Safe power estimate for #16 two in hand (#13)

[Dave B]

I'm looking for a safe power estimate where it would be unlikely to burn up my stator. I will be heating water direct designing my own load controller. I want to output 120 VAC at a max. 200 RPM for the 18' diameter. I am currently testing the 20 mag / rotor 15 coils 3 phase with a single test coil of 60 winds 2 in hand #16. I have an accurate reading of 6.0 VAC @ 180 RPM from this one coil. Am I figuring correctly that this should be about 90 VAC @ 180 RPM for 15 coils 3 phase star ? For those of you who have run 3 phase and have a pretty good feel for fairly safe outputs per wire size and coils etc. I would really appreciate a conservative power estimate that I could expect to be safe to run this at. (I promise not to hold anyone to this) I would think that 1500 watts continuous should be reasonably safe with expected peaks of 2000 watts short term to be typical. It's my understanding that #16 two in hand is equal to #13. Any ideas on either rectifying to DC load or maybe 3 phase AC to 3 seperate loads etc. ? Stator will be West System Epoxy. I appreciate your suggestions.  Dave B.  

[Flux]

If you have 6 vac per coil, you will have 30v for the 5 series coils and 30 x 1.7v line if star connected. This is 51v not 90 at 180 rpm.

If you rectify to dc you will have about 51 x 1.4 = 71.4v dc.

I am not convinced that West System epoxy is much good for the temperatures you will need to operate at.

flux

[Dave B]

Flux,

  I still get confused with 3 phase. Would this mean then that lets say a 10 ohm load. If rectified to DC then this would be approx. 70 / 10 = 7 amps x 70 = 490 watts ? I get that but now with the 3 phase are you saying that the voltage across each of any 2 of the three outputs would be 51 volts AC ? If I put a 10 ohm load across each of these 3 outputs (I believe called delta) would then each produce 51 / 10 = 5.1 amps x 51 = 260 watts ? This times 3 equal to 780 watts ? I guess resistive heating with 3 phase is not so simple and maybe not any more efficient than a single phase set up. Sounds simple, all I want to do is heat water. Any ideas to best do this with what I have so far ? Dual 16" rotors, 20 neos each 1x2x 3/4. Thanks for the help.  Dave B.  

[scoraigwind]

yes well it seems a rather small alternator for such big blades but I think you can do 1500 watts out, at 50 odd volts and 30 amps.  It is hard to suss this without any info on magnet sizes.  It is really great if people regularly repeat all sorts of basic data such as number of poles, magnet size, battey voltage etc as often as possible for that sake of my tired brain.  I don't remeber stuff even if I get told it, so tell me it again.

I am not sure how big this thing is?  I would reckon about 50 to 100 watts (max) dissipation per coil is acceptable in a good wind for cooling.  What does anyojne else use for max output calcs?

[wdyasq]

"I am not convinced that West System epoxy is much good for the temperatures you will need to operate at."

- You are correct Flux. A more proper resin for stators will be Vinyl-ester.

Ron

[Nando]

DAN:

I have sent 3 message to Your email, in reference to the design of this stator.

To produce 120 volts per phase that if STAR connected the AC voltage would be 210 Vac @ 200 RPM.

Nando

[Dave B]

Hi Hugh and all,

  My rotors are 16" diameter and each rotor has 20 neos 1x2x 3/4" N40. It seems I am breaking new ground here by wanting to heat direct with no batteries. Can't compare apples to oranges so I am hopeful that those who are heating direct with their wind generator in this mannor can offer some suggestions. All opinions lean toward the 3 phase as being the way to go, I can do this or single phase. I can rectify for DC or run wild AC and if anyone has a proven load controller set up to do this I'd be greatful to see the schematic. (I know you had a sketch of a type of controller previous which I will search for which may be helpful) I see some amazing power figures out there for charging batteries. I may be wrong but if many are running 2,3 even 4K watts at times with the dual rotor design I should be able to lazily watch 1000-2000 watts turn out with my design in winds of say 15-25 mph. Vinyl Ester for the stator ? Suggestions and brand ? Thank you all for your help. (see 18' fabrication taking shape back several positings) Dave B.  

[Dave B]

Nando,

  You may have sent your reply(s) to DAN B. I am Dave B. If not I have not received these in my e-mail but I sure appreciate your help. If you could   try again my e-mail address is :  bruggelog@madbbs.com   Thank you, Dave B.

[willib]

Dave , check some of Mr. Zubblys posts , he is heating air , i think it was..

and he is using contactors (relays)

i think without some sort of relay system , your blades will have a hard time starting , because the heating elements will be attached directly to the alternator , and consequently it will be bogged down in low winds , and may need a strong gust the get them started , without relays

something like at (x)rpm connect relay 1

at (y)rpm connect relay 1 & 2

ect.

hope this helps

[Flux]

Dave

I have had a look at this using the details you gave to Hugh. I don't think burn out is going to be an issue if you load it sensibly, your problem is going to be obtaining the power you want at the low speed of 200 rpm.

When you come to heating or mppt for battery charging you need an efficient alternator that means big and yours is relatively small for a 16ft prop. I assume you have chosen such a large prop to obtain more power in low winds. This works fine for battery charging, but for heating, the lower powers are of little use. 200W of battery charging is very useful, but 200W of heat will not do much.

If you want to keep the 16ft prop and also keep to the 200rpm top limit then I think you are looking at about 1500W and at an efficiency of probably 65% so stator heating is not going to be an issue.  You could of course hold it into higher winds with a lower value of load resistance to drag the speed down into stall but then you would see much higher stator losses and still not see much over 1500W. It will be much better to furl at a low wind speed that gives 1500W at high efficiency than stall limit it to keep the speed down. This may mean that you will need a good alternator offset to make it furl properly, the offsets used for stall limited machines may not work with the prop tracking peak power.

All depends on your wind and how much heat you want and how often. If you came down to 12 ft and let the speed go up to 270 rpm ( same tip speed) , you could probably easily exceed 2kW for the same stator heating, but of course you would need higher winds to get it.

At present if you want to use 120v heaters then you will need to double your turns with a single wire for raw AC.

Whether you use ac or dc depends on your load control, switching dc is a major problem, I think you will be forced to use mosfets (or IGBTs) with pwm or use a phase controlled thyristor(scr) rectifier and solve the variable frequency firing circuit problem.

For 3 phase raw AC you can use mechanical contactors or triacs.

There is a strong case for considering single phase from the control point of view, but it means making the alternator 50% bigger for the same power out and it is already very small.

Flux

[Dave B]

Thank you Flux for the information. I will be interested to know more about the 3 phase control as I move further along with my testing. You mention "contactors" is this what I would call mechanical relays ? I really want to keep things simple and under control. Early furling and possibly a manual way to pull the tail for high winds as well as of course the possiblity of shorting the output for a brake besides will be considered. After seeing my 12' overspeed at 800+ rpm loaded this will seem slow and easy. How critical is it for exact balancing of the loads for 3 phase ? Any help with the control circuit and ideas is appreciated. Thanks again for your help, updates to follow.  Dave B.

[Flux]

Contactors are mechanical relays intended to switch power loads.

Exact balancing is not important until you get near full load but I don't think it will simplify things much if you don't keep it balanced, depends on the loads you have available.

For contactor control you will need sensors preferably to monitor speed( frequency) to keep adding steps of load as the speed increases. You will need dead band ( hysteresis) to prevent rapid switching. The larger each step is, the more hysteresis you need to prevent rapid switching.  

With electronic relays (triacs) it doesn't matter so much if things keep switching on and off, but a reasonable amount of hysteresis will still be a good idea to keep radio frequency interference low.

I think Zubbly used voltage sensitive relays, this will work but will probably need more dead band as you have the alternator internal volt drop as well as the drop in speed with load step.

Flux

[Michael G]

I am also planning on heating water with my wind genny.  The genny is finished and just waiting for the rain to quit and the wind to drop a little to put her up.  I decided to wire it in star and rectify each phase and use the DC to power the elements.  I wired the elements in parallel to get the resistance down to about 6 ohms.  If you have 5500 watt elements you can get the resistance down to around 5 ohms.  I have seen some water heaters with a mounting area for a third element too. but that was an older heater.  Good luck !

Michael

[scoraigwind]

I use 3-phase for heaters on wind turbines.  I have a circuit on my web page http://www.scoraigwind.co.uk/circuits

I prefer to balance the load.  I did it at first with heaters on different phases and suffered a lot from the vibration it produced.  I would not use single phase if you can avoid it, although it does simplify the wiring.  It will vibrate badly.

I agree with what flux is telling you (as usual).  Low windspeed performance is great for batteries but not so good for heating.  use a smaller blade and run faster in stronger winds and get a lot more power during those times.

Happpy new year!

[tecker]

 You really need to rethink running a stator coupled to a dead short in power numbers . Take a look at most power transformers .They all have good cooling (lots of room inside or oil filled) . Maybe set the coils up in a jig and see if they will handle the power before you pot them If you have hot spots in your winding or a big startup 15 or 20 times a day ( or more)as the wind rises and falls you could simulate that . Thats the beauty of using DC for a small unit ,You can control the power into a load and let the genset rise and fall and furl normally and stay cool enough to keep the plastic from breaking down .