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Author Topic: 12v SLA battery .....how many AH do I really need  (Read 1397 times)

sigfortunata

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12v SLA battery .....how many AH do I really need
« on: July 06, 2016, 12:49:48 PM »

I have a TID tug, 36" powered by a 12v 800 motor.  Quite powerful and quite quick ...a little too quick for scale.


Anyhow I currently power it with a 12v 10AH SLA battery which weighs a ton and makes the hull sit really low to the point that crossing a wake or turning the scuttles let water onto the deck.


Now I didn't build this boat and it had some ballast in it but I have had to remove it for obvious reasons but it seem to me my battery is the real ballast problem!! 


So fit a smaller battery you say but there is the rub.  How small in term of AH and run time is 10AH excessive? 
I sail probably for and hour max with a club and occasionally tow a barge and the battery hardly breaks a sweat not really dropping much below 12v and fully charged showing 13v..


your thoughts please


Steve 
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J.beazley

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Re: 12v SLA battery .....how many AH do I really need
« Reply #1 on: July 06, 2016, 01:20:37 PM »

Drop down to a 12v 7ah that will last you ages going on your sailing time estimation and bring the hull up out the water a little bit.

I run  12v 10ah and 12v 15ah in my HMS Mersey and have yet to even consider swapping motors or battery configuration running the pair of Torpedo 800 size motors, i can run for easily 3-4 hours before dropping any voltage.


Lets face it how often are we flat out with the motor for more than half hour.


Jay
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Bob K

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Re: 12v SLA battery .....how many AH do I really need
« Reply #2 on: July 06, 2016, 01:35:43 PM »

I have two fairly large warships that happily run for at least 4 hours on a 6V 7Ah SLA.  I run continuously, but seldom on full power / speed except in an emergency.  Always best to have a boost in reserve to take evading action.
As previously stated, most of the time you will be running on a fraction of power so a smaller Ah battery will probably not affect your run time appreciably.  If you normally run for just an hour then a lower Ah will be fine.
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sigfortunata

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Re: 12v SLA battery .....how many AH do I really need
« Reply #3 on: July 06, 2016, 05:34:56 PM »

Thank you Gentlemen for your advice, just weighed my 10ah battery and its a whopping 2.8kg!!


I think I will down-size a 5ah battery at 1.8kg


 :-))
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Fastfaz

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Re: 12v SLA battery .....how many AH do I really need
« Reply #4 on: July 06, 2016, 05:40:20 PM »

    Re scale speed, try it on a 6volt 7ah. This will make it far more realistic, the 10 ah is way too much I run my Portgarth on a 12volt 7ah with a spare one in the stern as part of the ballast, I can run it all day depending on what she's towing when she slows I change the battery, easy. Hope this helps.
     Cheers,
          Faz.
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nemesis

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Re: 12v SLA battery .....how many AH do I really need
« Reply #5 on: July 06, 2016, 06:39:25 PM »

disconnect all your electrics from the motor and then connect it up with an amp meter in line with the battery, that will tell you what amps the motor is drawing. Then select the battery to suit. nemesis
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