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Oil filled 12V alternator

  1. Oct 29, 2007 #1

    I need to build a 12V alternator inside a pressure casing that will be driven by a propellor. This will be mounted on the rear on an oceanographic sensor platform that will be towed behind a ship on a long cable with the ship's forward motion providing the spinning of the prop, for the alternator to charge batteries (very low gassing) and run electronics.

    The ship's speed will vary between 2 and 10knots. The ideal current output would be between 6 and 10 Amps. Ideal operating depth would be 1000m to allow "sinking" when the ship slows.

    I envisage a small car alternator inside a pressure casing. The problem is the link shaft through the case to connect the alternator to the prop.

    I can o-ring seal it, but at depth the pressure on the o-rings will "pinch" the shaft.

    There are also magnetic couplings, as a last resort.

    My question........

    anyone have any experience in running a car alternator submerged in light oil? If I can fill the casing with oil, I won't have to do such radical shaft sealing.

    Thanks in advance.

  2. jcsd
  3. Oct 29, 2007 #2
    I don't have any experience running an alternator submerged in oil, but my gut instinct would be that any kind oil around the alternator would severly impead its ability to turn at a speed sufficient to generate the required amps.

  4. Oct 29, 2007 #3


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    The first thing that pops into my head is whether or not the windings and associated coatings are made to be submerged. I have seen plenty of oil cooled generators so this is nothing new, but using something that is normally air cooled may cause a bit of a problem. I'll have to ask around to see if anyone I know knows the answer to that.

    Can you tell me what the size of the shaft is and what the max rotational speed is? I would like to take a look at the sealing of the shaft too.
  5. Oct 30, 2007 #4
    Thanks for the replies........

    >Can you tell me what the size of the shaft is and what the max rotational speed is? I would like to take a look at the sealing of the shaft too.

    If we use a standard car alternator, we will have to extend the shaft to penetrate the casing. I guess work on a 13mm (1/2") diameter, with a small outboard engine prop.

    Have not done sums on prop pitch and speeds needed to produce 6 to 10A, as first need to see if whole sealing concept will make the idea feasible.

    I'm geared up to produce o-ring sealed cases that survive 6000m, but penetrating with a spinning shaft at 1000m is a challenge.

    Other issues are if a car alternator's bearings will handle the pulling force on the shaft will the drag of the prop.


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