4 ft turbine advise

[Seekscore]

My boss lady wants to make a small 4ft turbine. I honestly haven't searched the board too hard and thought I would take a shortcut and just ask. I see several people are interested in micro wind and would like to know what they think works best for the coils and magnets. She isn't going to power anything long term and is just looking for a way to use a small wind turbine to charge a battery in a disaster preparedness kind of way. She wants to do this herself and I don't have the experience on something this small. We made some blades last week after some training on the CNC router. She did a pretty good job.

I have in mind that it will be three phase, 12V with no charge controller. Probably no furling

I've seen where there are differing opinions on how many wraps and size of wire and magnet sizes.

What better place to ask since I know there are some experts out there.

Thanks kindly!

Mike

[Flux]

I agree on everything except the no furling. You can build a 4ft machine that won't self destruct but it will be fast and noisy in high wind or you will have to stall it so hard that the performance will be miserable.

If you do go for the fast and noisy approach you may have to choose an alternator design that will current limit through reactance ( intentional or added). if you use too many blades you may get it to protect without as long as the alternator is not very efficient and limits on resistance.

You either use fairly small magnets and make it conventional or you use the standard blocks 2 x 1 x 1/2 and make it single rotor.

You could do worse than look at Hugh Piggott's 4 ft machine it uses a bit more magnet than really needed but the standard blocks are often cheaper than small specials. You can tune it easily by altering the clearance from rotor to stator and it runs fairly slowly and quietly it will need furling though.

Flux

[Seekscore]

I was thinking standard 2x1x.5" magnets with single rotor but was wanting to hear what people with actual experience have to say. I haven't played with anything this small so I really don't have enough experience to voice an educated opinion. I figured it would spin pretty fast and be noisy. What do you consider fairly slowly? Do people design these to furl to the side or up and down like Dan did on his previous post?

Mike

[Flux]

Using 8 magnets and 6 coils the one I played with cut in about 300rpm and loaded up fairly quickly. The prop was tsr5 and it was near silent.

I think Dan's new machine is much faster. Mine furled horizontally as normal. In really clean wind areas vertical furling can work on small machines but it is near useless on turbulent sites. It nods backwards and forwards as it yaws ( gyro effect). Damping the yaw is far from easy, damping the vertical motion is evading the issue.

The machine is still running but with a rotating backing plate and a 5ft 6" prop. The gain in flux from the plate reduced the speed enough to accept the bigger prop. It was a good machine in it's original form but the site is about as bad as you could imagine and the extra prop size has been very worthwhile.

On a good clean windy site it would perform very well in the original 4 ft form. The winding stands 250 w with the bigger prop so with a single rotor and better cooling it may be ok for 300W intermittent. It would do way more than that and burn out in a good wind area without furling.

Keep the stator thin for single rotors, anything over 3/8 thick will not see much flux at the back of the coils and mainly adds resistance.

Can't remember the coil details but it was actually Hugh's 24v version but split into two sections with their own rectifiers for 12v. It was originally tested at 24v but converted to 12v for it's present site.

[jlt]

 I  Don't advice building anything without some kind of furling. In a 50 mph wind  it be trying to put out about 2000 watts .  The result is Every thing  is melted or destroyed . 

[ghurd]

"just looking for a way to use a small wind turbine to charge a battery in a disaster preparedness kind of way"

The machine will be flying and maintaining an unused 12V bank, waiting for a disaster?

The battery bank will not be huge AH?  (seems kind of silly to spend big bucks on a mostly unused battery)

"with no charge controller"
~300W of 12V into a lowish AH battery with no charge controller does not sound like a great idea to me.
100W for a whole day can do some damage to a fully charged smallish 12V battery bank.

You have heard of the "ghurd controller", right?   
G-

[Seekscore]

Thanks for the advise. I'll have to look at the library or purchase the recipe book and use that as a good starting point.

I forgot about the Ghurd Controller. I'll have to get one.

I doubt this would be used for permanently charging and keeping batteries charged. I'm sure what she has in mind is set it up in an emergency in case of worse case scenario. As a backup.

Thanks.

Mike

[fabricator]

She would be better off setting up the desired size battery bank and charging them from the grid, with a smart type charger. If the grid goes down you could easily have two days of battery power for critical loads.

[ghurd]

Grid charging is no fun!
G-

[fabricator]

Grid charging is no fun!
G-

This is true.