Video summary

Alternator to motor conversion howto

Main summary

Key takeaways

Technology

Summary of the Video’s Main Technical Idea

The video explains how to convert a car alternator into a controllable brushless motor by:

  • Removing the diode pack Alternators generate AC internally; diodes normally rectify it to DC for battery charging.

  • Identifying the alternator’s three-phase stator coil connections All three phase coils converge on one common node, which is not used for motor control.

  • Supplying the alternator’s phases using a 3-phase RC brushless motor speed controller (ESC).

  • Powering the alternator’s field coil (rotor excitation) like an electromagnet, using a separate low-voltage controller for the two field brushes.

Key Components / Product Features Used

  • 3-phase RC airplane speed controller (ESC)

    • Takes DC input and outputs controlled three-phase power to the stator coils.
    • The speaker mentions a unit in the ~40–60A class (exact rating uncertain).
    • Tested with approximately ~24V (6-cell Li-ion/LiPo) input to the ESC.

  • Brushed motor speed controller (small, for field coil)

    • Used to vary voltage/current to the field coil via the two rotor brushes.
    • Tested with approximately ~7V (2-cell LiPo) supply.

  • Radio control (receiver + transmitter) to command throttle

    • One throttle channel controls the 3-phase ESC (motor speed).
    • Another channel controls the field-coil voltage via the brushed controller.

  • Jump leads / alligator clips Temporarily connected to the field brushes to apply excitation.

How the Alternator Connections Are Identified

  • The speaker states that most alternators have four connections where the stator/diode wiring terminates.
  • They claim you only need three:
    • Three phase connections that feed into the ESC.
    • The fourth connection, where the three coils converge (the “common” node), is not used.

Why resistance testing was confusing

  • Coil resistance is very low, so resistance testing didn’t clearly reveal the correct wiring.
  • The speaker recommends tearing the alternator apart to visually trace where all three coils meet.

Control Behavior and Tuning Observations (Important Analysis)

  • Field coil voltage is highly sensitive and strongly affects:
    • starting behavior,
    • RPM,
    • and stability.

Key tuning observations reported:

  • There is a “happy range” where the motor runs best.
  • Around 1.0 to 1.5 volts to the field coil was found sufficient.
  • Above that range, performance can worsen due to magnetic saturation of the field coil (more voltage doesn’t linearly produce more torque/power).
  • Tuning behavior example:
    • increasing/decreasing field-coil voltage changes whether the motor starts smoothly and can affect maximum RPM.

They also note the setup can be picky, requiring careful wiring to avoid issues like shorts or bare connection contact.

Power Claims / Scalability Discussion

  • The speaker has heard alternator-to-motor systems may operate at very high voltages (they mention up to ~300V) but they haven’t personally tested that claim.
  • They want to attempt an electric go-kart build (possibly 48V using two packs), but cost is a concern:
    • larger ESCs suited for higher voltage/current (airplane-style) are expensive ($100+).
    • they suggest brushless scooter/go-kart controllers might be cheaper alternatives for the three-phase portion.

Suggested Improvements / Future Plans

  • Ideally, use an Arduino-based controller to manage:

    • field-coil excitation voltage, and
    • throttle/speed together, so the system can maintain the optimal excitation point under different loads.

  • They also mention possibly using a servo tester-style knob/controller for field-coil testing.

  • They’re concerned ESCs may draw significant amps under heavy loads (go-kart/scooter conditions). They cite a belief that some go-kart setups using two units ran around ~30A, though details are uncertain.

Practical “How-To” (Condensed Tutorial Takeaway)

  1. Disassemble the alternator.
  2. Remove the diode pack so the alternator can function as a motor rather than a rectifier output stage.
  3. Identify the three stator phase wires/connections that will go to the ESC.
  4. Keep the regulator mounted (or otherwise retain access to the brush/field-coil terminals) so you can energize the rotor field via the two brushes.
  5. Use:
    • a 3-phase ESC to drive the stator phases, and
    • a small brushed controller (variable voltage) to power the field coil.
  6. Use RC controls to tune:
    • speed via the ESC, and
    • excitation via field-coil voltage, targeting roughly 1.0–1.5V based on their findings.

Main Speakers / Sources

  • Speaker: Unnamed creator (“Just Go Make It” channel owner), demonstrating their alternator-to-motor conversion and setup.
  • Referenced sources: Mentions of other YouTube videos and a paid website book behind a paywall (no specific name given).

Original video