[PSUBS-MAILIST] battery compensation

[Alan James via Personal_Submersibles]

Hank,the calculation is easy with the metric system.If your battery is 30x20x20 for example, you multiply those dimensions.This gives 12,ooo which is the cubic centimeter figure. Divide this by1000 to give you how many liters volume it is. So 12 liters. This means youwill displace 12 liters of water which weighs 12 kg. If your battery weighs 30 kg then subtract the 12 kg from that &  your batterywill weigh 18 kg in water.Another way would be to fill a container to the top with water (fresh not salt) then put the battery in. Fill it up again to the top with water, measuring what you pour in. If you pour in 10 liters of water then that is how much it displaces, whichequals 10 kg that you subtract from your battery weight to get the weight in water.   As for oil compensating, there is a section in the manned submersible book.Deep sea power & light make a sea battery.http://www.deepsea.com/products/seabattery/
It is a battery box with cables entering it & has a flexible diaphragm over it.In the diaphragm is a bleeder valve to bleed off gas that mainly accumulates during charging. You would only need blue globe cable glands or similar for thebattery leads as the pressure is always ambient.In the early days of car batteries, topping the battery up with oil to stop evaporation wastouted, so that isn't a problem.Alan 

      From: hank pronk via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Friday, January 15, 2016 5:48 AM
 Subject: [PSUBS-MAILIST] battery compensation
   
Thinking ahead, I need to reduce the weight of my deep diver.  I am now planning external batteries- lead acid in oil.  This reduces the amount of syntactic foam needed.  My deal on CNG  tanks fell apart.  The ebay seller would not honour the sale, can't blame him.   I may go with store bought syntactic foam if business looks good with 30 dollar per barrel oil, Yikes.  
I am not sure how to go about the oil filled battery set up.  I assume the batteries are filled as high as possible with water then topped up with oil, then the compartment filled with oil and a rubber lid on that.  I assume you take a syringe with distilled water to top the batteries up from time to time.  This way you wouldn't have to drain the oil.Does anyone know how heavy a battery weighs under water compared to in air?
I also am thinking about having the reversing relays for the motors in the oil tank to reduce the amount and size of wires penetrating the hull.  I will just send small wires for messaging to the relays.Hank
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