Polarity has reversed!!!

[cmedsailor]

Now this is something really strange.
I installed last year a 747 cafrano fan above the chart table drawing the cables from the panel (connected to the switch for turning the plotter on and off). Till recently was working fine. Suddenly, without installing or changing anything "electrical" the fan rotates on the different direction. From my limited knowledge I think that means the polarity has reversed! How is this possible? The plotter (Raymarine C70), thanks God, still works OK and nothing else seemed to have changed. Could it be something wrong with the fan?

 

[David2452]

If it's a permenant magnet motor maybe the poles have somehow become reversed.

 

[William_H]

Fan motor

A permanent magnet fan has a peculiar lumpiness as you rotate it by hand. This comes from the magnets inside. A motor with field coils will feel quite smooth to turn. Usually the magnets of PM motors are quite strong so unlikely to reverse in polarity. If you reverse the wires of a PM motor it will go in the opposite direction but if you reverse those of a field coil type the direction will not change. You need to reverse the wires of the field coils. Anyway no answers to your question. olewill

 

[TopDonkey]

The slip ring could have come unglued from the shaft maybe ?, this could reverse the polarity by applying the power at a different timing to the armature resulting in a backwards running motor.

If this is the case, the only thing holding the slip ring stationary on the shaft is the copper wire windings, and if they give way one day, they could potentially short out, so make sure you have a sensibly sized fuse going to the fan

 

[Alex_Blackwood]

Once sailed on a ship,220 volt dc. we had three fractional HP. series wound fan motors providing "Forced draught" for the diesel fired galley. Every time we changed from ship to shore power,or vice versa, these three fans would reverse.
Never found out why and it never happened on the two sister ships.
Doesn't answer your question but it may help to know you are not alone!

 

[DaveS]

I'm not familiar with that fan but by any chance is it a symmetrical type mounted on an adjustable bracket? If so is there any possibility that it could have been knocked round 180 degrees?

 

[savageseadog]

Solar Storm?

Perhaps you've transited a parallel universe?