Fan Motor Electrical Problems

[Rotax100uk]

I have been on a project of building a blast chiller, only a small two pallet one but we have installed 6 fan motors into the side if the coldroom panels to force the chilled air into the pallets harder, anyway the fan motors are 240v (single phase) with start capacitor (4uf) i have taken a single phase off of the outdoor unit which is 3 phase to run the fan motors, the supply comes from the outdoor unit to the top of the blast chiller on the roof and to a contactor so that the thermomax controller turns them on and off.

Right heres the problem when you try to run all 6 fans off the one phase they cause the fans to run backwards, (in other words they blow back into the ductwork)

So with this i then tried to find out how many could run the right way until they changed direction anyway two fans is all you can have running off the one phase before they change direction,

So again trying something else i brought all 3 phases from the out door unit to the contactor and decided to wire 2 fans per phase which from what i have already found out should be fine and they will all run the right way, BUT still they dont run the right way at all when there is six wired,

Any help would be great thanks.

[Lowrider]

How did you wire them? Perhaps a drawing will help!

[p_p]

Try running each fan indipendant of the others to see if rotation is correct.

[Electrocoolman]

Hi Rotax,
Firstly I assume all 6 fans are the same in all respects (Size, Voltage, Speed (# of poles), cfm).
The capacitor is a RUN capacitor (Split phase motor).

As 'P P' says, have you checked to see each fan runs correctly when connected independantly on a single phase supply.

Has your 3 phase supply got a Neutral? or is it only 3 phases. You need a Neutral in order to get 240v.
You should be using one phase and neutral to supply a fan. (240v)
To keep your 3 phases in balance, you should run 2 fans on each phase and neutral.

hope this helps

[The Viking]

My guess (Based on what happened on one of our sites with a VAV system, different application but same principle):

All six fans blows in to the same space and get their air from the same suction chamber.

When you run more than 2 of the fans together, the pressure differential across the fans increases, so much so that you get above the threshold of when the fans are guaranteed to start correctly. After you reached this critical point there will be a randomness as to whether an individual fan starts the right or the wrong way.
The only way we found to overcome this is by installing 3 phase fans but better quality single phase fans, with a higher stalling pressure, should work as well.

[Brian_UK]

Also, don't forget to fit your electrical warning notices regarding the voltage potential across the fans.

[Rotax100uk]

Hello again, we have been back to see the blast chiller on friday and have made a conclusion.

when the fans are in situe and fixed to the duct work they spin the wrong way.

when the fans are taken out of the duct work and held by hand they spin the correct way?

So we came to the conclusion that there must not be enough air in the duct work for the fans to spin the right way?

Does that make sense to anyone?

any help would be great?

[The Viking]

Makes perfect sense to me,

See my previous post...