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question about fan

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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question about fan

Unread postAuthor: Mr.Russ » Tue Sep 18, 2007 6:18 am

hey guys, im looking to put a fan into my new combustion, and i was wondering if it matters if the wires run inside the chamber to connect the fan to the battery. will they get fried from the heat?

thanks.
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Unread postAuthor: Hubb » Tue Sep 18, 2007 6:19 am

They will not get fried. The combustion flame only last for a very brief moment. The wires on my fan run into my chamber and have never had a problem.
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Unread postAuthor: Mr.Russ » Tue Sep 18, 2007 6:57 am

okay, thanks mate.

and tips on mounting one in a 2" chamber?

im jut usiong a PC fan, just a little motor with plastic fins on it from an old RC boat.

EDIT: Im going to house this in a piece of 40mm PVC. i want to have a switch in the end cap, and then an LED on the side of it somewhere. there will be a 9V battery in there also. How would i wire it up so the LED comes on when the fan is on? will an LED blow from the 9V if its only a 3V LED or something?

My switch is a 3way switch, I have it wired so it you flick it to the left, it is off, in the middle its off and it comes on when its on the right.
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Unread postAuthor: Hubb » Tue Sep 18, 2007 7:35 am

I'm confused. Are you using a PC fan or the fan from the boat? I used a 20mm PC fan for my 2" chamber. I simply grinded down the corners of the fan so that it fit into the cleanout adapter.

As far as wiring an LED, this site has some pretty good information on that subject.
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Unread postAuthor: dongfang » Tue Sep 18, 2007 8:03 am

Hi

Make sure it is a brushless motor in that fan! It could sound like one from an RC boat is not..

Brush motors make sparks ... and sparks in the chamber can ... well you know..

Otherwise, get a small (just 1 inch) fan from an old CPU cooler.

Regards
Soren
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Unread postAuthor: Mr.Russ » Wed Sep 19, 2007 1:01 am

uhh i dont know if it has brushes or not, but if im pressing the wire against the motor it sparks. didnt think that would happen if it was soldered on.

Ill probably find another one, i know a friend who has a pc busniess.

Any ideas on the wiring? thanks.
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Unread postAuthor: jimmy101 » Wed Sep 19, 2007 11:23 am

The usual way, but not the only way, to wire the fan is;

1. Use an "L" shaped bracket to mount the fan inside the chamber. One screw connects the bracket to the chamber wall, another screw connects the fan to the bracket.

2. Connect one wire of the fan to the bracket. Connect a battery that is outside the chamber to the outside of the screw that holds the bracket to the chamber.

3. Add another nut and bolt through the chamber (that doesn't touch the L bracket). Connect the other wire of the fan to the nut/bolt inside the chamber.

4. Connect a piece of wire to the outside of the second nut/bolt then connect the wire to a switch. (A toggle or slide switch works best, don't use a pushbutton switch.)

5. Connect the other terminal of the switch to the battery.

All done.

Put the battery and switch in a small project box (or Altoid tin or whatever) to make it look pretty and to protect them.

A common alternative method for a fan that is a bit bigger than the chamber ID is to grind the corners off the fan housing and wedge and/or epoxy the fan in place. The electrical contacts are passed though the chamber wall using a pair of small nuts+bolts. An external box contains the switch and battery as in the first method.

Another common method is to put everything in the chamber (fan, battery+ switch). The switch can be mounted in the chamber wall with it's paddle outside the gun. Gives a very clean look to the gun but replacing the battery can be a PITA. This method is often used when you have a cheap "personal fan" from Kmart. A "personal fan" is the motor, blade, switch and battery all mounted in a handheld container. Some of these fans are small enough to fit completely in the chamber. So, people just epoxy/screw/nail the fan in the chamber close to the cleanout plug. To turn the fan on and off you reach a finger into the chamber. For this setup the fan runs continuously during a firing session, which is OK.
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Unread postAuthor: Mr.Russ » Thu Sep 20, 2007 1:01 am

okay, thanks.

are the 'personal fans' okay to use? as in they dont spark in the motor?
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Unread postAuthor: jimmy101 » Thu Sep 20, 2007 11:05 am

Mr.Russ wrote:okay, thanks.

are the 'personal fans' okay to use? as in they dont spark in the motor?


Well ..........

1. They have been used frequently with no reports of the fan causing a premature ignition.
2. People have tried to use brushed fans as igntion sources. It would be so easy to make an igntion sysetem if it worked. Nobody has ever posted on getting it to work.

Bottom line, a fan with brushes might cause ignition but it seems unlikely and has never been posted. Note that "unlikely" is not the same as "impossible".

To be as safe as possible, you might consider controlling the fan with a pushbutton switch outside the chamber. That way you know when the fan is running and when it isn't.
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Unread postAuthor: Mr.Russ » Thu Sep 20, 2007 7:12 pm

okay. they have fans at the cheap shop down the road for me, the little personal ones. the fan blades are soft plastic, like thick glad wrap. One of the fans has a strip of LED's in them, so i thought that would be cool. I would wire it up to there is a switch on the outside, but it wont be a pushbutton one.

Thanks for the help
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