Technical Area
Technical Area

.: adding regeneration to a system with a dc motor

There are some who don't think braking regeneration on a system with a DC motor is worth the effort or cost. I'm not in that camp.

The focus for regeneration and power conversion is for lead-acid batteries because they are the most common battery pack.
However, once the power conversion issue is addressed, the information can be expanded to other battery chemistries.


Suggestions for regeneration on a system with a DC motor

  • Control the current
    • Be kind to your batteries by limiting current to 25 amps. If your pack voltage is above 144 this shouldn't be an issue.
  • Controlling voltage
    • With a 12 volt lead-acid battery, don't exceed 14.7 volts per battery
  • Alternator RPM
    • Faster is better - don't worry about high RPM. The RPM has a major impact on the achievable voltage.
  • Additional weight
    • The additional weight is minimal compared to the battery pack
  • Use an alternator from a home generator
    • A 3500 watt home generator (alternator) with 240volt capability is easier to modify than an automobile alternator because it uses windings that control the output. An automobile alternator allows only the rotor current to be controlled. 3500 watts is about 5hp.

Some Useful Equations

V  = I  x R
(volts = amps x resistance)
P  = I  x V
(power (watts) = amps x volts)
746 watts  = 1 Horsepower

Alternator Dynamics

From an efficiency point of view, an alternator should not be used to charge the batteries while you are using the motor to accelerate as you will use more energy turning the alternator than it will return. This is because no machine is 100% efficient!

  • An alternator should only be engaged when your foot is off the accelerator - this does not mean that it must be physically disengaged.
  • An alternator needs to turn at relatively high rpm. Generally speaking, the alternator needs to spin faster than the motor. On an internal combustion engine (ICE) an alternator generally spins twice as fast as the engine.

Regulating the Alternator's Voltage and Current

Physically Attaching the Alternator to Your Vehicle

Using the Alternator to Assist in Braking

Using the braking energy