Crazy waveforms and poor performance maybe

[solarengineer]

Hello all, I recently put up a 30ft tower with my generator on top. It's the one with 12 magnets per rotor(1inch x .25 inch) dual rotor and 9 coils 70 turns 2 in hand of #20

it has super power on the bench, so i think. i puts out .051 volts per rpm on the dc side. it cuts in at 250rpm which is higher than i was hoping.

at cutin its only producing .2 amps and at 330rpm 2.5 amps its a 12v machine.

the blades i carved i was having some trouble with so i decided to carve a 10ft diameter set and then I cut 6 inches off the tips to make it a 9 foot diameter. the reason i did this is because flux had suggested 8ft with tsr 7 because winds here are terrible. usually 5-12 miles per hour. but i couldnt figure out how to lay the blades out to carve tsr of 7 so i though rather than bugging the list I would try carving a big set and then just keep cutting back as needed.

Right now the diameter is 9 feet. I would have thought I would get far better power out of this thing than 2.5a at 330 rpm.... if i cut the prop back to 8 feet is it possible that it would spin faster at the same wind speed and give me more output?

I have since figured out how to carve an 8ft tsr 7 i think so i will give that a try. i know the hub will spin faster at tsr 7 but would that give me more power? I know this machine is capable of around 400-600 watts because Flux and a few other on this list helped me and I have faith!!!

I have the machine connected through 2 bridge rectifiers and I also noticed something strange watching my digital osilliscope today.... I get perfect sine waves from the machine until it just gets to cut in then the tops and bottoms of the waves become sharp and slanted.. see pic below.... i'm not sure if this is normal but the coils are round as well as the magnets and the center hole is only a few turns smaller than the od on the magnet.... I took great care in making this machine and would love to know if it's performing well.. the high cut in voltage is puzzling since the airgap is only slightly larger than a half inch and with 70 turns.

When i tested this genny on the bench with a motor i got 60V at 900rpm and sparks galore. it also ran a 60w bulb with only slight loss in rpm.

is it my blades? what could be wrong? I know our winds have been gusty and shifty but the blades never stop, it only jumps in and out of cutin every now and then.

thank you for any suggestions. its a great looking machine i will post some pictures soon.

Respectfully,

Jamie

[hiker]

hey......

is it wired in star or delta?

hmm-even your bench test should have put out more power..

i would think at least 200 watts--with a electric hand drill..

i easly got that with my small ceramic powered mills[lowes mags]

maybe you have a break in one of your 2 in hand wires...

that would be a tuff one to find..good luck.....

[hiker]

looks nice --how thick is your stator-with that small wire you should have been able to get it down to 1/4" or 1/2"... max out on the power of the mags..

[willib]

have you tried warlock's blade calculator

http://www.warlock.com.au/wind.htm

it is really a fantastic program

it even does feet and inches..

anyway your cutin is very high i guess you know that .i plugged some numbers into warlock , 2m dia , 6.6 feet , blade , tsr 7, will spin at 300 rpm in a 10 mph wind and give approx 61 Watts. good luck and have fun

[Ungrounded Lightning Rod]

Low voltage.

High cutin.

Little current.

Check your gap.  (The space between the magnets on the two rotors, not the sum of the spaces between each rotor and the adjacent face of the stator.)  Sounds like it's too wide.

Cutting the ends off the blades reduces your TSR in proportion to the reduction in length.  Also:  Power fades out at the end of the blade because the air runs around the end (giving no push) rather than around the side (which is what you want.)  It does it for an amount of the tip proportional to the width of the blade near the end.  So you get a double whammy cutting the blade down:  The inactive tip if it were the same lenght is a larger fraction of the blade, and since the blade is wider the inactive amount of tip is actually larger.

If you can't recalculate the blades for the shorter length, it's far better to just scale them down in all dimensions, rather than cutting off the ends.

[Ungrounded Lightning Rod]

Also:  Except for the very tip, the farther out the blade the more power you get per unit of blade length - because you sweep more air far from the center than near it.  Power is proportional to the SQUARE of the radius.  Cutting a little off the end cuts a LOT off the collected power.

[RP]

"I get perfect sine waves from the machine until it just gets to cut in then the tops and bottoms of the waves become sharp and slanted."

This would be expected.  What you're seeing is the voltage being clamped by the battery.  That flattens off the tops and bottoms of the sine wave.  You'll also see some spikey stuff from the recitifers switching on and off (into the clamp effect of the battery) and some inductive effects from the coils during the switching.

[Flux]

Jamie

i have been looking at your earlier post and I see that you asked the question about magnets 1" x 1/2" thick.

In this post you say they are 1/4" thick. That will explain the high cut in.

There are discrepencies in your data, you say that you got 60v dc at 900 rpm and that would give a cut in of about 200 rpm allowing for diode drop.

That is a fair way from your 250 rpm cut in so I suspect one of your speed measurements is not right.

Half inch air gap is quite wide for 1/4" thick magnets and the 250 rpm cut in may be realistic. I have never used round magnets, but with rectangular ones of the same area I would have expected cut in about 220 rpm.

With the thinner magnets I think we have to lower your expectations somewhat.

250 rpm is a good cut in speed for a 6 ft prop, you could manage perhaps 7 ft but with a tsr between 7 & 8.  You may still be able to have a maximum rating of 400W but remember these maximum figures are always based on what the alternator will stand and will only be reached in high winds.

In low winds the larger the prop the larger the output but you have to have the alternator speed suit the size of prop.

You seem to have de-rated your wind speed since an earlier post, so you are not likely to see big power very often.

Starting with a big prop and cutting the blades is an uncertain process, it will make it run a bit faster but not that much. If it is based on Dan's type blades with little twist and taper it works better than using ones based on the blade calculators with lots of twist and wide at the root.

To scale tsr with diameter you need to scale everything together. If you shorten a blade you increase the tip angle and also the chord width, both of which reduce tsr.

I think you may be able to modify the present blades to something nearer what you want. Cut them down to about 3'6" to make the diameter 7 ft. Make them about 3" wide or a bit less at the tip and about 6" at the root, plane the tips to an angle of 3 deg by removing material from the front face leading edge. Try to get an angle of about 6 deg at the centre and a width of 3.4 to 4" and just blend in the bit near the root best you can with the outer part .

See how this works out, it should spin much faster, but remember that the power in low winds is very limited. Don't expect anything below 7 mph. You should get about 100W at about 12 mph.

Flux

[solarengineer]

Thanks everyone..it seems smaller turbines are off my diet. I will make a 7ft tsr 7 flux and see how that goes... i also learned about saddling the dead horse... my pole actually bounced....Yikes!

I am building a clone of the 10ft tims turbine with 2x1x.5 inch magnets

he uses 2 in hand #14 and 34 turns...naturally i misread that and used 36 turns but that should lower the cutin somewhat. his cuts in exactly at 150rpm which is what my 9 ft blades do all day.

The coils themselves are about 1/2inch thick(will crush them with vise). they were hard to make. i don't know how some of you manage to just not hold the wires at all as they wind and end up with neat coils. i hold lots of pressure on my wires(till my hand hurts) and they still skate all over the place and make ugly coils... maybe i will try just leaving them alone(not touching them) and let the winder just go.

anyhow, based on this post am i shooting myself in the foot with this machine at 36 turns with dual rotors and these neo's?

i'm going to use 1/4inch plates 12-13 inches in diameter. since my coils are ugly ducklings i cant space them side by side touching. i have to space them about 1/8th of an inch apart because a few wont center properly any closer.

then i will try the 10-11ft tsr 7-8 and see how it goes.... i now totally see how a few more windings(5-10) makes a huge difference on cutin speed and our crapy winds.

I'm excited anyhow and am producing electricity at least so i'm thankfull for that. i think with enough carving and design i CAN make this thing happen... and of course without all of your help NONE of this would have been possible!!

MANY THANKS!!

Jamie

"Kuuu lew ku ku.... ku ku ku ku!" - bob and doug mackensie LMAO

[willib]

Jamie

this is a link to my coil winder , the coil in question is not one of my best , but it shows what can be done .

http://www.fieldlines.com/story/2006/1/22/5177/17966

my best one to date was a two-in-hand #17ga that came out perfectly flat and was wound with no pigtail comming from the center ,because i left about two feet of wire at the start , connected to that holder in the photo,then i wound one layer out and back , and while keeping pressure on the outer winding , i disconnect the start , and wind it twice , reconnect it , and go again with the outer winding.

i use polyester resin , and a small paint brush and coat the coils as i wind them ,

ie, coat each layer as i finish .

and let it sit for an hour ,

there is a type of plastic , that the resin will not stick to , try any of the clear thin (0.010)" thick approx., pakaging.

most anything uses this stuff from toys to pc mice to cell phones.

i save it whenver i buy something , and cut out  the flat parts with scisors