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Need urgent calculation!!

Need urgent calculation!!

Need urgent calculation!!

(OP)
Hi there,
My manager requires a 5 watt device connected to a 12 V battery until it dies out.  I would like to know how much the 5 watt device can run on the 12 v battery?
Alternatively will using NiCAD hi performance 7200 amp battery for radio control cars make substantial endurance better ?
Thanks.

RE: Need urgent calculation!!

Of course, it's not quite that simple because cells have different capacities depending on the discharge rate. At a high discharge rate the cell will appear to have a lower capacity than at a low rate.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Need urgent calculation!!

5W at 12 V [10 series battery of 1.2 V each one, I think] I=5/12*1000=417 mA as tarantado101 said.
If your old battery was a usual primary 1200 mAh battery for 10 h discharge for 2 h discharge the capacity will decrease to 80% as ScottyUK said. So 1200*.8=960 mAh will be the new capacity of the old battery.
Roughly the full charged battery of 1200 mAh will die in 2.3 h.
Now, the new battery of 7200 mAh capacity will die approx. in 7200/417=17 h -since the full capacity will remain the same for more than 10 h discharge time...
 

RE: Need urgent calculation!!

Actually just knowing the voltage of the battery is not enough, you need the Amp-hour rating (A/h or Ah). Without that you know nothing about the capacity. You also must know the minimum voltage at which your device will continue to function because as you approach the end of the battery capacity, voltage will begin to drop and if your device's tolerance is narrow, it may affect the overall run time.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
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RE: Need urgent calculation!!

wow.. you guys must be feeling generous today.. Normally a thread like this would have started with "Is this for school?..goodbye"

RE: Need urgent calculation!!

I dunno... Identified as an Automotive Engineer, 12VDC source. I was thinking he's working on some small accessory device that will connect to an auto power system and he wants to know how long it will last at a 5W drain. Seemed reasonable to me.  

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
  
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies  

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