View Full Version : Can faulty run/start cap cause high amps?

27-07-2012, 02:40 PM

I have two new exhaust fans I'm looking at that are both exactly the same models that are have
similar issues. both with access issues that are being fixed.

Fan info.

1ph 240v 50hz 1.08a

Fan A running at 1.6 amps then tripping the overload.
Fan B running at 1.4 amps and also tripping overload.

Im not sure if the have both a start and run cap.

My question is if one of the caps are faulty could it cause the fan to run over rated amps?

Any help would be appreciated.


monkey spanners
27-07-2012, 06:40 PM
Faulty or out of range capacitor will put the run current up, best test the capacitor and see if its ok. Doubt a fan would have a start cap, it'll be a psc motor if its got a cap. What are the bearings like? Airflow restricted?

27-07-2012, 11:15 PM
Motors can run over-current if the air resistance is well below the design for the fan blade; allows the motor to over speed sometimes.

28-07-2012, 11:38 AM
yes, a failing capacitor will cause a motor to draw excessive current. an exhaust fan wont have a start capacitor, as it doesnt need excessive starting torque, as monkey said it will be a psc motor with a run capacitor.

it will likely also cause the motor to be hotter than normal too.

01-08-2012, 06:52 AM
Being new then check they are wired correctly.

03-08-2012, 06:57 PM
mr, 1piece,

It seems ur amps is ok , both r having same prob, it means manufactureing fault or wrong application?


03-08-2012, 09:46 PM
You should be looking at the air flow and external static resistance and comparing this to the fan curves.

Are both fans producing the extract rates you are expecting?

Anything outside of the design (assuming they have been selected correctly) will cause the fans to perform unexpecedly.

robin r33 gtr
07-08-2012, 09:01 PM
May sound silly are the fan blades on the right way ?

08-08-2012, 10:24 AM
Turns out the manufacture of the fans miss printed the motor info stickers. Had the fan info and curve sent to me and both fans were operation fine to the design. just have to up size the overloads to suit correct amp range to stop the fault.

09-08-2012, 07:06 AM
Thanks for reply and resolve to the problem