Author Topic: Taking the 10Kw plunge anyway (Read 1708 times)

solarengineer · « **on:** May 24, 2007, 06:41:15 PM »

Hey Dan, after some carefull financial consideration I said screw it and I'm going to build a 10Kw machine.

You had offered some advice previously on my dual stator thread:

Hi Jamie - just my own thoughts..

You know the drawback of doing things this way - if you stick all those magnets and all that same wire in two rotors and 1 stator respectively you'll get 4 times the power I did at the same rpm. If you divide it into 4 rotors/2 stators you'll only get twice the power. Trouble is - at some point the diameter starts to become a problem. My first 17' machine has 16" rotors and things are crowded - so you'd need 32" rotors. I expect such a machine would be quite good for 10KW as mine seems good for 3, but keeping in mind it will have to turn more slowly then 10KW might be precarious. But I dont think something like that would be unreasonable and I bet you could run 25' blades on it - give or take a bit.

Trouble is - if you go with the smaller diameter machine - basically two of mine, and if mine is about 50% efficient at 3KW (which it is) - then that double stator machine will be good for maybe 6KW at the same rpm mine is good for 3- but youll have to turn more slowly (larger blades) so youll need to downgrade it further.

Some of this stuff could be solved Im sure with electronics that improve alternator efficiency, but if you're just matching things up with resistance then I think you'd be way off the mark for 10KW with your current plan."

Well I'm going to use the same materials as your 17' except twice of it and 37" rotors.

I think I'm going to wind it for 200-400 volts and grid inter tie it, so the losses in the stator shouldn't be as bad as battery charging. I'm thinking 75% efficient perhaps.

Now This machine will be 4X more powerfull than your 17' alone so if you get 3Kw@50%

then I should be safe around 8-10KW???

Any thoughts on this before I begin? or from anyone else?

Heating concerns??

Thanks

Jamie

Flux · « **Reply #1 on:** May 24, 2007, 01:08:50 PM »

"Now This machine will be 4X more powerfull than your 17' alone so if you get 3Kw@50%

then I should be safe around 8-10KW???"

At the same speed! You will need to run it about 50% slower so that knocks your power down a fair bit.

You can probably ignore the matching in low winds as a few dozen watts for grid tie wouldn't be worth chasing so that may let you raise the efficiency at the top end ( unfortunately it will also raise the speed so you may not be looking at something as docile as the effectively stall limited things that Dan builds). Not sure how much extra forces and loading this is going to cause you.

I think you can manage something that may get close to the occasional 10kW peak rating, if you call that a 10kW machine then fine. If it produced 10kW continuously for 15 mins then I think you will see smoke. If it is furling it will probably be ok, the power out usually falls in higher winds. With a true constant speed pitch control hub I doubt that you will rate it anywhere near 10kW if you ever get clean high winds.

Flux

solarengineer · « **Reply #2 on:** May 24, 2007, 01:49:17 PM »

Ya, I forgot about it being the same speed. Bottom line I will build it bigger the I want the 10Kw so one way or another it has to be a matter of scale. Smoke is something I dont want and I have the resources available to me so i would like to build this machine properly. I never thought for a second I would ever go from 400W to 3Kw and it happened with success. so now 8 to 10Kw is where I have my sights. Thicker wire more magnets and it should be a reality.

The grid tie inverters I believe do MPPT which should also help.

As I say I'm looking for some realistic ways of doing this and there seems to be many boundaries around 10Kw and I want to go past them... there were boundaries from 400w to 3Kw also.

I know its doable, question is "what's required" If I have to go 2X what his 20ft will do then I'll have at it. but i dont simply want to toss money either.

Regards

Jamie

thefinis · « **Reply #3 on:** May 25, 2007, 12:33:24 AM »

I think that the 10kw range(average output around 15-20 mph) is about where a good gearbox might come in handy. By the time you are spending that much time and money then a really good gearbox starts to look cost and energy effective. It should be fairly light, stout and have a long life expectancy. If you only double the rpms then it should cover the slow down in rpms from the increased diameter. A gearbox should let you match blades and genny better/easier for that size but you get back to having to really protect the genny from overspeeding in higher winds.

Finis-Who has not built one with a gearbox yet.

dinges · « **Reply #4 on:** May 25, 2007, 03:58:28 AM »

Have you considered doing a 10 kW motorconversion?

If I were to build a 10 kW generator, it would definitely be a conversion and not an axial flux.

A6D9 · « **Reply #5 on:** May 25, 2007, 06:46:00 AM »

I think this is a great idea....

think of it, if during the summer month you have slower winds...you might be able to change the gearing to better accomodate it for a small increase. and then when it is the windy season (perhaps the winter months) you can go to another gearign to prevent overspeed and save the stator form over heating.

Sur you would lose a bit of power with friction and what not. but the trade off in my mind would be worth it.

Gary D · « **Reply #6 on:** May 25, 2007, 09:59:34 AM »

I'm curious on the grid tye inverters. How big/many are you planning? The windy boys that I'm aware of are rated under 3 kw each, so 2 at 220 would give you much less than what you need. I think they were only approved for African Wind Power machines (that Hugh Piggott[sp] helped on I think). Have you found larger ones rated for 5 kw or more? Good luck! Hope to hear good news! Gary D

Ungrounded Lightning Rod · « **Reply #7 on:** May 25, 2007, 02:40:53 PM »

Ditto with me. Cooling is a major problem for potted-stator axial-flux designs, resulting in serious burnout risks for high-power mills. A motor conversion of suitable size will have more than adequate cooling, along with thermal mass that can easily handle short-term overloads from gusts while the mill gets around to furling.

The biggest advantage of the coreless axial-flux designs is the complete lack of cogging, which is great for a small mill, and the ability to construct one without the use of a machine shop. But a big mill has lots of leverage so delayed startup due to cogging isn't usually an issue.

Flux · « **Reply #8 on:** May 26, 2007, 01:34:03 AM »

I agree that the axial construction will have serious trouble with heat removal in the form used here. Core type machines have direct transfer of heat to the teeth and will be far better cooled.

I am not so convinced about a simple motor conversion being entirely suitable. What you need is a low speed slotted core construction. If you think of large industrial alternators then the high speed turbo alternators are long and lean whereas alternators for hydro are very short and large diameter.

The sort of motors you are likely to find are all relatively high speed machines and the proportions are not right to make a very low speed pmg. Even if you took a very large motor and used a portion of the core pack and got the right proportions you would still be left with slots that are far too deep for the multi pole magnet system.

I think you will need to use a conventional motor conversion with a gearbox or you will end up with an absolute monster if you directly couple it unless you go to the extreme trouble of producing a suitable core pack. You need to be looking at very large pole numbers. Conventional motor cores limit you to about 12 poles maximum and even then the slots are far from ideal even if you start with a 6 pole motor.

Although the cooling is far better I think the motor conversion will be larger and far heavier for the same output unless you can get the correct core. It may become reactance limited with deep slots and lots of leakage flux and may refuse to load up with increased speed.

Even the torus with or without slots still needs a core that is difficult to produce on a one off basis. Large one off machines are difficult to produce on a cost effective basis.

For your nominal 10kW on a short term basis it may be safer to stick to an axial, keep the diameter and number of magnets up and make a better effort at cooling the stator. With it loaded efficiently the heating is far less serious than with the bogged down into a battery connection.

Using a gearbox and motor conversion will get you there quickly with good results but you may regret it in the long term, gearboxes have proved rather troublesome for wind power with speed increase and high instantaneous loading.

Flux

wdyasq · « **Reply #9 on:** May 26, 2007, 07:27:43 AM »

Flux,

That was an elegant presentation of how difficult it will be to build a 'homebuilt' 10kW mill.

If he does continue on this path I hope he considers a toothed belt as a speed increaser. There should also be enough 'room' on the driving end to incorporate a real brake off an automotive or motorcycle application to positively stop the thing when necessary. This could also be rigged where the 'safe action' released the brake so if there was a failure, the mill would automatically stop.

I do wish the man good luck and hopes he considers all the forces involved in such a large endevour.

Ron

thefinis · « **Reply #10 on:** May 26, 2007, 09:19:25 AM »

While I have only tried stopping one fairly big blade set it seems to me that the idea of using brakes has some pitfalls. One is that it is like trying to stop your car while gunning the motor. The brakes will pull it down but rarely are they sized to stop while fighting the full force of the motor. Two is that if it does not stop the turbine quickly then the brakes overheat and slip even worse till they fail. Three I guess is that they add a lot of weight at the top of the tower for something that is only used once in a while.

Brakes would work fine in lower winds to stop the turbine and hold it for repairs etc but for high winds it should furl or have an alt that can pull it down to stall speeds. LOL if the alt can pull it down to stall then the brakes would work to bring it to a complete halt and hold it without being oversized and extra heavy.

Toothed belt should work as long as it is sized for overload. Light weight strong but don't know the life span rating for one. Would not want to be around if the belt broke. Maybe the brake would need to be between the belt and the blades but that puts us back at oversizing the bakes. 10 kw is around 13-14 hp isn't it? That should put overload at around 20 hp or 15 kw aprox at least if I wanted 10 kw at normal output that is where I would aim for max power output.

Finis

jimjjnn · « **Reply #11 on:** May 26, 2007, 10:00:57 AM »

In case the toothed belt breaks, he should have the brake on the blade rotor to prevent rotor runaway.

RP · « **Reply #12 on:** May 26, 2007, 10:05:24 AM »

I think if it was a disk brake sized for a large automobile it would be able to stop it. Think about the kinetic energy of an SUV or loaded pickup truck at 70mph. Even divided by four (4 brakes), there's still a lot of stopping power. 20hp is probably equivalent to less than 1/4 throttle for many vehicles.

One idea would be to arrange an idler pulley on the belt such that if the belt breaks, the movement of the idler and a spring applies the brake to the turbine shaft.

solarengineer · « **Reply #13 on:** May 26, 2007, 11:40:16 AM »

Hey Flux, since this machine is going to have a computer guided yaw system could I put ram air scoops in the front of the turbine and have them drop in diameter to speed up airflow and blow that air directly between the rotor plates?

solarengineer · « **Reply #14 on:** May 26, 2007, 11:46:06 AM »

Thanks for the input Ron, one thing I am considering is a neodynium electromagnetic braking system that has no physical contact and is also a completely separate addition to the shaft and it would run from some very large supercapacitors. it would be a shutdown once type of operation not for speed control.

have a good one

Jamie

Nando · « **Reply #15 on:** May 26, 2007, 02:17:41 PM »

Jamie:

Now that most have talked, what about a Pitch controlled Mill, like the one I presented sometime back from England producing around 11 KW.

The ideal case for you in this case would be to get a Tractor PTO generator with a 4 pole gen to be able to have around 160 - 190 or so RPM.

The generator is one having an AVR that can be removed and if the rear shaft is available you may even place a small DC generator to replace the AVR which can be easily controlled with a PLC,

In your case , if you want a grid tied system you could make, not with Windboy units, but with a dc motor and an Induction motor, though the efficiency may run around 60 %.

This way you will have an easy to build system .

Nando

Flux · « **Reply #16 on:** May 27, 2007, 12:44:02 AM »

Not sure what you mean about ram air scoops but I am sure that you can drastically increase the cooling over what is normally obtained at the centre of a prop where the air flow is questionable.

If you are using active yaw then you must have some method of limiting power. I assume you have sorted that out.

Flux

solarengineer · « **Reply #17 on:** May 27, 2007, 09:53:45 AM »

That sounds like a project I would also like to do Nando, I'm not sure what a tractor PTO generator is but I assume it runs slow?

What is the AVR you mentioned?

If I can piece these together I would have a good understanding of your post.

Thanks Nando

Jamie

Nando · « **Reply #18 on:** May 27, 2007, 10:34:59 AM »

A PTO generator is designed to be attached to a tractor PTO shaft to produce energy in remote areas, normally they are designed to a 540 RPM PTO take off but one can get PTO gear multiplier and a 4 pole generator with AVR ( Automatic Voltage Regulator) which some are brushless some are not, that are located in the rotor area.

The power is done by removing the AVR circuitry and supplying the biasing externally with a PWM controller that can produce MPPT power and can, as well, be used to overload the Turbine to make it stall to be able to use a hydraulic brake to stop it if necessary.

The generator runs around 1800 RPM, though since the power is going to be converted the frequency is immaterial and 35 to + Hz is OK. If you rectify and drive a DC motor directly and the motor coupled to an induction motor connected to the GRID, then you have a GRID tied system with automatic cut OFF when the GRID disconnects or drops and you may have the added capability to use the power to charge batteries is so desired, or for heating.

Using a pitch controlled hub you may not have the problems that the furling system often suffers and the power is always searching for peak power and properly limited .

Nando

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Author Topic: Taking the 10Kw plunge anyway (Read 1708 times)