Why do you need a different alternator for lithium batteries?
Lithium batteries have different charging requirements than Lead Acid or AGM batteries that can severely affect their lifespan and performance. The key factors in safe and reliable lithium battery charging are the output DC voltage ripple and average output voltage.
The key differences between the original Bosch-style alternators (including the EDL1 and EDL3, which uses the same design) and our EDL4Li system.
The original Bosch, EDL2, and EDL3 alternators are excited field alternators, meaning they rely on the voltage regulator to supply a pulsed current to the rotor. This pulsing—visible as a square wave on an oscilloscope—controls the rotor’s magnetic field strength. In simple terms, the regulator is constantly switching the field current on and off, adjusting frequency and duration to manage output voltage. While effective, this process inherently produces fluctuating or “erratic” voltage. This voltage behavior poses no problem for AGM or traditional lead-acid batteries, which consist purely of lead and acid and do not have internal electronics. However, lithium batteries include a Battery Management System (BMS) to monitor and protect the cells. The voltage fluctuations from an excited field alternator can stress or prematurely damage the BMS over time.
By contrast, the EDL4 is a permanent magnet alternator (PMA). PMAs generate a clean AC output directly from fixed magnets rather than an energized rotor. The accompanying regulator-rectifier converts this AC current to DC and caps the voltage to prevent overcharging.
There are two main regulator types used in powersports applications:
- Shunt regulators, which control voltage by diverting excess energy to ground (producing heat) as used in the EDL4.
- Series regulators, like the one used in the EDL4Li, which use MOSFET switches to open and close the AC circuit as needed. This method operates much cooler and offers superior voltage stability and efficiency, making it particularly well-suited for lithium batteries.
The ripple effect is all that matters?
Charging voltage ripple in a powersports application is the difference between the highest and lowest voltages from the voltage regulator output. By nature, a common shunt style voltage regulator will have a fairly high voltage ripple due to the regulation shunt switches opening and closing frequently. Each on/off transition will cause some variation in the output voltage, this is unavoidable. Keeping this to minimum is critical for Lithium batteries.
In a perfect world, a ripple of less than 10% of the output voltage (~1.5V for a typical regulator), would be ideal, however is not practical for this type of regulator. The EDL4Li-VoltRect Lithium Specific regulator is able to maintain a less than 4 Volts output ripple, compared to verified test results of our competitors 8 volts. Keep in mind this ripple voltage is only seen via an Oscilloscope sampling the voltage 1000’s of times a second, and is not the same as your average charging voltage as measured by a multimeter.
