turbine back up at last

[bob golding]

after much re redesigning and a long time i have finally got my turbine back and producing power following my rebuild. photos to follow when i get a chance. what i did was change the configaration from 16 magnets 12 coils,to 12 magnets 9 coils. i used the same magnets but stacked them. this was to give me a chance to make the stator bigger and get  better cooling for the coils. 12 coils with the volvo discs was a bit tight. i now have 14 inch rotors. i am using eds wedge magnets. 3 stacked to give me around 1/2 inch thick. i cast the rotors in vinyl ester with 50% filler. i can definitely recommend vinyl ester over polyester for casting. even though it is more expensive. wont ever go back to polyester. all good so far. i am getting around 100 watts at 15 mph at the moment. the blades are 9 foot and to eds design. tsr should be around 6. will get some data on true wind speed and blade speed when i get time. but so far so good. remains to be seem if this one survives the winter storms. can get 90 mph winds here in  the winter, and it is very exposed to the Westerlies from the atlantic which is only 1/2 a mile away. still working on the block and tackle system for lowering it by hand. nearly there just need a couple more blocks. will measure all the loads with a spring balance but well within the swl of the blocks and the rope. blocks are rated for 2 1/2 ton rope is 8 mm wire rope. i can almost lift it by hand already and nothing seems to be over stressed.

cheers

bob golding

[Flux]

If your wind speed is accurate I suspect you are fairly well stalled. Keep an eye on things for a while and if the power doesn't go up quickly with wind speed then try some resistance in the line.

Flux

[David HK]

Bob,

Two things. Where are you on the globe?

Secondly, can you offer a short narrative about why you have preferences over resin types - poly and vinyl.

Resin differences are of interest to me.

Thanks.

David in HK

[Dave B]

 Not to hijack Bob's reply but now I am sure he will agree. If you feel the need to cast your rotors do it with a quality adhesive resin. Bondo (body filler) is cheap and looks good when first used but is not an adhesive. It will crack, fall apart, look ugly and basically then hold water. The magnets will rust, there is nothing holding them at this time and the situation just gets worse. There are many reports on this.

 Fully embedding the magnets is also not necessary with a quality epoxy adhesive and proper preperation. Casting looks nice and maybe more marketable but also allows less magnet area for cooling. Just some thoughts, spend the money on a quality adhesive and do it once.  Dave B.

[bob golding]

thanks dave,

the main differences i have noticed is  far less shrinkage with vinyl ester, plus it doesn't need as much catalyst so set up times are longer. this is really useful when you have to reposition things like glass cloth. plus it is waterproof and a lot tougher. the only downside is it costs twice as much as polyester,but as dave points out you only have to do the job once. i have only used it with filler so cant say what it is like without the filler.

i am in the UK very near to lands end.

bob

[bob golding]

hi flux, i suspected it was stalled. the wind speed was not that accurate. taken from the local weather station 1 mile away but about the same height. my stator resistance is around 1 ohm and the line resistance is about 0.5 ohm as close as i can tell. the wind has died completely now following the law of wind turbine erection. i have reconfigured my doc wattson so it is now measuring power into the batteries from the turbine. this should give me the peak power. hopefully when i get everything set up right i can try removing the  line resistance and opening up the gap a bit. if it runs away in a gale i can close it up again. does this sound  a sensible way to go about it or is this asking for trouble. i am hoping with the block and tackle system i can get it down quickly if i know a storm is due,or i have to leave it unattended. we usually get plenty of warning of big storms.

bob

[Flux]

I would aim for cut in at 7mph and if it seems earlier then I would increase the air gap. Otherwise leave the gap as it is and choose a suitable line resistor to get best performance in normal winds.

Try to get it to furl at a safe power level with this best resistance in the line. If you have to stop it in high winds then you may have to short before the line resistor.

If you can't get it to furl then you may be able to run it with no resistor and fairly hard stalled. In normal winds I suspect it will stall regulate. The danger of this method is that if it should pull through stall in a high wind it will fry unless you can lower it quickly.

Only if you can get it furling with optimum resistance in line can you be confident that it is completely safe to leave it to its own devices. When properly furling the power will actually drop in very high winds. Unless you see this drop and you see it running almost parallel to the wind ( compare prop to some reference vane) you can't be sure it is really furling.

Running stalled many of these things bend their tail and look to be furling but in this case the power will still rise with increasing wind speed. If it breaks out of stall it may do well over its safe power.

Plenty of offset, optimum line resistance and change the tail weight or reduce the hinge angle until it furls is the safe way to deal with it and you get the best available power in normal winds. you will probably see a significant falling in power in very high winds but this is safe and you will have plenty of power on those days.

Just a few comments about resin rather than another post.

Polyester is virtually useless for magnets, it sticks to nothing but may hold the whole block together. If the climate is mild it may be fine. In a wet climate disc and magnet corrosion is likely. For magnets epoxy is best and vinyl is better than polyester,

For stators polyester is satisfactory, it stands temperature reasonably well. Vinyl is far better, it is rated for higher temperature and has better mechanical properties and is worth the extra cost.

Normal epoxies don't have the temperature ratings for stators. There are specials that will do the job but you have to get the right ones and they are expensive. DaveB has obviously found a satisfactory source but in general I wouldn't use normal epoxies for stators without being absolutely sure of what is on offer.

You can expect the resin in close proximity to the coils to be reaching temperatures that are over 160C and that is being modest ( I am sure many are exceeding 200C) and normal epoxies are completely soft at this temperature.

I have to admit that I have used polyester for stators with no trouble but with my loading the temperatures are not that high. I am not sure that any of these materials are rated for much over 150C so you are probably on a limited life cycle but that may be a few years with just the occasional overload.

Flux

[David HK]

Thanks Bob.

I used to be a policeman based in Cornwall (Camborne) in 1967/68. On August Bank Holiday in 1968 I created the biggest traffic jam Redruth and Camborne had ever seen to that time. It stretched all through Camborne and went past the Redruth bypass and way back up the A38. It took hours to go away!

I used to live in a house that overlooked the beach at St Agnes - wonderful life as a teenager growing up in a village!

Still have a house in St Austell.

Thanks to all on the notes above.

David in HK

[imsmooth]

Dave,

I cast my stator with Bondo and coated the final casting with marine epoxy.  I cast my magnetic rotors with marine epoxy.  Both had chopped glass.

Two questions:  do you think this is ok; and, if vinyl ester is much better for the stator where can I get it and what is the product I should order?

[Flux]

The polyester will be ok. You will need to keep the current reasonable but that shouldn't be difficult as I think you are using a grid tie inverter.

The limiting factor will probably be the wire for most of these machines but it depends on the severity of overload and the time scale. Most of the better grades of wire are rated for 200C. You can reach that at the centre of a coil with the outside way below that figure.

I have never seen a temperature rating for polyester, it's not normally intended for this sort of application but it does stand heat fairly well at least in the short term without falling to bits. I suspect like most things the long term survival will not be so good but with sudden severe overloads the thing will hold up as long as the wire. Most of the failures I have seen have had coils completely burnt out and I can't help feeling that they may have run for months or years like this.

I think vinyl ester has a specified temperature rating of something like 160C so it will probably out last the wire during overloads.

Failure will be instantaneous if the wire shorts between turns, otherwise it may run burnt for ages. The only way resin failure will bother you is if the thing is no longer strong enough to hold the coils in position against the magnetic forces.

Next time choose vinyl, it is better all round but don't expect to be able to push more out of the thing, it will just have a longer life at the same power level.

With mppt I think you will get near 3 times the rating if you push to the limit but better to keep the rating lower and it will last a long time.

Can't help with supply, here in the UK vinyl is only available from a few suppliers and you have to buy quite a lot. I am sure others can point you to a supplier in your part of the world.

Flux

[imsmooth]

Thanks Flux.  Hopefully, someone will jump in here and give a source for the vinyl resin.  My wire is 200c rated and I am using MPPT.  I have an IR temperature probe, so I can test the temperature tolerance of the polyester by loading one of my test stators on my bench.

[Tritium]

If you are in the USA.

http://www.fibreglast.com/showproducts-category-Vinyl%20Esters%20Resins%20&%20Hardener-11.html

Googleing Vinyl Ester Resin also turns up others.

Thurmond

[Dave B]

Fully furl plenty early and admit that these machines are not continuously rated at what most think. Fully furl at what you think the machine's max. rating is and if you are close then when the good continuous winds near that speed come (and they will) you will burn it up, period. So many are concerned with the heat factor, if so build a bigger machine and derate it to get the same output without burning it up. The design has limits, push them and you will kill your machine. Dave B.

[bob golding]

hi david,

the traffic hasn't improved much. gosh all the way from cambourne to the A38. woud need a computer to do that now. glad i was a help with the resin.

bob