How to Program a 40A PWM Controller for Lithium Iron Phosphate (LiFePO4) Batteries
2026-06-03
Programming a 40A PWM Solar Controller for LiFePO4 batteries requires precise voltage settings. Unlike lead-acid, lithium batteries need no float stage and have strict absorption limits. Kosun provides reliable 40A PWM Solar Controller units designed for lithium compatibility. Follow this guide to avoid overcharging or undercharging.
Step-by-Step Programming Guide
| Step | Action | Parameter Value (12V System) |
|---|---|---|
| 1 | Enter programming mode (hold Menu 3 sec) | – |
| 2 | Set Battery Type to “User” or “Lithium” | Li / USE |
| 3 | Adjust Absorption Voltage | 14.2V – 14.6V |
| 4 | Set Low Voltage Disconnect (LVD) | 11.0V – 11.6V |
| 5 | Set Low Voltage Reconnect (LVR) | 12.2V – 12.6V |
| 6 | Disable equalization (if present) | 0.0V / OFF |
Note: 24V system values are double. Always verify with your battery BMS specs.
Critical Settings for LiFePO4
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No Float Charge: Set float voltage equal to absorption (14.2V) or 0.1V lower.
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Temperature Compensation: Disable completely. LiFePO4 does not require it.
-
Equalization: Must be turned off. Equalization destroys lithium cells.
40A PWM Solar Controller FAQ
Q: Can I use my existing lead-acid 40A PWM Solar Controller with LiFePO4 batteries?
A: Yes, but only if the controller has a customizable “User” battery mode. Most Kosun 40A PWM Solar Controller models include this feature. You must manually set absorption to 14.2V–14.6V, disable equalization, and adjust LVD/LVR. Without these changes, the controller will undercharge or overcharge lithium cells.
Q: What happens if my 40A PWM Solar Controller keeps charging after LiFePO4 reaches 100%?
A: Lithium batteries stop accepting charge via their internal BMS when full. However, if your 40A PWM Solar Controller continues applying absorption voltage, the BMS will disconnect as a safety measure. This causes sudden load loss and may reset the controller. Proper programming (no float voltage above 13.8V) prevents this cycling behavior.
Q: Why does my 40A PWM Solar Controller show a lower voltage than my LiFePO4 battery’s BMS?
A: Voltage drop occurs due to wire resistance or connection corrosion. A 40A PWM Solar Controller measures at its terminals, while the BMS reads inside the battery. Differences under 0.3V are normal. To fix, tighten all connections, use 6 AWG wire for 40A, and measure voltage at battery terminals with a multimeter. Kosun controllers include remote voltage sense on advanced models for precision.
Need Expert Help?
Setting up a 40A PWM Solar Controller incorrectly risks damaging expensive LiFePO4 batteries. Kosun offers free configuration support for all customers. Contact us today with your panel wattage and battery BMS specs – our engineers will send you the exact parameter list for your system.