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Topic: voltage, amperage, and wire temperatures (Read 572 times)previous topic - next topic

arduinopi

Jun 18, 2013, 12:43 am
I am a little confused on a core concept of electronics.

lets say I have a DC motor that is using 2 amp at 12 volts.
lets also say I have another DC motor using 1 amp at 24 volts

assuming all the wire gauges are the same
1) which motor will be hotter and which is more efficient?
2) will the wires that come out of the motor temperatures be the same?
3) what advantages do the motors have over each other?
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majenko

#1
Jun 18, 2013, 01:04 am
My gut instinct is to say:

If the windings are the same gauge wire, then the length of the 24V winding must be longer, and so the resistance would be more, and the current reduced.

Say 12V is 2A, therefore the resistance must be 6?
At 24V 1A the resistance would be 24?, so 4 times longer.

P=I²R, so 2²*6 = 24W
P=I²R, so 1²*24 = 24W

The two motors are the same power rating, but the mass of the 2A one will be smaller, so the heat will be more concentrated.  The amount of heat energy will be the same, but the heat per square inch will be greater in the smaller motor.

The higher current motor will have more torque than the lower current one.

?=kt?I
kt is a constant, ? is the torque

MarkT

#2
Jun 18, 2013, 01:04 am
1) The efficiency of the motor depends on its construction - if the motors are the same except for the windings then
they ought to be the same.

2) The same wire carrying more current will dissipate more power as heat - this is simple
to calculate, find the resistance of the wire per unit length, multiply by the length (all the way round the
circuit).  That's the total resistance of the wire.  It will dissipate I-squared-R (current squared times resistance)
watts.  It will "drop" I-times-R volts too.

3) With the 2A 12V system the wiring will cause more losses than the 1A 24V system because of the higher
current.  If you have long wires its better to use higher voltage and lower current so your wires don't need to
be as thick (copper is expensive).  For short wiring the difference will be that the 12V 2A motor has lower
impedance windings (which might allow it to spin faster if winding inductance is the limit to performance).
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#3