...where Sid said "since what the motor COULD draw is exactly the amount the motor WILL draw if it needs to."
...& I also remember him telling me/us (one time or another) that a motor is simply a power convertor.
(it turns electrical energy into mechanical/rotational energy)
...kinda like a light bulb converts electrical energy into luminous/light energy
....
Yes, but let me emphasis this part:
"since what the motor COULD draw is exactly the amount the motor WILL draw
if it needs to."
If the current demand on the motor is low..
the drawn power will be too..
(cruising is still an option with powerfull motors
)
Think about it this way:
If a 60W light bulb connected to a 110V power supply will emit
X amount of light
…& a 75W bulb connected to the same voltage power supply will emit
Y amount of light
…& then, a 100W bulb also with the same voltage power supply will emit
Z amount of light.
(each convertor happily drawing exactly what it needs)
You see, (again, if I'm understanding this correctly)
...a larger convertor (motor or light bulb)
will produce more...rotational or light energy, from the same power supply.
Does this make sense?
Kindof.. but a Lightbulb is a bad comparision really..
once On it tries to draw as much as it can and while it can be limited (dimmed) actively.. it sucks as much power as it can at all times..
unlike a motor that draws as much power as it NEEDS
(only) up to it's internal limits if so required (load)
And while that's a fuzzy line really (constant, peak, with and w/o active cooling etc)
motors with less or even no load draw less currents than the exact same motor under significant load at the same speed.
It's even worse actually.. a higher power motor at the same load can run more efficient (and thus draw LESS current) for the same mechanical output power than a motor that is on the edge of it's capability under the otherwise exact same conditions.
But assuming the power supply fullfills the demand of both motors reliably
(say a [constant] 100A for either a 20 or a 60Amp motor)
the 60Amp motor of course delivers a bigger punch if needed
but
only if needed.. if not it doesn't make any significant difference really.
Most motors have limits by means of RPMS.. well all do in fact..
but it's the simpler idea that we care about the most.
1) commutation (3+ phased Brushless motors need a pulsed signal.. and they can only run as fast as the controller can switch)
2) brushed motors commutate as fast as they turn and are limited by the physical limitations of their windings.
current must rush through, create a magnetic field, that has to interact with another field (of the permanent magnets usually),
those forces have to move the rotor until the commutator toggles the coils...
if little that still takes time.. and different coils (number of windings, wire gauge etc)
have different specs in that regard and that's usually the limiting factor for brushed PM DC motors.
(there's also loss due to resonating frequencies in brush springs, limiitations by bearings .. air resistance and so on and so forth... but that'd take things way too far for a forum like this I guess
)
Essentially it's best to pick the motor for the task.. just mildly oversized
(to keep it from reaching it's limits too frequently)
a more powerfull motor means a quicker (not necessarily faster) setup with more acceleration..
and that's tempting to draw more power...
so you might end up using more battery juice for no other reason than grin
(more batteries more weight.. higher demand.. an the dog bites it's tail)
'sid
and find the top speed and see how the motor does.