wind turbine

[Dr_Doggy]

my scope is a 4" pipe with no more flow than a small leaf blower

what makes a computer fan bad to be used as a wind turbine?

if i use one to run another one how much RPM losses can i expect?

what would make it better as a generator.. more blades? different shape ... brushless motor?

 

[alec_t]

Most computer fans have a brushless motor.

 

[Dr_Doggy]

lol ... what is the best type motor to use>?

if a fan is 33% efficient(is it?) then i would loose 33% of that on the input then another 33 percent of that on the motor then ...
my input output power ratio would be 10% ?
so if leaf blower works at 33cfm then i can expect 3 cfm on the output?

am i on the right tracks?

 

[shortbus=]

lol ... what is the best type motor to use>?

if a fan is 33% efficient(is it?) then i would loose 33% of that on the input then another 33 percent of that on the motor then ...
my input output power ratio would be 10% ?
so if leaf blower works at 33cfm then i can expect 3 cfm on the output?

am i on the right tracks?

But the leaf blower or most of them, are centrifical fans, bot the type in a fan like a computer fan. That's how they make so many CFM for their size.

 

[Dr_Doggy]

but what would make a good turbine?

 

[tomizett]

Most small turbines use permanent-magnet alternators, I believe. They're good at low speeds.

 

[Dr_Doggy]

THats Grrreat!!
ill get me one of these then:
https://www.amazon.ca/Permanent-Rev...ocphy=1002464&hvtargid=pla-562253781833&psc=1

what should i get for propeller?

 

[dknguyen]

THats Grrreat!!
ill get me one of these then:
https://www.amazon.ca/Permanent-Rev...ocphy=1002464&hvtargid=pla-562253781833&psc=1

what should i get for propeller?

The most easily available source of blades is model aircraft propeller blades...You want the ones with large diameter but low pitch (high diameter to pitch ratio). Probably want wide chord too. Wood is lightest so you might want that. Not sure how well they would actually work as wind turbine blades though.

That motor is supposed to run at 3000RPM on 12V though so you won't get anywhere near 12V out of it unless the wind is able to spin it at 3000RPM which seems unlikely.

Low KV brushless would probably be more efficient (like a model airplane outrunner motor) but you would need a simple 3-phase diode rectifier to turn the output into DC.

 

[shortbus=]

my scope is a 4" pipe with no more flow than a small leaf blower

Maybe a better explanation of what you're trying to do would be of some help. To me the above quote seems like you're wanting to make some sort of a ducted fan to generate electric, one based on a 4" pipe. But then you talked about a leaf blower, and later a turbine comes up. All of these things can create a breeze/wind but not all of them are suitable to be used to make a wind generator.

 

[Dr_Doggy]

I am wanting something similar to a turbocharger ... or like a jet engine compressor/turbine.
it will be for a wood stove(outdoor) that i want to force airflow through mostly to increase o2 and to solve for back draft ... the leaf blower was just going to be for cold startup... but i guess i dont need leaf blower if i run fans from battery!
It will be difficult for me to use a driveshaft to connect the two as is usually done
i will be far enough away from heat source that fans will not be getting hot

 

[tomizett]

So you're building a blower, not a wind generator?
I think that for your purposes a centrifugal blower from a car heater would work well - you just need a long enough air duct to keep it cool. How practical that is depends upon the precise layout and aesthetics if your burner.

 

[shortbus=]

I am wanting something similar to a turbocharger ... or like a jet engine compressor/turbine.
it will be for a wood stove(outdoor) that i want to force airflow through mostly to increase o2 and to solve for back draft ... the leaf blower was just going to be for cold startup... but i guess i dont need leaf blower if i run fans from battery!

Guess it was the "generator" comment in the first post that was throwing me off. That and the brushless motor comment.
But like tomizett said the easiest way would be a heatter blower from a car in a wrecking yard. Just be aware that many of the newer cars are using brushless motors now in the blower. You would want one from and older car say in the 1990's or older. Another way if AC is available would be to use a hair drier an old one that the heater coils are burned out would work just fine. What your looking for in the fan part of any blower is called a "squirrel cage blower" -

 

[Dr_Doggy]

i dont think you were off anytime guys,
I do want a blower that is going to push air in at the input,
I just so happen to coincidentally acquired this little guy:
https://www.robotshop.com/ca/en/12v-16cfm-33mm-blower-fan.html



but i also want a generator too at the air output
just like in a jet engine ... the generator speeds up the blower using the additional forced air from combustion

although my stove will not be using high power combustion like a jet, i will only be using convection forces from a slow burn.
my concern is matching a generator to the blower since i am coupling with magnetic fields(of the bldc) instead of the conventional drive shaft

 

[alec_t]

the generator speeds up the blower

How? Are you proposing to use electrical power from the generator to boost the electrical input of the blower motor? That's the sort of thing the over-unity crowd attempt.
The generator would actually block part of the air flow from the blower.

 

[dknguyen]

How? Are you proposing to use electrical power from the generator to boost the electrical input of the blower motor? That's the sort of thing the over-unity crowd attempt.
The generator would actually block part of the air flow from the blower.

It sounds like that but he's just describing it poorly.

He wants to basically have a turbocharger in his stove, harness the energy in the exhaust pressure to increase airflow into the stove to improve it's efficiency or performance.

 

[tomizett]

alec - I don't think this is an over-unity project, just a way of building a forced-air stove without the need for external power. Any additional energy would come from the burning.

I think I see what you're getting at, but I'm not sure it will work. There might be better ways to extract energy from the fire.
Do you want to just get enough energy to power the blower, or are you hoping to extract extra energy for an external load?

 

[dknguyen]

I'm not sure it will work either, especially if you are trying to convert the exhaust pressure to electricity and then use that to electricity to turn the fan. At such low airflows, the generator is going to have crap efficiency and then there's another efficiency loss when the electricity gets converted back into mechanical motion to turn the compressor fan which is also going to have crap efficiency for the same reason (there's not enough power available to turn it quickly). Can you even get anywhere near 10% efficiency in either the generation or motoring stages at the low RPM that I imagine convection airflow would be capable of?

Is there no way to pull things off mechanically? So the exhaust can directly turn the intake fan?

 

[Dr_Doggy]

Do you want to just get enough energy to power the blower, or are you hoping to extract extra energy for an external load?

lol im not sure! what is the relationship between a jet compressor and turbine?
by how i read the answer is yes, just enough

the excess heat energy will be mostly dumped into thermal masses,
i could try conventional mechanical driveshaft but those are trickier for me to pull off ..... plus then i need additional blower for startup and cold drafts .. if i could convert to electrical i can also think of regulation and braking circuitry.

... i wouldn't mind using a small power supply to kick start things if that helps.

 

[shortbus=]

Then why not attach several Peltier elements to the flue pipe? But in the end there is no free lunch or energy for that matter. Anyheat you take from the flue, will probably increase the creasote build up in the chimney increasing the risk of a chimney fire. And those are very scary.

Any increase in the speed of the gases coming from the flue like the proposed "jet engine" I can't see happening with solid fuel in the combustion chamber of the burner and then where are the compressor fans that a jet engine uses to make it's thrust?

 

[Dr_Doggy]

compressor fan:
https://www.robotshop.com/ca/en/12v-16cfm-33mm-blower-fan.html

i thought about peltier ... I expect my exhaust to be about 40celcius , but those are less efficient than fans? also my intention is to use convection forces not thermal ones