# Battery life

Discussion in 'General Electronics Chat' started by brendyboy, Jan 4, 2006.

1. ### brendyboy Thread Starter Member

Dec 21, 2005
27
0
Hi there

Can someone tell me (and explain how to calculate).....

How quickly a 50watt appliance will drain a 12volt battery (4x1.5 AA batteries)
assuming its constantly draining supply.

Do I simply devide 50 by 12 to get the current and then compare it to the amp hours stated on the battery???

Thanks
Bren

2. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,317
1,110

You will need to know the AH rating of the battery.

3. ### Iodem_Asakura Senior Member

Sep 14, 2004
140
0
Time = AmpHr / (Power / Voltage)

PD.: If you have a pack of 4 AAA Batteries of 1.5V, you only get 6 Volts not 12.

4. ### brendyboy Thread Starter Member

Dec 21, 2005
27
0
My mistake, i meant 8

so if the batteries are rated at 1500mAh each... am I right in saying that you get 12amp hours (1500x8) ??

therefore the sum is 12/ (50/12) = 12/4 = 3 hours?

5. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,317
1,110
Batteries connected in series will increase the total voltage, but the AH rating remains whatever the published value is. This assumes you use the same rating for each battery. Don't mix and match.

Batteries connected in parallel will have a voltage consistent with the rated voltage, but the capacity (Ampere-hours) will add. Again, don't mix and match.

Your eight batteries at 1500mAH will supply 12 V @ 1500 mAH, typically for 20 hours. The battery specifications are probably at the 20 hour rate. Aircraft battery specs are typically at the hourly rate ... it's best to review the specifications for your situation.