To calculate IPS size in Bangladesh, sum the running wattage of all simultaneous appliances and divide by 0.8 (power factor) with 25% safety headroom to find the inverter rating in Volt-Amps (VA). Then determine battery Ampere-hours (Ah) based on desired backup runtime, DC voltage, and 70% depth-of-discharge.
Interactive IPS & Battery Sizing Calculator
Engineered by TNS Application Engineering Division
1. Select Your Simultaneous Electrical Appliances
2. Desired Continuous Backup Runtime
Engineering Calculation Output
Kenson LX-0812 (800VA / 12V)
Most popular home IPS for 3 fans, 4 lights & 1 LED TV.
Step 1: Audit Your Connected Load in Watts
Before choosing an IPS (Instant Power Supply), list all electrical loads that must operate simultaneously during a utility power outage. In Bangladesh, typical household power ratings are standard across major brands:
| Electrical Appliance | Standard Running Power | Starting Surge Factor | Waveform Sensitivity |
|---|---|---|---|
| Ceiling Fan (Standard 56") | 75W – 80W | 1.5x (~120W) | High (Hums on Square Wave) |
| BLDC Energy-Saving Ceiling Fan | 28W – 35W | 1.1x | Medium (Needs Pure Sine Wave) |
| LED Tube Light (4 Feet) | 18W – 22W | 1.0x (No Surge) | Low |
| LED Bulb (Standard E27/B22) | 9W – 15W | 1.0x (No Surge) | Low |
| Smart LED TV (43" to 55") | 60W – 100W | 1.2x | Medium |
| Wi-Fi Router + Fiber ONU | 15W – 20W | 1.0x | Low |
| Desktop Workstation + Monitor | 200W – 300W | 1.3x | Critical (Needs Fast Switchover) |
| Refrigerator (Compressor) | 150W – 250W | 3.5x to 5.0x (~1000W) | Critical (Requires 24V Pure Sine) |
Step 2: Convert Total Watts to Inverter VA (Power Factor Formula)
Inverters are rated in Volt-Amperes (VA) (apparent power), whereas household devices consume Watts (W) (real power). In alternating current (AC) circuits, the relationship between Watts and VA is defined by the Power Factor (PF):
Why do we multiply by 1.25? Adding a 25% engineering safety margin prevents the inverter from operating at 100% thermal stress, accommodates inductive starting surges (such as fan capacitors), and leaves room to plug in a laptop charger without tripping the overload alarm.
- 3 Ceiling Fans: 3 × 75W = 225 Watts
- 4 LED Lights: 4 × 20W = 80 Watts
- 1 Smart TV: 1 × 80W = 80 Watts
- 1 Wi-Fi Router + ONU: 1 × 15W = 15 Watts
- Total Real Load: 400 Watts
- Inverter VA = (400W / 0.8) × 1.25 = 625 VA
- Engineered Recommendation: Select the Kenson LX-0812 (800VA / 12V Pure Sine Wave) for generous headroom and silent operation.
Step 3: Calculate Required Battery Capacity in Ampere-Hours (Ah)
The inverter determines how much electrical load you can power at one time. The battery bank determines how many hours that load will run during a blackout.
Here is how each parameter affects your runtime in Bangladesh:
- System DC Voltage:Typically 12V for single-battery inverters, 24V for dual-battery inverters, and 48V for 5kVA+ systems.
- Depth of Discharge (DoD = 0.70):Lead-Acid, Tubular, and AGM batteries should never be discharged below 70% to avoid damaging lead plates and premature battery death.
- Inverter Efficiency (η = 0.85):High-quality copper transformer inverters operate at approximately 85% to 88% DC-to-AC conversion efficiency.
- Effective Divisor:For a 12V system: 12 × 0.70 × 0.85 = 7.14. Multiply load by hours, then divide by 7.14!
Required Ah = (400W × 3 Hours) / (12V × 0.70 × 0.85) = 1200 / 7.14 = 168 Ah.
Since standard battery sizes in Bangladesh are 130Ah, 150Ah, and 200Ah, you should choose a 200Ah deep-cycle battery (such as a Kenson 12V 200Ah VRLA-SMF or tubular battery) to guarantee 3 to 3.5 hours of uninterrupted backup without deep-discharging.
Step 4: Waveform Selection — Pure Sine Wave vs. Modified / Square Wave
Many consumers in Bangladesh are tempted by low-cost local square-wave or modified sine wave IPS units. However, electrical engineers strongly discourage square-wave inverters for residential and office environments:
- Causes ceiling fans to vibrate and emit an audible humming drone.
- Overheats fan motor windings, reducing fan lifespan by up to 50%.
- High Total Harmonic Distortion (THD > 25%) damages SMPS power supplies in modern Smart TVs and LED drivers.
- Cannot safely start inductive compressor motors.
- Produces pure 50Hz AC electricity identical to commercial grid power.
- Completely silent fan operation with zero humming noise.
- Ultra-low harmonic distortion (THD < 3%) protects sensitive electronics.
- Runs computers, monitors, medical equipment, and appliances with high efficiency.
Step 5: Choosing 12V vs 24V vs 48V Architecture
A common mistake is attempting to run a 1500VA or 2000VA load on a single 12V battery. Electrical physics dictates that Current (I) = Power (P) / Voltage (V). High current requires thick copper cables and generates dangerous heat:
| System Voltage | Optimal Inverter Rating | Battery Bank Structure | Typical Application |
|---|---|---|---|
| 12V DC | 600VA to 1000VA | 1x 12V Battery (130Ah–200Ah) | Apartment backup (2 to 4 fans, lights, TV, Wi-Fi) |
| 24V DC | 1500VA to 2500VA | 2x 12V Batteries in Series | Large duplexes, office floors, refrigerators & PCs |
| 48V DC | 3kVA to 10kVA Industrial | 4x 12V Batteries in Series (or 51.2V BESS) | Commercial buildings, schools, clinics, factories |
Recommended Pure Sine Wave IPS Models in Bangladesh
Kenson LX-0812 (800VA / 12V)
Best-selling home pure sine wave IPS for 3 fans, 4 lights & 1 TV. Microprocessor controlled with battery life optimization.
Kenson LX-1012 (1000VA / 12V)
Handles 4-5 fans, 6 lights, Wi-Fi, TV and computer desktop setup. Includes bypass switch and digital LCD screen.
Kenson LX-1524 (1500VA / 24V)
High-efficiency 24V DC bus designed for larger apartments, multi-room offices, and high-wattage electronic equipment.
Frequently Asked Questions (IPS Calculation & Maintenance)
Expert answers from the electrical engineering team at TNS Engineering Ltd.
Can an IPS run a refrigerator or deep freezer in Bangladesh?
Yes, but it requires a high-capacity Pure Sine Wave IPS (minimum 1500VA to 2000VA, 24V DC bus) like the Kenson LX-2024. Refrigerators have compressor motors that draw 3x to 5x their rated wattage during startup surge (up to 800W–1200W momentarily). Attempting to run a compressor on a smaller modified sine wave IPS will trip the inverter or damage the compressor motor.
What is the exact difference between IPS and UPS?
Both invert DC battery power to AC mains, but their transfer time and waveform differ. An Offline/Line-Interactive UPS transfers within 4 to 10 milliseconds, preventing computers and servers from restarting. A traditional Home IPS has a slightly longer transfer time (15–25ms), which is completely fine for fans, lights, and TVs, but might cause desktop computers to reboot unless equipped with modern fast-transfer relays (like Kenson LX Pure Sine Wave models).
Why do ceiling fans make a humming noise on cheap IPS inverters?
Cheap square-wave or modified sine wave inverters produce stepped electrical waveforms with severe harmonic distortion (THD > 20%). The inductive copper coils in ceiling fan motors vibrate when exposed to these harsh harmonics, creating an annoying audible hum and causing the fan motor to overheat. A true Pure Sine Wave IPS produces a smooth sine wave identical to utility power, eliminating hum completely.
How many years does an IPS battery last in Bangladesh?
A properly maintained deep-cycle battery typically lasts 3 to 5 years in Bangladesh. Lifespan depends on Depth of Discharge (DoD) and ambient room temperature. Sealed Maintenance-Free (SMF / VRLA AGM) batteries like Kenson require zero water refilling and avoid acid fumes, whereas flooded tubular batteries require regular distilled water top-ups.
Why is a 24V IPS system better than a 12V IPS for loads above 800 Watts?
Under basic electrical physics (Power = Voltage × Current), delivering 1000W from a 12V battery draws ~98 Amperes through the cables, creating severe resistive heat loss (I²R loss). Running the same 1000W load on a 24V system cuts the battery current in half (~49A), keeping cables cooler, reducing voltage drop, and delivering higher operational efficiency.
Need Help with Commercial Load Testing or Battery Sizing?
Contact our engineering headquarters in Dhaka for Single Line Diagrams (SLD), on-site harmonic audits, and customized industrial power systems.