Fan Running With 1/2 Current.

Four possible things could impact this.

1) The voltage level of the source feeding the fan has changed.

2) A restriction in the inlet air flow to the fan has changed causing less of a restriction so it is easier for the fan to do its job.

3) A restriction in the outlet air flow from the fan has changed causing less of a restriction so it is easier for the fan to do its job.

4) There could have been a change in the state of the bearings, or more then likely bushings, inside the motor reducing the mechanical restriction.

5) The impeller may have fallen off.

this issues is on 6 to 8 of the most recent unit on the production line. an old unit was pulled from stock and connected to the test cunnections and it showed the orginal amp draw.

If you are running on the same voltage and it is drawing less current, the first thing I would believe is either less mechanical resistance or possibly more electrical resistance. Basic circuits theory states V=IR , if your voltage is the same when tested, your resistance must be higher.

Manufacture installed the wrong impeller on 6 of the 8 fans. Or the fans are of a different hp.

So this is on different fans? It would have helped if you had of stated that up front.

I agree with the last poster. The electrical characteristics of the fan motors you are using has changed.

a third factor is not mentioned, is the fan performing the same amount of work? (CFM same?) also,was it lubricated lately?

Maybe someone has sucked all the air out of the room?

Somebody reduced the impeller effective diameter by thirteen percent? Power consumed by the impeller is proportional to its diameter raised to the power five.

Mark
http://www.fourth-axis.com

Agree with all the comments so far. You have to figure out some way of measuring the actual performance of the fan (CFM with all other physical conditions fixed).

If the performance has changed then try to figure out if the impellers are identical: if you can't see a difference; can you swap impellers.

If the impellers are identical, the next step is to try to measure the RPMs.

Of course if the performance has not changed then either the motor or bearing (or both) must have improved.

Swapping bearings/motors/impellers etc. will quickly show you which component has changed.

Please let us know how you get on.

What typoe of fan is it? An Axial fan or centrifugal? This wil make the difference on load and if you are blocking the entrance or exit of the fan.

Andy Hall

andy@cds-concrete.com

In addition to everything mentioned above, are you sure the motors being compared are identical? The manufacturer may have changed something to account for the lower current. You may want to ask if they changed the bearing type, winding material or configuration, core steel, etc.

we are in the process of checking this with the fan manufacturer.

because they are in Europe there has been a delay doing this so I'm hoping that there is an answer that can be found here.

Regards !

In The Question the gentleman is talking of his fan, no other fan he has.

He has tesed it with related test equipment for the change in parameters.

Fan seems to be a "Sealed-Unit" as he cannot check the Start-up capacitor without destroying the unit.

Need more info from him:

Post #3 He is talking of if he is working in a factory & has checked a lot of similar units

The Question he placed in forum should have all the info about the problem 1st hand & all the trials & results he had gone through; otherwise he is wasting posters' time & getting irrelevant answers.

Can he confirm the products from its name-plate if thses are identical on all units?

Change in any parameter; electrical[ Post #13 ], pneumatic [posts #7 & #11] or mechanical will change test parameters.

Post #1 2) & 3) suggests the air filters impedance due to deposit of dust