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IT hardware bods advice needed.


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I'm building a fan assisted wood gas stove for the apocalypse* and I need to use a fan with about 8-10 cfm air flow. 

Perusing ebay I noticed the square 12v fans would be ideal I can round these off and fit in a section of 39mm ID steel pipe I have and then insert into the outer body of the stove. 

https://www.ebay.co.uk/itm/12V-DC-4cm-3-Pin-Wire-40x40x10mm-4000RPM-Brushless-PC-Computer-Fan-4010-40mm

However they have 3 wires. Red, black and yellow. 

Is it safe to assume that if I connect the red to a positive terminal of a 12v battery and black to the negative the fan will run? The yellow is something called Tachometric Signal....

 

* once built and operational I shall share with the DOSBODS brotherhood (including the burds) for nothing more than reputation points!

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3 minutes ago, Chewing Grass said:

Yes you are correct, it will work fine off the red and black wires on a battery supply.

Just make sure you are blowing into the stove rather than sucking it off.

cheers. You a most knowledgable member of the ovine community

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57 minutes ago, 5min OCD speculator said:

Sounds like a fun project...I'm confused by 'wood gas stove' bit.....so the gas is actually air and not propane? lol

You weren't tempted by a rocket stove?

Works similar to a rocket stove but the air supply in is fan assisted - much less smoke.

Can build at a fraction of the cost 

Basically the parts will be

2 S/S stockpots of slightly different size £16

1 stockpot lid (from the larger model)

1 150mm length of 39mm ID S/S pipe £10.00 (300mm section)

1 40mm 12v Fan - £3.50

M6 S/S nuts, bolts & washers.  (have a big pile)

12V battery (got 5 Yuasa 12A/H units sitting in the garage. 

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Note that the fan's rated airflow will be for zero pressure differential.  If the fan is having to 'push the air hard' then you won't get this throughput.

I'd go for a centrifugal fan for this type of work -- it'll maintain throughput against a variable/uncertain pressure.

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3 minutes ago, dgul said:

Note that the fan's rated airflow will be for zero pressure differential.  If the fan is having to 'push the air hard' then you won't get this throughput.

I'd go for a centrifugal fan for this type of work -- it'll maintain throughput against a variable/uncertain pressure.

I have assumed a 50% drop in pressure it will give an air flow of about 4.5cfm into the stove

This will basically combust 13g of wood a minute. its 200% of what is needed. 

13g / min of clean burned wood is 3.25KW. Deduct 10-20% to allow for some smoke and particulates and you have a very powerful stove

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cool

I started building a rocket stove, another project i haven't finished <doh>

but it was similarly cheap tbh

old gas bottle, needs the top cutting off and 2 holes through it for 10cm square, 2mm thick steel tube - 1.2 meter was only €16 I think

I decided to use square tube cos you can get away without welding if you carefully cut the holes...

then some thin steel sheet €4, goes inside the gas bottle, sand filler and an old inverted cast iron pot on the top

I do need to buy some flue to connect it to the old chimney in the basement....

Looking forward to seeing your finished product!

Looking forward to seeing mine finished too xD

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3 minutes ago, Kurt Barlow said:

I have assumed a 50% drop in pressure it will give an air flow of about 4.5cfm into the stove

This will basically combust 13g of wood a minute. its 200% of what is needed. 

13g / min of clean burned wood is 3.25KW. Deduct 10-20% to allow for some smoke and particulates and you have a very powerful stove

Fair enough.  

[OTOH centrifugal computer fans cost about the same and should have a more predictable performance]

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2 minutes ago, dgul said:

Fair enough.  

[OTOH centrifugal computer fans cost about the same and should have a more predictable performance]

Do you know where I can get one with a round outlet. All the ones I have seen have a square / rectangular outlet. 

The advantage of the one I propose to use is I can trim off the bolt holes and file it down to fit tightly in a 40mm pipe. I can then drill a 40mm hole in the side of the outer pot to insert in. The 150mm length of steel pipe keeps sufficient distance to prevent the plastic fan casing melting. 

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9 minutes ago, Kurt Barlow said:

Do you know where I can get one with a round outlet. All the ones I have seen have a square / rectangular outlet. 

The advantage of the one I propose to use is I can trim off the bolt holes and file it down to fit tightly in a 40mm pipe. I can then drill a 40mm hole in the side of the outer pot to insert in. The 150mm length of steel pipe keeps sufficient distance to prevent the plastic fan casing melting. 

Sounds like you have a plan -- it'll probably work.

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  • 2 weeks later...
Posted (edited)
On 22/05/2020 at 21:25, Kurt Barlow said:

Do you know where I can get one with a round outlet. All the ones I have seen have a square / rectangular outlet. 

The advantage of the one I propose to use is I can trim off the bolt holes and file it down to fit tightly in a 40mm pipe. I can then drill a 40mm hole in the side of the outer pot to insert in. The 150mm length of steel pipe keeps sufficient distance to prevent the plastic fan casing melting. 


Cut a piece of wood, maybe 10mm thick, to a square just a bit larger than the fan, cut a hole in the centre of it the size of the pipe, bond/glue the wood to the end of the pipe, let it dry/set, screw the fan into the wood.........

Should be good, just be prepared for the fan to fail (it shouldn't but it might) and make sure that won't cause the pipe to reach dangerous temperatures.

Edited by Snark
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