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Posted by Pete C. on March 23, 2008, 4:04 pm
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Johnny B Good wrote:
>
> from phoneme@025379386.for.email.address (Eric Sears) contains these words:
>
>
> > >Yup!
> > >
> > >Today I spent some time trying different nozzles just to see if I could
> > >wrangle out those last few RPMs needed to get past 12 volts ..
> > ...........
> > >
> > >Put them in and just ran the hydro with a multi-meter and was getting
> > >around 7 volts with a single jet. Pretty sweet .. the most I ever got
> > >before was around 5.5. With both jets on and with some fiddling with the
> > >angles I hit 13!!
> > >
> > >So I turned connected them to the batteries and whadya know.. its
> > >charging. The battery bank is at 12.4 and when I hit the switch to
> > >complete the circuit the alternator comes under load and keeps on
> > >spinning!!!
> > >
> > >So thats that then.
>
> > Well I'm not sure it is! Its great that you have exceeded 12v, but as
> > I have said previously, you need to get to about 24 volts (not
> > connected to the battery) , in order to extract something like the max
> > power available from the water. At 13v, its likely you are not getting
> > more than 10%.
> > Exactly HOW much current is going into the battery? Simply measuring
> > the voltage is not sufficient. You need an ammeter in series with the
> > wire to the battery. I seriously doubt that you are doing any damage
> > to the batteries by overcharging!
>
> > As someone else said, either you need more speed from the jets (which
> > you might have done by improving the nozzles, or you may just have
> > applied more water which is overcoming the frictional losses in the
> > wheel and generator), or you need to gear up the generator with a belt
> > and pulley. Believe me (because I've done it hundreds of time and
> > understand the theory) - you MUST get the "runaway voltage" to about
> > TWICE the battery voltage with pelton or turgo wheels (its slightly
> > different for a turgo, but close enough not to matter). If its
> > charging with a significant current with you present setup, then you
> > are extracting very little of the available energy (that is in the
> > jet).
>
> Actually, the 'runaway voltage' on a PM generator (where the open
> circuit voltage is directly proportional to speed) should be around 1.9
> times (but a figure of two times will make allowance for the volt drop
> under load :-).
>
> The reason for the c1.9 times unloaded speed is on account of the way a
> pelton wheel extracts power from the water jets. When unloaded the
> buckets will have a linear speed equal to just slightly less than the
> jet speed with the energy of the water exiting the turbine only slightly
> reduced (ie a lot of wasted energy in the exiting water flow). the small
> amount of energy extracted by the pelton wheel in the 'runaway'
> condition being that required to overcome 'windage' and other friction
> losses.
>
> When the generator loading is optimised to the water jet energy, the
> water flow exiting each bucket will have close to zero energy as it
> drops out into the housing to be drained off to the lower level (it's
> most important that the exhaust water does _not_ flood the turbine
> housing). The water gives up its energy by having its flow reversed with
> respect to each bucket the jet impinges upon. the maximum energy
> extraction only occuring in this type of turbine when the jet speed is
> twice that of the loaded linear speed of the buckets.
>
> > The "runaway voltage" is the voltage from the generator with no load
> > attached (ie the battery). When you then connect the battery, the
> > wheel to go down to about half of the runaway speed. That's how it
> > works when its working correctly.
>
> This only applies to an unregulated PM generator (which I understand is
> the case here).
>
> > Try connecting the tail lamp bulb as I suggested (directly to the
> > generator). If the whole things slows dramatically, then you really
> > don't have much power.
>
> Assuming you don't already have sufficient power to blow the lamp!
>
> > If you connect it and the voltage drops to say 9 or 10 volts - then
> > you have some worthwhile power.
> > If you connect it and the voltage hardly drops at all (ie it remains
> > close to 12v), then you probably have quite a "lot of power", but at
> > the wrong voltage. If this occurs, either you have "gear up" the
> > generator, rewind it as someone suggested (not easy), or find a
> > generator with the right characteristics.
>
> Best method of controlling power in a pelton wheel generator setup is
> to automatically (via voltage or charging current feedback) adjust the
> the water jets using needle control valves in each jet. This minimises
> on hydro energy wastage. Any other method (except as a fast response
> fine tuning augmentation) such as that suggested below will needlessly
> use up your hydro energy resource at times of low demand.
>
> > It CAN be done with a transformer - but you really need to know what
> > you are doing. (You would have to circumvent the diodes). Yes, I know
> > its three-phase! I'm saying there are answers (because I do it, and
> > I've built systems that do it this way). You could even use a step-up
> > dc-dc converter - though I don't think much is readily available off
> > the shelf.
>
> Power stations control their output by controlling the fuel input. In
> this case, your 'fuel' is the energy contained in the water flow. Since
> the desired speed of the generator is basically constant (the small
> speed variation being needed to compensate for volt drop in the
> effective ohmic resistance of said generator over varying loads), you
> want to maintain the water jet speed but vary the effective diameter of
> the jet (and, hence the mass of water per second that hits the runner).
> The best way to do this is by using needle valve controlled jets in the
> turbine housing. This method is the most efficient way to control the
> hydro energy input to your turbine.
>
> If you are using multiple jets in the turbine you can extend the range
> of control by shutting off the feed to individual jets using low
> turbulence valves (rotating ball valves), perhaps electing to fit needle
> control to only one or two of the jets as a means of retaing fine
> control whilst minimising the expense. In this case, the ball valves
> will be either fully off or fully on (although they can be used as a
> throttle, but only during transitions in order to allow time for the
> needle valves to respond).
>
> A properly designed pelton wheel generator system should allow you to
> extract a good 80 to 90 percent of the hydro energy over the full range
> of demand (this presupposes a properly designed and sized penstock feed
> system to match the maximum demand).
>
> HTH
>
> --
> Regards, John.
>
> Please remove the "ohggcyht" before replying.
> The address has been munged to reject Spam-bots.
On the part about regulating via the water input to avoid wasting the
resource, unless you have a low flow water source that you have to dam
up and allow to fill and then generate power until drained again, I fail
to see how you would be wasting the resource. If your water feed to the
turbine is less than or equal to the flow rate of the source then all
that water would be flowing over the dam anyway.
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