So for a university project i'm wanting to produce a working prototype of a portable hydro kinetic turbine. For this I need a small waterproof generator / gearbox. The generator can be ether AC or DC and the gearbox should be a ratio of around 1:10. I'm struggling to find a component which is fully sealed. Is it better to attempt sealing / waterproofing a component my self?
Just my 2 cents worth here. I'd like to hear more about your project. I read somewhere that a in stream generator made in England Contains mineral oil? Does that make sense. Or is it a jacket of mineral oil that seals a outer and inner seal? Double sealed. I forget the brand. They dont produce a lot of watts. I think 100 watts would be on a good day. And I think there's no gearing inside.
Low head hydro and in stream hydro is what is needed.
The cleverest one I've seen was a "Polish" stream generator.
It had cross shafts with vanes welded at 45 degrees (one vane on opposing ends of each shaft, trailing the shaft as it pivots into the flow) the flow was channeled to force the water to one side of the shaft pivoting the vane down into the flow (and concurrently rotating the opposing vane flat to minimize drag.
Both cross shafts were pivoted in a central axle that protruded through the deck of the float that suspended it into the stream, with the upper side of the shaft turning /geared to, a permanent magnet alternator.
There used to be a YouTube video but a cursory search didn't turn it up.
The beauty of such an arrangement is it makes replacement parts economical, off the shelf, non waterproof components can be installed under a cheap sheet metal cover. If a gearing arrangement is required the hole piercing the deck can be offset from the shaft of the alternator eliminating the need for (and inherent drag of) a seal.
The downside is surface flotsam must be directed out of the flow path.
Nothing is impossible to a sufficiently talented fool!
This is based on some engineering intuition and quick research. I think if you absolutely must put an electric generator underwater, sooner or later the sliding seal on the motor/generator shaft is likely to fail. So that failure mode would be nice to avoid if possible. Here's a solution. Use a motor/generator design like this, even if it means you have to build the motor yourself. http://www.efficientplantmag.com/2008/09/understanding-canned-motor-pumps/ Put a solid, stationary, waterproof "can" between the rotor and stator of the motor/generator, likely made of a higher-temperature plastic or maybe ceramic. As long as the "can" is not electrically conductive then there won't be eddy-currents causing a loss of efficiency. And as long as the "can" material is as thin as possible (maybe around 0.010" to 0.030" thick), then the magnetic field can pass through, allowing it to work. Note: the thicker this gap is, the lower the motor/generator's power-density will be. It will essentially "de-rate" the motor/generator's normal power rating that would otherwise be expected. Also for better power density gear-up the drive speed *before* going through this "magnetic coupling" and/or use more magnetic poles.
posted 7 months ago
Thanks for those ideas; have decided to place fixed magnet alternator inside an old sump pump housing. Those things operate submerged for long periods, so the housing arrangement must be reliably waterproof at depths of a meter or so. The alternator will not be submerged (it will be on the back of the raft), just might get temporarily swamped.Now to find a second hand sump pump with sufficient internal dimensions for my generator..
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