 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Windmills : Windmill cant get up to speed
| Author | Message | ||||
| Ben Newbie  Joined: 10/08/2007 Location: AustraliaPosts: 18 |
I built a f&p mill with 2.4 mt blade, Hugh Piggott design. The mill does not get up to speed, even in high wind. When i disconnect the load from the mill, it gets up to speed and will stay there, usually blowing my three, 100w spot lights. I think it is wired correctly. Can any one tell me if this could be 'clogging', as I have not declogged my motor? |
||||
Highlander Senior Member  Joined: 03/10/2006 Location: AustraliaPosts: 266 |
G'day Ben, welcome aboard. Cogging is only an issue on start up. It referrs to the attraction of the magnets to the "fingers" in the stator. Once it's running it's of little or no concern. The 7 phase has almost no cogging, but the 3 phase has quite a bit, so stronger winds are required to start it up. As to your F&P 1 how did you wire it? 2 what is the "load" your using 3 have you tested the output with a multimeter with and without your "load" 4 did you connect the rectifiers up properly? 5 have you tested each phase before and after the rectifiers? Central Victorian highlands |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5116 |
Hi Ben Adding to Highlanders comments, yeah it sounds like too much load at low RPM. A well made set of blades, like the Hugh design, are a bit like a high performance two stroke engine, in that they have a "power band". Below the power band they make very little power. Normally we use a rectifier and battery as our load, and this means until the alternator is spinning fast enough to reach charging voltage, there isnt any load. Once the charging voltage is reached, the turbine is already spinning fast and is in its "power band", so it can take the extra load. By putting a set of spot lamps across your windmill, you've applied a load at low rpm, and the windmill just hasn't got the grunt to get into its power band. Like you said, if you disconnect the lamps and let the windmill speed up, it then has enough power to blow your lamps. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| Warpspeed Guru  Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Agree with Gizmo. It sounds like way too much load on the machine which is probably stalling the blades. There is somehow a fairly bad mismatch between the blades, the generator, and the load. What I would do is allow the generator to run up to full speed with no load in average sort of wind conditions and then measure the voltage. Then apply a series of gradually increasing loads, measuring both voltage and current. Power (watts) produced will be volts multiplied by amps. You will discover that as the load is increased, the measured power output will also increase, but only up to a certain point. Increase the load more than that, and power output begins to fall off. With no load there will be maximum volts and no amps, so zero power. With a dead short, there will be maximum amps, but zero volts, and again zero power. At some optimum load resistance there will be maximum measured power. So as Gizmo says, your machine has a definite power band, and the load must ideally be arranged to be reasonably near the most efficient operating point. Do the test, and give us some figures. Cheers, Tony. |
||||
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
As a rounding off to the other comments, You could pack out the hub as a way of reducing the load the blades have to turn. This will reduce your output, allowing your blade low rev power to meet the load at low speed. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
| Ben Newbie Joined: 10/08/2007 Location: AustraliaPosts: 18 |
The generator is wired 3 phase star. I hooked it up to 2 100 amp deep cycle batteries.The voltage with no load 50v was as high as I was game to go.I am using dick smith rectifiers as on web site.Each phase is the same OHMS and puts out 9.8v .I got an amp meter it is putting out 1.5 amps when not in powerband range and 15 amps when spinning fast in the same wind.Are my 2.4 m blades the wrong size .If I pack out the stator will it reduce my maximum output from the machine. |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
Hmmmm.... I am wondering if this is a case of blades too big? Everything else being equal a bigger diameter turbine will turn slower than a smaller one, is this a case of blades reaching their optimum RPM before the F&P is turning fast enough? |
||||
| Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669 |
Exactly. IF the max power you are trying to extract is more than your blades can put out, then you either need to make more powerful blades OR reduce the power you are trying to draw off them. Now IF Kiwi Johns assessment is correct, will not packing the hub out from the stator have a lesser effect than if it is Gizmo's assessment? Either way is it not a DO IT TODAY & NO COST diagnostic tool to allow you to decide on the true cause? I would hate for you to cut the tips off the blades only to find that did not make an improvement. was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
No, I am not suggesting cutting the blades! They are likely very good blades! But as Tony has said there is a mismatch in the system somewhere. I think maximum power for a particular wind will be obtained at a certain voltage and current combination and these of course are influenced by the load. In the absence of knowing how to calculate the optimum load I would be playing with some sort of adjustable dummy load. Here are some ideas (which invite comment on): First off you need something to measure both volts and amps at the same time and something to multiply these together to get a watts reading. PLEASE DONT DO THIS IF YOU DONT KNOW WHAT YOU ARE DOING OR DONT UNDERSTAND WHAT I AM DESCRIBING! THE F@P HAS THE CAPABILITY OF RENDERING YOUR SUPERANNUATION PLAN WORTHLESS! 
1. Resistance wire dummy load. Rat the heating element from an old clothes dryer. The resistance wire can handle about 4 amps so for a 20 amp load you will need to run 5 wires in parallel. Stretch out the wires and mount them to nails in a dry plank. Connect your mill to one end and with a big battery clip on the other power lead start from the other end and move along the dummy load watching the meters and doing the calculations to find the point where you have maximum load. If the wires glow you need another strand to share the load. 2. Salt water load Get a metal container, half an oil drum or some such. Place some planks or such like across the top of the container supporting metal plates that hang down into the container. Fill the container with water and connect to the generator, one wire from the generator goes to the container and the other to the plates. Throw salt into the water until the current starts to rise. More salt reduces the resistance. As before log the various voltage and current values. I have no doubt that when the optimum load is found it wont be at a convenient voltage, however we do have F@Ps and we can easily rewire for a range of voltages.  |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Excellent description there John. Ben, plot the watts versus load resistance and find out at what output voltage the output power peaks. My guess is that the optimum wind machine output voltage is far higher than your battery voltage. There are several more or maybe less convenient ways to go about fixing this. But first we all need to understand the problem with some figures. But do the test first to find out exactly what you have. Cheers, Tony. |
||||
| Ben Newbie Joined: 10/08/2007 Location: AustraliaPosts: 18 |
Thanks for the help I was going to isolate the batteries,and charge one to 13.5 volts .I could be wrong but batteries take less current the closer they are to being fully charged.Then when that battery is fully charged use the ohter as my dump load.I have an old dryer so I think I will try the load idea. |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
There is no need to actually know what the exact load resistance is, just keep connecting up different amounts of load over a very wide range. In practice, that just means hooking up a whole lot of different odd stuff in various combinations to your machine. Simultaneously measure the voltage and current for each different amount of load. Maybe between 6v and 40v output, something like that. Just write down a whole list of voltages, and the current that goes with each load variation. Cheers, Tony. |
||||
| KiwiJohn Guru Joined: 01/12/2005 Location: New ZealandPosts: 691 |
You are right Tony, knowing the optimum voltage is the key. Ben, if you have the dryer element to play with you are in business. |
||||
| Ben Newbie Joined: 10/08/2007 Location: AustraliaPosts: 18 |
Are you saying to hook up say a 24v battery to my machine warpspeed.I dont know what I did wrong no one else has this problem do they .Will I damage the windings by running at a higher voltage. |
||||
| Highlander Senior Member Joined: 03/10/2006 Location: AustraliaPosts: 266 |
G'day Ben, nah you won't damage the windings, they normally run at 240 volt anyway. Just curious, the batteries your using for a load, are they new or old ones you picked up? Do they charge up ok? If they were/are rooted they could act as a short which would explain your situation. Try using your car battery or another which you are sure is operating fine. Using two batteries in series IE 24v and maybe three at 36V might give a better idea of the power band. A resistive load will be acting on the mill as soon as it starts to spin, however a battery bank will only apply a load when the output of the mill is greater than the bank voltage. Also what controller are you using? Have you tried to connect up without the controller to eliminate that as being faulty? Central Victorian highlands |
||||
| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
Ben, You have several things there. The rotor has a blade diameter and a blade pitch, and it will run most efficiently at a specific rpm, at a particular wind speed. You also have a generator which creates a rising voltage with rising rpm, and a battery load which requires a certain fairly fixed system operating voltage. Something in all that is causing your generator to be grossly overloaded, and it is slowing the rotor blades down way below where they can operate effectively. In theory, the blade pitch angle adjusts the operating rpm versus wind speed. But a better approach for very large changes, is to rearrange the electrical connections to the windings in the generator to change the relationship between rpm and output voltage. There are other solutions possible, such as a gearbox between rotor and generator, or a transformer between the machine and the rectifier. But those are far more complicated and should not be required. A moments thought will tell you that a wind machine designed to charge a 12v battery is not going to be exactly the same as a wind machine designed to charge a 120v battery. But a very similar machine could probably do either after a few modifications. Cheers, Tony. |
||||
| Ben Newbie Joined: 10/08/2007 Location: AustraliaPosts: 18 |
Thanks for your help .I have had to lower the mill to fix a bent tower.I think the batteries are OK but I will try some others.I have bypassed my controler from outback marine ,but it does not make any difference.I read in Hugh Piggotts book this morning that the alternator can be too slow for the blades causing the machine to stall at a moderate output as the wind increases.I will have to wait till next weekend now,I will let you know how I go. |
||||
 Print this page |
 |
The Back Shed's forum code is written, and hosted, in Australia. | © JAQ Software 2025 |
