Pylontech US-Series CHG-OV — Charge Over-Voltage Protection

What it means: The BMS has stopped the charge because the pack, or one cell inside it, went above its voltage limit. CHG-OV is this site's label for that condition and not a code the battery displays — the US-series front panel carries only RUN, ALM and SOC lights and a buzzer, and shows no fault code at all, so identify the fault by the light pattern described here. Pylontech's US-series troubleshooting states that if charging voltage goes above 54 V the battery protection will turn on. There is a louder version of the same fault — the buzzer sounds and every LED on the front panel flashes — which the manual identifies as high voltage protection with a cell above 4 V or the module above 55.5 V. The published charge window for these modules is 52.5 to 53.5 Vdc, and the troubleshooting section asks for the charger to be set to 52.5 to 53.2 Vdc. In nearly every real case this is the inverter or charger being set too high, not a defective battery. The manual's own words for this condition are that the battery system requires properly established communication with the inverter and correct settings on the inverter to run safely.

Why does Pylontech show CHG-OV?

• Inverter or charger absorption voltage set above the Pylontech window. This is the most common cause by a wide margin.
• No BMS communication, so the inverter charges to a fixed voltage it was given at commissioning rather than following the limit the battery is asking for.
• The inverter left on a lead-acid, tubular or gel charge profile after a battery upgrade. Those profiles boost and equalise well above 55.5 V, which is above the point at which Pylontech's high voltage protection fires.
• Cell imbalance, where one high cell reaches its ceiling while the pack voltage still reads normal. Pylontech treats that as a separate condition — see CELL-IMBAL.
• A poorly regulated charge source, or a charger sized and configured for a different battery chemistry.

The Pakistan factor

The commonest route to this fault in Pakistan is the tubular-to-lithium upgrade where the inverter was never taken off its lead-acid charge profile. A tubular profile that boosts to 56 to 58 V sits above the 55.5 V module figure at which Pylontech's high voltage protection fires and far above the 52.5 to 53.5 V charge window, so the pack is being over-charged from the day it is installed. The second route is the Axpert-platform inverter with no BMS handshake, charging to a fixed number that somebody typed in at commissioning and nobody has looked at since. Both look fine for weeks — the pack sits high, the protection trips on a bright afternoon, and the house has no backup that evening. Neither is a battery defect, and both are expensive, because Pylontech's manual excludes warranty claims for damage caused by connecting the battery to a faulty or incompatible inverter. If your installer cannot tell you what charge voltage your inverter is set to, that is the first thing to fix.

How to fix it

1. Safe for a homeowner — read the front panel and note exactly what it is doing. A solid red ALM light means the BMS is in protection. Buzzer plus every LED flashing is the high voltage protection specifically. Those are two different messages and the technician will want to know which one you saw.
2. Safe for a homeowner — write down what your inverter's battery charge voltage is set to. Read it, note it, and do not raise it. If the number is above 53.5 V you have most likely found the fault.
3. Safe for a homeowner — this is the recovery Pylontech itself gives for the buzzer and flashing-LED case. Leave the module switched off and wait about fifteen minutes for the pack voltage to fall naturally, then restart it. The manual states that under this condition the BMS remains functional without damage, and that if no alarm returns the module is ready for work.
4. Understand that the restart is not a repair. Nothing about the cause has changed, and it will happen again, usually on the next good sunny afternoon. Book the settings fix.
5. Installer work — bring the inverter's charge voltage into the manufacturer's window and select the correct Pylontech or lithium protocol rather than a generic entry. Pylontech's troubleshooting for this fault asks specifically that the charge voltage be set to 52.5 to 53.2 Vdc, that communication between battery and inverter be checked, and that the address switch on the battery be checked.
6. Installer work — if the pack voltage reads normal but the protection still fires, one cell is running high and the pack needs balancing, not a higher charge voltage. Raising the setting to force the pack to reach full will drive that cell further over its limit.
7. Do not disable or widen the protection, do not open the module, and do not attempt to discharge a single cell. If the alarm returns after a correct restart with correct charge settings, stop and call your distributor.