Pylontech US-Series TEMP-PROT — High and Low Temperature Protection

What it means: The BMS has suspended charge or discharge because the cell or BMS temperature is outside the range the module is allowed to work in. TEMP-PROT 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. High and low temperature protection at cell and BMS level is one of the basic BMS functions Pylontech lists for these modules. The published working temperatures are 0 to 50 degrees C for charging and minus 10 to 50 degrees C for discharging, and the troubleshooting section states that above 60 degrees C or under minus 10 degrees C the battery could not work, with the remedy given as moving the battery back into the normal operating range between 0 and 50 degrees C. Separately, the rated currents only hold for a cell temperature of 10 to 40 degrees C and are derated outside it, so a hot pack is being quietly limited long before it ever alarms. This is a fault of the room the battery is in, not of the battery.

Why does Pylontech show TEMP-PROT?

• Ambient temperature above what the module can shed. These are IP20 indoor products with natural cooling, rated for 5 to 95 percent humidity with no condensation.
• The rack boxed into an unventilated cabinet or cupboard, which removes the natural convection the design depends on.
• Direct sunlight, a roof cabin, or a west-facing wall. The module's own danger label says to avoid direct sunlight and not to cover or wrap the product case.
• Sustained heavy charge or discharge current heating the cells, on a pack that is already warm.
• Cold weather in the north of the country. Charging is blocked below 0 degrees C even though discharging is permitted down to minus 10 degrees C, which is routinely misread as a failed battery.
• Storage in a hot space. The shelf temperature specification is minus 20 to 45 degrees C, lower than the working range.

The Pakistan factor

Heat is the defining Pylontech failure mode in Pakistan. Rooftop store rooms, stairwell cupboards and unventilated utility rooms across Punjab and Sindh routinely run above 45 degrees C through June and July, and Jacobabad, Sibi and Larkana go considerably further. Pylontech's charge limit is 50 degrees C and the current derating begins at 40 degrees C cell temperature, so a bank in a hot store room is already being limited for months of the year before anybody sees an alarm, and the owner experiences it as the battery quietly getting worse each summer. Two local installation habits make it worse. The first is boxing the rack into a sealed wooden or metal cabinet to keep the dust out, which defeats the natural cooling the module is designed around. The second is mounting the bank against a west-facing wall that soaks up the afternoon sun. The opposite case shows up every winter in Murree, Gilgit, Skardu and Quetta, where a pack discharges perfectly well but refuses to accept charge below 0 degrees C and gets condemned on a mistaken diagnosis. The one remedy never to accept is moving the battery outside — these are IP20 indoor modules, and a shaded, vented indoor wall beats an outdoor location every time.

How to fix it

1. Safe for a homeowner — measure the room, not the battery. Put a thermometer where the modules are and read it at the hottest part of the afternoon. If the room is running above 45 degrees C, the pack has no chance and no setting will fix it.
2. Safe for a homeowner — improve the room. Shade the wall, open a vent or air brick, add extraction, and clear anything stacked against or on top of the modules. Pylontech's own danger label says not to cover or wrap the case and not to sit on the battery or put heavy things on it.
3. Safe for a homeowner — cut load during the hottest hours. Because the rated currents only apply for a cell temperature of 10 to 40 degrees C, a hot pack cannot deliver its full rated current anyway, and pushing it just adds more heat.
4. Safe for a homeowner in the north, in winter — if the battery discharges normally but will not accept charge on a cold morning, that is the 0 degree C charge limit working as designed, not a fault. It will take charge again once the room warms. Do not let anyone replace a battery for this.
5. Installer work — relocate the bank if the room genuinely cannot be improved. Modules weigh around 40 kg each and this is not a homeowner job. Never solve heat by moving the battery outdoors or under a shed roof. Pylontech's safety instructions prohibit installing the product in an outdoor environment or outside the stated temperature and humidity range, and water ingress is a far more dangerous fault than heat.
6. Do not point an evaporative cooler or a water cooler at the pack. The humidity specification requires no condensation, and the danger label says to avoid moisture and liquid.
7. Stop and call your distributor if the pack reports a temperature fault in a room that is demonstrably cool. A false high reading points at a sensor or the BMS board. Switch the module off and do not open it.