www.awea.org/smallwind/succes...ories_026.html

And just a little down the page here:
https://www.kansaswindpower.net/used_wind_generators.htm

Interesting, because a co-worker and I have been talking about grid-tie for a while and we came to a similar conclusion that this would be the cheap way to do it. The theory is sound and should work. It would be great to have a set-up with an over running clutch so you can start the motor and then bring your primemover (you) up to speed and attempt to overspeed the induction motor. You could use the rear end of a bicycle with the freewheel. It could run off the perimeter of the tire, or grab a bent up rear wheel and remove the spokes and rim. Connect the motor so it spins the hub thru a sproket and chain or something then start pedaling and shifting gears until you can overrun it(all while mounted on a stationary exercise thing of course:) ).

If that bike test set-up works out good, then you could find the right DC motor to run off your homemade windgen and/or PV array to overrun the right induction motor thru a direct drive set-up. Some simple relay logic could make things more efficient so the induction motor doesn't pull from the grid when no alternative energy is available to overrun it. It could be fairly efficient if the motors were carefully chosen and some motor control were used on the DC motor to effectively load the system.

I love alternative energy but am put off by the thought of massive battery banks and grid tie seems like a good alternative. Of course you still lose power when the grid goes down though :o .

Sorry I'm kinda geeked about trying this :D . A simpler take on the bike test set-up; You could leave the tire on a road bike in a stationary stand, and put some kind of 2.7" wheel on a 6 pole motor and mount it to run against the tire. You should be able to begin overrunnig it by pedaling around 10 mph. Now you just need to be able to detect the change in current direction and magnitude to check your results.

this is right up my alley. i am facinated with power and electricity. ive been known to spend 6 hours, 12 hours, even days at a time researching one subject. my latest facination is with synchronus condensors. id love to build one, but plans on the internet are sketchy and i doubt i could do it.

dont use a ceiling fan motor or any other small motor. most of them are not good for generating power. they are shaded pole motors and not good for this. by not good means i wasnt even able to make one generate power. i got a shaded pole motor out of a box fan, applied come capacitors to it and spin it up with a powre drille. it wouldnt generate power no matter what i did. ven briefly energysing it with 110 while it was spinning wouldnt make it work.

you need a squirrel cage induction motor. squirrel cage are easy to generate power from.

you spin a squirrel cage motor at about 5% over its rated rpm, add an appropriate sized running capacitor, and BAM it generates power at a TRUE sine wave. the frequency is dependant on the rpm's, as is the voltage. you use the capacitor size to set the voltage.

good motor for generating power are continous duty motors, like that found on air compressor, water pumps, maybe a washing machine motor, but fans, etc are no good.

i have a bunch of squirrel cage motors, i collect them for enegry expirements. my best expirements are this. anyone want one? ill sell some at a good price as i have more than i could ever use.

induction motor driving another. the driven motor produces power. 1/2hp driving motor, and 1/3 hp driven motor. i even have a pair of electrical outlets wires up to it. this was my own proof of concept, and it works. i used a couple of pulleys with one being slightly bigger than the other to overdrive the driven motor.

5hp lawnmower motor driving a 3 phase 330v 1/2 hp induction motor. i converted the 3 phase motor to putput single phase 120v clean sine wave power. and it works good as a low wattage generator for powering lights and other resistive power loads.

the one real problem with all induction motors such as the squirrel cages i use, they do not work good for reactive power loads, at all. i can power a huge string of lights with my 3 phase generator but i cant even power a jig saw or box fan. induction motors are only good at true power loads, not reactive power.

Good tip, any ideas on likely appliances to find a squirrel cage motor in?

air compressor, waterpump, maybe a washing machine spinner motor. perhaps a dryer spinner motor. an industrial type fan usually come with squirrel cage motors. but things like ceiling fans are almost awalys shaded pole. box fans, blenders, hair dryers, etc are all shaded pole. pretty much any motor under 1/4hp is a shaded pole. there are awalys exceptions though.

find an junk waterpump like a sprinkler pump. they can come with upto 1 or 2hp motors. these make excellent generators. they are also super easy to fix with bearings and stuff readily available.

an easy way to tell is to look at the armature. it looks like a squirrel cage.

the BEST motor to use could be a generator head off a gas generator that has blown the gas motor. this type of head can power reactive loads, resistive loads, pretty much anything you throw at it.

it has been said that any motor can be a generator, and any generator can be a motor, but i never had luck with shaded pole. and to top it of shaded pole are very inefficent. so even if you got one to generate power, chances are its going to be a very inefficent setup. and expirements like this count on every last watt of efficency you can extract.

I typed too slow.
most washers and dryers have split phase or capacitor start induction motors. The washers may have multiple speeds too, same with furnace blowers. Some high performance fans use capacitors on their motors for star/run windings, they don't need a centrifugal switch because the second phase created with the capacitor circuit stays on. dish washer pump motors and pool/spa pump motors should work (most are probably 2 pole 3600 rpm machines though).

I remember years ago playing with a 3 phase motor at work and running it off single phase and connecting a cap between one of those leads and the unused wire (don't remember exactly how I did it). The motor would run but I don't remember if it would self start. The whole point was to see if I could get 3 phase out of the same motor. It worked, I could start a normally wired 3 phase motor off of the other motor that was running as a rotary phase converter. I didn't run it long or load the 2nd motor down so I don't know how well it would work in the long run. I thought it was cool :) , bring 3 phase to your garage.

Thanks csrmel!

That kind of experience is exactly what I need - both getting me excited and dashing my hopes in one post :p You pretty much listed all of the motors I have available for free :p I'll have to seek out alternatives :p

Do you know of any squirrel motors that are rated less than 1hp? Less than 1/2hp even?

What about a power drill motor?

Most shaded pole motors have a rotor like most other induction machines. They just use a modified pole that has a copper shorting ring to provide a phase shift to get the rotor turning. It is still an induction motor with shorting bars running the length of the rotor ("squirrel cage"). https://en.wikipedia.org/wiki/Shaded-pole_motor
btw The motors in blenders are typically universal motors with brushes and commutators, same with vacuum cleaners, hand drills skill saws etc and other devices needing high rpms. These are not induction motors and will not work the same way as the O.P. brought up.

Oh duh... now that you mention it -- I knew that.... Perhaps it's time for a trip to the surplus store :p

You can save yourself a lot of time and effort and energy loss by powering the devices you want to power with DC power directly i.e. a laptop likes about 20 volts DC into the power plug in the laptop - voltages vary, some only take 15 volts and they are a bit flexable in voltage too. It is better to just feed the DC directly into the laptop than to invert it to AC and run it through the power pack which wastes 20% converting from AC to DC. If you want to setup a generator then get a bigger motor instead of a small motor because it will be more efficient and will not have the shaded poles. Anything that runs at the multiple of 60 would be a good motor. The idea is to have the same number of field poles as there are rotor poles so there is no slipping and the core material should be straight not rotated from one end to another (shaded). Typically these are capacitor or induction start motors containing a secondary winding and a starting switch. A 3 phase motor should also work perfectly if you just use one phase since they are equal poled stator and rotor. As for getting them up to speed simply put a few series connected light bulbs inbetween the generator and the AC grid and spin the generator motor until the bulbs stay dark (indicating an in phase condition) then close the switch across the bulbs.

according to a friend of mine who installs wind turbines for a living, some of the large scale turbines work simaler to what it sounds like you are talking about, with an air speed indicator to tell the generator that the wind speed is fast enough to start the feild windings in the generator, the generator then spins at a consistant speed no matter the wind speed, producing a perfectly matched sine wave.

ac motors with brushes are universal motors. im not too framiliar with them except that i remember them being frequency independant. as though they could run on anything from 50hz to 400hz. i seem to recall a 400hz generator you could attach to youre truck motor with a v belt next to the alternator to power universal motors. i guess this is usefull for a recluse building a log cabon with no electricity. universal motor MIGHT generate power, but i dont think they have magnets so its doubtfull. i stay away from them since i have little expierence.

you can find a nice induction motor in smaller hosepowers in things like table saw, drill press, air conditioning fans, etc. but my main interest is in l;arger 3 phase motors. single phase motors top out at about 5hp. do a search on ebay for a single phase motor and youll be hard pressed to find anything bigger than 5hp. but 3 phase is everywhere in huge sizes as big as cars to the size of 1/4hp and less.

you are right that you can connect a 3 phase motor to single phase power, but as you said it wont start turning on its own. it will just sit there and vibrate. you have to spin the shaft and plug it in and it will catch and spin on its own. but one big part of the motor wont be used for power, but it can be used to generate power. thats how machinists use 3 phase cnc's in their single phase houses. they have a big 3 phase motor running off 220v and the 3rd leg generates power. a friend of mines got a big 3 phase motor as big as a 55 gallon barrel to convert single phase to 3 phase for his cnc, bridgeport and lathe in his garage.

like i said this stuff facinates the crap out of me.

That would work, but that's not the audience I'm trying to reach - unfortunately :/


I was going to use an ammeter - but that sounds a lot easier :D

Hey trebuchet03, I got a chance to test a cheap inefficient 6 pole, shaded pole box fan motor today on our motor test stand. I was curious to see what would happen if I tried what you proposed at the start of the thread. I directly coupled it to a variable speed dc motor and plugged the box fan motor in thru a directional watt meter (like a utility power meter). When I powered up the fan motor I noted the direction of rotation and speed, then I powered up the dc motor and checked it with a tach until i was going around 1256 rpms (not quite 5% over speed). The watt meter was still turning the same direction but much slower. I continued to speed up the dc motor and could never get the meter to spin backwards :( it did slow way down though. I will try this test with other motors when I can get the chance.

I tried a different motor today with good results. It is a 6 pole capacitor start/run induction motor off an industrial airmaster fan. I was over driving it with a 3/4 hp 1725 rpm motor thru a step down pulley set. With the 3/4 hp motor at full speed it would be trying to spin the fan motor at 1400 rpm. I used the wattmeter and an inline multimeter reading amps on the fan motor. Running the fan motor by itself it was drawing 1.5 amps and spinning the wattmeter ccw. As I brought the 3/4 hp motor up with a variac (variable output transformer) I noted the speed when the wattmeter stopped as 1233 rpm. At this point you'd think the ammeter would show zero amps but it still showed around 1.3 amps. This is because there is still current in the stator but it is 180 deg out of phase with the voltage (90 deg is the normal phase shift). That is why the wattmeter stopped spinning. Anything above this speed started spinning the wattmeter cw and causing a phase shift in the other direction. I was able to get the wattmeter to spin faster cw than it did ccw as a motor :thumbup: . The fan motor did start to get warm though so I wouldn't expect to be able to do that continuosly. Looks promising :thumbup: :thumbup: .

I would like to eventually check the input vs output power though. That will require the torque meter in between the motors so I can use actual shaft input power and not worry about the inefficiency of the drive motor (which could be any type of prime mover). I'd like to monitor the voltage and current phasing on the Tekscope too.

Nice :) I still need to get to the surplus store... perhaps this weekend or next... Curses I hate waiting so long :p

Interesting results with the shaded pole....

I've read that motor temperature as a generator should excess 170-180F or so for continuous use. 180 is about the limit for touching something - although briefly. 170, you should be able to hole on for a few seconds before it feels too hot.... Not sure how empirically accurate 170-180 is though :p

First I have to say the power loss converting power this way is a LOT, but the cost of a sine wave inverter is a LOT as well ;)

Before inverters were common they had motor-generators, basically a 12vdc motor tied to a 120vac generator. With this you could easily create 120vac from 12vdc. The problem is they were not very efficient, like 50-60% at load. The huge advantage of them was motor starting, since you physically had two motors spinning when the load hit the flywheel effect kept them moving when an inverter would trip out.

I had one of these as a kid and it did work both ways. If you plugged the 120vac side in it made nice 13.4vdc power and yes I even tried pushing the 12v side up to 18vdc and it did push power back out to the grid.

That’s what I know about it...

Here is a good on-line source for cheap motors and other stuff. https://www.surpluscenter.com/electri...tname=electric

They even have a Wincharger made rotary converter :) . https://www.surpluscenter.com/item.as...tname=electric

Brock, your right about low efficiency, but low dollar and ease of DIY is a plus.

A home built wind generator with a speed switch to enable grid power only when the turbine attains a speed high enough to back feed would be ideal.

I wonder how the total system efficiency would compare between a carefully selected induction motor as a direct drive grid tied wind generator (grid acting as "storage") vs. a system that charges batteries and uses an inverter? How efficient are lead acid batteries anyway?

Sweet! Even with the low price, it's still a bit high for a 1/2hp (as compared to, I found it for free in an abandoned appliance). I guess it won't hurt divulging the plan :)

So the task to complete is: converting energy from a bike trainer into mains power. I must go from the bike (perhaps through a trainer stand) to some sort of conversion to electrical and then plug into the grid.

Is it safe to assume an a/c motor with a capacitor is suitable for generation?
This would have been perfect if it wasn't for it's non continuous duty cycle :/

I think 1/2hp ideal, even a 1/4hp should work. cruising at moderate pace around 100 or so watts, 200 watts for more strenuous training... And then the occasional non sustainable burst...

From what I've seen so far it should be safe (especially if it is free :) ).

I have tested a couple more motors lately and noticed a couple things. All have been capacitor run motors. The one I just finished testing was off my Lakewood 20" high velocity fan. It seemed to generate best on the lowest speed setting (it has 3). With a fixed input on low I was seeing 136 watts going out, on medium I saw 130, and on high I only saw 32 watts. It is rated for just over 2 amps on high and is the size of most box fan motors but axially longer.
I tested a 1/2 hp garage door opener motor and had trouble getting any output power from it. I think it was needing more power than the 3/4 hp motor I was driving it with could provide. It was quite small for a 1/2 hp motor (about the same as the lakewood motor) but it was intermittant duty rated for around 5 amps.
So far the motor that seemed the most efficient was the 6 pole airmaster industrial fan motor. It did best on the high speed setting (it has 2). It's a low torque motor rated at 1100 rpms 2.5 amps input on high and air over continous duty. No hp rating is given but physically is the largest motor I've tested (6" diameter x 6" long).
I plan to try some appliance motors soon, I think I have a dryer motor and a washing machine motor plus some 2 pole pump motors.

So far the lower power density motors look to work the best. For the application you are thinking of trying I would try 1/4hp or less, 1/8 or 1/6 hp may be best to start with.

^^ wait, that high velocity fan... Is that a typical $10-$20 box fan - shaded pole? Or a more "industrial" fan (the type with metal blades and a metal cowl)?

I was thinking about that after I posted.... It would seem prudent to do a very low scale proof of concept - on a bike and everything before going to a full scale larger capacity system.

So you're going to power your place by stationary bike?

Not entirely :p Perhaps enough to run my laptop - in ideal situations, that + a few light bulbs :p

It's not a typical cheap box fan, it's similar to this one. https://www.lakewoodeng.com/fanpgs/hv18c.html
It isn't a shaded pole, it has a capacitor on it.

Another tip if you shop for a motor on-line; if they say it is an induction motor and it can be reversed then it is most likely NOT a shaded pole motor, and should be a good candidate.

That reversible tip I posted earlier got me thinking about ceiling fan motors. I have a spare lying around that I decided to tear apart. It is a capacitor run induction motor (not shaded pole)with maybe 14 or 16 poles :thumbup:. It is a common style using 5 blades and 3 speed settings. I think most will be this way that have a reverse switch. It is an inside out motor, so it looks pretty interesting. I plan on testing for output today, but am not expecting many watts since the unit is only rated 85 watts input max.

Edit; Just tested. Sorry, don't get too excited, it didn't back feed. I tried all three speed settings and even spun it way up over 800 rpms and it didn't even lower the input wattage by very much.

just because a motor has a capacitor does not mean its not a shaded pole. i have seen plenty of shaded pole capacitor run motors. one which is a squirrel cage fan out of a microwave. another is a table fan, my box fan has a running cap and its a shaded pole too.
the main reason shaded poles are used is because they are cheap to produce compared to a good induction motor. but shaded poles are energy inefficient, have low starting torque, and just plain bad for generating electricity.

if you guys want a good induction motor, i have 3 sitting here im not doing anything with. a 1/3hp delta 1725rpm, a 1/2 ge 1725.
if you add a capacitor to the output of these motors and run them a little over 1725, they generate electricity. you can use the rpm's to vary the voltage but this also varies the frequency.
the best way to set an induction motor up for generator power is to put a capacitor on it, get it generator power and then adjust the rpm of the motor to get 60hz. then adjust the UF of the capacitor to get about 125v out of it.
i can ship them for $9 to anywhere in the usa, and i only ask $15 for each motor.

the odd thing about induction motors is that they generate amps weither you use them or not. i think the power bounces between the cap and the motor windings. so if you set a motor up on a excersize bike and have nothing plugged into it, the load is the same compared to running a set of lights.

That may be true, but I've examined the stator poles on the ones I've been testing to be sure of weather they are shaded or not. I'm simply testing different types and sizes of induction motors for suitabilty for grid tied generation.

csrmel, It sounds like you are talking about using induction motors as a stand alone generator. That isn't the ultimate goal in this thread. A typical induction motor will not generate power without the grid current in the stator (without modification), and that is a good thing for grid tied apps. It is a safety benefit if the power goes out, nobody wants power sent back into the grid under these conditions.

someone at otherpower.com said this
I just tested a 1/3hp 4 pole wound rotor induction motor and it worked very well as a grid tied induction generator. I was easily able to get 500 watts back into the grid. This motor has the ability to be adjustable in it's rotor circuit so it may be even better with tweaking. I removed grid voltage from this motor while testing and the output went to zero. This looks like the motor I will integrate into something for grid tie.

an induction motor works equally well as a standalone generator or a grid tied generator. either one requires exactly the same wiring job and the same over speed characteristic and you still need to actually power the generator via some other means than electrical (bike, lawnmower, etc)

so i dont see why you want to distinguish the 2, because there really is no difference. perhaps nobody understands that. ill respectfully bow out of the topic and leave you geniuses to you're work.

Yeah, I'll leave this thread alone now. I get all into a subject like this which involves things I work with everyday so I act like a know-it-all but I don't know it all. I mean to help but I should just tell about what I've had work and focus less on other details, sorry guys.

I'm sorry csrmel :o . I wasn't trying to say you were wrong but I guess it seems that way when I reread it. It is true that an induction motor will work as a stand alone generator as long as it has exitation current of some sort, and you are right about adding a capacitance across the output to enable self excitation. I guess I considered adding a capacitor as a modification in my above post which it really isn't. I was only trying to say that without this modification they work safely grid tied which I think is what we're after.