How to build you own emergency AC pwr generator

[Texasrocker]

For all my Pfilco Pfriends living up north, you can build your own emergency AC pwr generators with a few items found at garage-sales. These type ac generators wont run clothes dryers ( heavy wattage items) but will supply you some minimal ac voltage to run a small refrigerator,tv,radio etc in limitation during blackouts. Start watching newspapers, garagesales,etc. for items such as a good-used 2 hp or larger ac type electric motor that runs at low rpms such as 1750 rpm or below.
Then, find a good used dependable running horizontal-shaft 6-8 hp gasoline powered engine, off old tillers,yard machines, etc. The elec motor shaft & gas engine shaft will need to be aligned on a sturdy metal base where a v-belt can be used to align on both pulleys, and spaced for alignment to use a automotive type v-belt that fits both pulleys. ( similar to a shop air-compressor setup)
Install a 6" or larger pulley on the gas engine shaft. Install a 2" pulley on the elec motor shaft. The gas engine will supply sufficient rpms to the elec motor to exceed 1750 rpms at fairly-low throttle from gas engine. This throttle can be adjusted to keep elec motor above 1750 rpms as you plug in needed ac items inside your home.
Where the orig ( incoming ac wires) to elect motor were previously used, add a 50' pc of romex #12 w ground. This wire now feeds your electric clothes dryer, or elec range socket, so add appropriate 220 type male plug.
( operation of your homebrew ac generator and how it works):
Turn off your main inhouse breakers before using the generator. Plug in your homebrew ac romex wire feed to either a 220 v dryer plug or elec range socket, whichever is more convenient to access thu a slightly-opened window. Keep generator at least 50' or more away from your house! Add appropriate size gas-tank to accomadate hrs/while in use generating homebrew power. That will take some experimenting. Never try to refill a hot gas engine if fuel runs out! Let it cool off first!! In freezing weather conditions, that wont take long at all. Make sure you are not getting any fumes from the gas engine back into your home or (room) you are supplying power too! In emergency cases, you dont need much ac! Be very diligent of your supply & demand! You will hear the gas engine slow down on rpms as you plug in your minimal items needed, re-adjust the throttle to keep elect motor well above 1750 rpms.
Once the electric motor reaches abit over 1750 rpms, it will start producing ac electricity into your home! Once the rpms are met & increased by the orig rpms the motor was designed for, you get it back in "reverse" from the elec motor generating ac current into your homes " small space 1 bedroom or so sq-footage " for emergency only uses!Keep spare gas to power the engine, fire up your wood-burning stove or fireplace, and have some limited ac use also!

[etech]

That is a cool idea. I never really thought about making my own generator, but it would be fun to experiment with. I do have an older 4kw gasoline generator that I use here during emergencies that I hook up in similar fashion to what you have described. As long as I manage the loads, it works fine to keep the furnace and refrigerator running. BTW, you forgot to mention to run all the fuel out of it before storing away, so that it is ready to go next time, by just refueling.

Regards,

Ed

[FStephenMasek]

Lack of a transfer switch is a serious problem with the suggested set-up. Yes, you may turn off the main breaker, but if someone else turns it on (yes, such things happen), you could seriously injure or kill somebody working to restore power, and would be fully liable for doing so. A transfer switch is not that expensive. Also, Type NM is a poor choice of wire, as it is not flexible enough. Type SO or some other heavy-duty #10 or #12 (depending on the output of the motor) three wire cord would be far better.

[terry h]

Interesting. Along a similar line, I read an article about a guy that sought out 3 phase high horsepower motors for the same purpose. Three phase motors can be bought cheaply used. His rig was powered by a 240 Ford 6 engine. Gas was fairly cheap then. The power company bought back his excess, and in the winter the engine helped heat his farm shop.

I long ago lost the article, along with the address to get the details. Don't know how he handled the 3 phase.

[Alan Douglas]

An induction motor will not work as an alternator.

[Texasrocker]

Once you get a 3 ph ac electric motor spinning over its rated RPMs, it starts generating electricity! Try it!! I built one of these homebrew generators a few yrs back. Sold it since. I had about $ 40 tied up in the whole rig. When testing, I could actually "stop" my meter-loop wheel from spinning just abit over 1750 rpms, ( running only a few low wattage indoor appliances fridge,tv,radio,clock) By reving it a few RPMs the meter-loop ran in reverse! Yes, these simple homebrew generators do work in a pinch! I purchased a new Honda generator since, & left it with my nephews in Houston after Ike. Not sure I will ever get it back ( hee hee), so I may be building me another homebrew-generator someday !

[Alan Douglas]

That was connected to the AC lines. You can't do that if the power has failed (and shouldn't tie to the lines at all, for reasons given above).

[terry h]

Hi, I believe there are auto switching devices available at some expense that take gen. power off line when the power company line is not energized. The power company may even sell them.

What I wonder about; I would think a 3 phase motor as gen. would produce 3 phase power? How to use that? Also, I would think 60 CPS or close would be desirable. How is that done?

[exray]

Here in PR they enacted a specific law against plugging in a generator 'backwards' via the house wiring because of the number of linemen who have been killed doing storm restoration.

Here in Vieques I can name three in two storms in recent years, we have a population of 8-9000. The legal wording on the law puts the offender at risk for manslaughter charges.

Nuff said.

[Alan Douglas]

You can use two of the three windings to get single-phase power from a 3-phase alternator, at about two-thirds of nameplate rating. It probably wouldn't run very smoothly. However you would get 120V on each leg or 208V between legs, not 240V.

To get 60Hz you need to run the alternator at synchronous speed, 1800rpm for a common four-pole machine. At 1800 you would get zero output, because there is zero slip between rotor and stator. The rotor of an induction motor gets its excitation current by transformer action ("induction") between rotor and stator. The stator field rotates because of the way the windings are distributed around the stator poles (I don't know any easy way to explain this in words). It's why a motor works: the rotor is pulled around by the rotating magnetic field.

However, as I originally said, an induction motor will not generate power without some source of magnetism in the rotor. Alternators have wound rotors excited by DC. Voltage is controlled by the field strength (DC current), and frequency by the speed. Without a magnetic field from the rotor, stator output is zero.

[terry h]

You did fine with your explanation Alan. Residual magnetism or an external power source would be needed to get things going it would seem.

At one time I could have owned three 3 phase motors in the 40/50 HP range for a pittance. One was a near new explosion proof. I owned a choice of governed engines, Largest being a 318 Chrysler industrial V8.

I was a lot younger then, and tended to build things. I wanted to give it a go really bad but didn't know enough.

Never bought the motors. The engines went to buzz saws and sawmills. Years later one small fitting went to exray! (I think he was perfecting a "Bomb")

[Alan Douglas]

If you got the setup running as first described, and then disconnected the external power line, I don't know if the motor would supply its own excitation and keep generating. It might. But that still wouldn't help any in an emergency. Now I suppose it's possible you could start this rig with a battery and inverter, then disconnect the inverter, but I've never heard of it being done.

50hp motors I think are likely to have wound rotors (if there were slip rings, they did) and might be used as alternators. Whether they would produce rated voltage, I wouldn't know, and the "breadboard" setup to find out, could get rather elaborate.

Incidentally I have an emergency "generator" (alternator) which I plug into a stove outlet using a male plug. I consider that safe because we have cartridge fuses (60A entrance) and I can physically remove the block that holds them and put it in my pocket. So there's no chance of anyone else throwing the breaker back on accidentally. But in the past ten years I've never needed emergency power.