Understanding battery power
From power tools to golf carts, there are a host of devices that rely on rechargeable batteries. But, how do you work out the best battery size for its application?
Often when we need to buy a battery or charger, we opt for a cheaper price without looking at the finer details. This mostly happens because of a lack of understanding. Find out more about what should affect your choice of battery.
Factors influencing battery selection
• Working conditions
Battery lifespan is susceptible to extremes in temperature. Ensure that you can maintain the ambient temperature indicated by the manufacturer – for this, battery covers are often recommended. Proper ventilation is essential as some batteries give off toxic fumes.
This is the power required by the motor or UPS in watts. Most motors indicate the input load and output load. If it is given in amps, remember the power in kilowatts is equal to the current in amps multiplied by the voltage in volts (P = V x I). The collective current (amps) of the batteries in series must exceed the input current required to the load (motor). The larger the car motor, the larger the battery required for the starter motor.
If your UPS supplier indicates DC bus, then that is the number of batteries required in series to achieve the inverter’s operating voltage. The charged voltage should always be slightly higher than the battery marked voltage. Compare the no-load voltage to the on-load voltage. Check the charger’s output voltage. A 12V charger should give an output voltage of approximately 13V.
• Run time
This is the reason golfers are often stranded around the 16th green. The longer the run time, the larger the battery capacity will have to be.
• Types of batteries
Lead acid: The most widely used battery. It is economical and reliable.
Lead crystal: A replacement to lead acid batteries, these have high internal resistance, which limits their peak discharge demands. There is no memory effect and they charge very quickly. A stable, environmentally-friendly battery.
AGM technology: Absorbent glass mat technology. Better cycle life and withstands high vibrations, delivering 30% more power. Ideal for cars that have a high number of stop-starts.
Ultra-battery: Ideal for electric vehicles or hybrid electric vehicles that require high peak power demands and brake recharging periods.
Nickel cadmium: Stands up to large amounts of recharges, delivering relatively constant power during discharge. It is susceptible to the memory effect caused by crystal formation. This can be avoided by completely discharging the battery before recharging. Low internal resistance allows for high charging and discharging rates. Once the battery of choice for all portable tools, it has now lost ground to the newer nickel-metal hydride batteries.
Nickel-metal hydride: This has 30-40% higher capacity over nickel cadmium. It is not affected as much by memory effect. It is less durable but delivers up to 40% more energy density compared to nickel cadmium batteries. It takes longer to charge, but is a more environmentally-friendly battery. This battery is used extensively in the satellite industry.
Lithium-ion: A fragile battery that requires a protection circuit to prevent total discharge. Otherwise it is a low maintenance battery and retains its charge for long periods. Deterioration occurs rapidly after exposure to temperature extremes. It has a limited service life, is expensive and sensitive.