Can I rewire this fan to run backwards?

[GarF]

Not having time to hang about for the perfect fan for my project at the ideal price, I've plumped for one which will do at a reasonable price right now. Ideally I could do with the fan blowing in the opposite direction so that I can mount it with the guard outermost. If not possible then I could always fashion a safety cage to protect the fan blades, but it would be more convenient if I could reverse the fan by altering the power connections.

I have read that a three phase motor can be reversed by switching over two of the three power connections. Not having any electrical training I am loath to experiment using our domestic supply. From the attached photo could anyone confirm whether this modification is doable(advisable), my understanding of the wiring diagram is that swapping over the brown and black motor connections would have the desired effect??
Many thanks
Gareth

 

[CHJ]

If both the motor windings are the same spec. then yes that would do it.

However if the capacitor winding is only rated for starting and run assist then it may not stand the current.

An option would be to move the capacitor connection from black to brown.

Regarding mechanical details of motor, you need to check the location and support of the motor shaft, the fan will no doubt be currently pushing shaft towards the frame and rear bearing. You need to make sure reversing does not pull shaft forward out of its housings.

 

[GarF]

Yes I think I see that switching the capacitor connection would have the desired effect on the phasing. There doesn't seem to be any play in the fan itself. I can't move the shaft (axially) by hand so I don't think it's likely to shift with the thrust developed by the fan
Thanks
G

 

[GarF]

Switching the connection of the capacitor from black to brown did reverse the motor, although it was reluctant to start (better with the blades moving).

However, the asymmetric profile of the fan blades meant that while the fan was running backwards it was creating turbulence rather than any noticeable thrust.

An interesting exercise in an area I haven't given much thought to for about twenty years! Now to devise a guard for the back of the fan .

 

[CHJ]

Switching the connection of the capacitor from black to brown did reverse the motor, although it was reluctant to start (better with the blades .

Sounds as though it would need the other end of the capacitor fed winding swapped as well then,and that would be beried somewhere.

Can you reverse the fan on the shaft?

 

[GarF]

Can you reverse the fan on the shaft?

It looks as though the shaft might be persuaded out of the fan with a drift. For the time being (I'm pretty pressed for time and need to get on with the actual task in hand) I've mounted the fan back to front. The draught wasn't as good as I'd hoped, and it seemed to be moving lots of air radially by paddle-wheel effect and not drawing much air through. Since I added a sort of add hock exhaust cowl (cardboard box and sticky tape) the draught is better, and the exposed fan blades are reasonably covered.

It's not exactly pretty, but I think it will work while I get on with things. Hopefully I can improve it later on.

 

[n0legs]

Can I ask what kind of project this fan is for ?

 

[GarF]

The fan is mounted in the back panel of this knock-down spray booth. I'll post more photos and details if anyone is interested.
G

 

[n0legs]

I see. Cool.
Nice job on the filter box =D>

 

[Eric The Viking]

Um, not to rain on your parade, but...

I think you've reduced the fan efficiency significantly, increased the noise level, and it may well wear out rather fast, too. It's supposed to run with a thrust bearing (of sorts), and you've reversed that so it will be running against whatever retains the fan and rotor on the end of the shaft, not a designed bearing at all. You might get away with it, but you might not.

FWIW, I'd put the wiring back again and use it as designed. It won't be huge effort protecting it (the spray booth looks really good, BTW), and you can make a virtue of a necessity by incorporating an extra carp filter (for the smaller "fish").

Also, it might be worth buying a second fan in case, if they're cheap enough: there's nothing more annoying than designing one in then finding you can't replace it later when it fails (DAMHIKT).

Sorry to be a bore,

E.

 

[GarF]

Eric,
I did put the wiring back- I didn't like the humming noise when the motor was trying to start, AND the fan basically didn't work in reverse. When you think about it aeroplane wings don't provide much lift in reverse either!

So in the end I just put the fan in the back panel facing the wrong way- the only problem with that is the built in guard on the fan is facing the inside of the box with the bulk of the fan blades spinning on the outside which is not only unsafe, but generated a huge radial draught instead of the strong flow along the axis of the fan with little pressure evident at the filter.

I found that taping a cardboard box around the fan stopped the air flying off the fan in all directions and produced the desired airflow. The airflow through the filter is SIGNIFICANTLY greater with this in place- a sheet of paper will hold on the filter. I ain't putting a picture of it on here yet though- it's just too ugly!