Battery Back-Up Systems

[Nic]

I have an old battery back-up system for a household computer which uses a 12 Volt battery.

I want to substitute a 12 Volt deep cycle marine battery and use is as a backup for the electric sump in my basement.

I'd like some guidance on selecting the correct battery for the job. Since the sump is on a float switch and doesn't run full-time, I thought with the right battery, I might be able to get many hours of battery back up.

So again; I know that the pump is 9 amps. What else must I take into consideration? If I wanted 24 hours of back up, How do I determine the number of batteries needed?

How would you approach this project?

Thank you in advance.
Nic

 

[CocaCola]

You have to establish an estimated duty cycle of the pump to get a valid backup time...

For quick and dirty, lets assume stormy weather where the pump will be cycling on/off, so lets say it's on 50% of the time...

So @ 9A and 50% of the time you have a drain of about 4.5A an hour... Times 24 hours is 108Ah... But, you have to factor in the fact the world is not perfect and thus a 150Ah battery would probably be closer to a real world 24 hour run...

If the pump is to run 100% of the time you would need a 216Ah (perfect world), and so on and so on...

 

[CDRIVE]

I'd advise you to check the specs on your UPS. They come in vastly varying capacities. I doubt that one made for a single PC is up to the task of driving a 9A pump motor. The start current can be over twice its run current. It's also a highly reactive load.

Chris