low revving generator for water wheel
low revving generator for water wheel
(OP)
I'm building a small water wheel and want to generate electricity. Not fussy about voltage or frequency but given limitations of site(2m head, perhaps 20 l/sec flow, so about theoretically about 0.5 Kw) it must be highly efficient. Everyone seems to agree that conventional generators are not suitable for water wheels because of the gearing necessary - expensive, noisy, inefficient and subject to heavy wear. There do not seem to be any very low revving generators available. It's outside my field so any information would be welcome.
Are there such low revving generators (say 100 rpm)?
If there are, where can I get one?
If not why not; is there a good reason why such a generator cannot work?
If it's possible but just unavailable, how can I make one?
Alternatively there may be a completely different way to turn low revvs efficiently into heat some 20m away?
Are there such low revving generators (say 100 rpm)?
If there are, where can I get one?
If not why not; is there a good reason why such a generator cannot work?
If it's possible but just unavailable, how can I make one?
Alternatively there may be a completely different way to turn low revvs efficiently into heat some 20m away?






RE: low revving generator for water wheel
A custom built generator for 100 RPM will probably be more inefficient than a belt drive.
respectfully
RE: low revving generator for water wheel
Mike Halloran
Pembroke Pines, FL, USA
RE: low revving generator for water wheel
RE: low revving generator for water wheel
http://www.fieldlines.com
Ian
Ian Rines
Harris Corporation
Palm Bay,FL
RE: low revving generator for water wheel
Anyone tried this?
If such a solution not possible, how efficient can a car alternator be at achievable revs?
My experiece with v-belts in this environment is that they get wet and slip; is there a belt dressing that would cure this?
RE: low revving generator for water wheel
A generator's output is very strongly affected by the air gap in its magnetic circuit. A minimum limit to that is imposed by the runout of the rotor and its bearings. You'd probably end up with an air gap of >6mm. An alternator's air gap is maybe a tenth of that.
Efficiency is a secondary issue. You want to maximize output, of course, but so long as there's enough flow available, you really shouldn't care how much water has to hit the wheel to achieve the output you get.
No belt dressing is going to offset the influence of water. Use timing belts. Here's a trick; you don't need a giant timing belt pulley on the wheel; just a big smooth pulley with 2..4 teeth. The limit on how big a drive pulley you can use is the length of the belt you can buy; find that first.
Consider a jackshaft and two belt drives. If you make the jackshaft long-ish, you can locate the alternator(s) remote from the waterwheel and just use the timing belt in the wet area. At the other end of the jackshaft, use the poly-v drive belts so you don't have to change the alternator pulleys.
Mike Halloran
Pembroke Pines, FL, USA
RE: low revving generator for water wheel
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: low revving generator for water wheel
RE: low revving generator for water wheel
I would consider building your own permanent magnet 3-phase generator. Look at www.otherpower.com to start.
Peter
RE: low revving generator for water wheel
As the speed increases, the output increases and the field demands drop.
With a 5-fold speed increase over the speed at which the alternator is just able to supply its own field, the field current will be one fifth. The field losses will be 1/5^2, or just 4% of the losses at the lower speed. As a percentage of the output, the percentage will be even lower.
If you are able to maintain your speed at design level, the losses will come off of the top.
That is, a 500 watt alternator will be able to produce 500 watts output plus the small field losses.
In a wind power application, the losses come off the bottom. That is, in light wind conditions, the speed is slow and the losses are high. There will be a significant loss of production during light wind/slow speed conditions.
There have been alternators developed for wind applications. I remember seeing a design similar to automotive alternators in which the field was supplied by a permanent magnet rather than an electromagnet. Try Googling.
For your application, the efficiency may not be a serioius issue. There are significant differences between wind power and water power.
respectfully
RE: low revving generator for water wheel
The nice part is that you can get field control.
h
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: low revving generator for water wheel
First guess: set it up for ~2000rpm at the alternator.
If the waterwheel approaches the pipe discharge velocity, then a ~1.5m dia waterwheel would spin at ~13.6 rpm at 20l/s. You lose about half a meter of head through your 6" pipe at that flow.
So, you need a pretty good speedup. If the last stage is poly-v belts and pulleys from a car at ratio ~2.5:1, you still need a speedup of 58.5 between that jackshaft and the waterwheel. Which probably means two jackshafts, ~8:1 speedup each.
... which is probably why most folks don't do it that way. Just too many moving parts.
;------
A Google search on | hydro alternator | produced a lot of relevant hits:
- Commercial Pelton turbines that need 20' of head but drive an alternator directly.
- Some Pelton wheels ready to bolt to an alternator shaft.
- Something called a Turgo Stream Engine that claims operation at 2m/6' head, turbine available separately to bolt to an alternator directly.
- The ElectroVent hydro alternator.
- Brushless alternators.
- Much discussion of efficiency by alternator brand and type.
- Photos good enough for you to duplicate nearly anything that's been done, so you can make your own tradeoff of time vs. money.
Mike Halloran
Pembroke Pines, FL, USA