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  #1  
Old 04-02-2017, 04:58 PM
Rae Reynolds Rae Reynolds is offline
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Induction motor grid tie help!

working on a grid tie setup... anyone have experience with large (7.5) single phase induction motors? I made a system setup with a smaller induction motor 1/2HP (didn't take photos of it with this motor hooked to it) that worked great so I went out looking for a bigger one an found a 7.5HP leeson model P215K17FB2L that I bought at an auction brand new an super cheap I'm having a problem getting it going it seems to cog or maybe have a start up clutch that its not letting the gas engine get up to starting speed before the motor seems to cog Iv looked for weeks on an off trying to find a diagram or schematics on this Leeson motor with no success like the inside inner workings are top secret lol.. as I try to start the gas engine the motor spins free (it is not hooked to anything yet, as in power) as the rpm's start to rise it seems to have a brake, clutch or something that will only allow it to get to so many rpm's not fast enough for the starter to start the engine I thought of starting the engine with the motor (using it as or like the starter) but I'm afraid it may rip $%^&* apart. any help on or about this motor would be awesome!
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Old 04-02-2017, 05:59 PM
bistander bistander is offline
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Quote:
Originally Posted by Rae Reynolds View Post
working on a grid tie setup... anyone have experience with large (7.5) single phase induction motors? I made a system setup with a smaller induction motor 1/2HP (didn't take photos of it with this motor hooked to it) that worked great so I went out looking for a bigger one an found a 7.5HP leeson model P215K17FB2L that I bought at an auction brand new an super cheap I'm having a problem getting it going it seems to cog or maybe have a start up clutch that its not letting the gas engine get up to starting speed before the motor seems to cog Iv looked for weeks on an off trying to find a diagram or schematics on this Leeson motor with no success like the inside inner workings are top secret lol.. as I try to start the gas engine the motor spins free (it is not hooked to anything yet, as in power) as the rpm's start to rise it seems to have a brake, clutch or something that will only allow it to get to so many rpm's not fast enough for the starter to start the engine I thought of starting the engine with the motor (using it as or like the starter) but I'm afraid it may rip $%^&* apart. any help on or about this motor would be awesome!
Hi Rae,

You can find basic wiring information with google about capacitor start capacitor run induction motor. I've not done this, but believe the method to get it to generate into the mains would be to start it across the mains turning the engine without fuel or ignition. Once up to speed, ~1750 RPM, bring on the engine and throttle to excess of 1800 RPM. The greater the speed over synchronous, 1800, the more power generated.

Likely it is illegal and hazardous to generate this into a utility grid without permission, inspection and safety disconnects. On your private stand-alone "island" system, you can do what you want, I think. But I'm no lawyer. Be careful.

bi
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Old 04-02-2017, 06:24 PM
Rae Reynolds Rae Reynolds is offline
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Thanks Bi,
Motor runs fine, gas engine runs fine but not belted together engine cant get to start up speed because motor wont allow it to. Id like to know why the motor is braking or cogging with no power to it that's my problem at the moment... A ceiling fan is a single phase induction motor, its legal, who's to say I wont spin it just a little faster making power rather than using it lol an once it no longer senses the main line 60hz it wont use or make anything it'll just spin by what ever is spinning it (arms getting tired lol)
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Old 04-02-2017, 06:50 PM
tswift tswift is offline
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^^^ what bistander said above, there could be legal issues and possible danger. There's no reason this can't be made to work from a technical perspective, you seem to have it mostly figured out since you made it work with a smaller motor. An induction motor used as a generator will indeed feed synchronous power into the AC lines, most micro-hydro installations work this way. Heck, even most large wind turbines are just big AC induction motors. I looked up some specs on this motor (Leeson P215K17FB2L) and it appears to be a special high starting torque motor. Possibly not the best choice in this application, but you got what you could. Probably the best thing to do is to disconnect the start winding and capacitors completely, since you would be using the engine to get the motor turning. I agree with you that using the electric motor to start the engine is probably a bad idea, even more so with a high starting torque motor like this.

If I might make a suggestion, some kind of mechanical clutch might be beneficial. This could be as simple as an idler pulley that tensions the drive belt, like the PTO clutch on riding lawnmowers. You start the engine with no mechanical load on it, then clutch in the motor and get it up to close-to-synchronous speed, then engage power to the mains. If the RPM is anywhere close, it will lock in to right at or just above 1800 RPM. Then increase throttle and watch the current on the ammeter climb (you do have an ammeter in the loop, right?) until you reach rated power. For that matter, this might work even if you leave the starter winding and caps alone. A phone call to Leeson for some tech support might not be a bad idea.

Many residential electric meters can detect reverse power feed because this is a common method of stealing power, by reversing the grid input and home output connections. I used to have several hundred watts of guerrilla solar grid-tie solar power until my cheapo chinese grid-tie inverter died, but I had enough devices running at all times that I knew it was unlikely that I'd ever go into an actual backfeed condition. If you do this, expect a phone call from your utility asking you to explain why your meter is running backwards, hopefully they won't just call the cops on you first for stealing power. You could get away with it in an islanded microgrid system, but the induction motor isn't synchronous and isn't self-exciting so that would be difficult to do. An open question, one I don't know the answer to, is what happens if you were to use a small generator or inverter to provide 60 Hz excitation (but with limited watts) and then an induction machine to deliver the bulk of the watts. In practice, with varying loads, I think this would get complicated in a hurry and very likely to damage the generator. Good luck with your project, and stay safe.
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Old 04-02-2017, 07:09 PM
tswift tswift is offline
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I realized I didn't answer the question as to why this is happening. Even though induction motors are "not self exciting", there is always some residual magnetism left in the steel of the rotor. So when you spin it, even though it's not connected to the mains, it will induce some voltage in the stator windings. Since this is a single phase motor, it has an additional start winding connected to some capacitors to provide phase shift for starting torque. This is what's causing your problem, because it's a closed circuit and voltage is being induced in it, it is causing drag and power loss. I suspect if you disconnect all the caps, so the bare motor winding wires aren't connected to anything, that your problem will go away. In this case you have a high starting torque motor, so the start winding is even beefier and it's making your problem worse than a normal motor. The starter motor is still having to spin the additional inertia and slight drag of the electric motor in addition to the gas engine, so it's going to have to work harder but probably will still start normally. Or you could go with the mechanical clutch idea and not worry about the electric motor starting characteristics.
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Old 04-02-2017, 07:22 PM
Rae Reynolds Rae Reynolds is offline
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You are correct about it being high torque and correct again prob not the best one to use but I bought this motor at an auction for $90 bucks brand new an unopened couldn't turn it down it list for over $2000 but seen them for around $800 at surplus stores .. been trying to find info via internet if it has some type of clutch or internal brake on it .. your right, I might have to get with Leeson and see if they can send me a internal diagram of parts and how or what they do .. I'm installing 1 now maybe 2 wind mills later on the property so there changing meter no chance of them thinking Im stealing power there .. PTO clutch like on a lawn mower yes good idea I thought of that also, but that would make it a little more larger and complicated but might have to go that route but first Id like to see if I can find the reason as to why the motor brakes or cogs as I try to start engine even with no power hooked to it .. Im almost 99.9% the motor has some type of internal something I can prob either take out or disconnect .. I think it may have or this may be my problem it may have a centrifugal switch mechanism that opens as the motor gets to just under rated speed (then it opens up) that is keeping the engine from even getting to starting speed .. I read somewhere (brains fried from reading no clue where I read it) the motor must be taken apart and it may have a centrifugal switch on one end of the motor or the other it must be made to be permanently engaged not just to engage as the motor gets to its rated speed .. but Im not sure if this is the cause just like to know before I get the tools out an dissect this 152lb beast .. this is where Im lost
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Old 04-02-2017, 07:25 PM
Rae Reynolds Rae Reynolds is offline
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ahh yes .. that could be the problem I never even thought of the caps maybe keeping some juice still in it or even Quoting you --> some residual magnetism left in the steel of the rotor I'll try unhooking them first
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Old 04-02-2017, 08:23 PM
tswift tswift is offline
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It almost certainly has a centrifugal switch. You can tell for sure by running the motor stand-alone, take off the belt to the engine. Spin it up with the grid connections, then disconnect it and let it slowly spin down. It will take a considerable number of seconds if the bearings are good and there's no other friction or load, but as the motor slows down and is close to stopping you should hear a distinct "click" as the centrifugal switch engages. You could defeat this switch to disengage the start windings, but pulling the caps will probably do the same thing, making sure that the whole "start" circuit is now open-circuit and can't cause any extra starting load.

If your utility connection is set up for backfeeding properly then this could work and be fairly simple. A suitably-rated breaker on the grid connection to the motor will be necessary, this will protect against either a short or the utility going down since obviously your generator can't do much to feed the whole grid and will trip. Some kind of overspeed protection circuit would also be a good idea, so if your house main breaker trips (for instance) and all of a sudden the motor sees a no-load condition then the engine is still delivering horsepower and will overspeed the whole assembly in short order. A flywheel for some extra inertia will slow this process down and might also not be a bad idea, but you'll need to make sure the engine either gets regulated to not much above normal operation RPM, or a brake or some kind of safety system kicks in.

I've done some research myself into this type of system, here's a link to a nifty design for a wind turbine using a similar size motor for the generator, including all the necessary electronics and safety considerations. They use a similar size motor, except that they use a mill motor with built-in electric brake that is capable of stopping the turbine if any fault condition is detected, and provides passive safety in the event the breaker trips or the grid connection goes down.

Prairie Turbines presents: Breezy 5.5 A Reliable 5500 Watt Homebuilt Wind Turbine Generator
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Old 04-03-2017, 03:19 PM
Rae Reynolds Rae Reynolds is offline
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I have relays on the main side and I fab'd a electromagnetic switch for the engine I have tested it many many times and in the event of power failure the relays cut off, the whole system shuts down cuts power to motor the electromagnetic switch I made grounds out engine everything stops I then have to go threw a few small steps to restart engine getting the motor to its slip speed and bring the motor back on the main line everything is good but Im still working on protection for the engine if it fails or breaks down the motor will take over Im sure ripping everything to pieces because the motor will then be running at normal speed on its own off the grid .. still working on that part .. Iv been looking for some type of speed governor or something that detects speed and if it over runs or under runs will shut off the engine .. I can then use relays to break the grid power so the motor stops in the event of engine failure .. no luck finding anything to do that yet any ideas? engine is over kill a Predator 420cc 13hp also got it new an super cheap at an auction .. but my plan is to couple several motor in line together prob smaller ones not high torque like the one I have now .. motors are so easy to find an most cheap or even free because the start windings are bad but they'll work perfect for what Im doing
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Old 04-03-2017, 03:27 PM
Rae Reynolds Rae Reynolds is offline
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Thanks for the link tswift .. very interesting design I'll have to read more about it .. looks like it would take up a 100'x100' spot with all those cables but it also looks pretty heavy too
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Old 04-06-2017, 04:31 PM
Rae Reynolds Rae Reynolds is offline
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Just got a few minutes to work on it last night .. I unhooked capacitor's have it belted to a 1hp motor surprised but the 1hp motor wont even spin it @10 RPM's .. I tried to hand spin it a little still wont turn it .. on the engine setup I also have a self exciting 100Amp Alternator belted to the engine I have battery switch to switch off from battery to alternator to crank engine the drag from alternator wont let engine start either once engine is up an running I switch battery back on line but that was easily done .. I'm bolting the motor back on the engine setup an see if it will get it turning with capacitors now unhooked .. Think my main problem now is I just grabbed the wrong, high torque cheap or not, motor to work with! Another hour into this with no success an I'm setting it in the corner an find another one I just HATE giving up or in lol
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Old 04-06-2017, 05:54 PM
Rae Reynolds Rae Reynolds is offline
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Thanks tswift for your help...

Got the motor belted to the engine setup just a few minutes ago, unhooking capacitors worked .. thought it wasn't going to then checked battery it was on 10.7 charged it a little then engine started as normal! .. I made a wooden frame to mount it all on (the one I made first was about the same but I used a very small motor and only a 5HP engine) temporary an cheap just to get it right first. This has been waiting on me for years to finish. at first I used a 11-3/4" v-belt pulley on the engine to drive the motor but the engine wouldn't start because of motor cogging .. then I found a 4-1/4" v-belt pulley still a no go wouldn't start never thought about the capacitors Thanks to tswift I unhooked them engine started like nothing was even belted to it. once started I have to switch on the battery switch disconnect then the self exciting alternator engages (engine wont get up to starting speed with it on line) I am now going to change the 4-1/4" v-belt pulley back to the 11-3/4" pulley .. the engine will then run at about 670/671RPM that's just under 5.4 times less the normal full speed of 3600 the motor will turn at about 1855 .. new here so not to sure how to add pictures of it (should ask my kids lol computer caveman!!)
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Old 04-06-2017, 06:24 PM
tswift tswift is offline
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Good deal, glad it's working for you! I never actually built a rig like but I did some research and calculations for it. Unfortunately, unless your grid power is extremely expensive it's going to be hard to save any money this way versus just buying grid power. The only reason I thought it might make sense was because of my biofuel research, I have a diesel truck with a greasecar conversion kit to run waste vegetable oil in it, and also two diesel tractors. If I had ever been able to grow large quantities of some oil feedstock crop like sunflowers or peanuts then I might have been able to make this make sense economically. Unfortunately, since induction motors are not self-exciting (so they say: this kind of proves that's not 100% true), you can't just produce regulated 120/240V 60Hz grid quality AC from one as a stand-alone island if the grid goes down. You can mill down the rotor and add some big neodymium permanent magnets though and you will have a self-excited machine, but regulating it in voltage and frequency is then a whole other challenge. It's probably easier to just rectify it and feed a grid-tie inverter with it, but that's considerably more money. As I found out the hard way, those cheapo imported grid-tie inverters sold on ebay are horrible. Not only did mine only last a year, the efficiency was only about 50%.

I have since ended my biofuel experiments, and my solar projects, now that my radiant energy research has started bearing fruit. Hopefully within the next year or two, I will have the last power source humanity will ever need....
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Old 04-06-2017, 06:29 PM
tswift tswift is offline
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Also, hopefully you can find the engine torque/power curves for that motor. I seriously doubt you'll be able to get 7 HP from a 13 HP rated motor at only 670 RPM. My first guess would be not far from 1:1 ratio with the motor would be more suitable. Less than 3600, though, so quieter and more fuel efficient. Most gasoline engines have a thermal efficiency peak around 1/3 of the full load RPM at full throttle, which is why most newer cars have so darn many speeds in the automatic transmissions....
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Old 04-06-2017, 09:32 PM
Rae Reynolds Rae Reynolds is offline
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went back to a 4.5" pulley on motor and a 3.5" on the engine correct again tswift .. got her down to just above 900RPM that's at the best idle I can get her down to with no problems (below 820 it has problems) just a slight increase in engine throttle engine RPM@1413/1418 to get motor turning 1850/1855 .. I didn't mention my fuel Im going to run it off of methane I have 2 IBC 275 gal setting them up as digesters they'll be connected to 6 maybe 8 separate tanks to hold the methane .. did years off an on research on the subject, smelling smoke!! (built a small 30gal one years ago had great success with it an ran the 5HP engine on it but not long didn't have enough gas built up) 6-275gal IBC tanks full of methane will be equivalent to more than 1.3 20lb tanks of propane or should be .. 20lb tank holds 4.7 gallons of propane 1-gallon is 35.97 CF in its gas state 1 IBC @275 (they will hold prob 300 gallons) has 35.76 CF @ holding 275-gallons 6 IBC containers will have 220.5 CF that should ? equal 1.3 Tanks of propane @ 6.18 gallons in liquid form whew I need a drink lol wont give up on this!!
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