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Project: Motor And Car Battery

Discussion in 'Power Electronics' started by pepper240, Jul 3, 2013.

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  1. pepper240


    Jul 3, 2013
    This is my first post to this forum, and I not the most knowledgeable on electronics and electronic hardware, so try to be nice. I have recently decided that I would like to build a personal submarine. I understand that this is a very ambitious project that will require a lot of research and hard work, but I am a mechanical engineer, so the all the mechanic technicalities make sense. What I need help with is the electronic portion of the project. Here are some general details about my current submarine design:

    1) It will fit one person.
    2) It will have a mass of approx 400 kg
    3) It will be partially streamlined at the front and rear.
    4) I would like the propeller to sit in the rear of the vessel.
    5) I would like the vessel to be powered by an electric motor and batteries.
    6) I would like enough battery power to last approximately 1 hour.
    7) I would like the battery to be rechargeable with a typical wall socket.

    What I would like to know is the following:

    1) What type, and how powerful of a motor should I use?
    2) What type, and how powerful of a battery should I use?
    3) Will I need a second/third battery to power the other electric systems in the submarine such as the fins/rudder, the interior and exterior lighting, the air and water pump for the ballast tanks, and various valves?
    4) If I do need a second/third battery to power auxiliary equipment, will it have to be a different type of battery?

    Any advice or guidance will be greatly appreciated. Many thanks to all :)
  2. Externet


    Aug 24, 2009
    Welcome and congratulations on a very nice, interesting project.
    Please do NOT be discouraged by anything and push the project to successful completion !

    Motor power... As powerful as fits your needs; you knew this answer was coming. How fast you want it to be, and how streamlined is it determines the power.
    I would attach a couple or more of these, which may eliminate rudder and controlling, and linkages :
    (I have one)
    And chinese:

    Yes, you can find more expensive ones, or buy just the motor/propeller section as spare parts from a vendor. The thing to consider is the depth; they are not meant to withstand leaks at very high pressure. Specifications may tell maximum tested depth. How deep you plan to go?

    DRY type
    Just below surface as :

    Or perhaps 100+ feet ?

    Batteries... Automotive type, sealed lead-acid, do not use anything fancy; Largest ones will give you longer run time; you knew that answer was coming.

    Yes, use several other batteries for different functions/controls. If something fails at least you have power to re-direct.
    A selector switch can re-route a failed/discharged battery out of circuit and bring another to share duty.

    Keep all batteries the same type if possible. Weight is not a problem in a submarine. You need the ballast !
    Never leave a lead-acid battery discharged over 24 hours. ALWAYS recharge immediately after use !

    Advise... Implement a cylinder of compressed air to inflate an external balloon to bring you and the submarine to surface no-matter-what-failed. (think of it as a reverse parachute).
    Think of heating and insulation.

    Seawater is a very highly corrosive unfriendly world for electricity, and high pressures always push to make things fail by flooding everything.

    Real underwater motors are expensive.
    Another approach is magnetic couplers; the motor is sealed dry inside; the torque transfers magnetically :
    Edited: Added---->
    With no seals to fail at any depth.

    WET type:

    Diver since 1972... until my belly grew :rolleyes:
    Last edited: Jul 3, 2013
  3. eKretz


    Apr 8, 2013
    Hope they make bigger magnetic couplings, the largest at your link is only rated to 1.25 lb./ft. torque. Interesting idea though, it'd be cool to have a submarine.
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    One important safety aspect is to always maintain slight positive buoyancy and to use motors to drive you down against it. This means that if power fails you come back to the surface (assuming you don't drive to "crush depth" :-o)
  5. pepper240


    Jul 3, 2013

    Thank you for your wonderful reply! Though I will likely not use the underwater towing device you linked to, it is an option I had not yet considered, so thank you. Here are a few more details. I have a budget of $3000. I would like vessel to have a maximum operating depth of approximately 25 feet. The vessel will only operate in fresh water for now, not salt water. I am not concerned with the mechanics, as I am comfortable with the necessary stress and pressure calculations that I must do, and more concerned with the electronic systems, as they are my achilles heel. How about a more specific question:

    Say I need a stock electric motor of 15 HP. Should this motor be AC or DC, and what kind of battery should I be using? I though that I may be able to use an electric golf cart motor and battery. Thoughts?

    Your other advice is very helpful! Especially about the emergency "reverse parachute". What a great idea. I will also consider insulation, compressed air supply, electrically controlled valves for the ballast tanks, the tanks themselves, and proper sealing. Thanks again for your input, kind sir.


    Very good point. I will definitely take that into consideration. I wouldn't want to end up at the bottom of the lake. Many thanks for your reply.
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Also, you need to have it remotely operable so you can take it down to its maximum depth a few times without risking yourself.

    Personally, I'd take it down until it failed so I could see how much safety margin I had. But that might be a tad expensive... (How much is my life worth?). OK, take it down to 50ft and if it survives that then I'd be happy at 25ft.
  7. Externet


    Aug 24, 2009
    A budget of $3000 is too tight, unless you go wet type.

    Your 400Kg mass does not sound right. How many litres of room will the cabin be in order to accomodate the occupant/pilot ?
    A 250 Gal =~950 litres vessel weighs only 215 Kg. You need 735 Kg more just to barely sink.

    25 feet makes it simpler. Fresh water needs another type of caution: Minimize protrusions that can get caught in drowned trees, branches, debris.

    15 horsepower is excessive. 1 HP should be more than enough. Direct current 12-24 Volt motor and automotive sealed acid batteries. One for single motor, one for controls, One spare lying around inboard. The best ballast that doubles as useful item.
    I would dare to insist on scuba scooter propulsion. If you insist on something else,
    these junkyard sourced motors are cheap, but at 130VDC provide over 2HP. Run with 24 to 48VDC instead, would come down in power to a better low figure:
    ----> motor on extractor/IM000920.jpg.html
    From a discarded treadmill.

    Deep cycle golf cart batteries will cost you triple, and for one-hour use and tight budget, I do not see the point.

    The hull, if you insist on dry type, could be a small gas tank that has been decommisioned and obtained for cheap from your local utility company:

    250 Gal ~950 litres---->

    A golf cart motor is still too powerful (3 to 8HP) unless you already have one, could ve underdriven with lower voltage. The attention is not to be aimed to the motor, but to the shaft seal. Your biggest headache will be making watertight things.

    Please do NOT misunderstand my poor wording for "reverse parachute" as this lift bag:

    It should be more like this :

    Or cheaper; for emergency surfacing, DUMP external belly held ballast with the pull of a lever. Ballast can be metal scrap, engine block, rocks...

    And you will need to think on a very good trailer, bubble plexiglass window, video cameras for under and rear views, propeller shroud and maaany other details... !

    If you do not want to use a diver scooter propulsion; an alternative simple suggestion is a plain DC motor inboard, driving an automotive hydraulic power steering pump and a hydraulic motor outside for the propeller. All can be found VERY cheap at salvage yards.
    The steering can also use the system with simple actuators. No water leaks risk with trough-hull fittings for the hoses.

    Hydraulic motor from car boneyard: I dumped one like this from a Lexus the last time I moved :-(

    Belt driven hydraulic automotive steering pump:

    Hydraulic actuators:

    A trolling motor is good for a couple of feet depth, I would not recommend the risk of failing flooded at 25+ feet depth.

    For your electrical Achilles heel, come with one by one specific question; there will be dozens. For a chosen motor, a correct battery of the same voltage is the norm.
    Last edited: Jul 4, 2013

    CDRIVE Hauling 10' pipe on a Trek Shift3

    May 8, 2012
    That's a good tip but please don't dump that stuff on coral unless you're sure you're going to drown. ;)

    RE, lead acid batteries. Am I mistaken that even the sealed variety still must vent? If they do that will be hydrogen gas.

    Last edited: Jul 5, 2013


    Sep 23, 2012
    I 'm curious and would like to folow your project.

    I work with some what large storage batterrries (I have a bank of (65) 2.0v cells rateed at 950 Ahrs. Hydrogen is a concern and I have hyrogen monitors connected to an exhaust fan for safety. Most iof the hydrogen generarted is when charging so maybe in your application its not a big concern; then again it's an enclosed vessel I would also be concerned about any arcing electrical devices like a dc motor or even a simple toggle switch. Remember the Hindenburg!

    Maybe you should consider using a AC induction motor with a variable frequency drive. AC induction motors with no brushes are not likely to produce a spark. A variable frequency drive ultimately runs on DC and will give you a great range of variable speed and torque. Using a dicarded 3 phase motor will reduce size and weight and are found easily in scrap yards. Since you will be using the motor for short periods you don't have to worry about cooling. (Inverter duty motors are designed for VFD operation.)

    I would definitly consider manual or pnematic controls for rudder and dive/surfacing.
    Last edited: Jul 10, 2013
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