Calculating hours of backup correctly

[choob]

Due to lack of local stock I've had to buy some ****ty off brand batteries.

Correct me if I'm wrong but is the following the correct way to calculate how long my battery should last:

Let's say I have 200Ah battery at 12 V, allowing 70% discharge and 80% inverter efficiency with a constant load of 100W

200*12*.7*.8/100 = 13.44 hours of battery?


Is my math correct?

[SunEagle]

Your math may be correct but your batteries will die an early death due to being discharged 70%.

A safer calculation to get as many "cycles" as possible out of the batteries is to never discharge them more than 25% on a daily basis.

That 200Ah battery should safely provide you about 600 watt hours a day (200Ah x 12v x .25 = 600wh) so a 100 watt load will use that up in 6 hours or less depending on the equipment efficiency and losses.

[RickyD]

Hi there,


This question has got me stumped so I was hoping there

Moderator note: RickyD, try it again, your message was truncated, possibly because you copied and pasted it from another application, or used something other than a computer (like an iphone). After posting, your message might not show up right away since you haven't been fully approved for posting yet, that might take a day or two. --Steve

[RickyD]

Thanks so much for letting me know what the problem was. I have never posted before, old school and to be honest I