I am trying to make a UPS(Uninterruptible Power Supply) with Arduino to power few WISP network equipment, one router, one switch, wifi router and two ubiquity antenna. For this the parts I need are Arduino which will used to detect ac main voltage using a voltage sensor(ZMPT101B), reuse my inverter for car which has 100W 12VDC to 220VAC, 50Hz rating and I need DC battery of 12V for the inverter. But what is the size of the battery capacity I need to buy? This led me to learn how to calculate battery capacity for diy UPS.
To choose the right battery for the Arduino-controlled car inverter-based UPS, following are consideration and calculation:
đ 1. Load Power Requirement
From your earlier message, your devices include:
-
MikroTik router: ~5–10W
-
Two Ubiquiti antennas: ~8–10W each
-
Network switch: ~5–15W
Total Power Estimate:
đ ~30W to 45W (Assume 50W for safety)
⏱️ 2. Desired Backup Time
Decide how long you want the UPS to run during a power cut:
| Backup Time | Target (Hours) |
|---|---|
| Short | 1 hour |
| Medium | 2–4 hours |
| Long | 6–8+ hours |
⚡ 3. Battery Capacity Calculation
✅ Formula:
Assume:
-
Battery Voltage = 12V
-
Inverter efficiency = 0.85
đ Example: For 4 hours backup, 50W load:
So you need at least a 20Ah, 12V battery.
đĒĢ 4. Recommended Battery Sizes
| Backup Time | Suggested Battery |
|---|---|
| 1 hour | 7Ah 12V battery |
| 2–3 hours | 12Ah–18Ah 12V battery |
| 4–6 hours | 20Ah–30Ah 12V battery |
| 6+ hours | 35Ah–50Ah or two 12V batteries in parallel |
So in this way one can estimate the battery capacity required for UPS or inverters. I wrote months back how one can build an inverter using Arduino and MOSFETS or built diy 555 Timer based inverter I have also written a note on how to make H-bridge using P-channel and N-channel MOSFETs.Maybe later on I will built that inverter and use that instead of the car inverter that I am using for this work.