Numerous trouble points of the heated clothes business, unstable temperatures, short run times contrary to expectations, or even early parts breakdown, all have a single origin: the inability to integrate well the heating system and the battery pack. In too many cases, batteries are selected only by mAh capacity or voltage rating, and the higher the better. However this is a trap that often works against him. A larger capacity battery coupled to a mismatched heating load may result in a voltage drop, poor power output or controller outliers.
The battery selection to use with heated apparel should start with the behavior of heating systems and not with specification of battery. In warm clothes, performance is determined by the compatibility of the heating mechanism and the battery pack, and not the performance of any of these elements.
Why Heating Performance Is a System Interaction
It is not a single component that defines the heating of performance of apparel such as jackets, gloves, or insoles. It’s a consequence of the dynamical electromagnetic interactions between the heating components, the controller (with its PWM or variable regulation control logic) and the power source, the battery pack.
Heating elements, usually carbon fiber wires, films or conductive fabrics, introduce a load of resistance forcing current flow depending on applied voltage (according to Ohm Law: Power = V²/R). This energy is adjusted by duty cycles or temperature feedback, to form variable patterns of demand: spikes at the start as the controller must set all current control elements high and then hold them steady until the machine enters the heating mode, spikes at the start of each zone or level change as the controller must ramp all current control elements high, and sustain them until the machine has reached a steady temperature.
Batteries are required to react to these practical variations with a minimum amount of voltage drop, overheating, or automatic shutdown. One aspect that makes isolated optimization, though, an optimization effort that does not take load characteristics into account, i.e. one that aims to maximize battery capacity regardless of load characteristics, is that the system as a whole contains amplification points that a single spec does not show.
To further discuss integrated solutions that can be used to mitigate these challenges at the ground level, explore our guide to system-level battery solution architecture.
Understanding Heating Element Power Requirements
Any successful match begins with the complete specification of the power needs of the heating element during working conditions.
Apparel heating elements are resistive in nature and the resistance value is normally optimized to a voltage platform (usually 5V, 7.4 V, or 12 V). The power scale is proportional to the square of the voltage implying that a small deviation in voltage may lead to a substantial change in heat output. For instance, 7.4V tuned system can misuse or exceed the current flow in response to a variable source or when it is incompatible.
Loads aren’t constant. Heat is supplied in many modern designs is multi-zone or PWM-controlled, and therefore has instigated pulse current demand or variable current demand, at least loading up to several amps in initial warm-up, then decreasing. Constant high-resistance loads in the same way might seem mild, yet when it comes to fast cycling the battery is not stressed like in slow draw.
The patterns have a direct impact on the behavior of battery discharge such as increase of internal resistance and losses of efficiencies. The knowledge of this at the beginning makes future surprises averted.
To learn more about the considerations of voltage that affect these requirements, see our analysis of selecting the appropriate voltage platform.
Battery Characteristics That Affect Heating Compatibility
Lithium-ion battery packs do not all perform similarly when subjected to the requirements of warm clothing.
It has important features such as:
- Voltage stability under load High quality packs do not significantly change nominal voltage even when peak current draws take place. Weak BMS designs or poor cells induce sag which minimizes heat production and results in controller damage.
- Discharge rate capability (C-rate) – Heated elements can have burst requirements of 1C-3C. Low-rate cell packs are unable to compete and it overheats or powers off.
- Capacity vs usable run time – Nominal mAh is without energy dissipated by cold temperatures and recalls, high discharge and voltage cutoffs. Real winter (°C -10 or less) capacity may be reduced 20-40 per cent. (room temperature).
These elements either result in regular warmth features or add the variability to the battery.
To better understand real-world implications, review our discussion on battery behavior under heating loads.
Common Mismatch Scenarios and Their Consequences
We would discuss battery behaviour under heating loads better in order to gain a better understanding of its implications in the real world.
- Existing imbalance with overheating- A battery designed with high discharge may be connected to an undersized controller or heating part and assist in drawing excessive current, resulting in small hot locations or heat runaway in components.
- Voltage sag leading to short operating times — An internal resistance increases with load, voltage falls below the minimum threshold set by the controller, and power is cut off before the controller draws large currents, yet there still remains a significant amount of capacity.
- Controller instability Controller circuits that are sensitive to voltage ripple (e.g. PWM control or feedback) can vary (wiggle and wamble) or they may not accurately maintain temperature.
These problems are expressed in the form of a customer complaint: clothes that die too soon, do not heat up evenly, or cannot be trusted in a very cold environment.
To take positive actions in the event of these issues,, see our guide to diagnosing battery-related heating failures.
Practical Guidelines for Matching Heating Systems and Batteries
Concerning engineering, an approach based on system-first logic instead of inflexible checklist leads to successful matching.
Start by plotting the heating load profile: record current through temperature settings, duty cycles, and conditions. Based on this information, establish minimum probability of tolerance of voltage, minimum required C-rate, and effective capacity objectives.
Test applicants in realistic conditions – cold chamber tests, multi cycle thrown out follower, and long life tests – to reveal vulnerabilities that datasheets do not reveal.
Take into consideration the variability of production: cell tolerances, connector resistance and assembly deviation may change performance. Add margin in design and add strong BMS capabilities such as NTC thermal monitoring and low volt cutoff based on load.
This is done to ensure minimum field failures and scalable and reliable production.
Conclusion — System Matching Determines Real-World Performance
Ultimately, it would continue to be necessary to match the heating system and the appropriate battery pack in order to have stable performance of the heated clothing. The true impact of the real world is not necessarily isolated component strength, but system compatibility; when it comes to reliable warmth, long run time, long service life and user contentment.
By reevaluating the system level knowledge in the idea of considerably spec-sheet competition, brands and engineers may eliminate most of the typical pitfalls at an earlier stage before they are introduced into the market. Thoughtful integration will always be better at prevention than cure.