Collection: DIY Direct Drive Coupler Generator

Create Your Own Emergency Power with a Direct Drive Generator!

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

A: With a Direct Drive Shaft Coupler Assembly

We have the components you need for your Direct Drive generator project including alternators, couplers, and a custom bracket. Detailed information about this project can be found at Build a High Power AC/DC Generator System and More Homemade Generator Projects: The Ultimate DC Charging System.

Couplers & Spider Insert

Connecting the output shaft of an engine to the input of something else (like a generator head input shaft), requires a special shaft coupler.

Three pieces are needed: Two (2) half jaw couplings and One (1) "spider" (BUNA-N) insert.

  • Outside Diameter: 2-7/64"
  • Coupler Half Length: 1.45"
  • Coupled Length (assembled): 2-1/2"
  • Torque Rating: 169 lbs max
  • Keyed with two set screws

Special Direct Drive Alternator Coupler

Modified Direct Drive CouplerThe Special Alternator Coupler is custom-machined to replace the nut, lock washer, and pulley on a standard GM 10SI or 12SI alternator. With this custom coupler and our direct drive bracket set, you can build an ultra compact and reliable charging system with no belts to wear out.

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 two Allen wrenches: one to fit the end of your alternator shaft, and another one that goes across two of the ears. Hold the shaft in position with the center Allen wrench, and turn the coupler with the other wrench. We will install this for you by special request.

Direct Drive Alternator Mounting Assembly (Direct Drive Bracket Set)

Direct Drive Bracket SetThe next thing needed is a way to mount the direct drive system to the engine. 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.

Spacers and bolts connect the two plates (we do not provide the bolts or spacer tubes for the bracket set). 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*.

*Note: The length of the bolts and the length of the spacers must be determined at the time of assembly and are not provided.

Related Items

Alternators and Regulators

Refurbished AlternatorFor use with any of our generator projects. 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.

Alternator Pulleys

Alternator PulleyIf 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.

We offer a special 2.5-inch Industrial "A" style pulley that fits the GM 10SI and 12SI alternator. This special pulley will fit any of the alternators we sell, and we will install it for you at no cost by special request. 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 an alternator from us, we cannot guarantee this pulley will fit your alternator. You may return it if it doesn't work out, but you will be responsible for shipping costs BOTH ways which may be more than the cost of the pulley.

Alternator Direction and Fans

An alternator will function in either direction. Cooling can be an issue, however 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.

Alternator FanA 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 cannot be removed and is not the ideal diameter. Bi-directional fans for use with our 10SI and 12SI GM alternators are available here at If you already have an alternator, we cannot 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.

NOTE: We no longer offer or provide technical support for Propane Conversions or Propane Conversion Kits. Please contact U.S. Carburetion Inc. in West Virginia.

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