HHO Generator Voltage Regulation: Keeping Output Stable Across RPM

The RPM-Voltage Problem

A car's alternator produces approximately 13.8–14.8V at idle and can rise to 15V+ at high RPM under full charging. Your HHO cell's current draw increases proportionally with voltage. A cell drawing 10A at 13.8V draws 12A+ at 15V — 44% more power, mostly becoming heat.

Why This Matters

If you tune your PWM for safe operation at idle voltage (13.8V), the cell is fine at idle but overheats at highway speeds when alternator voltage peaks. Conversely, if you tune for highway voltage, the cell may produce insufficient HHO at idle.

Solutions

• PWM with voltage sensing: Advanced PWM controllers measure actual cell voltage and adjust duty cycle to maintain constant current regardless of alternator voltage variation. This is the cleanest solution.
• Voltage regulator inline: A linear voltage regulator set to 13.5V between the relay and PWM clamps maximum input voltage. Simple but the regulator itself dissipates the excess as heat.
• Buck converter: A DC-DC buck converter maintains constant output voltage efficiently with minimal heat waste. More complex but thermally efficient for large systems.

Current vs Voltage Control

The ultimate solution is constant-current control rather than constant-voltage control. A constant-current PWM maintains a fixed amp draw (e.g., 10A) regardless of voltage, temperature, or electrolyte concentration changes — the most stable approach for automotive HHO.