Low Head System

[Eirbyte]

After reading through the experiment with direct drive PM alternator at Scott's place it looks like the system I have been thinking about for our place not to hard to make and was wondering how it's going now so words of wisdom could save me a lot of reinventing

Our stream is seasonal and works best when we get plenty of rain so I went out today and put a 4" pipe in it and got 2L/S the best place for mounting a turbine is 60' away from the intake and the fall is 6' but and here is the worst bit the wire run one way is 250'. We run a 24v system so the alternator needs to be high voltage for that distance but I don't know how high or what wire size to use and how to drop down to 24v at the batteries.

I'm not to fussed with efficiency if I get a few amps going into the batteries when its foggy and calm and use as lots of old scrap in the making I'm happy. Would it be a good idea to make the runner first and see what rpm it gets up to then make alternator.

Looking forward to your thoughts all the best Jimmy

[Flux]

You have about 30W of energy. If you get 50% efficiency at that level you will do exceedingly well, so your line drop is not going to be a big issue.

If you end up with 1/2A at 24v you will have done exceedingly well.

Flux

[Nando]

Power available = 2 l/s * 6 feet * 0.3048 meter/feet * 6 = 21.9 watts

You may be able to get around 18 or so watts for a total of 0.432 KW/day.

Then You need to carry the power 250 feet = 76 meters, and for you case then it is best to carry it as a 120 volts AC and place a transformer converting to the battery bank voltage then you end up with about 16 to 18 watts of power.

Alternative topology would be to send DC current, high voltage with a charge controller at the end to charge the batteries -- maybe more expensive

Enough power to run some fluorescent lamps, like 3 ( 13 watts).

The basic problem is to make the turbine that is efficient enough for this power level and specially the low head matching it to the generator.

Are you ready to tackle this extremely low power system ?.

Nando

[bigdan]

Is 4" pipe all the flow you can harvest? Could you maybe build small dam and fill say an 8-10" pipe? That could help output considerably, another foot or two of head, maybe twice the volume of water. More that double the power. Just thinking out loud!

 Have fun , bigdan

[bigdan]

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[Eirbyte]

Thanks for the info. I can get more head another 6' but the wire run gets longer I will have to measure it tomorrow but how long is to long. And yes I will do it if I can get 1A it'll be fun.

[Eirbyte]

Just measured the flow again after some rain and now we are getting 11.5L/S and after finding another way to run the wire we can now have a head of 16' and a wire run of 80M and a pipe run of 160' so how dose that work out on turbine design

[Ian823478]

Jimmy

You'll have top decide whether you are designing for the normal or `after rain' flow!

With a 4 ft drop and 2 litres/sec I am getting 10-12 watts compared to 23.5 available (according to my calc - 2 kg/sec x 9.81 x 1.2m = 23.5W. Not sure whether Nando's calc includes efficiency - I reckon you have 36W available with 6ft at 2 litres/sec).

I made a version of the 3" diameter firefly turbine (twice as long)

(http://www.microhydropower.net/mhp_group/portegijs/firefly_bm/ffbm_index.html)driving a alternator based on Hugh Piggots 4ft 24V wind turbine design. The air gap is ca 1" so there's plenty of spare capacity in the alternator, or it could be made smaller in diameter so it can be mounted a bit lower - a bit more head is then available. I actually intend to make a turbine 6" in diameter to see if its any more efficient (I should be able to make a bigger one more accurately and its likely to be more tolerant of rubbish!).

Good luck

Ian

[Eirbyte]

Thanks for that it's a good link will study it later and I would like to see some photos of your system if you have them. The system that would work well for us is after rain as we have wind and PV and the calm dark days are usually wet I found this posting http://www.fieldlines.com/story/2006/8/13/6320/26408 and tried to work out the size of runner for our system what I don't understand is (L*D1) = (210,6 * Capacity water/H ½) = 210,6 * 0,33/7' = 9,93"

(L*D1) should be L*6,1

What is the figure 210,6?

0,33/7'   -  0,33 is the capacity, what is 7'?  (H ½ = 50/2 = 25)

L = 9,93" (L*D1) = 9,93" /6,1" = 1,62"

L*D1 should be 9,93*6,1 not 9.93/6.1

Should this read L/D1 ?

N = speed turbine = (862/D1) *H ½ = (862/6,1") *7 = 990 rpm;

Where does 862 come from?

Again H ½ = 7 not 25,

Or is it simpler to do say use a 6" or 12" runner and go wit that I plan to make it out of wood and plastic pipe and see how it goes then if it's ok maybe make it out of steel.

[Ian823478]

I work away from home so I can't put any pics up till the weekend.

I think the calcs from steelico are based on the design info in this link:

http://sleekfreak.ath.cx:81/3wdev/VITAHTML/SUBLEV/EN1/BANKITUR.HTM

I'm not sure about the 210.6 (some constant or other!) but the H1/2 is H to the power 1/2 ie the square root. The square root of 50 is near enough 7.

I think the design method is to pick a suitable diameter to give a reasonable rpm and then the width is adjusted to cater for the flow.

I haven't got any experience of making from wood/plastic but there seems to be several guys who have. With 16 ft head I guess it wood(!) have to be fairly sturdy

Regards

Ian

[Ian823478]

Hi Jimmy - I've never posted pics here before but hopefuly heres a couple

src="http://www.otherpower.com/images/scimages/6524/croppedwater2.JPG" width=80%><BR><BR><img src="http://www.otherpower.com/images/scimages/6524/water3crop.JPG" width=80%><BR>

Ian

OK - I'm doing something dull here - what??<BR><img

[Eirbyte]

It's ok I could see them if I opened the url in a new window thanks look good.