Re: [Paddlewise] battery life

>               AA Alk.   2850 MAH = Milliampere Hours. 
>               C Alk.   7800 MAH 
>               D Alk.   15,000 MAH 

>To translate what this means, if you put a AA Alk. battery in a
>circuit that uses 40 milliamperes to operate, the battery will have
>a useful life of 71.25 hours. At the same rate (40 MA) a D size
>would run for 375 hours.

OK,
lets see if I got the theoretical background right.  My rule 500 bilge 
pump draws according to the manufacturer's data sheat 1.9 A.  I 
run it on alkaline AA batteries (8 in line to get up to the 12 V).  
Theory: Based on the math the pump should work for ~1.5 hours 
on those 8 batteries.  2850 mAh/1900mA = 1.5h

Practice: In fact I burned 1 battery set during the last season 
during my rescue practice being to lazy to use the hand pump -I 
carry one as back up.  At the end of the season the pump 
performance went a bit down, i.e. took longer to get the water out 
due to the lower voltage, but still sufficient fast. I never stopped the 
life time of the batteries, but I was already wondering for how longer 
 they will last.  Initially I gave them a couple of minutes life and was 
surprised how long they finally lasted.  
Maybe I should mentioned that I use 2 packs of batteries, one 
while doing rescue drills, and another fresh one for real life paddling.

Conclusion:  I will keep my battery solution, in the beginning I was 
looking for other power sources like motocycle batteries and 
rechargable stuff. But since battery life, the costs of AA batteries, 
space and weight are absolutely sufficient and the whole assembly 
fits into my cockpit behind the seat I decided to stick with that 
solution.  Switching to C or D cells (still a good space and weight 
option) are for another reason 2nd choice.. I carry a bunch (~10) of 
spare AA are anyway in my EVAC-bag, since GPS and VHF use 
the same size -advantages if all electronics uses the same battery 
size are obvious. 
A similar size/capacity Atwood pump draws 1.4 A and should 
therefore last for 2 hours on a battery pack.  I think I will get one of 
those for my new boat what is currently under construction (S&G, 
reduced the beam from 25 inch to 22 inch, and reduced the profile 
above the waterline, 2 more weekends and it should be done and I 
will see how tippy it is).

Cheers

Ulli

P.S. The switch, batteries and wiring are in a Nalgene bottle.  
Drilled a hole in the lid to mount the switch and another hole to 
guide the wire to the pump.  Switch outside covered and sealed 
with a rubber cap, waterproofed with Sikaflex and Silicone.  
Connection pump to power unit with a waterproof trailer connector.  
Price tag for the whole construction ~ 50 CAD.   So far after one 
summer no problems with waterproofness and corrosion. 


(All spelling errors are intentional and are there to show new 
and improved ways of spelling old words.)

Ulli Hoeger
Dept. Physiology and Biophysics
Dalhousie University
Halifax, B3H4H7, Nova Scotia
Canada

Phone I : 902-494-2673
Fax: 902-494-1685
Phone II :902-488-6796
http://is.dal.ca/~uhoeger
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