# Formula for calculating run time of apc ?

## Ask a question - edaboard.com

elektroda.net NewsGroups Forum Index - Electronic for beginners - Formula for calculating run time of apc ?

Andy
Guest

Mon Jul 30, 2018 10:45 pm

I am looking for a formula for calculating the run time of my APC battery system.

I did a search but what I found required a particular model of apc.

Total watts of computer and monitor is about 120 watts.

Battery in my apc is 12V 18 Ah

Thanks,
Andy

Ralph Mowery
Guest

Tue Jul 31, 2018 12:45 am

andrewkennedy775_at_gmail.com says...
Quote:

I am looking for a formula for calculating the run time of my APC battery system.

I did a search but what I found required a particular model of apc.

Total watts of computer and monitor is about 120 watts.

Battery in my apc is 12V 18 Ah

Thanks,
Andy

Simple except for one missing piece of info. How efficent is the system
?

The Ah (amps the battery can put out for one hour). As Amps and voltage
equals watts, your battery is rated for 12 times 18 or 216 watts for one
hour. So you get 216 devided by 120 or 1.8 hours. Then multiply by the
efficency (loss of the system) that is unknown, but 50 to 80 percent
would be inthe ball park. So at 50 % you get half of the 1.8 hours or
..9 hour.

All that is provided the battery can put out enough current to last that
long. Often the more current the battery is required to put out, the
less time it will last.

Andy
Guest

Tue Jul 31, 2018 3:45 am

On Monday, July 30, 2018 at 6:41:01 PM UTC-5, Ralph Mowery wrote:
Quote:
andrewkennedy775_at_gmail.com says...

I am looking for a formula for calculating the run time of my APC battery system.

I did a search but what I found required a particular model of apc.

Total watts of computer and monitor is about 120 watts.

Battery in my apc is 12V 18 Ah

Thanks,
Andy

Simple except for one missing piece of info. How efficent is the system
?

The Ah (amps the battery can put out for one hour). As Amps and voltage
equals watts, your battery is rated for 12 times 18 or 216 watts for one
hour. So you get 216 devided by 120 or 1.8 hours. Then multiply by the
efficency (loss of the system) that is unknown, but 50 to 80 percent
would be inthe ball park. So at 50 % you get half of the 1.8 hours or
.9 hour.

All that is provided the battery can put out enough current to last that
long. Often the more current the battery is required to put out, the
less time it will last.

Thanks.

It ran for an hour just on the battery backup.

It said I had around 15 mins left when I went back to A.C. power.

Andy

Phil Hobbs
Guest

Tue Jul 31, 2018 12:45 pm

On 07/30/2018 07:40 PM, Ralph Mowery wrote:
Quote:
andrewkennedy775_at_gmail.com says...

I am looking for a formula for calculating the run time of my APC battery system.

I did a search but what I found required a particular model of apc.

Total watts of computer and monitor is about 120 watts.

Battery in my apc is 12V 18 Ah

Thanks,
Andy

Simple except for one missing piece of info. How efficent is the system
?

The Ah (amps the battery can put out for one hour). As Amps and voltage
equals watts, your battery is rated for 12 times 18 or 216 watts for one
hour. So you get 216 devided by 120 or 1.8 hours. Then multiply by the
efficency (loss of the system) that is unknown, but 50 to 80 percent
would be inthe ball park. So at 50 % you get half of the 1.8 hours or
..9 hour.

All that is provided the battery can put out enough current to last that
long. Often the more current the battery is required to put out, the
less time it will last.

UPS batteries have to provide the magnetizing current for the big iron
transformer, so battery life is disappointing at light loads. Nowhere
near as good as a DC-DC converter.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics