Blade help

[(unknown)]

Hello all

Ive recently finished a 1/2 hp garbo gen. I have my bench test results and was hoping someone can help me decide what diameter blade I need to make. We get winds up to 35mph one day and 5-10mph the next. It looks like I will hit cut in below 300 rpm. Cogging is minimal.

Here's my numbers:

open circuit

16. 7v dc @ 400 rpm
    
54. 5v dc @1100 rpm
    
    

amps into 2- 125ah marine batteries @12.5v:

1. 3a @ 400 rpm
   
8. 18a @ 1100 rpm
   
   

Thanks

Fused

[Flux]

Your cut in is reasonably low but it needs to go a fair speed to produce much. I think Jerry uses something a bit over 4ft for those Garbogens and that seems quite reasonable.

You could get the 300 rpm from something larger such as 6ft but the top end power would be very limited. I would think a good compromise would be 5ft with tsr about 6.

Depends to some extent on whether you want small power often in low winds or whether you get enough high winds to go for the higher power but suffer in low winds.

The larger the swept area the better for low wind and I think your cut in is probably low enough to go up to 6ft at tsr7. The larger prop will not get you enough speed for high currents ( 1000 rpm is pretty fast for 6ft).

The smaller props will get you up to 1500rpm or more for large high wind output but the small area limits the low wind results.

Flux

[ghurd]

Hi Flux,

This one is a 1/2HP, and Jerry's are 1HP.

Any idea how something smaller and slower would match?  Maybe 4' and 5.5TSR?

G-

[Flux]

I hadn't spotted the 1/2hp. That explains the need for higher speed for decent output.

For a good all round match I agree that about 4ft would be good and although it doesn't cog much it will need a bit of starting so yes tsr 5 or a bit more should suit.

Much depends on the desire for the best results in low winds. There is no substitute for swept area if that is what you want as long as the speed is manageable . Hugh's 4ft blades with tsr 5 would probably be an excellent match in low wind. For some people the aim with tiny machines seems to be to get very high power in a gale, it sounds impressive but on most sites it happens very infrequently and a better overall power extraction comes from lower outputs more often in modest winds.

Having seen a 5ft machine and a 5ft6" machine on the same site, the extra prop size is a very definite advantage on low wind days. Both of these machines have suitable cut in for the props fitted, otherwise the larger one may have come off worse.

Flux

[Fused]

Thanks Flux!

Ghurd, many thanks to you for all your help and questions answered.

[Flux]

Just one additional comment. I don't know the shaft size but the shaft size of many 1/2hp motors would limit my choice to 5ft diameter maximum although some more modern motors have larger shafts than the old things.

Flux

[Fused]

I added a few pictures of my progress. Thanks for the advise.

[Jerry]

Hi Fused.

Those are some awsome looking end caps, very beefy and nice. What are they.

I used my 49" tip to tip blades with a TSR of aproximetly 6.5 with good results. You may go a littel smaller with this unit as the guys have said. Depends on your harts desire. Do you want a littel power at low wind speed or a lot of power at high wind speed?

Keep up the great work and keep us posted (more picture to please).

What coil configuration have you gone with?

                        JK TAS Jerry

[Fused]

Hi Jerry

Those end caps are 7/8" thick AL. My father made them up for me.

I split the start coils and left the runs alone on this stator. My runs actually cut in first, but the starts cut in shortly after.

Im going for less amps, but more often in less wind.

Ive decided I want to build a set of DanB's blades at 4.5ft dia. Im planning on a TSR of 5.5-6.5. This way I can get the cut-in rpm in the lower wind.

Jerry how do my bench tests look for a 1/2hp?

Ive added a few pictures to my profile on this genny yesterday. I may do a diary once its complete and tested in the air.

Thanks for all your help guys!

Fused

[Fused]

Jerry, I wanted to add that all bench tests were done at the end of a 50ft run of cable. I set it up to test the genny as it will be, when connected and finished. I do have some voltage drop through this 50ft run. Ill have to live with the voltage loss until I upgrade the cable run.

Ive set up my 12x20 barn on RE. 45 watt HF panels and a 1700watt (max) inverter. I can run all hand tools and lights off this tiny set up. Its been a great learning process.

Thanks

Fused

[Jerry]

Hi Fused.

Are your test #s 1.3 amps @ 400 rpm and 8.18 amps at 1100 rpm? Theres quite a space between the . and the second #s.

If the #s are as above Your right on track for a 1/2 hp.

I don't have bench #s for a 1/2 hp. Here are my bench #s for my 1 hp.

 1 amp 371 rpm

 2 amp 410 rpm

 5 amp 485 rpm

 7.5 amp 544 rpm

 10 amp  621 rpm.

I do the wiring scheem the same for both the starts and the runs.

                        JK TAS Jerry

[Fused]

Yes Jerry those numbers are correct, thanks for the advise. Ive followed your Diaries since you started posting. Ingenious you are, and a great contribution to the board.

Flux, thanks for your knowledge and help on blade sizing. I consider your replies as fact and final when it comes to the many questions asked of you.

Ghurd, when it comes to electrical, you are a Guru. You have helped me plan my dump load and even sold me the resistors to do it at a very reasonable cost. I recommend people to check out your site before buying from others at a much higher price.

Although Ive not posted in the past, I feel its worth mentioning us side liners appreciate the knowledge found on this site.

Fused