small but powerful motors

[vipulan12]

Hey guys, i have been wondering
when we put too much current or voltage to a motor the motor will eventually be destroyed
but how exactly is it being destroyed,i know heat builds and burns the coils and insides of a motor but what if you were able to cool it some how
because if that were the case wouldn't it be possible to build a small motor that could produce a large amount of torque
the more current=stronger magnetic field=more torque=but will generate more heat unless cooled down somehow
 unless i am missing something or i am completely wrong why would this not work?

[Azraels]

Because the amount of energy needed to cool the motor would eventually be to great and would most likely exceed the energy needed to run the motor which would not be efficient system at all.  We already have superconducting magnets but they require large cooling systems to keep them superconducting and from not burning out.

Also heat causes expansion, which can throw that motor out of its specs, cause warping, etc.

[waltr]

Yes, that idea can work ans is a way to increase the specs of a motor. I have seen DC motors with a heat sink mounted around the motor body to dissipate extra heat from run a higher voltage/current.

The biggest problem is that the windings in a DC brushed motor are in the armature and it is difficult to transfer the heat out. Some motors have a small fan built onto the shaft inside the housing to help remove heat.

The other consideration is the Duty Cycle of higher Voltage and load. Due to thermal mass it does take a finite amount of time for the heat to build to damaging levels (melting the wire insulation) so a higher Voltage could be applied for a short time but then the Voltage needs to be greatly decreased to allow the motor to cool.

Also note that if you use PWM to control the motor speed/torque you could run a higher voltage since the PWM duty is averaged. But YMMV.

All this is mostly theory can results will be different among different quality motors. So some experimentation is needed. One parameter to measure would be the motors case temperature. The armature temperature is really more important but very hard to measure. Also expect to burn out a few motors during the experiments.

If you really need a small powerful motor then its probable better, and more reliable, to buy a high quality small, powerful motor. There has been some advances it motor technology including stronger magnets, light armatures, better windings that have improved motor performance.
Then there are the BLDC motors and Coreless motors as well as improved gears for speed reduction.

[vipulan12]

Thanks for your input, I was just curious if the concept I through out made sense
by the way what's warping?

[Azraels]

Warping: Become or cause to become bent or twisted out of shape, typically as a result of the effects of heat or dampness.

or if your on a star ship, to travel faster than light. 

[jwatte]

Most high-performance DC motors do exactly this: design for high cooling to run more current through the same windings. Also, brushless designs are generally better because there are fewer parts that need to see the current and heat -- brushes can wear out quick from too high current, which leads to massive arcing!

Unfortunately, the insulation for the windings, and the mechanics of the motor, only lets heat escape from where it's generated (the actual inductive coils) to where it can be dissipated (fins, flanges, casing, heat pipes, etc) at a certain rate, so there are physical limits to how far you can take this kind of design.

From what I understand, the main "normal" limit is the temperature at which the winding insulation (and perhaps other parts) of the motor break down. Even if you could fix that (bathe the windings in liquid nitrogen or something) there exists a current at which the temperature inside the copper itself will become so high that it burns out the copper before it even gets to the outside. If you try to chase *that* down, you end up with super-conducting windings, which might be a possibility in the future but isn't terribly practical right now :-)

[vipulan12]

but why does it brake or how exactly does it brake?

i get that it might melt but how else can it break (other than snapping)

[jwatte]

but why does it brake or how exactly does it brake?

Some ways I can think of:

If the insulation melts, it will form contacts between windings, which will reduce resistance, draw even more current, and generate even more heat.

Things expand with heat, and may come into contact with moving parts, and thus be torn.

Solder may melt at high temperatures, and break a connection.

Enough heat, and pieces of the motor will simply burn or even evaporate (needs lots of current for the "evaporate" part :-)

Why don't you buy a couple of motors, feed lots of voltage/current into them, and study the problem yourself?

[vipulan12]

I would but asking someone else the question is much easier besides it would be a waste of money and a good motor if i were to overpower it

[jwatte]

it would be a waste of money and a good motor if i were to overpower it

If the goal is to learn how motors fail when overpowered, why would it be a waste of money to pay $30 to learn that? Or even paying $200, burning out ten motors, and learning various things?

[waltr]

There are many cheap 'toy' motors available from surplus electronic suppliers.
Also, there a many small gadgets with motors inside that can be salvaged for free.
Learning how they fail is not a bad thing and can be fun to see all the smoke pour out.

but why does it brake or how exactly does it brake?

to brake a motor, force it to slow down to a stop, is usually done by shorting the two motor terminals.