Root Cause Analysis of Difficult Startup of Electric Forklifts in Winter

The core cause of difficult startup of electric forklifts in winter is the superposition of triple negative impacts of low-temperature environments on battery performance, hydraulic and transmission systems, and electrical circuits. The deterioration of low-temperature characteristics of various components directly leads to insufficient power output, excessive mechanical resistance, and abnormal control signals during startup, which can be specifically divided into the following three categories:

I. Low-Temperature Attenuation of Battery Performance (Core Root Cause)

The battery is the power source of an electric forklift. Low temperatures directly weaken its energy output capacity at the electrochemical level, making it the primary cause of difficult startup.

Low-Temperature Deterioration Mechanism of Lead-Acid Batteries

1. At low temperatures, the viscosity of the electrolyte increases, the ion migration rate decreases, and the polarization phenomenon inside the battery intensifies, leading to a significant attenuation of discharge capacity: for every 10℃ decrease in ambient temperature, the discharge capacity of lead-acid batteries decreases by approximately 10%–15%. When the temperature drops below -10℃, the discharge capacity may be less than 50% of the rated capacity, failing to provide the instantaneous large current required for startup.
2. Low temperatures are prone to causing battery sulfation: if the forklift is parked in an undercharged state, hard lead sulfate crystals will form on the plates, blocking the plate pores and further reducing the charge-discharge performance of the battery. During startup, the voltage will drop below the threshold instantaneously, unable to drive the motor to operate.
3. Risk of electrolyte level fluctuation: the volume of electrolyte contracts at low temperatures. If the original level is at the critical value, the level may drop below the plates, resulting in oxidation and corrosion of the plates, increased internal resistance, and intensified energy loss during startup.

Low-Temperature Limiting Factors of Lithium Batteries

1. The rate of ion intercalation/deintercalation reactions of lithium batteries slows down as the temperature decreases, and the low-temperature discharge rate is limited: at -20℃, the maximum discharge rate of lithium iron phosphate batteries may drop from 3C at room temperature to below 1C, failing to meet the instantaneous large current demand of the motor during startup.
2. Low-temperature protection mechanism of the Battery Management System (BMS): to prevent battery over-discharge or internal lithium plating, the BMS will actively limit the discharge current at low temperatures. When the startup current exceeds the limit value, the BMS will cut off the output circuit, resulting in startup failure.

II. Increased Low-Temperature Resistance of Hydraulic and Transmission Systems

Low temperatures in winter will cause an increase in oil viscosity and shrinkage jamming of mechanical components, increasing the load resistance during startup and exceeding the power output threshold of the battery.

Excessively High Pump Load Caused by Viscous Hydraulic Oil

The viscosity of hydraulic oil is negatively correlated with temperature. When the ambient temperature is below -5℃, the viscosity of ordinary hydraulic oil will increase by 2–3 times. The hydraulic pump needs to overcome greater oil resistance during startup, leading to a sudden increase in motor startup load. The battery output current exceeds the rated value, triggering overcurrent protection.

Low-Temperature Jamming of Transmission and Braking Components

1. The increased viscosity of transmission oil leads to greater gear meshing resistance, the hydraulic motor of the hydrostatic transmission system responds slowly, and the power transmission efficiency decreases during startup.
2. Components such as brake shoes and calipers shrink due to low temperatures, resulting in reduced fit clearance and even seizing. The wheel rotation resistance increases significantly, making it difficult for the battery to drive the entire vehicle to start.

III. Decreased Low-Temperature Reliability of Electrical Circuits

Low temperatures will accelerate the aging of electrical components and increase contact resistance, leading to abnormal control signal transmission and intensified energy loss in power circuits.

Increased Contact Resistance of Wires and Connectors

At low temperatures, the wire insulation layer shrinks and hardens, and the metal components of the wiring terminals expand with heat and contract with cold, resulting in loosening or thickening of the oxide layer. The contact resistance can increase from ≤0.01Ω at room temperature to more than 0.1Ω. The large current passing through during startup will generate a voltage drop, and the actual input voltage of the motor is lower than the rated value, making it unable to start normally.

Deterioration of Low-Temperature Performance of Electrical Components

1. The pull-in voltage of the coils of startup relays and contactors increases as the temperature decreases. When the battery voltage attenuates due to low temperatures, the coils cannot generate sufficient electromagnetic attraction, the contacts cannot close reliably, and the power circuit is disconnected.
2. Electronic components such as controllers and sensors have a limited operating temperature range. At low temperatures, the switching speed of semiconductor devices slows down, and sensor signals drift, causing the controller to fail to accurately identify the startup command or mistakenly trigger overload and undervoltage protection.

Failures Caused by Decreased Insulation Performance

Low temperatures will make the wire insulation layer brittle and cracked. Moisture intrusion is likely to cause short circuits or leakage. The insulation resistance of core components such as motors and controllers decreases, triggering the operation of leakage protection devices, cutting off the power supply, and showing no response during startup.