Low speed (rpm) gen head?

[guyd]

List -

I have a CS - but thats not what this is about...

I also have a water wheel - on my house. I want to generate from it. I want a very slow speed generator head for noise reasons (the 'mill room' is next to the bedroom). To this end - I want to run a (an?) ST head at somthing like 500rpm. The output will be rectified (three phase) and fed to a (clever, and complex) inverter.

My question is - what size head do I need to generate 5 to 10kw at 500rpm - and what voltage and current would I require for the field? I accept that I will need external ventilation / forced air cooling for this. I will assume the original spec for the gen head is 1500rpm (415v / 50Hz)

Thanks in advance

Guy

[mike90045]

Look at the Axial flux style of generators - if you increase the diamater large enough, you get enough magnet velocity to get voltage - but a 12' generator will take a lot of magnets !!   I see some adjusting being needed.

http://www.scoraigwind.com/axialplans/index.htm

[Tom]

That must one HUGE water wheel. Could your power estimates be a bit high? Would you give us the size and flow we are dealing with, we may be able to save you a bit of $. If your converter takes "wild" AC you might be able to take a 3 phase ST head and run it at slow speed.

[guyd]

The wheel is 15' diameter, 6' across, its overshot, iron - and for the yanks - its very similar to an IXL design. The flow is hundreds of litres per second (I estimate 300 - or 75 gallons - UK). It weighs about 8 tons. There are some pics on www.gotopia.co.uk/index.html of the un restored wheel. The wheel is difficult to photograph with a sense of scale

The wheel turns at 3rpm - and in theory generates 3800 ft lbs of torque (about a ton of water)



PM gennys - I have bought on a whim a pile (80) of small (1" x 0.5" x 0.125") - and thought about installing them on the rotor of a 9kw induction motor. I have yet to do this.

I have also thought that its just easier to lob money at this - and make it work - rather than muck about making small home made gennys.

edit address to add an L

[MacGyver]

Hmmm.   Horsepower = RPM X Torque (in foot-lbs)  / 5250

(3 X 3800) / 5250 = 2.17 HP.

It sounds like about a 1 - 2KW alternator is more like it...

Is my math wrong?

Does it really make more torque than that, or are you seriously overestimating how much power you'll get?

[MacGyver]

Guy,
I get a 404 error on that URL.  Got another one?

[Tom]

Ok that is a BIG water wheel and based on the figures you gave Steve's calc looks about right to me. That is still a LOT of power over the course of a day. What to use for a gen head in this size has me stumped though.

[guyd]

My numbers must be wrong.


I am currently generating 1.8kw @ 5rpm with the buckets 1/10th full - and no where near full flow on the sluice gates. The limitation is the heat generated by the PM gen head(s)  - if I ask more of them - they will overheat. Hence my need to get bigger genny heads. The current head run at 300 ish rpm from belt drives - each is 1.5kw rated at 500 rpm.

at 5 rpm - I have a lot of losses - mostly splashing at the bottom of the wheel. If I reduce this to 3rpm the losses will be less. and the torque will be more (as the buckets will fill more)

anyway - 500 rpm (ish) gennys.....

[guyd]

http://www.gotopia.co.uk/index.html

sorry - argument with ISP..

[cschuerm]

This had got to be one of the more fascinating threads in a long time!  I, at least, am fully intrigued and my engineers juices are at full flow.
Guy, I've seen a number of fairly large gen heads made by Fairbanks-Morse that operated in the 450 RPM range.  They've all been considerably larger than what you're looking for though - 100kw range.  They were used on steam engine power plants.  I know Fairbanks coupled some 40-80kw heads on their one and two cylinder vertical diesels - those might be much closer to what you have in mind.  Don't know how many pole those are, but they're physically pretty large in diameter.
Your place is absolutely awesome and so is your idea.  Please share more details and pictures!

Chris

[MacGyver]

Wow! neat project...
And a beautiful place!

I hope the buckets on that mill are a little less leaky now than in those photos!
Got any newer pics?

Since you say the wheel is about 15' diameter, I assume that you've also got about 15' of head?
My spreadsheet shows that with a 4 meter head and 300 L/S flow, that your gross power is about 11.7KW.    How much of that you can harvest is the question...

Looks like fun!

[mobile_bob]

if it were me, i would go with a purpose built axial flux machine or
get a large (maybe 20hp) 3 phase motor, and make a pm rotor for it

what kind of voltage are you looking for?

that is an interesting resource an i too would be all over exploiting it to the fullest.

not many folks have access to an installed hydro site, and over here if it isn't already grandfathered
in, it can be very difficult to get approval to install one, in most area's.

gotta save those fish you know!

damn fish huggers anyway!!

bob g

[oliver90owner]

Your continuing saga (from the Navitron forum)!

Thats then going on a tractor gearbox, of which the lowest (highest?) ratio is 300:1 and the highest (lowest?) is 30:1  (from the other discussion)

Why not pick a suitable gear ratio and run it at rated rpm?

Presumably you are running the gearbox backwards (ratio-wise) and are using your 20 or 40 to 1 ratio sprockets?

Or have things changed?

Regards, RAB

[sailawayrb]

Guy, by IXL and being a yank, I assume you mean your wheel is an "overshot wheel" typically designed for small streams (i.e., relatively low head).  I believe overhead wheels are in excess of 90% efficient.  If you know the flow rate (cubic feet per second)) and the head (feet), than the power available (kilowatts) equals flow rate times head divided by 11.8.  Then divide by 0.746 to get horsepower.

I am thinking that if you can only generate something less than 15 kilowatts (or whatever you think your peak AC requirements will be), you may want to consider generating DC power, then charging batteries, and then inverting to AC.  You could also use wind/solar to supplement your hydro.

Bob B.

[Jim Mc]

...My question is - what size head do I need to generate 5 to 10kw at 500rpm - and what voltage and current would I require for the field? I accept that I will need external ventilation / forced air cooling for this. I will assume the original spec for the gen head is 1500rpm (415v / 50Hz)...

You would need a 15-30 kW 1500 rpm machine.  The field would be operated at its normal nameplate-rated current.  Thus, the output voltage from the machine would be about 1/3 of it's rated 1500 rpm value, and so would the power.  And, the frequency would 16.7 Hz.  But that's OK, right? - you'll just run it into a 3-phase full wave rectifier and make DC.  You're right about needing additional cooling air as the internal fan in the machine isn't likely to move enough air across the windings at the lower speed.