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			Here are the main components in the AC subsection. The project could stop here if DC is not required. Please Note: We do not sell AC Generator Heads.
			These are the components that add DC charging capability. Also see below.
			Add this bracket to mount the alternator to the engine! Makes it easy. Add cables for the final touch.

Generator Questions

Q: So why would I ever want to build my own generator when I can just buy one ready to go?

A: That's a darn good question!

Then again, it might not cost as much as you might think to build your ideal system if you already have one of the key components.

You might be one of those guys who might have a spare engine sitting around and could use it to drive a generator head without needing to purchase an expensive and dedicated AC generator system. In some cases it could be less expensive to purchase the generator head and reuse an engine from something else that you no longer have a need for, or only need for a few months each year.

A good example would be a guy who has a pressure washer sitting around that has a large engine, possibly a high quality and expensive one like a Honda.  In that case you could remove the pump assembly from your washer and attach a generator head when needed in the winter, and in the spring you could remove the generator head and reattach the pressure washer pump assembly.

A better case could be made for building a multipurpose power generation system because it is not something that you can currently buy.  In this application you might need to charge of bank of batteries as an example at the same time as having some AC power available.  In this application the same engine can direct drive a generator head while belt driving an alternator for DC charging purposes.

In general, when someone wants to charge a bank of batteries there's often excess horsepower available which could be used to run an AC generator head at the same time. Or on the other hand, you might need AC power to make repairs around the house with power tools, or you might need to run the microwave, refrigerator or something, and would like to charge your batteries at the same time.

Shown here is a prototype of a project I'm experimenting with for my own use.

The AC generator head is direct coupled to the Tecumseh 8 HP motor, and has a belt driven 12 volt alternator mounted to our Horizontal generator bracket which is attached to the motor. To get the full rated output of 6,000 W peak from the generator head, this particular motor is under powered. To develop the full rated output power from this head, the engine should really be a 10 HP model like the HM100, or better yet an 11 HP model for a bit more headroom. Of course running an alternator exclusively on this engine is an example of overkill but the combination of the lower output of AC at the same time as DC is available makes for a fairly efficient use of fuel and resources.

In my application I don't require more than 2500 watts of AC power which would normally require about a five horsepower engine. The remaining three horsepower can be devoted to the DC charging subsystem using the attached alternator.

Here is another view where you can see the direct drive and the belt drive components.

For full power, an 11 HP motor is specified by the manufacturer but other motors could be used if you do not violate the general rules outlined below. Trying to draw more power than shown below using an under rated engine horsepower rating will result in the generator producing an AC voltage lower than the specified output. In some cases this could cause a "brown out" condition which could result in electrical damage to the devices being powered. Special precautions should be taken to ensure that the example horsepower ratings and output power or levels below are not violated.
 

So, if you are using an 8 HP motor with this AC generator head and can insure you never will use more than say 2500W of AC power, then there is enough horse power left to be able to belt drive a 12 volt alternator running at say 40 amps (14.4 volts x 40 amps = 576 Watts) with some head room when belt driven off the same shaft.

Although the manufacturer specifically states that to develop the full rated output an engine size equivalent to eleven horsepower is required, smaller versions of this generator head produce lower continuous ratings shown in the table and require less horsepower. We have extrapolated the data shown from the specifications for the smaller generator heads, and although the larger 6000W peak head has more mass in the rotor, we would realistically expect that it doesn't require that much additional power to spin the rotor especially since sealed ball bearings are used on both ends of the head.

I guess what I'm trying to say is that if you can guarantee that you would never try to pull too much AC from the generator head, then even a small engine will not bog down and there would be extra horsepower available for other uses like running an alternator as shown in the prototype.

So, let's talk about some of the issues:

Typical Gas engines rate their horse power at 3600 RPM.

However, running an engine at a lower RPM increases fuel efficiency and decreases wear and tear so there are always trade offs.

You should also note that these small engines output shaft rotates in counter clock wise direction as viewed from the output shaft side of the motor. This is something that will come up again!

Because most engines are rated at 3600 RPMs, you will note that many generator heads are also designed to be rotated at  3600 RPM.

If you attempt to run the AC generator head a speeds below the rated RPM of 3600 in this case, the AC output voltage will not be 120 volts, but will be a lower value. Some equipment you intend to power may be more forgiving about the lower voltage, some equipment might be damaged, so it is critical that you spin the generator at the correct RPM.

More discussion on setting the RPM of the engine and generator head can be found in the next section.

You will also want to note that the generator heads shaft needs to rotate in a clockwise direction as viewed from the shaft side of the generator head. So, place the shafts facing each other and guess what? Both the motor and the generator head rotate in the correct directions. This allows for direct driving the generator head by using a shaft coupler.

Now, let's talk about connecting the motor to the generator head.

Select a coupler half that is the correct size to fit the motor shaft (or driving shaft size), then select a coupler half that is the correct size for the generator head (or Driven shaft size).

Then the two shaft couplers are joined using what is called a spider.

Notice that the shaft couplers each have 3 fingers and the spider has 6 slots. The three fingers from the motor side fit into three of the spider slots, and the three fingers from the generator side coupler fit into the other three slots on the spider. This coupler assembly allows for several degrees of misalignment between the two shafts and protect the bearings from seeing side loads that would result from misalignment.

These couplers are available in a bunch of sizes. We stock several sizes and they are available at the bottom of this page.

Setting the system for the correct output voltage and RPM:

Q: When you're building your own AC generator using a gas engine and an AC generator head, how do you set up the combination so that the system produces the correct output voltage, and turns the generator head at the correct speed?

A: There are two approaches that can be taken.

Q: What if a guy (or gal) has an engine that doesn't turn at 3600 RPM? Can a generator head like this be used some how?

A: Yes! But it's a bit more complicated.

If you are unable to define a pair of pulleys that are standard, available and give you the exact ratio, then there are three choices:

2. Use the pair that give you the least ratio error, and then adjust the throttle of the engine to compensate. This method can not be performed by simply using a tachometer without doing some computations to correct the tac reading. A better choice would be to use a volt meter and adjust the throttle until 120 volts output from the generator is achieved.

3. You could use an intermediate shaft and a combination of two pulley ratios. This option is only needed in EXTREME cases where the ratio is such that no combinations come close, or you don't have access to pulleys that fit one of your shafts. I'm not going to discuss this much as it gets a bit complicated, but there is an example of an intermediate shaft being used below.

We put together the table below to help you find pulley sizes that are considered standard in the industry. We don't stock all these sizes but can special order one for you if you can't find one locally that fits your need. The cells marked with "X" indicate that a pulley is available in the combination of shaft and diameter. Cells that are blank (or black depending on your browser) indicate that a pulley is not typically available in that combination of shaft size and diameter.

Notice that the "pulley size" shown below is the outside diameter. The actual pitch diameter depends on what belt is used. For example if an "A" style belt is used, they ride down in the groove such that you can subtract 0.25" from the size shown.
 

Here is a practical example of using an intermediate shaft and dual pulley arrangement.

For testing purposes, I wanted to use the motor on the left to spin the motor on the right at the correct speed so but I could test the conversion of the induction motor, and verify the output voltage. However, the motor on the right had a very small pulley which was frozen on the shaft and there was no way to remove it. My original plan was to remove the pulley and put a multi step pulley on both motors so I could achieve the gear reduction from a 3450 rpm driving motor through one belt to the 1725 rpm motor. That would require having a pulley 1/2 the size on the faster motor as the pulley size on the slower motor. Like I said, I couldn't get the pulley off the motor on the right.

So, what I ended up doing was to drive the motor on the right through an intermediate shaft which had a multi step pulley on it. The two pulleys were of equal size so the speed on the intermediate shaft would be exactly the same as the speed of the motor on the right side. Next I placed a multi step pulley on the motor which normally turns at 3,450 rpm (the left motor) and belt drove that to a pulley groove on the intermediate shaft that was twice the size. So for each revolution of the motor on the left, the intermediate shaft would rotate 1/2 of a revolution which would cause the gear reduction from the left motor to the right motor to be exactly 1/2. Thus, when the motor on the left rotated at 3450 rpm the motor on the right would rotate at 1725 rpm.

Let's pretend that I could have installed the correct size pulley on both motors in the first place. And lets pretend the motor on the left is a gas engine and the motor on the right is a generator head. Then, the situation is best shown with an equation:

Ratio of RPM = Ratio of pulley size

In more detail,

Engine RPM / Generator RPM = Generator pulley size / Engine Pulley size.
Knowing that I needed the engine to run at 3450 RPM, and the generator to run at 1725 RPM, then...

3450 RPM / 1725 RPM = 2

Then say I've got a 2" pulley that fits the engine side, that means that the generator side needs to be twice as large or 4".

Let's take another belt drive example:

For this application the same formula applies and is shown below:

Engine RPM / Generator RPM = Generator pulley size / Engine Pulley size.

Knowing that we would need the engine to run at 3600 RPM, and the generator to run at 1800 to RPM, then...

3600 RPM / 1800 RPM = 2

Since I had a 3" pulley already for the engine, I needed to determine the pulley size that would be correct or the generator shaft. Again, from the above equation:

2 = Generator pulley size / 3"
So, the Generator pulley size would need to be 6".

Wiring it up:

• One 120 volt Duplex (two outlets) 20A Receptacle, 5-20R
• One 240 volt Duplex (two outlets) 15A Receptacle, 6-15R

The wiring depends on which alternator you choose. All three alternator types are shown.

Do not wire the alternator unless you are sure about what type you are using. If you make a mistake in the selection of the alternator or wiring diagram you run a very high risk of damaging your battery, electronic devices, or worse yet causing personal injury! Consult a parts professional for additional information!

This Tip o'da Week is intended for educational purposes only. No guarantees are expressed or implied as to the accuracy of information presented here! Consult with an automotive wiring expert before attempting to carry out any wiring.

One final note:

If you are using an alternator that requires an external switch, you will need to turn off the switch prior to attempting to start the generator. Once the motor is running, the switch can be set to the on position.

Universal Horizontal Shaft Generator Bracket

Now several versions of our famous Universal Generator Bracket

You can now build your own AC / DC generator!

A unique bracket that mounts a GM 10si alternator to a horizontal shaft gas engine.  The simple way to build your own generator!  Add a DC to AC power converter, and you have a super high output DC charging system, as well as an AC generator. Be aware, you must have a battery hooked up to the alternator, or you will damage the internal voltage regulator.

We have designed and manufactured a simple, one piece universal mounting bracket specifically for this task! This bracket bolts to the motor (using a universal bolt pattern), and allows the alternator to bolt directly to the bracket. The bracket also has an integral belt adjustment slot which allows the alternator position to be adjusted, which serves to tension the belt.

We now have 2 versions of our bracket. The long one is the one we have been selling for years. The short version is a new one that is intended for applications when you want a more compact system, and have an engine with no obstructions on one side.These brackets are designed for the small footprint GM 10SI Alternator. Larger alternators will not fit!

Dimensions for Long version:

• 19.5" long x 8" tall.
• 13" from center of motor shaft to center of alternator shaft with belt adjusted in center.
• 6.6" between standard 2 bolt mounting bolts for GM 10si alternator
• Made from 10 gauge Steel or Stainless Steel (0.135" thick)

Dimensions for Short version:

• 16.5" long x 8" tall.
• 9" from center of motor shaft to center of alternator shaft with belt adjusted in center.
• 6.6" between standard 2 bolt mounting bolts for GM 10si alternator
• Made from 10 gauge Steel or Stainless Steel (0.135" thick)

See our "Tip O'da Week" on the subject.

Example Mounting for Horizontal Shaft Bracket
Short version mounted on a Tecumsineeh OHV engine.	.	Long version mounted on a Tecumsineeh OHV engine.
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Bare Steel Universal Horizontal Shaft Generator Bracket, Short version. Price: $24.95 Black Powder Coated Universal Horizontal Shaft Generator Bracket, Short version. Price: $29.95 Stainless Steel Universal Horizontal Shaft Generator Bracket, Short version. Price: $39.95 28" belt (for the SHORT version of the bracket).  Price: $9 (Use with our 4" pulley on motor and standard 2.5" alternator pulley  4" pulley for 3/4" engine shaft.  Price: $14.85	.	Black Powder Coated Universal Horizontal Shaft Generator Bracket, Long version. Price: $29.95 Stainless Steel Universal Horizontal Shaft Generator Bracket, Long version. Price: $42.95 37" belt (for the LONG version of the bracket).  Price: $9 4" pulley for 3/4" engine shaft.  Price: $14.85
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A Note about Alternator pulleys and belts.

The normal 2.5" pulley (shown here) on a GM 10si alternator is a 3/8" automotive pitch belt.

You will not be able to find a 3/8" automotive pitch pulley to go on your engine. The only commonly available pulleys available in standard engine shaft diameters that have key ways are Industrial "A" style models. These require Industrial "A" style belts.

The pulleys and belts we sell to go on the engine are industrial "A" style, 1/2 inch wide. Although the combination of automotive and Industrial "A" style belts is not the ideal solution, it works well for most customers and is the least expensive option. The belt rides a little higher in the alternator pulley, and at the correct depth on the engine pulley. Extreme power users may experience some belt wear, especially if the belt is not tight, or if the pulleys are misaligned even to a slight degree because of the reduced contact area between the alternator pulley and belt side.

There is a better solution.

Special Industrial "A" belt pulley for GM 10si alternator.

We are now offering a special 2.5" Industrial "A" style pulley that fits the GM 10si alternator. These will fit any of the alternators we sell, and we will even install it for you at no cost by request. Shown here is the same belt as it would fit our new special alternator pulley. So, for people who plan to run their systems near capacity for extended periods of time, we recommend replacing the standard pulley on the alternator with one of ours.  If you already have your own alternator, or did not buy it from us, we can not guarantee this will fit your alternator. Please look very closly at the diagram for measurements. You may return it if it doesn't work out, but you will be responsable for shipping costs BOTH ways which may be more then the cost of the pulley.

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Special Industrial "A" belt pulley for the GM 10si alternator.

Special pulley for Alternator, 2.5 inch,  "A" style industrial. Price: $19.95
Install this pulley to any alternator purchased on this order (No Installation Charge For This Option)

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Notes about alternator direction and fans:

Stock fans for 10si (left) and 12si alternators (right).

Above are the stock fans for the 10SI alternators (like the 63 amp model), and the 12SI alternator (to the right).

Most asked questions:

Q:Doesn’t the alternator run backwards?
A:Yes, in several of these projects the alternator turns in the opposite direction. An alternator will function in either direction.
Q: Is cooling an issue when the fan runs in the wrong direction?
A: In most situations, no. The fan still functions but at reduced efficiency. The alternators in our projects are bolted to a metal mounting plate which acts as a large heat sink. We do offer a special bi-directional fan that can be used in place of the stock fan. This fan is as efficient when rotated in either direction.
Q: Where can I find a reverse fan?
A: A bi-directional fan is available from us. For a true reverse direction fan you will find them used on '65-'69 Corvairs. But the Corvair fans have an integral pulley which can not be removed and is not the ideal diameter.

Bi-directional fans for use with our alternators

(back face on left, front face on right).

These fans fit the 10SI and 12SI alternators we sell. If you already have an alternator, we can not guarantee these will fit. They will only fit if the existing fan has a dish in the center, and the dish points toward the alternator. See the above pictures.

Bi-directional fan for GM 10SI or GM 12SI alternator. Price: $24.75
Install this fan to any alternator purchased on this order (No Installation Charge For This Option)

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Vertical Shaft Generator Bracket

Now build a generator from a common-style lawn mower engine with our new Vertical Shaft Generator Bracket!

Universal mounting pattern fits all lawn mower engines. Same integral belt adjustment slot and alternator mounting provisions as our horizontal design.

(Bracket allows you to mount alternator as in the photo below):

See our "Tip O'da Week" on the subject.

Dimensions for Vertical Bracket:

• 24" long x 12" wide.
• 11" from center of motor shaft to center of alternator shaft with belt adjusted in center.
• 6.6" between standard 2 bolt mounting bolts for GM 10si alternator.
• Made from 10 gauge steel or Stainless Steel (0.135" thick).

Bare Steel Vertical Shaft Mounting Bracket.  Price $29.95
Stainless Steel Vertical Shaft Mounting Bracket.  Price $43.95
Pulley for engine, 2 1/2" cast iron, 3/16" key way, 7/8" shaft, "A" style industrial. Price: $19.95
30" Belt for vertical shaft bracket and pulley above, "A" style industrial. Price $9.00

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Alternators and Regulators

For use with any of our generator projects.

Sold outright! No core charge!
All alternators are remanufactured  with new brushes and bearings, right here in Eugene, OR.
If you plan to run your system near capacity for extended periods of time, we recommend replacing the standard pulley on the alternator with one of our special Industrial "A" belt alternator pulleys above.
Be aware, you must have a battery hooked up to an alternator or you will damage the internal voltage regulator if you try to rotate it at normal RPMs.

Model 7122, 63 Amp - External regulator type.  Price $49.00
Model 11710, External voltage regulator for 7122 alternators.  Price $27.50
Wiring Plug for 7122 (you provide switch).  Price $5.50

Model 7127, 63 Amp - Internal regulator type, 12 volt. External switch required. Price $69.95  (RECOMMENDED MODEL)  (Also see wiring plug below)
Model 7294, 94 Amp - Internal regulator type, 12 volt. External switch required. Price $102.00
Wiring plug for 7127, 7294 alternators (you provide switch).  Price $5.50

Model 7127X, 63 amp - Single wire, internal regulator type, 12 volt. Price $75.00
Model 7294X, 94 Amp - Single wire, internal regulator type, 12 volt. Price $128.39

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Direct Drives

Q: How do you direct drive a generator head with an engine?

A: Direct drive shaft coupler assembly.

To connect the output shaft of an engine to a generator head input shaft (or anything else for that matter), a special shaft coupler is required. Basically, three pieces are needed.

Select a coupler half that is the correct size to fit the engine shaft (or driving shaft size), then select a coupler half that is the correct size for the generator head (or driven shaft size). Then the two shaft couplers are joined using what is called a spider. Notice that the shaft couplers each have 3 fingers and the spider has 6 slots. The three fingers from the engine side fit into three of the spider slots, and the three fingers from the generator side coupler fit into the other three slots on the spider. This coupler assembly allows for several degrees of misalignment between the two shafts and protect the bearings from seeing side loads that would result from misalignment.

These couplers are available in several sizes, but we have marked the ones that are needed for our projects:

Special direct drive alternator coupler

This coupler is custom machined to replace the nut, lock washer and pulley on a standard GM 10si alternator.With this, and our direct drive bracket set you can build an untra compact and reliable charging system with no belts to wear out.

Installing our custom direct drive alternator coupler.

We have had a few customers ask for the easy way is to install our custom direct drive alternator coupler. First you have to remove the nut, lock washer and pulley from the alternator. The only practical way is to block the fan on top of a piece of wood, and use an air impact wrench on the nut. If you don't have one, take your alternator to any shop and pay them a few dollars to do it for you.

Now, to install our alternator coupler you will need an allen wrench to fit the end of your alternator shaft, and a second one goes across 2 of the ears. Hold the shaft in position with the center allen wrench, and turn the coupler with the other wrench as shown. Again we will install this for you on request.

Direct drive alternator mounting assembly.

The next thing need is a way to mount the direct drive system to the engine.  Shown here is the complete assembly.  Note that we do not sell completed assemblies, just the two plates.  The engine plate has mounting slots such that it can fit all engines with bolt circles smaller or equal to 7.5 inches.  This covers everything from 3 HP to 20 HP. The plate with the large hole is where the alternator mounts.

Notice from the picture that there are spacers and bolts connecting the two plates. We do not provide the bolts or spacer tubes. The engine plate comes with nuts pre-welded to the side of the plate that faces away from the engine.  This is done so that the surface of the plate that touches the motor is free of obstructions.  The spacer tubes need to be large enough in diameter that they can sit over the nuts (the nuts sit inside the tubes).  In the example shown, we used square tube for the spacers but we have also used 3/4 electrical conduit for the spacers. The length of the bolts and the length of the spacers must be determined at the time of assembly and are not provided.

At this time we only offer these direct drive bracket sets in Bare Steel, unpainted. We are looking at doing them in powder coat, and stainlesssteel  if enough people are interested in those options. Call if interested.

Black Powder Coated Direct drive bracket set - Price: $55.95
Stainless Steel Direct drive bracket set - Price: $65.95
1/2" Direct Drive Coupler.  Price $18.50
5/8" Direct Drive Coupler.  Price $18.50
3/4" Direct Drive Coupler (most 5 HP and smaller horizontal shaft motors). Price $18.50
7/8" Direct Drive Coupler (use with most vertical shaft motors).  Price $18.50
1" Direct Drive Coupler (use with 8 HP horizontal motors and others). Price $18.50
Special-threaded and counter bored for GM alternators. Custom made to direct drive GM alternators with gas engine  Price $32.50
Spider for all couplers.  Price $7.85   ONE SPIDER REQUIRED FOR EACH PAIR OF DRIVE COUPLERS.

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