Reversing A Single Phase Fan

[moose man]

i all i come across somthing new to i am working o a capacitor singlephase fan which is running in the wrong directon need to reverse capacitor is wired in serise so no centrfucal switch

i am used too doing dol and delta motors just woundering if anybody could advise on how to do it thanks

moose man

 

[Andy™]

do you have access to start & run connections, or just L&N?

if you have access to them, swap either start or run connections, but not both

 

[moose man]

thanks andy for reply only got access to line and neutral is that a problem

the way its wired is supply line to one side then out off the capacitor to the line side of the fan its on a benson suspended heater

 

[Andy™]

where are connections to capacitor?

 

[moose man]

in a junction box between the two fan unit and the capacitors are on the side of each unit fan wireing is br /bl blk comeing out of the fan to the jb

 

[moose man]

thanks mate so what you are say that you only swap around one side i will take some picis tom and post them when i do it tom

so on the motor post say u1 u2 z1 z2 you would swap u2 to post1 and u1 to post 2 and leave z terminals alone

sorry for sounding dumb but it been a long day with man flue

moose

 

[Andy™]

yes, but dont swap both. or polarity. otherwise it will still spin the same way

 

[moose man]

thanks andy and canoeboy much appreciated for help

moose man

 

[Marvo]

My first thought is why is the fan running the wrong way in the first place. If you reverse the direction of most fans so they're running the opposite way they were intended to then they often become innefficient because of the profile and aerodynamics of the bladeset. This causes high noise levels and can also cause a higher shaft power requirement and motor overload...not to mention lower air volumes and less static pressure abilities.

If the fan is running the way it was manufactured to do so but the wrong way to your liking then physically removing it and reinstalling it in the opposite orientation might be a better option. If it's running the wrong way because someone originally wired it wrong then changing it electrically is the best way to go.

 

[Marvo]

Yes, not all fans overload, backward curved /radials tend not to but axials especially tend to be unpredictable in reverse. Some fans are designed with a bi-directional bladeset but because of the efficiency sacrifices involved these are usually for a specific purpose and not general use. Fan manufacturers almost never give operational curve info for absorbed power in reverse rotation direction so I'd exercise caution unless the results are being closely monitored.

 

[Andy™]

I did say or :slap

i know, but i have known people to swap both before

 

[moose man]

finaly gotto have a lookat fan motor today and on looking at it my self it turned out to be a permanent split capacitor motor (psc)

now i have to identifiy the comon so four wire on fan brown blue black earth to find common measured between br blk 5 ohms br blu 11ohms then between blu blk gave me a reading of 16 ohms so am i right that the blu and black would be the run across the cappacitor and the brown is connected to feed line as the start winding as i did not disconnect wireing i need to start from begining

with no wireing diagram

moose man

 

[Marvo]

This would be my guess from your resistance readings. Brown would be common, the blue would be the end of the start windings and the black the run winding. Live supply goes to common (via any thermal overload protection first) Neutral directly to the run winding and cap between the neutral on the run winding and the start winding.

I would check the run current drawn is less than the stated running current on the motor tag plate. If the run current is higher then there's a problem so disconnect it quickly and go back to the drawing board if this is the case.

Note, if there's only 3 wires coming from the motor it means you won't be able to make it run in reverse, you can only do this if common isn't internally bonded and all 4 winding wires are brought out into the termination box.

 

[Marvo]

Just as an afterthought, seeing as it's game set and match electrically as far as reversing rotation goes, your only option now is to physically turn the fan around backwards on its mountings.

The question still remains why do you think it's running the wrong way. From what you now say about the lack of wiring options it's looking pretty likely it's running the way it was intended to do. Call me a cynic but I can't help thinking that reversing it isn't going to end well.

Correct, I would scoob but i knew that :innocent

Lol, thanks...I think.

 

[moose man]

as for wrong direction its what i told but when i had a looked at it my self as it turned out to be runing corectly but not up to speed it was replace by a a contractor so thats why i wanted to go and look at problem my self

thanks for info

moose

 

[Marvo]

You can start with the dissection of the windings, sometimes it's possible but sometimes it gets very messy, sometimes there's a 3 way connection with the two winding wires and one leg of a thermistor which is usually tied up pretty well tight. It will also void any warranties.

You can always try and lift the connection on the windings and split the start/run point - its a 50/50 chance depending on the varnish and where the connection is and the size of wire.....

I knew about this as well but I was feeling Scoobolicious so you got one anyway but unfortunately I've reached my quota

 

[moose man]

This would be my guess from your resistance readings. Brown would be common, the blue would be the end of the start windings and the black the run winding. Live supply goes to common (via any thermal overload protection first) Neutral directly to the run winding and cap between the neutral on the run winding and the start winding.

I would check the run current drawn is less than the stated running current on the motor tag plate. If the run current is higher then there's a problem so disconnect it quickly and go back to the drawing board if this is the case.

Note, if there's only 3 wires coming from the motor it means you won't be able to make it run in reverse, you can only do this if common isn't internally bonded and all 4 winding wires are brought out into the termination box.

just to be correct br off the fan connects to line supply then blue from fan connects to the neutral onsupply and blue on cappacitor then blk connects to black on cappacitor

 

[Marvo]

The capacitor (like one of my ex-girlfriends) is bi-polar so you can connect it either way around as log as it's between the blue and black of the motor wiring..

 

[moose man]

thanks marvo for advise its what i thought so its back i lift tom a box full off wago cage clamps and wire it all up my self then get my clamp meter out to test cuurent

thanks again

moose man