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Brushed motor query

ACharnley

Member
I bought a motor on aliexpress, which from the specs states 400rpm at 12v. The sticker and the specs seem wrong. I've measured it at around 100rpm at 12v.

My understanding is voltage makes it spins faster but it's current which causes it to heat, so as long as the bearings and gearbox can sustain say 48v to give 400rpm then all I have to watch is that the current doesn't rise above the rated amount, 2A.

Is this correct, or should I be complaining to the seller that the gearbox is way off spec?!
 

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rjenkinsgb

Well-Known Member
Most Helpful Member
It may work for a while, but it would probably burn out the brushes / commutator in a fairly short time due to excess current and arcing. The start current would be far higher than the commutator was designed for, as well.

It may even burst the armature, as it would be rotating far faster than it was intended to run..

Just get a replacement.
 

ACharnley

Member
I'd be controlling via Ardrino/PWM so inrush isn't so much a problem and the intention is to monitor current with a fail condition if 2A is met.

According to the spec it's intended to run at 400rpm, I just don't get by they've called it a 12V motor when 400rpm will be achieved at 48V according to my measurement. It's annoying as I need 400rpm and otherwise it fits nicely into my project.

With little load the motor is at 0.3A, which doesn't increase much or at all as the voltage is raised.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
From the data listing different motor-gearbox combinations, I'd say they just sent the wrong one or it is mis-labelled.

100 RPM output @ 12V is right in the middle of the list; 400 RPM is next to last.
 

ChrisP58

Well-Known Member
I agree with rjenkinsgb that they likely sent you the wrong motor.

But there may be a way to check that. In the upper right corner of the spec sheet they show that a dimension changes for different speeds. The tabble is not labeled, but I suspect thast it is dimmension L, since that is the only variable on the drawing.

Unfortuanately, the two speed brackets don't include 400RPM. But I'd check that dimension anyway.

As for heat, it's not just current, it's power that generates heat.
2 Amps at 12 volts is 24 watts.
2 amps at 48 volts is 96 watts. That's four times the 'spec'd' power for the motor.
 

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