Author Topic: Looking for Amps (Read 8281 times)

Shadow · « **Reply #33 on:** March 12, 2005, 08:27:06 AM »

Why are my photos so big now? They never used to be, and I havnt changed anything.

DanB · « **Reply #34 on:** March 12, 2005, 08:44:29 AM »

Hi Shadow -

I wish I could be there to look at all this.

Im really thinking something may not be quite right with the blades here. 10 ohms is a lot of resistance to be adding, I would think 1 -2 ohms would make a huge differance here. Adding 10 ohms, and having 18mph winds, this thing should be running really fast and I cannot imagine that the alternator is powerful enough to hold back the blades with all that resistance.

The resistor shouldnt affect cutin speed at all - and in very low winds, there will be almost no losses with the resistor in there. In higher winds - there will be losses in the resistor, but once things are tuned up, the losses in the resistor would be the same as they would've been in the stator if it was a good match for the blades i think. So its not hurting you too much - but again, 10 ohms seems way too much. My 48 V 17' machine leans towards stalling the blades a bit (though not too badly) and half an ohm made all the differance in the world. In this case, 10 ohms should be causing it to overspeed severely I think. It makes me think something is not right with the blades, there doesn't seem to be enough power available here somehow.

Dumb question... (Flux asked pickster about this) - but there's no chance you've got the blades on backwards is there? Flat side needs to face the wind...

Shoot me an email Shadow if you dont mind, I've got a thought here - something I think you should try.

DanB · « **Reply #35 on:** March 12, 2005, 08:56:45 AM »

It would be fun to see some close up pictures of the blades from different angles. Looking at your other pictures... they look great, but I cannot find any closeup veiws.

Shadow · « **Reply #36 on:** March 12, 2005, 09:12:32 AM »

I'll get some photos of the blades here shortly, I'm very confident they are installed correctly , flat dished out root side towards the wind, 30% cord rounded side on back. I think the fact the blades start so easily and are consistant with cut in speed, and producing 50 volts at 165 rpm is an indication blades are right on track. Now by adding resistance blades speed and volts both rise accordingly. I double checked the resistance in the element 9.8 ohms with ohm meter set at 200. Ok So If theres 70 volts going into the elements at 10 ohms resistance is that 7 amps? Or we have 70 volts going in 50 volts coming out,would you divide 20 volts by 10 ohms and get 2 amps? Which is correct way?

Flux · « **Reply #37 on:** March 12, 2005, 09:44:49 AM »

Even the sums tie up. 2A into 10 ohms gives 20v plus 50 for battery makes 70.

This agrees with your measured 2A.

Have you really got wind? How are you measuring the wind speed and is it in an area so turbulent that there is no energy in it.

2A at 70v is 140W, for 10ft cp = 0.2 this equates to about 13 mph, may seem fairly windy in a turbulent area.

Alternator seems to be working fine, blades seem ok, if there was a winding fault it would not speed up, I really cant get my head round this one.

Flux

DanB · « **Reply #38 on:** March 12, 2005, 10:00:37 AM »

Yes - Ill second Flux's question there...

is it down in trees or anything? If it's got trees and such around it the wind you have may simply be the problem.

I have a 9' stand in my yard, it's got a few short trees around it and some taller ones about 200' away. Machines sittin on that will barely turn while the one on my tower is producing gobs of power - simply due to turbulance.

If you build a tower that goes up, and down easily - it might be simply best to not worry about all this untill you can get it up into some clean air - or... if the stand is in a turbulant spot, perhaps take the whole rig to a hilltop somewhere and play with it there some.

Shadow · « **Reply #39 on:** March 12, 2005, 10:20:25 AM »

Yes there is plenty of turbulance here in the yard right now wind has increased to about 20 mph. I check my environment Canada website for my city updated every hour. About 2 miles away. So I feel the wind speed I'm using is fairly accurate. The wind turbine is swaying a certain amount maybe a foot slowly back and forth either way. I think I'm totally missing something here on what we are trying to determine. Ok we've determined that cut in speed is around 150 rpm 48 volts How many amps should be in those 48 volts? Ok then we speed up to 200 rpm 60 volts How many amps should we now have? Then speed up to 250 rpm 70 volts. No matter what speed we go up to the volts are increasing but still only shows 2-3 amps. I fail to see where this is blade related, like I say maybe I'm not understanding something. But the way this is working, wind increases... blades speed up...volts increase..that should be normal.Ok by putting on faster better blades the machine (Lets say two times better) Same wind, Now instead of 250 rpm were doing 500 rpm 140 volts but still only 2-3 amps. What did we gain? I'm looking to get more amps.. by speeding this machine up I'm increasing volts but not amps, so I fail to see the effect of better faster blades. Clue me in.

Flux · « **Reply #40 on:** March 12, 2005, 11:16:35 AM »

On no load, before cut in, there is virtually no power needed to bring the blades up to the cut in speed, perhaps 4 mph will do this.

As soon as you reach cut in speed the alternator starts to make power. If it was perfectly efficient the current would rise with no significant increase in speed but your prop would not be happy, to produce optimum power its speed should rise directly with wind speed.

In practice it is a compromise, resistive losses in the alternator mean that its speed will rise with increasing current. If it is 50% efficient it will be running at twice cut in speed. It is usually reasonable to expect a prop to work over a 2 to 1 speed range and accept a wind speed range of 3 to 1.

Normally the battery voltage remains substantially constant so the current ought to rise with the cube of wind speed. If the alternator speed does not rise quickly enough the prop falls below an acceptable tsr and fails to deliver the necessary power.

With the size of your prop and the resistance of the alternator winding the thing ought to just about work with the prop tsr falling to its lowest value without stall

but it is close and that is why we are encouraging you to increase the speed to see if this is what is happening.

You have indeed gained power as you have gone from 2A at 50v to 2A at 70v, but with this extreme amount of resistance in circuit, as Dan has pointed out, the thing ought to be running at a frantic speed.

All the indications at first pointed to stall, but now everything points to low power from the prop. You can't get more current unless you put more power in. Indications are that the prop just isn't producing anywhere near the power that it ought to be in a 20 mph wind.

There can only be 2 reasons for this low power, a faulty design prop, which seems unlikely unless you have done something very silly that we haven't noticed or more likely the power is not in the wind for the prop to capture.

If you are in line of site from the weather station and there are no obstructions within 200yds you can probably take those figures as reasonable but if there are local things closer than this upwind the figures may be meaningless.

Alternator speed is a secondary issue , what decides the amps you get out is the power you put in, the speed affects how efficiently the prop extracts energy from the wind but if the necessary energy is not there you cant get power out.

I hope this makes sense. If you really have good quality wind at 20 mph there is still something we haven't spotted.

Flux

Shadow · « **Reply #41 on:** March 12, 2005, 11:32:55 AM »

Thanks Flux, There is no doubt turbulance in the yard, but that should just mean the prop will speed up and slow down as opposed to running at a constant speed. Ok I understand that. So will not the current rise and fall accordingly?.Isnt an rpm an rpm, say the wind gusted to 20 mph and I got a reading of 200 rpm at that shouldnt there be a set number of amps at that 200rpm?I have this mind set that if you have 2 amps at 200 rpm , you should have 4 amps at least at 400 rpm and 8 amps at least at 800 rpm.And so forth, but if I understand you correctly speed will increase your volts but not your amps? Still cnfused..

Shadow · « **Reply #42 on:** March 12, 2005, 11:39:38 AM »

Ok, I re-read your last few lines, and the turbulance factor may be the problem, the faster the wind blows the more yawing I'm seeing but not so much increase in prop speed. It changes pitches (sound-wise) but that is not neccesarily speeding up.

rotornuts · « **Reply #43 on:** March 12, 2005, 11:58:25 AM »

Shadow, I'm an alternator amature and know only what I've read but I've done lots of experimenting with blades and rotor design using hub drag to simulate alternator load. I'm with Flux and DanB on the clean air thing. Your blades appear to be running in the TSR 3 range and that's too slow in a 20 MPH wind, they wouldn't have been designed to run that way so you've got stall. So far it seems that alternator problems have been ruled out and the fact that the machine is on a 12' test stand seems to be the most likely culprit, it's the one thing that's different from other machines that are performing correctly. The air at ground level in close proximity to obstructions, even ones that aren't directly "in the way", will be rolling and swirling and gusty and this is preventing your blades from hooking up with the wind and taking off. Untill your blades approch their designed TSR they will be operating in a heavily to semi stalled condition which is normal, but if your wind speed is very inconsistant and the air across the blades turbulent your not going to reach the point where your blades really perform well. They will remain in an undesirable amount of stall as thet try to accelerate then loose the airflow that was accelerating them then get it back and have to try accelerating again only to loose it again and round and round it goes. Add in turbulent air that induces additional drag and doesn't flow properly across the profile of the blade and that's it. Go up and away from obstructions and keep one hand on that knife switch.

Nuts,

rotornuts · « **Reply #44 on:** March 12, 2005, 12:03:55 PM »

I should say that I think you blades are "hooking up" just not as well as they should be.

Flux · « **Reply #45 on:** March 12, 2005, 12:06:41 PM »

Yes it does seem to be the only real explanation, if you have any significant obstruction upstream it could make what seems a windy site useless.

If there are unobstructed directions available I would wait for the wind to move to a more favourable direction.

I have just run a few rough figures for your alternator into a 50v battery with no added resistance, don't pretend these to be very accurate but near enough as a guide.

For cut in 150 rpm, 4A at 180 rpm, 8A at 217 rpm, it is quite a steep rise with speed, that is why the concern about about the possibility of stall.

It may be a possibility that you have a combination of stall and lack of real wind.

If you get what seems a better wind and it still doesn't produce then try the resistor again. If you get lots of speed and volts across the resistor then you have wind power but too much resistance. If you can manage about 2 ohms that would be a good value to try.

Flux

Shadow · « **Reply #46 on:** March 12, 2005, 12:13:46 PM »

Thanks Rotor, What you say makes alot of sense. The more I watch this thing and listen,that is exactly what is happening. I know the blades are probably not the most effecient, being first ones I built and all.I guess I just related current to speed regardless of turbulance.I have a 35 foot tower, I just need to go get. I thought I would do all the testing I could before I put it up that high, but I think some testing will have to done ,only after it is that high.I'm glad Flux and Danb and all have lots of patience, I would have thrown my hands in the air by now. Thanks Everyone

Dave B · « **Reply #47 on:** March 12, 2005, 05:53:03 PM »

Shadow,

I have built my 12' single phase from the start with the only intension to pre-heat water. Here's a brief summary of what I have found. My first stator was wired with 18 guage and over 100 turns per coil. Plenty of volts, very little "push" of current. I could light up a 100 watt bulb and nearly burn it out just spinning by hand. Here's where it gets interesting : Measuring the resistance of that bulb with my meter (approx. 10 ohms.) What ? Yes, now look at ohms law. I was spinning my alternator at a known rpm that would measure 100 volts no load. With the bulb in series at the same rpm 100 volts / 10 ohms = 10 amps x 100 volts = 1000 watts

Now, a 120 volt 1500 watt hot water heating element measured 10 ohms with my meter. Replaced the bulb with the heating element and I could not hardly turn the alternator half the rpm (there was just too much physical resistance). I have since wired a new stator with 16 guage and 80 turns per coil. Much more "push" of current at lower voltages and therefore less stalling of my blades depending on the load vs. rpm. Bottom line is : You could smoke a 10 ohm 1 watt (rated) resistor quick and easy with a flip of the wrist but try that with a 10 ohm hot water heating element (same measured resistance) It takes alot of power to generate any useful volume of heat and with your 17 guage wire and large number of turns you stator is half the load itself. You must consider the "total" resistance of your circuit including the resistance of your alternator. Maybe this helps, maybe not but I've learned from the same frustration. Dave B.

Shadow · « **Reply #48 on:** March 12, 2005, 06:07:01 PM »

Interesting stuff, Thanks for the input Dave.That was gonna be my next project, to build a wind turbine specifically to heat water.(and a back up for electricity). What conclusion did you come to that would be more or less ideal for running some heat elements? I would like to stay with my 48 volt system, but maybe increase some current. The more I learned about this the last couple days I think it is performing as it should/or is capable of in it's current turbulant location. Be interesting to get it up on a tower.

Dave B · « **Reply #49 on:** March 12, 2005, 09:20:18 PM »

Shadow,

I've learned from all the experience on this board and from my own design that my alternator (as with many here of similar design) is capable of at least 1500 watts without any concern at all of it burning up. My 12' blade set designed for approx. TSR 6 can no way crank out this much power unless running in 40 mph winds connected to a 10 ohm heating element, this would make very usable heat for water. Right now as the rpms increase (I have designed a variable load controller to allow no load start up and selectable load "turn on" set points) it really takes 15 - 25 mph winds to "lock in" the blades for a constant output of usable power (300-600 watts using 48 volt heating elements). I want to heat water and not worry about charging batteries (I can rectify my output and do that anytime later if I want). By the way, my mill is on a test tower of 10' also so I know all about gusty, turbulant winds and never allowing the blades to grab to turn up to speed, especially under load. In the Spring I hope to get this up near 100' on a tilt tower. Over time average winds can heat water so I'll be monitoring this closely. My next step to more power is a larger blade set with my same alternator and to be certain to furl it just before it's max rating. I think I can get 500-700 watts at 15 mph winds with a 16' or 18' blade set. Keep me informed, I'll do the same. (this is my mill, foam and epoxy nose cone to be mounted soon) Dave B.

Shadow · « **Reply #50 on:** March 12, 2005, 09:32:00 PM »

Very nice looking setup Dave, So You are useing AC power for your 48 volt elements? How many elements in what capacity of water? I tossed around the idea of using either 12 volt in series or 24 volt in series so they came on at different stages, low winds you may only have 24 volt elements heating, as wind increased you got up to 48 volt. Something so as to be heating water no matter how strong the wind.Yours sounds like a good setup.

Dave B · « **Reply #51 on:** March 12, 2005, 10:13:05 PM »

I'm still experimenting to get the load switching right on the power curve. Right now I can switch on 2 solid state relays at selected rpm (ac volts) There is also hysteresis built in to allow a delay of turn off when the activation voltage drops below level, this dampens the cycling of the relays. With solid state this is not an issue from a physical stand point but definetely helps efficiency in gusty wind conditions. I purchased 1 48 volt 350 watt heating element and I am experimenting with this as you say and also the 120 volt elements in series parallel combinations. I think a 24 volt 350 watt element would kick on too low in the blade power curve to be useful (you have experienced this condition, too much alternator not enough blade.) Exactly what a larger blade set would correct. As is frequently mentioned on this board there is very little useful power available from the wind below say 7-8 mph unless you have a very large efficient blade set and extremely efficient alternator which are both expensive propositions. I am convinced now that my next re-designed alternator and blades for heating water will need to be in the near 20' range and more magnets on larger rotors of maybe 18-20". Slow turning maybe 200 - 225 max rpm, fixed pitch, tapered blades. I am very convinced of the efficiency of the silicon laminants, single rotor axial design, especially if you can slot the laminants to receive the coils (Ed at windstuff has been very helpful for me with this) Keep us posted. Dave B.

ghurd · « **Reply #52 on:** March 12, 2005, 10:35:46 PM »

Dave,

Did you look more into mosfet switching?

They can give a 'almost' on, a 'little more' on and 'all the way on' in a narrow voltage range.

A big mosfet ('44' or irf510 - 530 or something) could handle the amps and volts, but switch the load on gradualy.

I think that could 'match' the blades automatically. A small V increase would greatly increase the effective load, increasing the amps. And that would lower the V, reducing the amps.

Self balancing. It would use what it can make. And it could get to the desired speed (volts) without drag before the load even came partially on.

I believe it would be like a variable resistance, changing to meet the avaliable power, and control the blade RPMs.

I don't know blades.

G-

Flux · « **Reply #53 on:** March 13, 2005, 01:03:08 AM »

Dave

Just a little digression to clear up the thing about the light bulb. Your 10 ohm heater will always be 10 ohms, but the bulb is a different animal.

You may have measured 10 ohms cold. but at working volts it will take 1A and its resistance will be about 100 ohm.

Tungsten has a very high change of resistance with temperature. A lamp has a different resistance for each temperature it runs at .

Flux

Vernon · « **Reply #54 on:** March 13, 2005, 03:58:26 AM »

Obviously you need more of those heaters !

Power is proportional to the square of the voltage, 120 is 2.5 x 48 ... square the 2.5 and you get 6.25 times the power at 120V. So divide that 1500 watts by the 6.25 and you wind up with a 240 Watt load when used at 48V. That number also results if you calculate the current at 120V and 1500W. You get 12.5 amps and working the next step on the calc gives 9.6 ohms. 48 squared divided by 9.6 also gives 240W .... and more number punching gives a current of 5 amps, just about what you had.

A fully charged 48V battery bank will show 50.4 volts so the batteries might be helping the current. I would disconect the batteries and just run the wind generator into the heater, measure the voltage and current at your typical wind speed and see what kind of power you get. I would then measure the open circuit voltage and also momentarily short the wind generator output and get a flash current reading (before the blades slow down). Say you get 60V and 10Amps .. that means that the internal resistance of the generator is 6 ohms and for maximum power transfer the test load would have to be 6 ohms. This internal resistance is a key to performance, if it is too high you can't get watts to a load. A good value might be 10 to 15% of the load resistance (maximum). A normal voltage for the end point of a charge on that battery bank would be 55 to 56 volts with a charge current of 1A or less, the machine at high winds should require shunt regulation to keep the voltage below that number on a fully charged bank. An objective might be the maintenance of 55V on a fully charged battery (~ 1A) while supplying 10AMPS to a system load for a total of 605 watts in a 25MPH wind. If the objective is not met it is neccessary to determine if the problem is a lack of mechanical power or electrical. This can be predicted by the internal impedance test above ... low impedance and the ability of the short to quickly slow the blades indicates that the generator can load the prime mover and that would indicate the blades are holding it back if you cant get enough output.

Hank · « **Reply #55 on:** March 13, 2005, 03:41:50 PM »

Shadow,

Have not read all the comments so if I'm off base I apologise to all.

To determine current:

I= (open voltage - Battery voltage)/Internal resistance.

Looks like you are getting about 3 rpm/volt so lets say your mill is rotating at 200 rpm that will give you about 66.7 open voltage. I guesstimated your internal resistance to be 2.5 ohms. So the current you should be getting into your batteries (assuming 48 volts)roughly:

I= (66.7 - 48)/2.5

I= 18.7/2.5 = 7.48 amps.

(I neglected to factor in diode losses)

Had a similar thing happen to my genny a while back, it would not go over about 135 rpm and not produce much more then 4 amps (12 volt system)

In my case I was stalling big time (8 ft rotor).

I rewired to delta (in effect increasing my rpm/volt and decreasing internal resistance)the net result was that my cut-in speed incresed to about 200 rpm it does not stall and I have seen in excess of 50 amps in 25-30 mph winds at which point it furls.

It starts to produce power (charging) in about 7 mph winds.

In my humble opinon you are stalling big time.

Don't get to hung up on amps but rather look at the wattage. 50 amps with 12 volts would be the same as 4 amps at 48 volts. Power is the same!

At the end of the day power is all that we are talking about.

Have fun

Shadow · « **Reply #56 on:** March 13, 2005, 09:05:33 PM »

I agree now Hank,After going through this whole process of trying to get more amps, I realize I'm probably getting just the right amount for the location of the windmill. I think once its up at 35-40 feet in nice even wind it will perform just perfect.It's all a learning process for me, and I've learned a bunch last few days.Thanks for all the input.

nothing to lose · « **Reply #57 on:** March 13, 2005, 11:00:55 PM »

Jerry posted me a link awhile back to one he has.

Trying to find it again myself, I didn't order it back then like I had planned to but will if I can find the link again.

Also Harbor Frieght has one now. I think the one Jerry linked was about $50 (and probably better too) and Harbor Frieght is more than that for theirs.

Don't recall exactly what it was called now. Infered remote TACH.? I found one match for that but wrong one, no link.

News:

Author Topic: Looking for Amps (Read 8281 times)