chris-biggins - 4-3-2007 at 11:39
hi all
i was really hoping that someone would be able to help me out. i am building a diving torch but i am stuck on how long my batteries will last and i
wondered if anyone can tell me how to work it out.
my batteries are 2x6vone is 10amp and the other one is 12amp. they will need to be powering a 12 volt bulb. i was thinking about a 50w downlamp
(mr16 type) or a 20w one or even an led one with 20 led's. i am really hoping that someone would be able to help me out.
many thanks for reading
chris biggins
Maya - 7-3-2007 at 03:51
It depends on the amount of electrode material inside the battery, the more electrode material = the longer it will last. assuming its non
rechargable. do you know how much electrode material you have?
For rechargeable, you have the Number of AmpHours = number of Amps x Hours you plan to use. Which depends on how many amps you draw, i.e., 50w vrs 20w
vrs LED.
The LED will ALWAYS last longest followed by 20w then 50w the least. Most LED work <3V so you could go in parallel instead of series saving even
more juice
YT2095 - 7-3-2007 at 04:02
2.88 hours according to my calcs for the 12A with the 50W bulb.
the Voltage is a constant here, that`s a Given, so 12V x 12A = 144 watts total power, then you divide your power drain into that (in this case I used
the 50W bulb), that will give you your time in hours.
Maya - 7-3-2007 at 04:58
yeah, and the LED will prolly give you Hundreds of hours....
Actually the 50w is less than 2.88hrs because the voltage will start to drop and the current is also less than 12A, closer to 10A . Your luminosity
will also not be constant but much dimmer at the halfway point
YT2095 - 7-3-2007 at 05:20
it depends entirely upon the batt actually, zinc carbons will do as you describe, lead acids ones will but closer to the end, and Ni-Cad types are
"sudden Death" and work very well almost to the end and then drop off sharply.
chris-biggins - 16-3-2007 at 08:02
hi all. thanks very much for all your help. i have decided to go with the led one at the moment as the halogen one melted my lense. 
.
many thanks again
chris