I'm trying to wrap my head around a UPS for my server that currently uses 150W and might go up to 200W in the future. I want it to keep my server running for at least one hour, ideally two. So, I figured I need something around 200Wh to 400Wh total capacity. However, I've seen UPS systems advertised as 1200W that only use two 12V 9Ah batteries. When I calculate it, 12V * 9Ah * 2 gives me 216Wh, which means it should last just over an hour, not 6 hours as some specs suggest. Am I missing something here, or is this just some marketing hype? It seems like I need a 1200W UPS that can only deliver 216Wh, therefore making it suitable for less than two hours of usage. Can anyone help clarify this?
1 Answer
The 1200W rating is the peak power you can draw from the UPS, while the 216Wh is the actual battery capacity. So, if your server pulls 200W, the batteries would last just a bit over an hour. If you tried to max it out at 1200W, you'd get around 12 minutes of power. It’s important to understand that the wattage rating is about how much power you can use at once, while the watt-hour is about how long you can use it before the battery runs out.
Got it, thanks! So I was just mixing them up in my head.