Experiment on whether and when a stuck up fan will break into flame.

Let us consider a typical home electric fan, and we put some obstacle to
prevent the fan propeller from turning, then we switch on the fan on the fastest
speed; will the fan and when eventually break into flame because the propeller cannot rotate?

Have there been experiments to see what will happen?



Marius de Jess

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iceng3 years ago

Depending on construction ( like coffey makers ) the motor will heat ;

1) due to a lack cooing air passage.

2) due to inductive energy converted to resistive energy.

Then the wiring will get hot and smoke the insulation

Some fan designs ;

1) will burn a wire open and cool down.

2) will short adjacent turns, trip a house circuit breaker and cool down.

3) will melt plastic housing, reach a flammable surface and start a fire.

4) will trip a rare thermal protection fuse and cool down.

A

Ah, but LESS power is dissipated if the fan isn't loaded.....Discuss.

Marius de Jess (author)  steveastrouk3 years ago

"Ah, but LESS power is dissipated if the fan isn't loaded.....Discuss"

I am no electrician, but I do know a bit about loaded and not loaded.

The question is as the fan is stuck up, there is no movement, so there is no consumption of energy?

But the fan is getting hot and hotter, that is the trouble, the energy is changed into heat, wherefore there is consumption of energy which does not result in movement but in heat.

What about that?

Lesson here is that we have got to be extra mindful and careful with all kinds of fans, and check all the time whether a fan is stuck up in any way at all and the current is on.

So, before you leave the place: your home, office, factory, shop, see to it that the fan is not stuck up and it is switched off.

That is the difference between a light bulb left on and a stuck up fan left switched on, and there is electric power in the place: your home, office, factory, shop, etc.

Back to a transformer, it is hot and getting hotter when it is not loaded, meaning supplying ampere to an electrical device, do we have frequent news about a transformer catching fire?

On the other hand, I read that giant transformers are cooled down by some way, is that to prevent it from catching fire owing to heat accumulating continuously without any stop when it is not loaded?

Next, any solution on how to prevent a fan from being stuck up while the owner is asleep and he has kept the fan on so that he could sleep in a hot night?

Solution, install a fire alarm that will wake him up, or water sprinkler in the ceiling that will turn on when it senses smoke and of course fire!

Anyone with a better idea?

The reason a stalled fan motor gets hot is largely down to the cheapness of its construction, and the losses in the iron and copper tolerated when the air is moving through the motor, but not when its at stall.

A power transformer will ALSO not get warm on no load. The monster ones are cooled because when they are on FULL load, even their minute % losses add up to a lot of heat - 100MVa is not an impossible rating for a large transfomer and it can be 99.9% effiicient, but that's still 100kW of heat to shift.

ANY fan which passes European CE standards MUST be fitted with a thermal fuse.

Marius de Jess (author)  iceng3 years ago

You say:

QUOTE

Depending on construction ( like coffey makers ) the motor will heat ;

1) due to a lack cooing air passage.

2) due to inductive energy converted to resistive energy.

Then the wiring will get hot and smoke the insulation

Some fan designs ;

1) will burn a wire open and cool down.

2) will short adjacent turns, trip a house circuit breaker and cool down.

3) will melt plastic housing, reach a flammable surface and start a fire.

4) will trip a rare thermal protection fuse and cool down.

UNQUOTE

Have you personally done an experiment as per my requirements?

You see, I have not done any experiments myself, but I read about electric fans causing fire in a house or building.

I read your background and it appears that you are most favorably qualified to undertake such experiments as described by me, and do the public a favor of enlightenment about electric fans causing fire.

Tell me if I am correct.

I have a transformer with capacity to deliver 1000 watts, it is a step up transformer, from 110 volts AC to 220 volts AC. It is on all the time even if there is no load actually being carried by the output current; it is hot but I never see it coming to combustion i.e. flame.

So, the way I think about it, the stuck up electric fan is no different from the transformer that is always on but without any load.

Marius de Jess

I have personally smoked a fan, and investigated several home fires caused by motorized appliances for a friend at Farmers insurance.

In my career I have seen copper wire elements get so hot that the surface cooling was all that kept molten inner copper from squirting out under the surface tension which it sometimes did anyway.

I have never seen a thermal protect fuse in a shaded pole fan motor but they (thermal cut outs) are common in integral HP induction motors turning large ventilators.

A transformer is not a perfect electrical device.

An unloaded power transformer has a resistance and inductive reactance that dissipates power in the windings even at zero output load !

See some of the transformer peculiarities in the simplified picture below.

IndReactance.JPG
Marius de Jess (author)  iceng3 years ago

Thanks, Iceng, for your kind accommodation.

You say:

"I have never seen a thermal protect fuse in a shaded pole fan motor but
they (thermal cut outs) are common in integral HP induction motors
turning large ventilators."

I think that home electric fans sold in my land are not assembled with a thermal fuse.

For protection, can I just connect a thermal fuse in the wire at the spot where it exits from the fan motor housing, assuming that if the fan gets stuck up, the wire in that spot is certainly hot enough to disconnect the thermal fuse?

What do you think?

A thermal fuse is imbedded in the motor windings in order to experience the same temperature as the motor in order to detect if it is in a stall damage heating situation.

I have two old 29" square metal frame 3 speed fans that have oi-lite brass bearings that do often refuse to turn the large triple blade. The motors are designed to survive the stall condition at least a half hour without smoking because it has taken me that long to reach and oil them..

There are multiple sensor electronics that can be used to detect loss of fan motion from IR beam, hall probe near armature, buffeting wind sound, etc.

A

framistan3 years ago

My brother owned a house trailer that burned down because of a small bathroom vent fan. It was winter time and he tried to stop warm air from escaping out the vent fan in the bathroom. So he put duct-tape across the fan to hold heat better. The next day, our old uncle turned ON the vent fan .... he didn't know it was blocked. Then he didn't turn it OFF. So it got hotter and hotter and finally caught fire. The whole trailer burned to the ground in less than an hour. Nobody was hurt in the fire but one FUNNY thing happened that I will tell you. My brother heard the smoke detector going off. So he went into the bathroom. He could not believe that the TOILET was on fire! He could not understand how a TOILET could catch fire, so he watched the flames for a few seconds. Then he saw something DRIPPING from the ceiling. It was the ventfan melting and dripping the burning plastic.

Burf3 years ago

I haven't personally conducted any tests but I know who has and I know where to look for the findings. Now I will give you the information you need to find out for yourself:

http://www.ul.com/global/eng/pages/

Marius de Jess (author) 3 years ago

Have there been at all any experiments done?

The requirements of this experiment is that you don't do anything else but only put some obstacle to prevent the fan propeller from rotating, like inserting a folded up handkerchief between a blade of the propeller and the grill-cage of the fan, so that the fan propeller cannot go into rotation when you switch on the fan at its fastest speed.

The purpose of this experiment is to ascertain that in fact a stuck up fan does cause a fire in a building or in fact it does not.

Marius de Jess

If you want to set it on fire it's easier and more effective just cutting one of the coil's wire. Last time I did that (accidentally) the motor immediatly started to smoke and a couple seconds later it caught fire. It was a hand blender, however.