Power-Tool Battery Pack AC Self-Heating for Cold Charging
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Solution Overview
Problem
Charging a cold battery pack for power tools is slow or impossible, and external heating methods can create temperature gradients that affect performance, requiring an efficient and controlled internal heating solution.
Innovation Solution
An AC heating system is applied internally to the battery pack, controlled by a control circuit that determines the heating current based on battery characteristics, using an AC resistance measurement and identification to optimize heating rate and temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If external heating methods are used to heat a cold battery pack, then the battery temperature increases enabling charging, but temperature gradients are created that affect performance
Solution Approach 1:
The battery pack uses its own internal resistance to generate heat through applied current, heating itself from within rather than relying on external heating sources. This self-heating mechanism ensures uniform temperature distribution throughout the battery cells while raising the temperature to enable charging operation.
2Productivity
If a cold battery pack is charged directly, then charging can proceed, but the charging rate is slow and charging may be impossible at freezing temperatures
Solution Approach 1:
The system applies heating current to the battery pack before charging to raise its temperature to an acceptable range. This preliminary heating action enables subsequent fast charging by ensuring the battery is warm enough to accept high charging rates, thus improving overall charging productivity.
3Productivity
If heating current is applied to the battery pack, then the battery temperature increases to enable fast charging, but overheating may damage the battery
Solution Approach 1:
The control circuit continuously monitors the battery pack temperature during heating and adjusts the heating current accordingly. When the temperature reaches the target range or exceeds safety thresholds, the control circuit reduces or stops the heating current, preventing overheating damage while enabling fast charging when conditions are appropriate.
4Loss of energy
If AC heating is used instead of external heating, then heating efficiency improves and temperature gradients are reduced, but additional control circuitry is required
Solution Approach 1:
The heating control functionality is integrated into the existing charging circuitry of the battery pack. The same control circuit that manages charging also manages heating operations, combining multiple functions into a single system. This reduces overall device complexity despite adding heating capability, as no separate dedicated heating control system is required.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The AC heating system efficiently reduces charging time for cold battery packs without damaging them, maintaining optimal temperature for charging by controlling the heating rate based on battery characteristics.
Implementation Method 1
The heating may be carried out using an alternating current (AC) coupled to the positive and negative terminals of the battery pack
Implementation Method 2
measuring an AC internal resistance of the battery pack using the heating device
Data Source
AI summary
Heating a battery pack for a power tool may be required to accelerate a charging time, especially in cold environments. Not all battery packs of a set of battery packs will heat at the same rate because of differences due to physical (e.g., mass) and electrical (e.g., AC resistance) differences. The disclosed approach includes determining an amplitude of an AC heating current based on characteristics of the battery pack attached to a charger so that all the battery packs in the set of battery packs may be heated at roughly the same rate regardless of their individual characteristics. The disclosure describes how this approach may be implemented in a variety of different charging scenarios.