Convert a Lawn Mower into a Generator

Discussion in 'Alternative Technologies & Energetics' started by nivek, May 4, 2018.

  1. nivek

    nivek As Above So Below

    Convert a Lawn Mower into a Generator - Horizontal Mount (Part 1)

    This article is based on a submission by David Hooper (with additions from the crew at, which discusses building a generator from an old lawn mower and a GM alternator. We wanted to share them with you -- we looked at David's idea and loved it! We think we have improved upon his idea though, presenting our version in addition to David's input!

    NOTE: This article 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.

    The Project in David's own words
    [​IMG]"My standby battery charger for drag strip / RV use is now a "one wire" Marine alternator of 75 amp rating on a board (a 2 x 8) with a 3 HP horizontal shaft Tecumseh running the pulley. My first one, since sold, was a 3.5 HP Briggs & Stratton from a vertical shaft mower. I cut a slot in the front of the mower deck (but in retrospect, if I had to do it over, I would cut it in the back); then I added brackets made from old 1.5" angle iron for the pivot and an old (from the junkyard) slotted alternator bracket for the adjuster. By re-using the mower deck, I had a place to mount the entire works, on wheels with an easily attached (and detached) handle. If I had been even remotely bright at the time, I would have cut into the back of the deck, so that the alternator and mounts were under the handle, instead of sticking out the front which made the entire rig about a foot longer than it needed to be. Oh well.... (Live & Learn!).

    "I actually used old bed frame rails for the angle iron to make the brackets. (My neighbor was tossing out an old bed, so the steel was free!).

    "It isn't difficult to make this work. If you are after a syrstem to charge a battery between rounds so you can run the race car without an alternator, it works great! As a standby power source, the most expensive thing is the inverter. It has the advantage that you can run it to charge batteries, and subsequently run the inverter off the batteries for some light and silence! In an emergency, there is a battery in your car, one in your spouse's car, one in your neighbors car, etc. so there is no shortage of ability to store some power. Deep cycle (marine/RV) type batteries are greatly to be preferred, but if you don't have a boat or RV already, you are not likely to have them around, and the object of this project is to keep costs down while still avoiding "being powerless". If you are only after some light, use 12 V light fittings and bulbs, and save the cost of the inverter. Or use an inverter to run the heat recovery fan in your furnace/fireplace, and cycle it with the refrigerator / freezer to minimize the size of the inverter required and still use the 12 V lights."

    We looked at David's idea and loved it!
    We think we have improved upon his idea though...

    Our Version of How to Build Your Own Generator (using a Horizontal Shaft Motor)
    [​IMG]We will discuss how to build your own generator that looks something like this (photo at left).

    This generator was built using a 3 HP Briggs and Stratton horizontal shaft motor, a GM 65 amp automotive alternator (with built in voltage regulator), a used car battery, a pulley and V-belt, a 12 volt cigarette lighter outlet box with fuse, a DC to AC power converter, a low voltage control switch, a scrap of 3/4" plywood, a few scraps of 2 x 4 lumber, 4 wheels, and two battery cables. We also used a custom designed bracket manufactured for to make it all come together in a snap.

    In the photo above, we used an 8" pulley on the motor. Subsequent testing indicates that a 4" or 5" pulley is the correct size to use for this application.

    Please note that a safety guard should be installed to cover the belt and pulleys! This guard is not installed so that the photographs show the most detail! If you plan to actually use a generator of this type. Please, Please make sure you install a safety guard!

    What can this generator be used for?
    The basic generator (gas powered motor, alternator and battery only) can be used as a 12 volt power source. This is extremely useful for charging battery banks in RVs, campers or in out buildings. The big advantage to this generator as a charging system is the high current output of the alternator, and thus, the reduced charge time over using solar cells, or AC battery chargers. The other big advantage to using this unit to charge batteries over merely charging them with a car, is that this generator [​IMG]uses much less gas to do the job (which is critical in an emergency). Some HAM radio folk use 12 volt equipment that can be powered from the battery until it is low in charge, and then crank up the generator to recharge the battery. The high output of this unit also makes it useful for car lots or fleets for jump starting cars.

    If a DC to AC power converter is added to the basic system, then a limited amount of 120 Volt AC power would also be available! DC to AC power converters electronically convert the 12 volt DC power to 60 hertz AC power at 120 volts. These devices just connect to the battery on the generator, and provide AC power outlets for standard household AC power.

    What Used Motor Should You Use?
    As David discussed, his first version of a home built generator used a vertical shaft lawn mower engine which are very easy to find (photo at left). These mowers can be had for a song and can be found just about anywhere. They have several of the key components that will be required in this project. They have a base that holds the motor, and a cable for adjusting the motor speed. They also have wheels which are very convenient if you ever plan to move it! The biggest task in making a home built generator is figuring out how to attach the alternator and motor so that power from the motor can be transferred to cause the alternator to spin, thereby producing electricity. The task is harder if a vertical shaft lawn mower engine is used.

    The problem is that there are so many brands on the market, and each one it seams builds there own base. To make matters worse, there doesn't seem to be a really standard shape to the base. Some models have flat surfaces where items can be bolted to, and some bases don't.

    You will notice that David's second generator used a horizontal shaft motor (photo at right) which greatly simplifies the whole project unless you have one of our special vertical shaft brackets for a lawn mower engine. The trick remains, actually mounting the alternator so a belt can be used to link the alternator to the motor. This task is simple when you use one of our horizontal mounting brackets.

    Please Note: It IS possible to use a vertical shaft lawn mower engine if you use one of our special vertical brackets:

    [​IMG] + [​IMG] + [​IMG] = [​IMG]
    Be sure to see the Vertical Shaft Project.

    Build it using a Horizontal Shaft Motor
    In this project, we will concentrate on how to build it using a horizontal shaft motor.

    In the simplest form, the motor and alternator can each be bolted to a base. The exact mounting configuration of the alternator depends on the model of alternator , the motor used, and the belt drive configuration. The next task is to come up with a way to tension the belt. What some creative people do, (like David), is use miscellaneous brackets from cars to mount the alternator to a base. Then, adjuster brackets found on typical car engines are used to tension the belt on the alternator.

    This method requires a high degree of "screwing around" to come up with (or build) the required brackets. Yes, a few trips to an automotive junk yard will result in finding miscellaneous useful items, but at a cost of several hours of time!

    Time is Money!
    The crew has designed a simple way to carry out the bulk of this project:
    [​IMG]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.


    Shown at right: Bracket attached to another style of engine.

    What will you need to build a home built generator?
    [​IMG]The first thing you will need is a used motor.
    The key to this design is that it will require a horizontal shaft motor, which can be found on old drum style lawnmowers, roto-tillers, and lawn edgers. The most common motor size you will find on the used market will be a 3 or 3.5 horse power model. Larger motors are harder to find because most of them are snapped up for building go-carts or mini bikes. The most common brand you will find is a Briggs and Stratton. Newer Briggs and Stratton engines have the gas tank, carburetor and exhaust on the same side of the motor. If you look at the old style Briggs shown here, you will note that the gas tank is mounted on the opposite side of the motor than the carburetor. This means that which ever side the alternator is mounted on, the alternator must clear obstructions. Yes, our bracket takes this into account!

    When buying a motor, note how the pulley is attached to the shaft. Most motor shafts have a square key way (or grove) cut in the shaft. This makes it super simple to replace the pulley with the type you will need for this project. Also note the shaft diameter. Most motors in the 3 horse power class have a 3/4"diameter shaft. Avoid purchasing a motor that only has a threaded hole in the end of the shaft! This configuration will prove to cause hours of wasted time figuring out how to attach the new pulley, as David found out when he built his first version!

    You will notice that after looking at several motor models from several manufactures, there are a few features that just about all of them have. The first is that most have the keyed cut out in the output shaft. Secondly, they all have four bolt holes at the base for mounting the motor to a flat surface. Thirdly, they all have four tapped holes on the output shaft cover plate. These output cover plate mounting holes are a key feature of horizontal shaft motors. Be sure the motor you purchase has them if you plan to use a bracket like the one we designed!

    How do you know if your motor has the required holes?
    [​IMG]Look at where the output shaft is on the motor. Then, notice that there are two holes above, and two holes below the shaft. They will be located on an imaginary circle, 3-5/8" in diameter, and centered at the shaft center. It sounds more complicated than it really is. Take a look at the diagram.

    We have looked at motors ranging from 3 to 10 horse power, and have discovered that these output cover bolt holes are in one of two patterns.

    The following motors use a 3-5/8th inch bolt hole circle:

    • Briggs and Stratton 3, 3.5, 5 horse power
    • Robin International 5 horse power
    • Tecumseh 5,6,7,8,10 horse power
    • Honda 5.5 horse power
    There may be other motors that use this bolt pattern. Larger motors than shown use another bolt pattern which is either 6 1/2" or 7 3/4".

    Check the location of the gas tank
    [​IMG]The photo at left is a Top View of a Briggs and Stratton 3 Horse Power Motor found on lawn edgers. It shows the location of the gas tank.

    Most newer motors have the tank, carburetor and muffler on the same side of the motor. In the case of the 3 horse power Briggs and Stratton we used, the tank is on the opposite side. The next thing to determine is if the side of the tank extends beyond the flat surface of the output shaft cover plate. As seen from this top view, the 3 horse power Briggs does (which adds a bit of complication to mounting the generator). Our bracket has a cutout which is designed to clear gas tanks of this type.

    The next thing you need is an Alternator (with built in voltage regulator)
    [​IMG]The power source: A GM alternator
    We also used a 65 amp GM alternator with a built in voltage regulator. It is critical that you only use an alternator that has a built in voltage regulator! If you make a mistake in the selection of the alternator you run a very high risk of damaging the battery, or worse yet, causing personal injury!

    Again, pay special attention to the selection of the alternator! You must select a GM alternator with a built-in voltage regulator. If you are in doubt, consult an expert or parts professional!

    To fully understand the reason for the special notice above, let's review a few things about how an alternator works:

    We are going to skip significant details relating to magnetics and take a leap of faith; here we describe the effect seen when an alternator is turned--either one that has a built in voltage regulator, or one that does NOT have a built in voltage regulator. (This discussion assumes that the terminals are connected as they would normally be, and no additional details will be provided for this discussion.)

    In the case of an alternator that does NOT have a built in voltage regulator: (very , very bad - don't use!):

    • As the unit is rotated, the output voltage increases. The faster it rotates, the higher the output voltage goes! So, if it is rotated at several thousand RPM, the output voltage would reach 70+ volts! This condition is enough to boil the electrolyte in a battery and could cause explosive results! Do not use this type of alternator!
    And if an alternator with built in voltage regulator is used:

    • Now, if an alternator that has a built in voltage regulator is used (and properly connected), the output voltage will increase until it reaches about 14 volts. That's it. No matter how fast it is rotated, the output will never go above that value. As it turns out, this is the ideal charging voltage for a lead acid battery (a standard car battery). Imagine that!
    If you select the alternator we used, there are four (4) connections that must be made.

    [​IMG]The pins on a Delco-Remy 1100934 37A, 3D10 12VNEG alternator with built-in voltage regulator.

    Consult a parts professional for additional wiring information!

    Another note: When the time comes to crank up your generator, you will need to turn off the switch that goes to the "R"terminal. If the switch is on, the generator will try to output voltage while you are pulling the starting cord on the motor. You will find that it will be nearly impossible to pull the cord! If the switch is off, then there is little to no resistance from the alternator.

    What else is needed?
    The Pulley (attach to the motor output shaft)
    [​IMG]In our prototype shown above, we used an 8" pulley (with a 3/4" shaft, and key way). What we found was that the gearing ratio was less than ideal. We have run additional tests, and determined that a 4" or 5" diameter pulley is correct for this application. Either a 6" or an 8" will work if you can't find a 4" or 5", but you will notice that the motor speed decreases as a load is applied. To compensate (if using a 6" or 8" pulley), the motor speed would need to be increased prior to a load being turned on.

    With the 8" on the motor, and the motor set to idle, we were able to kill the motor when a 150 Watt load was applied. If the motor speed was set above idle, there wasn't much of a problem, but the alternator was spinning much faster than is required. A 6" pulley under the same conditions resulted in a slight motor speed decrease when the load was applied. The alternator speed was about right. But when a 4" or 5" pulley was used, there was no motor speed change for the same load. In fact, it handled the load while running at idle speed, and turned the alternator at a speed more like found in a car.

    Pulley and Belt Data when using's Alternator Bracket
    Diameter Usability Minimum belt
    length Maximum belt
    4" Excellent 35" 37"
    5" Really good 36" 38"
    6" Usable 38" 40"
    8" Undesirable but works 41" 43"
    The following email conversation between crew and David Hooper illustrates the problem: asked David Hooper the following:
    "David, I noticed that when I built up a generator using an 8"pulley on the motor, that the motor was not in its normal power range. The Alternator was also spinning like crazy, and I think it would all work better if the pulley ratio was closer to something you would find in a car, like a 5"or 6"pulley on the motor. That would spin the alternator more at a speed like found in the car, and would also increase the torque seen at the alternator, so load changes would have less affect on the motor."

    David responded:
    "I'll go measure, but it seems to me that I tried to use one about an inch or two bigger (diameter) than the size of the alternator pulley so that, with the engine at its 'cruise speed' (about 2500 RPM) the alternator would be at reasonable speed as well - it doesn't put out its max power unless its really humming, but you can't run it 'flat out' forever either, and you've only got about 3 or 3.5 hp to power it! Everything is a compromise!"

    "I'd try the 5"but it seems to me that mine was more like a 4"- memory fails at this point...Yes the alternator will drag down the engine speed, but if you are over geared, it will REALLY do it!"

    In a follow-up email from David:
    "The 5 inch pulley should do it. You are absolutely correct in assuming that one of about the same size as is used in the car (about a 6") would be correct to give the right alternator speed. But remember that most cars spend much of their lives well BELOW 2500 rpm, so the pulley is sized to give a compromise belt speed for water pump, fan, alternator, etc. In fact many cars have a 'stepped' pulley with a different size for running the Power Steering pump, and yet another for the A/C.

    "Here we have a dedicated unit, with only a 3 - 3.5 hp engine, so somewhere in the 5 - 6 inch range should be about it. I never really did any experimenting with different sizes and measuring max output of the alternator. Does going up from the 5" to the 6" increase output, or drag the motor rpm down for a net loss? Interesting question!

    "I just used some 'stuff on hand' and it worked, so I the proceeded to the old maxim 'If it works, don't fix it!' Perhaps a bit of tinkering might be order after all!"

    The Cables
    [​IMG]The small 2 wire plug (shown at the right) is also available from This molded connector (with wires) is a replacement part for hooking into the two terminals (R, and F) on the alternator. It saved a bunch of time making two of the alternator connections and is well worth the cost.

    Next, we used standard 6 gauge, 15" battery cables to connect the alternator to the battery. Yes, they are a bit over-kill, but the amount of time you would spend making your own cables of lesser wire size (crimping the terminals etc.) is more than the cost of just buying a pair!

    We had a note from David on the subject, and will share it with you:
    "I suspect that the use of 'full on' battery cables is overkill; there are battery terminals that take wing nut & screw (post) connectors available at many auto/RV stores, and you don't need to have all that much thickness of wire here. Check out the gauge of the wires from the alternator to the battery of a car--about 8 ga should do, 6 ga if you really want a safety factor. The "2", "1", "0"or "00" ga. wires in battery cables are just overkill in this application; they ARE needed in a car to transmit the large current needed by the starter, but at no other time. Leave 'em in as optional, but costs can be possibly reduced by using cheaper wires (unless the auto parts store has battery cables at really cheap prices!) My concern is the size of connector needed at the alternator end. Getting that connector to fit the 'hot' terminal of the alternator without any danger of it touching the case or any other 'ground' is easier with smaller terminals, hence smaller wires!"

    The actual length you will require may be longer depending on how you mount everything. 15" is about the minimum length.

    OK, so how does all this junk hook together?
    [​IMG]Shown at left: A top view of the components (belt guard removed).

    The first thing to do is to lay out all the components on your shop floor. This will give you an idea of how much space you will need to mount all the items on a base. We found that the smallest size for the platform was the size of some scrap plywood from out back. The minimum size is 28" long, and 15" wide if the battery is mounted close to the alternator. This allows the use of less expensive 15" battery cables. Also note the location of the power converter. You will need access to the front of the unit to plug in AC devices; this access needs to be away from the belt and pulley.

    This configuration also provides easy access to the motor starting cord.

    Please note! Add about 4 inches to the minimum width of the platform so that a guard can be built to cover the pulley and belt! This prototype was built without a guard so that pictures could be taken, and was not intended to really be used! This is a very dangerous configuration when a belt cover is not installed! Please, Please install a belt and pulley guard for the safety of others! A safety guard can be built using scraps of 2 x 4s, and another scrap of plywood.
    The next step is to bolt the alternator adapter bracket to the motor, and bolt the alternator to the bracket. Then check the placement on your mounting platform. You will also need to verify the mounting hole dimensions for your motor. The Briggs and Stratton 3 HP we used has a bolt pattern as shown below:

    [​IMG]Shown at left: The Briggs and Stratton - Motor mounting hole pattern for a 3 HP

    Be sure to check your motor for the correct mounting hole locations. Then drill the holes in the plywood mounting base slightly over-size to aid in positioning the motor. In the case of the motor we used, the bolt holes are 1/4", so we drilled the holes 3/8" to give a bit of slop so the bolts go into the base a bit easier.

    Now position the battery on the base.
    [​IMG]Provide at least 3" of space between the rear of the alternator and the battery. This will provide ample space for access to the alternator terminals. Next, use some scrap chunks of 2 x 4s positioned with the 2"side down, to build a 4"tall box around the battery. We cut them to length, and then secured them to the base from underneath using 2" wood screws.

    It's much easier if the holes are drilled before trying to install the screws. What we did was to cut the first 2x4, then positioned it on the far side of the battery. We marked the outer location with a pencil. Then we moved the battery, and marked the inside of the 2x4. We did the same thing for the other 3 scraps. Once the outlines of the 2x4s were marked, we "pre drilled"the holes in the base. Next, we positioned the 2x4s (one at a time) back on the base, and drilled into the bottom of the 2x4s from the opposite side of the base, using the holes in the base as a drill guide. Then we installed the screws through the base and into the 2x4 scraps. Once complete, the battery fits right in the box!

    Next, install any type of wheels you might have on hand. We used a few wheels with casters, but if you have an old lawnmower around, those wheels would work even better!

    And finally, bolt the motor to the base, do the required wiring, and install the battery.

    How to Wire it Up
    This information 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.

    [​IMG]The basic wiring.
    This is the basic configuration using a Delco-Remy 1100934 37A, 3D10 12VNEG alternator only. Consult with a parts professional for wiring information.

    In this mode, it can only be used for 12 volt DC applications. A 12 volt cigarette lighter outlet box can be added to provide an easy way to connect 12 volt devices to the unit. I f a cigarette lighter outlet is added, be sure to install a fuse in line with the outlet box. Most boxes that can be purchased at an auto parts store come with one. But remember that the amount of power that can be delivered when cigarette lighter sockets are used, can only be as much as follows:

    Say the lighter outlet box you select has a 20 amp fuse. Then the maximum power that can be delivered through the connector is 12 Volts x 20 amps = 240 Watts. That means that no appliance can draw more than 240 watts or the fuse will blow. So, if you plan to use a 140 watt, 200 peak DC to AC power converter at full load, it will work fine. But if you elect to use a larger model at full capacity using the cigarette lighter plug, you will blow the fuse! Larger models than the 140 watt unit will require that you wire it directly to the battery.

    Do not attempt to replace the fuse with a higher value!

    What does it look like when finished?
    Front View of Completed Generator
    [​IMG] Rear View of Completed Generator
  2. nivek

    nivek As Above So Below

    Convert a Lawn Mower into a Generator - Vertical Mount (Part 2)

    About the Parts Needed
    1. The Motor
    [​IMG] The generator project will require a vertical shaft gas engine from a lawn mower. The typical lawn mower engine will be 3 to 5 horse power and will have a 7/8" shaft, with a 3/16" key way and a threaded hole in the bottom of the shaft. Most of these engines have either 3 or 4 bolts holding them down to the existing lawn mower base.

    2. The Alternator
    [​IMG]A GM 10SI or 12SI style automotive alternator.

    The alternator will fall into one of three categories:

    • A) External voltage regulator type.This type of alternator does not have an internal regulator and must have one connected externally to control the alternator field intensity and thus the output voltage and current of the alternator. The disadvantage in using this type of alternator is that connection is a bit more complicated and the regulator is an added component that must be mounted and connected properly. This type of alternator is typically less expensive than the other options shown below, but like the model with an internal regulator, it too requires an external on / off switch or the alternator and regulator pair can discharge batteries when it is not charging and the switch is left on.
    • B) Single wire connection type with internal regulator.The single wire connection type alternator automatically starts producing output power when the RPM of the input shaft reaches a minimum speed. And, when the RPM drops below a preset speed the output stops. A big advantage is that it does not require a switch to isolate the alternator from the battery source to keep the alternator from draining the battery when not in use. The disadvantage in using this type of alternator is that the alternator will start to charge the batteries as soon as the minimum speed is reached, and will place a load on the engine as soon as the minimum RPM is achieved. In some cases, you might need to throttle through this minimum RPM range to insure that the motor does not bog down at low RPM when the alternator begins to produce power. Another disadvantage is that these alternators are more expensive than other options, but it provides a very simple connection method.
    • C) Internal regulator type with external control switch.Another option is to use the type we used on our last project. This alternator has an internal voltage regulator but requires an external switch to start or stop power production. The advantage in using this model is that the alternator can be switched off while the motor is still running and power output stops. This aids in connecting and disconnecting batteries or other loads.
    One note in the Single wire connection type with internal regulator:

    We found that the single wire configuration is not ideal for this application. Because the lawn mower engine mentioned above doesn't have much throttle adjustment, if a single wire configuration is used with a 2 1/2 inch pulley on the motor the alternator doesn't kick in without manually moving the throttle butterfly to a higher setting and then releasing. This problem might be eliminated by using a 3" pulley. However, a single wire configuration can be used on our last project using a horizontal shaft engine. The problem we have right now, is that we don't have all the answers yet for this configuration. Feel free to experiment, but with the motor we used and the pulley we used, it wasn't convent in that you had to reach under the carburetor to throttle up manually to start generation.

    3. Electrical Wires
    [​IMG]A positive and a negative car battery cable is needed, as well as an alternator connector and associated wires. The alternator wires are not needed if a single wire alternator with built in regulator is used.

    4. An "A" Style Industrial V Belt
    This V-Belt transfers power from the pulley (which will be mounted) on the motor to the pulley on the alternator. Various belt lengths can be used if your mounting system provides for several inches of belt length adjustment. Keep in mind that the belt length should be kept to a minimum to reduce belt slap and associated wear.

    We have found that the Automotive V-belt used on a standard alternator is not compatible with the industrial "A" size belt that mates with all pulleys you will find for the motor. However, if you use an industrial "A" style V-belt, it will provide an exact fit for the motor and an "OK" fit for the alternator. Replacing the pulley on the alternator to match the pulley on the motor is an option (a more expensive option) but would be the ideal solution.

    Since the motor is the source of the toque, and after looking at the wear pattern of both automotive and "A" belts used in this configuration, we feel the "A" belt (which matches the motor pulley) is the better choice, and modifying the alternator by replacing the pulley is not required for most applications.

    Remember that an automotive belt will work in a pinch if you can't find an "A" belt for this project. Just plan to buy the most expensive V belt you can find. Price matters! An inexpensive automotive belt usually doesn't have any nylon cords in the center, only on the outside of edge of the belt, and since the angle of the belt (mainly the inside area) doesn't match the "A" size pulley on the motor, excessive wear of the belt can result. Be sure to keep a spare around after you determine the correct size.

    5. Cast Iron Pulley
    [​IMG]The motor pulley needs to be high quality cast iron. The mass of a cast iron pulley tends to act as a flywheel, taking the place of the mass of the lawn mower blade. Remember that most lawn mower engines have a very light aluminum fly wheel and use the steel blade as part of the effective fly wheel mass. The added weight of the cast iron pulley (compared to the mass of an aluminum pulley) helps the engine idle smoothly and helps keep belt slap to a minimum.

    Full discussion of the pulley can be found below.

    6. The Mounting Bracket
    [​IMG] The mounting bracket is the most complicated part of the project. We custom designed and manufactured one out of 1/8" steel and they are available for purchase at a very cost effective price! With this bracket the project comes together in a snap, and eliminates many hours of frustration.

    The great thing about this bracket is that it's Universal in design and allows use of a wide variety of engine manufacturers and engine models. Our first prototype (shown above) was made with a 3.5 HP Briggs and Stratton engine, but we have since built one with a 3.75 HP Tecumseh, and another version with a 5 HP Tecumseh .

    It not only eliminates hours of time figuring out the bolt pattern of your motor, but also eliminates the trial and error guess work in finding a belt length that will work once the motor and alternator are mounted. Additionally, this bracket can be bolted down to a simple base of your own design and the rest of the work is done!

    Further discussion of the mounting bracket can be found below.

    Putting it All Together
    [​IMG]The first step is to remove the motor from the lawn mower base. Typically, there are 3 or 4 bolts holding the motor to the base, but before you remove them, you will need to remove the mower blade and the shaft coupler that holds the blade on the motor shaft. Getting the blade and the coupling off is a bit of a pain. Removing the blade is not nearly as difficult, but still requires a bit of ingenuity to figure out a way to "jam" the blade so it won't rotate while you remove the bolt which holds it in place on the motor shaft.

    We found that we had to use a "pulley puller", to remove the shaft coupler after the mower blade was removed. A "pulley puller" which can be rented or purchased at most auto parts stores. Removing the coupler is difficult to impossible without use of this tool.

    [​IMG]You will also find that it's a bit of a pain to work under the mower to remove the blade, especially if there is still oil in the motor or gas in the tank. We found that some oil leaked when we tipped the motor over and the mower smoked like crazy for a few minutes when we started it. The ideal way to approach motor and blade removal is to elevate the mower on some type of platform and not to tip the motor at all. We ended up using a fork lift to hold the mower up in the air for the blade removal as shown in this photo.

    [​IMG]The next hassle will be in finding the required pulley. Our research indicated that nearly all the motors used in vertical shaft lawn mowers have a 7/8" shaft, and a 3/16" or 1/4" key way. However, horizontal shaft motors under about 7 HP use a 3/4" shaft. The 3/4" pulleys can be found at most hardware stores, but the 7/8" pulleys are impossible to find. What we had to do was to set up an account with a company that supplies Heating and Air Conditioning Systems, Motors, Blowers and Components to be able to order the correct pulleys. We will be making the correct pulleys available for purchase to folks who can't find them locally.

    Another catch is that a 3/16" key way is not standard on cast iron pulleys. What we found was that a 1/4" key way is the norm because most high horse power AC motors use a 1/4" size key way. A pulley with a 3/16" key way is not typically available in a 7/8" shaft diameter configuration. It is possible to use a pulley with a 1/4" key way on a motor that has a 3/16" key way provided that the set screw is on top of the key on the motor shaft and NOT on the shaft itself. If close attention is paid to this detail the pulley will stay in place without vibrating or loosening.

    As expected, the biggest problem is figuring out how to bolt everything together. In our first attempts, we tried to figure out an easy way to reuse the lawn mower base, and somehow build something that could be attached simply to the base (so that a belt could be run to the pulley on the alternator). That proved to be an impossible task for various reasons. All the bases we looked at on the most common mowers were constructed a bit differently, so whatever would work on one mower would not fit the base for another brand of mower. In some cases, (especially with side discharge mowers) a pulley could actually be run out the discharge shoot. Some mowers did not have the required clearance, or had extra sheet metal that directed the cut grass in such a way that the metal would need to be cut in order to be able to run the belt out from under the mower.

    [​IMG]So, what we ended up concentrating on was coming up with a universal base that just about any motor could fit on. Yes, there were some complications there, too. Some motors have the head on one side and the tank on the other and some have them set 90 degrees apart. So, our base had to allow for rotating the motor by about 30 degrees, and allow positioning the motor in any of the 90 degree quadrants. That allowed the motor to be in any position with clearance for the alternator and a method for hooking up the belt. We also wanted to allow the alternator position to be adjusted allowing for several belt sizes to be used. The bracket also has an integral belt adjustment slot which allows the alternator position to be adjusted, which also serves to tension the belt.

    Let's talk a bit about lawn mower engines.
    [​IMG]The lawn mower we used had a 3.5 Horse power Briggs and Stratton 4 stroke gas engine. That particular model motor has a safety shut off lever on the lawn mower handle which has a cable attached to the motor, and the attached cable must be activated to disengage the motor shut off break and to allow spark to reach the spark plug. What we decided to do was to cut the cable off and deactivate the motor shut off feature. If your motor has this feature, you will need to spend some time looking at the cable and the levers on the motor to figure out a way to deactivate or preserve the feature. In either case the motor will not start unless something is done about the cable and levers.

    We found that there was a small hole in one of the lever plates on the side of the engine, and after pulling the cable, a small nail can be inserted into the lever to keep the mechanism from retracting and shutting off the motor. Like I said, it will take a bit of time to figure out how your motor shut off mechanism works (if there is one installed on your motor).

    Most of the lawn mower engines you will find have a 7/8" shaft and a 3/16" key way cut into the shaft. They also have a threaded hole in the bottom of the shaft.

    The Big Issue: Pulley Size and Type
    [​IMG]The vertical shaft motor from this lawn mower would not throttle as high as the same horse power motor we used in the horizontal shaft generator project. That motor was from a lawn edger, and could be set to a higher maximum speed. After talking with some lawn mower experts, we were told that the throttle mechanism on the lawn mower has the maximum throttle set to be about 75% of the maximum butter fly valve position of the carburetor. We were told that the lawn mower manufacturers set the throttle mechanism that way so there is extra throttle capability for when the mower hits some heavy or wet grass. The motor could then self throttle to a higher setting if necessary, then throttle back to the pre set throttle setting.

    The reason we mention all this is that the pulley size we used on the horizontal shaft motor project would not work on this project. In testing this motor with the throttle set as high as possible without modifying the carburetor, and using a 4 3/4" pulley on the motor (similar size to the one on our other project), the motor would bog down and die with a 39 Amp load on the alternator. Without modifying the carburetor, we couldn't keep the thing running when the load was switched in with the large size pulley.

    What size pulley works without modifying the carburetor or throttle linkage?
    We had excellent results with a 2 1/2" pulley. It allowed the alternator to output voltage at even half or lower throttle settings at a slightly lower output current. So, with less than full demand, the motor speed could be reduced without killing the motor, and providing fuel savings.

    Testing notes:
    The largest load we had available during testing drew 39 Amps with the alternator output of 14.4 volts or about 560 Watts. Testing was conducted with an ambient outside temperature of 82 Degrees. We ran the load for 2 hours and the case temperature of the alternator only reached 148 degrees.

    Another thing to note: Lawn mower engines have a rather small gas tank. We found that we could only run the generator for about an hour at a time with the standard gas tank without re-filling in use (which is not a good idea). We plan to continue using the standard tank, but other folks out there might want to figure out a way to attach a larger tank, or select a lawnmower with a large tank.

    Mounting the Motor and Alternator, Made Easy!
    [​IMG]Shown here is a bottom view of the bracket, motor, alternator and 2x4 base.

    Mounting all this stuff is the tricky part of this project. But like last time, we designed and manufactured a bracket to make the task simple!

    The bracket is made from 1/8" steel and has provisions for mounting the motor and alternator, and additional holes for mounting the plate to a base of your own design.

    What we did for the base was cut two 2x4’s the length of the bracket, and another 2x4 as a cross brace to be installed under the bracket at the bottom of the long 2x4’s. Imagine the base as being an H. The two long pieces were installed so that the base was 4 inches in height, and the cross brace was installed on the two length wise 2x4’s at the bottom, and on it's side so that it stood 2" in height. That provided the necessary clearance for the belt and provided stabilization of the two side pieces. A further improvement would be to install two more short 2x4 at each end of the assembly to completely box in the rotating pulleys (for added safety).

    [​IMG]As in the last project, we elected to mount the alternator in such a manor that it actually runs backwards. This simplifies the hook up and it still works. Many astute readers questioned the alternators rotation direction and what affect would be seen if the alternator fan (which is attached to the alternator input shaft) also runs backwards. Well, the fan still functions, but instead of pulling air through the back and exhausting through the front, the air flow direction is reversed. Also, the fan blades are not as efficient when running backwards so air flow is reduced slightly. But, remember that like in the other project, the alternator is mounted to a steel plate which also serves as a large heat sink. And from the two hour test run at 39 Amp output, the alternator case temperature was only 148 degrees (ambient temperature was 80 degrees). So, I guess what I'm saying is that it really doesn't matter. These alternators normally spend most of their lives under the hood of cars stuck in traffic jams on hot days, and see temperatures much higher than this.

    Now, getting back to the mounting issues: The lawn mower engine has a longer shaft than the alternator, and if the pulley is installed in the ideal location on the motor shaft the two pulleys do not align. So, what we found on our project was that the alternator needs to be mounted flush on top of the bracket but the motor needs to be spaced 1" above the mounting plate. This is easily carried out by using 1" longer bolts, and 1" long spacer tubes. Then the alignment of the pulleys is correct.

    Take a look at the photo of the generator in operation charging a bank of three deep cycle marine batteries. A spacer tube is visible at the bottom of the motor, and provides the necessary height adjustment to keep the pulleys aligned. The pulley is also visible beneath the mounting plate. This motor had three mounting bolts, so three extension tubes were needed.

    So What Can This Thing Be Used For?
    [​IMG]In its simplest form this is a high current DC charging system. With the addition of a DC to AC power converter, it also becomes an AC generator system with battery back up.

    This charging system can be used to recharge a battery bank which can be used later to power a DC to AC inverter for your household AC power needs like the 21" TV as shown. Imagine being able to charge your batteries during the day, and then to be able to silently extract power at night for entertainment, lighting or cooking needs without disturbing your neighbors! This system can also be used in conjunction with other alternative energy system components like solar panels or wind generators as back up power for when the sun isn't shining or the wind isn't blowing![​IMG]

    The addition of a DC to AC power converter allows 120 Volt AC devices (like the television above) to be powered either from the lawn mower DC generator or by the batteries the system can charge. These converters are available in sizes from 140 Watts to 3,000 watts from our power related page.

    DC to AC power converters are available here at DC to AC Power Converters

    Wiring It Up

    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 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. If the switch is on, the generator will try to output voltage while you are pulling the starting cord on the motor. You will find that it will be nearly impossible to pull the cord! If the switch is off, then there is little to no resistance from the alternator. Once the motor is running, the switch can be set to the on position.

    To Recap
    [​IMG] + [​IMG] + [​IMG] = [​IMG]

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