Best Alternator Generator DIY Reviews – A Complete Guide for 2023

Are you looking to build your own alternator generator for off-grid power or as a backup energy source? With the right parts and some mechanical know-how, you can assemble a high-quality alternator generator yourself for a fraction of the cost of buying one pre-built.

In this comprehensive DIY guide, we will walk you through everything you need to know to choose the best alternator, other components, and how to put it all together to create your own reliable and efficient alternator generator system.


An alternator generator allows you to generate your own electricity by converting mechanical energy into electrical energy. This can be a great option for off-grid living, energy independence, or as an emergency backup power source.

Building your own alternator generator DIY-style allows you complete customizability and the satisfaction of creating your own system with your own two hands. However, it does require some mechanical aptitude and the right components to get a properly working set-up.

This guide will provide alternator generator reviews and suggestions for the best DIY alternator generator build. We will cover:

  • Key components needed
  • How to choose the right alternator
  • How to size your alternator properly
  • Alternator wiring and connections
  • Choosing the right engine or motor
  • Other parts like the voltage regulator and inverter
  • Safety tips and considerations
  • Step-by-step assembly and installation

So whether you’re a novice or experienced tinkerer, read on for everything you need to know to choose the best alternator and parts to create your own quality alternator generator system!

Best Alternator Generator DIY Reviews

Key Components of an Alternator Generator

The key components you’ll need for a DIY alternator generator build are:

  • Alternator – Converts mechanical energy into electrical energy. Choose based on amperage rating.
  • Engine/Motor – Provides mechanical energy to spin the alternator. Can use gas-powered engine or electric motor.
  • Batteries – Stores the energy generated; deep cycle batteries recommended.
  • Voltage Regulator – Helps provide stable voltage from the alternator to the batteries.
  • Wiring – To connect all of the components securely and properly.
  • Frame/Mounting – For securely mounting all components.
  • Inverter – (Optional) Converts DC output to 120V or 230V AC power if needed.

We’ll go over how to choose each of these components in more detail in the following sections. Your alternator generator DIY project will only be as strong as its weakest component, so choose wisely!

Choosing the Right Alternator

The alternator is the heart of the system, so putting thought into choosing the right one is key. Here are the factors to consider:

New vs Rebuilt Alternators

New alternators will generally provide the highest quality and most reliable performance, but cost more. Rebuilt alternators are cheaper but may have a shorter lifespan.

If choosing a rebuilt unit, inspect it thoroughly and buy only from a reputable source. Make sure the diode trio has been replaced and that the alternator was properly cleaned and tested.

Alternator Amperage Rating

This indicates how much current (amps) the alternator can deliver and relates directly to power output.

Choose an alternator that can produce slightly more amps than your planned power draw needs. Most DIY builds use a 100-200 amp alternator.

For small builds under 2000 watts, a 100-140 amp alternator usually suffices. For larger power draws choose a high output 200+ amp unit.

Other Considerations

  • Pulley size – Make sure pulley aligns properly with your motor/engine.
  • Rotation direction – Alternators are made for clockwise or counter-clockwise rotation.
  • Voltage – Typically 12V or 24V output. Match voltage rating to your batteries and system.
  • Brand – Stick with reliable brands like Denso, Hitachi, or Bosch.

Ask specifics when sourcing your alternator and provide your intended use case to determine the best choice.

Now let’s go over properly sizing the alternator…

Sizing Your Alternator Properly

Your alternator must be powerful enough to handle the amperage draw you need, plus have some extra overhead. To size it correctly:

1. Calculate total wattage needed

Add up the wattage of all devices/appliances the alternator generator will power at peak use.

2. Convert watts to amps

Divide total watts by system voltage (usually 12V).

Example: 2000W ÷ 12V = 167 amps

3. Add at least 20%

Take your amps needed and add at least 20% more as a safety buffer.

167 amps * 1.2 = about 200 amps for our example.

4. Choose an alternator

Select an alternator with an amperage rating above your calculation. For this example, choosing a 200-amp alternator would work well.

Properly sizing the alternator ensures your system can handle peak loads without overload. Oversizing slightly is ideal to allow for future expansion too.

Wiring Your Alternator

You want robust and well-connected wiring for power flow from the alternator. Here are some tips:

Connecting the Alternator

  • Use 6-10 gauge wiring for the main alternator cables. The larger the wire gauge, the more current it can handle.
  • Ensure tight and clean connections with the proper bolt size. Use locking washers or nuts.
  • Protect all wiring from rubbing and vibration with grommets and wire loom.

Using a Voltage Regulator

  • A regulator keeps voltage steady at around 13.5-14.5V for optimal charging.
  • The regulator should have at least a 20% higher amperage rating than the alternator.
  • Install it as close to the alternator as possible.

Other Wiring Tips

  • Use ring terminals instead of alligator clips for robust connections.
  • Keep wiring neat and away from moving parts or heat sources.
  • Have a qualified electrician inspect all wiring for safety and congruency with electrical codes.

Proper wiring and connections ensure efficiency and help your alternator perform to its full potential and rated output.

Best Alternator Generator DIY Reviews

Choosing an Engine or Motor

The engine or motor provides the mechanical input that spins the alternator to generate electricity. You have two main options:

Gas-Powered Engine

  • Can use a 5HP or larger engine for small builds. For larger systems, a 15-20+ HP heavy duty engine is recommended.
  • Make sure the engine RPM rating aligns with the alternator pulley ratio. The alternator typically needs 3000+ RPM.
  • Engines allow long run times without refueling. Gasoline models are most common.

Electric Motor

  • Typically need at least a 5HP electric motor. Larger builds may use 10HP+ motors.
  • Gets power from batteries charged by the system itself or another power source.
  • Very quiet and low emissions compared to gas engines.
  • Runtime is limited by battery capacity before recharging is needed.

Either an engine or electric motor can work well – choose based on your needs and preferences!

Additional Alternator Generator Parts

Beyond the core components, here are some other parts you’ll need:


Deep cycle lead-acid batteries are most common for storing generated power. Use at least a 400Ah 12V battery, and have 2-4 batteries for larger systems.

Choose AGM or GEL batteries for longevity, performance, and safety. Make sure connections are secure and properly sized.


If you want to power AC devices/appliances, you’ll need a power inverter to convert the DC output to 120V or 230V AC power.

Choose a true sine wave inverter rated for at least 20% more wattage than your peak power draw needs.

Fuel System

Gas-powered generators need a properly sized fuel tank, fuel lines and fuel filters rated for the engine. Make sure all connections are leak-proof.

Frame and Mounting

You need a rigid metal frame or mounting system to hold all components securely in place as the generator operates. Consider vibration dampening too.

Use quality mounting hardware – don’t skimp here!

Safety Tips

  • Have proper guards/shields over all moving parts.
  • Ensure adequate cooling and ventilation.
  • Follow all electrical safety codes and have an electrician inspect wiring.
  • Use protective gear like gloves and goggles during construction.
  • Keep fire extinguisher on hand.
  • Make sure engine exhaust travels safely away from enclosed area.
  • Learn safe generator procedures – don’t exceed capacity.

Building your own alternator generator takes skill and attention to detail. But taking the proper safety precautions reduces risk of injury or damage.

Step-by-Step Assembly and Installation

Once you have all your components and parts gathered, here is a general process for constructing your DIY alternator generator:

  1. Design your frame allowing room for all parts and wiring.
  2. Mount the engine/motor securely to the frame.
  3. Mount the alternator using proper alignment and tension on pulleys/belts. Double check rotation direction.
  4. Install wiring loom and terminals for connections from alternator to batteries/regulator.
  5. Add oil and fuel (for gas engines). Perform any pre-start checks.
  6. Connect batteries and mount securely to frame. Link to regulator and inverter as needed.
  7. Do initial start and testing without a load. Check for leaks, odd noises or vibrations and monitor voltage.
  8. Connect devices or appliances and test on load. Check performance at different wattages up to your target.
  9. Make any adjustments needed for optimal functioning.
  10. Finalize installation according to your context – vehicle, boat, off-grid residence etc.

Taking the time to properly construct, test and tweak your system will ensure you have a high quality and effective alternator generator that will provide reliable off-grid power for years to come!

Frequently Asked Questions (FAQ’s)

What size of alternator do I need for 2000 watts?

For a 2000 watt system, you would want at least a 140-200 amp alternator, erring on the larger size. To get the amperage needed, take the watts (2000) divided by system volts (usually 12V). 2000/12 = about 167 amps. Add 20% buffer means a 200 amp alternator could optimally handle a 2000W load.

Can a car alternator be used as a generator?

Yes, a car alternator can easily be repurposed as a generator. Just make sure it is a high output model rated for at least 100 amps or more. You will also need to add a voltage regulator, batteries to store power, and proper wiring.

What motor should I use to power an alternator?

Smaller builds can use a 5HP or 7HP gas engine, or an equivalent 5HP-10HP electric motor. For larger alternator systems producing 2000W+ continuous power, use an industrial 15-20HP gas engine, or 10HP+ electric motor. Just ensure alignment with alternator pulley ratios for proper RPM.

How many batteries do I need for a 2000 watt system?

For a 2000W system, you would need 400-600 amp hours of battery capacity at 12V to give suitable energy storage. This would mean around 2-4 typical 100Ah deep cycle batteries wired in parallel. Make sure your batteries can handle the amp load for your inverter size. Use at least 200Ah batteries.

Can I get 120V/240V AC power from an alternator generator?

Yes, by using a power inverter you can convert the DC output of an alternator generator to 120V or 230V AC current that powers appliances, tools, household items etc. Just make sure the inverter continuous and surge wattage ratings can handle the load and are at least 20% over your calculated power draw.


Building your own alternator generator allows you to produce off-grid electricity on your own terms for much less than buying a pre-made generator. With the right mechanical skills and quality components, you can assemble a high-performing system tailored exactly for your power needs.

The keys are choosing an alternator with ample output capacity for your loads, robust wiring and connections, adequately sized batteries for energy storage, and a properly matched engine or motor for spinning the alternator.

Take the time to carefully design and build your system, and your DIY alternator generator can provide reliable energy independence for your off-grid homestead, vehicle, boat, or project for years to come.

Just remember to take all necessary safety precautions during construction and operation. If you follow sound electrical and mechanical principles throughout the build process, you can have a top quality alternator generator on a DIY budget.

Have you built your own alternator generator from scratch? Let us know your tips and experiences in the comments! And don’t forget to share this guide if you found it helpful. Thanks for reading, and happy building!

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