That smell from an overloaded motor: what is it?

[Michael63129]

@Napier

Motors vary in how much excess heat they can dissipate. It is typical of high speed brush motors to have pretty high power densities, and a cheap one in a home appliance is all the more prone to this. I wouldn’t be surprised if it could smoke in a few seconds. Some other motors, such as some small shaded pole induction motors, can sit stalled indefinitely and only run a little warmer. Indeed, torque motors in the form of high slip induction motors are intended to operate in the stalled condition or even while being spun backwards.

The example I posted was of a vacuum cleaner motor, which is fairly high power density, probably higher than that in a blender, plus the motor had its field windings bypassed, with power directly fed to the armature (normally the windings are in series). You can find other such videos on Youtube of people doing things like that, including applying 240 volts (or even 400+ volts) to 120 volt motors, etc; most take more than a second or two to overheat.

This makes sense if you take the specific heat of copper (windings) at 0.386 J/g per degree; in order to heat it up by 100C in one second, you will need 38.6 watts of power; if the motor has 100 grams of copper in its windings (ignoring heat conduction to the metal frame), you would need 3.86 kW of power, which is not going to be drawn by a 100 W or so blender motor, not even close, stalled or not.

Also, I regularly solder enameled wire and it usually takes a few seconds to melt the insulation off with a soldering iron (around 300C); you probably need something around 200C to start melting the insulation (which is rated up to 250C for high-temperature uses; some doesn’t even melt with a soldering iron and has to be scraped off).

[robert_columbia]

@jz78817

Ozone. The electrical arcing between the brushes and the commutator of the motor produces ozone.

Hmm. How many electric motors would we need to run and for how long to repair that hole in the ozone layer? Or is that fixed?

[Malacandra]

@robert_columbia

Hmm. How many electric motors would we need to run and for how long to repair that hole in the ozone layer? Or is that fixed?

I don’t think ground level ozone is going to get up to the ozone layer in time to be at all useful. It’s heavier than air and breaks down naturally in about three weeks in the troposphere.

[johnpost]

@robert_columbia

Hmm. How many electric motors would we need to run and for how long to repair that hole in the ozone layer? Or is that fixed?

ozone rapidly reacts with whatever is oxidizable so it doesn’t get far or last long in the lower atmosphere.

[ftg]

@robert_columbia

Hmm. How many electric motors would we need to run and for how long to repair that hole in the ozone layer? Or is that fixed?

Ground produced ozone won’t make it to the upper atmosphere, it will break down before it gets there. The high ozone is produced on the spot by UV light.

(In addition, ground level ozone, mainly produced by pollutants, is not good. So producing more down here is very bad.)

The ozone layer is not getting worse. As the old CFCs and such become less common, it’s expected to get better in a few years and return to normal levels later in the century. OTOH, global warming and NOx emissions aren’t helping.