Essential for heat dissipation design| Accurately calculate the heat generated by telecommunication batteries: principles, formulas and examples

The Ultimate Guide to Calculating Heat Generation in Telecom Batteries: Principles, Formulas, and Practical Examples

The stable operation of communication systems (such as base stations and data center rooms) relies on backup batteries. However, batteries generate heat during charging and discharging, and accurately calculating this heat generation is a key prerequisite for effective cooling design (such as air conditioner selection and cabinet air duct planning). This article will explain in depth the principles of calculating heat generation for communication batteries (covering both lead-acid and lithium batteries), how to obtain key parameters, and provide specific calculation formulas and examples for different operating conditions, helping you accurately understand battery thermal management requirements.

What is the core source of battery heating?

The heating of communication batteries mainly comes from two parts:

1.Internal resistance loss (dominant factor): 

When current (I) flows through the inherent resistance (r) inside the battery, Joule heat will inevitably be generated. The calculation formula is: I² * r. This is the main source of battery heating.

2.Extra reaction loss (under specific conditions):

Under non-ideal conditions such as overcharging, side reactions will occur inside the battery to consume energy and convert it into heat. For example:

• When a lead-acid battery is overcharged: water electrolysis reaction will occur (producing hydrogen and oxygen), consuming electricity and generating heat.
• When a lithium battery is overcharged: harmful side reactions may also be triggered, resulting in additional heat release and even the risk of thermal runaway.

How to obtain the key parameters for calculating heat generation?

For accurate calculations, you need to understand the following core parameters:

1.Operating current (I):

• During discharge: This is equal to the load current. This can be measured directly with an ammeter or calculated based on the load power (P load) and the battery terminal voltage (U terminal voltage): I = P load / U terminal voltage.
• During charging: This is typically set by the charger (e.g., the current value during constant current charging).
• During float charge: Telecom batteries are often in float charge to maintain full charge. The float charge current is typically very low (e.g., approximately 0.005C to 0.01C for lead-acid batteries, where C is the battery's rated capacity in Ah).

2.Internal resistance (r):

• Definition: The total resistance within the battery that opposes current flow (including resistances of the electrodes, electrolyte, separator, etc.).
• Important characteristic: Internal resistance is not a fixed value! It varies significantly with temperature, state of charge (SOC), and aging (e.g., it increases with decreasing temperature or aging, and is generally lower when fully charged).
• How to obtain:
  • First choice: Check the official technical specifications (Datasheet) provided by the battery manufacturer. (Typical reference: lead-acid single battery ≈ 0.001Ω - 0.01Ω; lithium battery ≈ 0.01Ω - 0.1Ω).
  • Actual measurement: Use a professional battery internal resistance tester for measurement (pay attention to the measurement conditions and equipment accuracy).

3.Time (t): The total heat generated in a specific time period is required, in seconds (s).

Detailed explanation of the formula for calculating heat generation under different operating conditions

1. Normal charge and discharge (no side reactions, only internal resistance losses)

• Thermal power (heat generation per unit time, unit: Watts):
  P = I² * r
• Total heat generation (unit: Joules, 1J = 1W·s):
  Q = P * t = I² * r * t

2. Float charge

• The float charge current (I float) is typically very low, and the internal resistance (r) is low when fully charged.
• The calculation method is exactly the same as for normal charge:
  Q = (I float)² * r * t

3. Overcharge (using a lead-acid battery as an example)

• Heat generation in this state is due to both internal resistance losses and losses from the water electrolysis reaction.
• Total heat generation (Q total):
  Q total = Q internal resistance + Q electrolysis
  • Internal resistance loss part: Q internal resistance = (I total)² * r * t (I total is the overcharge current)
  • Electrolysis reaction loss part: Q electrolysis = I electrolysis * U electrolysis * t
    • I electrolysis: The current component actually used to electrolyze water (usually close to or equal to the overcharge current minus the very small current required to maintain full charge).
    • U electrolysis: The theoretical electrolysis voltage of water ≈ 1.23 V

Practical Calculation Example (12V/100Ah Lead-Acid Battery Pack)

Assume a 12V/100Ah lead-acid battery pack consisting of six 2V cells connected in series. The total internal resistance, r total, is 6 * 0.005Ω = 0.03Ω.

• • Scenario 1: Discharge
    
    • Discharge current (I) = 10A
    • Duration (t) = 1 hour = 3600 seconds
    • Heat power (P) = I² * r = (10)² * 0.03 = 3 W
    • Total heat generation (Q) = P * t = 3 * 3600 = 10,800 J (or 10.8 kJ)
      
  • Scenario 2: Float charge
    • Float charge current (I float) = 0.5A (example value)
    • Duration (t) = 24 hours = 86,400 seconds
    • Total heat generation (Q) = (I float)² * r * t = (0.5)² * 0.03 * 86400 = 0.25 * 0.03 * 86400 = 648 J

Important Notes & Engineering Practice Recommendations

1.Internal resistance (r) is a key variable: Calculations must always use internal resistance values under actual operating conditions (especially current temperature, SOC, and aging). Datasheets provide typical values or values for new batteries; actual values may vary significantly.

2.Lithium batteries have their own unique characteristics: Overcharging lithium batteries not only reduces efficiency, but also releases significant excess heat due to side reactions (such as those preceding thermal runaway in ternary lithium batteries), which can be very dangerous. Calculating overcharge heat generation requires extreme caution, and overcharging must be strictly avoided.

3.Utilize manufacturer data: Many battery manufacturers provide heat generation power curves or data sheets at different currents and temperatures. Directly referring to this data in engineering applications is often simpler and more accurate than theoretical calculations.

4.Clear Application Objective: The core purpose of calculating heat generation is to provide scientific input for the design of cooling systems (such as air conditioning cooling capacity requirements and ventilation requirements) in communications equipment rooms or battery cabinets, ensuring that batteries operate within a safe temperature range and extending their lifespan.

Conclusion

By understanding the principles of battery heating (I²r losses + specific side reactions), accurately determining key parameters (operating current I, actual internal resistance r, and time t), and applying calculation formulas corresponding to operating conditions (discharge/charge/float charge/overcharge), we can relatively accurately estimate the heat generated by telecommunications batteries. This data is essential for assessing equipment room heat loads, designing efficient cooling solutions, and ensuring the safe and reliable operation of backup power supplies for telecommunications equipment. When making critical cooling design decisions, it is crucial to consider the battery manufacturer's specific data and actual operating conditions.