New blades

[Capt Slog]

It's horrible weather over here in the UK (still), but that hasn't stopped me and Chip going up into the tree house and changing the blades.

The new ones are 5 foot 7 inches in diameter (170cm) and have a lot more curve and solidity than the last set, (which were 3 foot 9 inches, but only really up there to get people used to seeing it; I'm building it by stealth).

The whole unit has now turned from a toy to a bit of a beast, it really looks powerful and slightly scary.  Even though the wind is quite light, perhaps 5 mph maybe getting to 10mph in gusts, they are turning nicely and I'm seeing 6-7 volts DC at the bottom of the tower.  Turbine is dual rotor, 12 pole, 1" N42 neos at 3/8" thick, 9 coils of 60 turn 16 swg, star and rectified at the back of the mill (just to save you having to read back).

I've lowered the turbine to about as low as it can operate untill I'm sure it's ok.

Looks like this.

In the secon photo you get a good idea of the blade end on at the base of the pic.

Thanks for looking, I'd be pleased to know what you think because I think these blades are a bit too wide.

[luckeydog]

what is your root chord measurement and tip chord?

what is the diameter of pipe used?

It looks about right but I believe you will need

a larger diameter turbine to achieve the full

potential of your alternator in lower winds.

with a 5 ft turbine I was able to achieve 15 amps

with a ametek 50 motor charging a 12 volt battery bank

in 25 to 30 mph winds

the bladed was made using a 9 inch diameter pipe

as a mould and then doing a fiberglass/carbon fiber

layup on the 9 inch pipe

you can see some photos of those blades in my files

as a comparison it might help you.

Luckeydog

.

[Capt Slog]

Ignoring the bit of the blade where it mounts to the genny, they are 9cm at the root tapering to 4.5cm at the tip over a length of 68cm.

I'm thinking of cutting them down a bit. I get the feeling that I won't get enough speed (rpm) otherwise.  The mill is currently driving a length of nichrome resitance wire as a dummy load, (about 2.5 ohms) but I might tie the whole thing up rather than risk damage.

[ghurd]

"The mill is currently driving a length of nichrome resistance wire as a dummy load, (about 2.5 ohms)"

That's the problem if you are looking to get it to 12V cut-in.

The 6.5V/2.5=2.6A, and 6.5x2.6=17W, plus losses.

Not as bad as the light bulb was, but it is, pretty much, being stalled.

Borrow a 25A meter and connect a battery.

Is that PVC?  Safety concerns.  I certainly wouldn't make the blades any narrower.  That's "too long" for the PVC we have in the US (personal opinion).  1m / 3' diameter can bend an awful lot in a decent wind.  Narrow would be worse.

If it needs to be faster, I (personally) would shorten the blades.

G-

[Capt Slog]

Thanks Ghurd.  

I know there are concerns about PVC, and I admit that I have some concerns myself, but I have had a set of smaller blades made of the same stuff running for over a year with no problems.  The old blades survived some pretty impressive winds through the winter.  I'm going to shorten them a bit, and then recut to give a bit more taper.  As you say, they do flex backwards with the wind, but I do have room for this and they are slightly bent forward at the moment. I've found with the old ones that this flex takes some of the edge out of the gusts.

The dummy load I mentioned is really there as a brake.  I didn't want a complete short as I read somewhere that this didn't do the coils any favours.  Although the mill is just about lowered out of the wind, I didn't want to risk it spinning out of control with no load at all, especially as the blades are not really tested yet.

Today I've bored out the slip ring assembly I was given, so that it will fit the pole, and I'm just about to start making up the charge controller. I'll post a diary entry about that when it's boxed and connected. :-)