Thread: Reversing a fan

Look here.

Reversing a single phase motor

You need to reverse the connections of EITHER the start coil OR the run coil but not both.

Because you only have 3 wires your problem turns into accessing the connections between the run and start coils as sometimes these are embedded within the motor coils and are impossible OR not worth digging out.

Anyway - read the above post and you will get an idea of what needs to be be done

Thanks for the link Bob It all looks as though it will be too much trouble. It would be a lot easier to just buy another fan that turns the right way. Another fan would also be better as the one supplied with the laser would not be looked on kindly by anyone with even a modicum of discretionary taste in quality.

If it's anything like a computer fan just unscrew it and flip it over

It isn't like a computer fan, it is a centrifugal type fan that is side on to the body of the laser.
So the blades are at right angles to the body.

If it WAS like a computer fan then I'd just swap the connections. They are all DC

Bob, the picture gives your question a whole new perspective. The angle of the rotor blades indicates that from this view, the intake side of the fan, the rotor must rotate clockwise. The problem is that the shape of the scroll plenum dictates rotation counter-clockwise with the blades angled in the opposite direction. It would seem that your fan has been assembled with an incorrect motor unit.

Chas.

Originally Posted by Chas

Bob, the picture gives your question a whole new perspective. The angle of the rotor blades indicates that from this view, the intake side of the fan, the rotor must rotate clockwise. The problem is that the shape of the scroll plenum dictates rotation counter-clockwise with the blades angled in the opposite direction. It would seem that your fan has been assembled with an incorrect motor unit.

Chas.

Nope - both directions (forwards and backwards curved, and dead straight) will work.
Each have their pros and cons which is why they are used.
Have a look here
https://en.wikipedia.org/wiki/Centrifugal_fan

Bob, as you have pointed out, both directions will work. However, the most common configuration is to have backward curved blades on the impeller for a given direction of rotation for maximum efficiency. In your photo the blades are backward curved relative to clockwise rotation. That would correspond to rotating in the wrong direction for your blower. As your original question was how to reverse the direction of rotation of your fan, I still think your fan has been assembled with the wrong motor assembly.
The most common application for straight bladed impellers is on electric motors where direction of rotation cannot be predetermined by the manufacturer.

Chas.

There's nothing wrong with the fan, the OP wants to change a fan that is correctly installed and sucks as it should, into one that blows.

I don't understand why the OP would want to blow the smoke away. If the smoke is blown away the inside of the shed will eventually be covered with grey gooey smoke and dust, not to mention the toxic stuff generated by the cutter getting into the operators lungs. If anything I would worry about the fan being too small to catch all the gunk.

You have to blow (suck) the smoke away Bob as otherwise the cabinet fills up with smoke and the laser beam is affected adversely. There is meant to be a 100mm dia tube attached to the fan to lead the smoke outside. I will get around to attaching that someday soon now.

Originally Posted by Bob Willson

There is meant to be a 100mm dia tube attached to the fan to lead the smoke outside. I will get around to attaching that someday soon now.

I assumed that would be the case.
What are you cutting?

Originally Posted by BobL

What are you cutting?

This laser isn't for me, it is for my daughter. I bought one of the cheap 40Watt lasers and it was almost unusable due to the crappy Moshi , software. They even put a dongle on their board so that nobody could steal it. What a laugh, who in their right mind would want to steal that pile of !@#$%^. However, to answer your question, it will be mostly 3mm hardboard and some plastic sheeting as well.

Originally Posted by Bob Willson

This laser isn't for me, it is for my daughter. I bought one of the cheap 40Watt lasers and it was almost unusable due to the crappy Moshi , software. They even put a dongle on their board so that nobody could steal it. What a laugh, who in their right mind would want to steal that pile of !@#$%^. However, to answer your question, it will be mostly 3mm hardboard and some plastic sheeting as well.

I guess I should now ask what sort of plastic but they nearly all generates some form of toxic gasses when burnt so it sounds like that 100 mm hose should be moved up the priority list.

That fan you showed a photo of is only going to draw about 100 CFM of air through it which is nowhere near enough to keep toxic gasses out of a room so I'd be looking throwing that fan away and using a much bigger fan on the very end of the ducting.
When the fan is connected at the start of the hose this pressurises the hose on the other side so if there are leaks they get back out into the room

Well, the way in which the fan attaches (and I use the word 'attaches' very loosely, almost as loosely as the way in which the fan is 'attached') to the body of the laser means that about 10% of the smoke will almost certainly escape into the air at the rear of the laser.


I am well aware of the dangers involved with cutting PVC, so that particular product is on our danger list. (When PVC is heated it releases chlorine gas, this mixes with moisture in the atmosphere and makes hydrochloric acid.) So, we will be cutting mainly acrylic plastic and some polypropylene. We won't be cutting any Kevlar, as I understand that this produces cyanide gas. I like the idea of a much better exhaust fan and I will probably get one for her as well as one for myself for my larger machine.

A centrifugal fan (whic is what this is) CANNOT blow or suck in reverese. So I don't understaand the original statement. A centrifugal fran running the wrong way will still suck through the middle of the rotor and blow on the outside of the rotor. However it will be very inefficient, becasue the air can only escape in a rirection opposite the vortex it is soinning in - but it will still escape and the fan will therefore still blow out of the open end of the scroll....