Electric motors

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Mr Ron
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Electric motors

Post by Mr Ron »

I am building an electric engine which will be powered by 3 electric motors, 12 Volts each. They are small motors. If I want the motors to all turn at the same speed, do I wire them in series or parallel?
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John Hasler
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Re: Electric motors

Post by John Hasler »

Parallel. In series they will all deliver (approximately) the same torque if they are identical motors.
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Steggy
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Re: Electric motors

Post by Steggy »

You didn't say what type of motors these are. If they are permanent magnet types they will all run at approximately the same speed for a given load and voltage, but will not produce real high starting torque. If wound-field motors, it would depend on whether series-wound, parallel-wound or compound-wound. A permanent magnet motor's performance approximates that of a parallel-wound DC motor.
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steamin10
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Re: Electric motors

Post by steamin10 »

Permag motors of the standard type are terrible n low speed high load situations and heat badly. The controls are better if you use current limiting or pulse wave at higher voltages for the low end torque. At one third of rated speed you are all good and can live there, but a dead creep is to be avoided in my experience. As far as speed, motors running on the rails are mechanically locked by the traction to the rail, so unless there is wheel slip, they will turn at exactly the same speed.

Getting pulse wave from battery power circuits is a problem as they can be complicated. The standard answer of Q4d and such drives have been reliable, as well as some wheel chair drives, if you match the loading.
Smaller motors tend to have higher inrush currents for longer until they turn over a few rpm. Larger motors have a bigger spike of short duration that must be accounted for.

Why three motors? They should be parallel to see the same voltages. One modeler I saw used the motors themselves to switch 4 motors for some speed control using one motor to be the resister for the next. step resistors in between wasted juice but evened out the steps in speed. 16 volt motors run up to 24 volts with two auto batteries.
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Mr Ron
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Re: Electric motors

Post by Mr Ron »

Recently, I have been turned on to brushless/coreless motors. I hear they have high torque at low rpm's They run at very high speeds, like 10,000rpm, so a good reduction gear set is needed. I didn't know that these are the same motors used on drones, computer disc drives, printers and RC cars and planes. Some of the motors I've seen can develop 1/4 hp and more. They seem to be perfect for trains in the 1/16 and 1/24 scales. Here is a video of a micro motor:
https://www.youtube.com/watch?v=RwViuRljJq0
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WJH
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Re: Electric motors

Post by WJH »

R/C airplanes are probably my most active long standing hobby. Those brushless DC motors have an important spec you should pay close attention to, kV. It's the unloaded rpm per volt. Besides that, you have in-runners used most on boats and cars, and out runners that have less rpm and more torque, used on drones, helicopters, and airplanes. Obviously the out-runners are preferred for traction. You also have to realize that each motor needs it's own speed control. To complicate things, there's also sensored motors that have better rpm control at low speeds but have fallen out of favor. With a low kV motor, you'll want higher voltage, so plan accordingly. These motors are powerhouses and could easily have your engine go 40mph if not planned appropriately.
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Re: Electric motors

Post by hanermo »

Mr ron ..
most motors apart from modern ac brushless servos have very low torque at low speeds, and usually high heat.

For traction apps like a train, you do not want a high rpm motor.
It is not hard to make a gearset to step down the speed, but it is VERY very very hard to make one able to deal with 10k+ revs, not be noisy, and last under any load over time.
Washing machines use a 1:11 transmission via a tiny flexible timing belt pulley, from 12.000 rpm to 1000 rpm. +/-.

You would probably get best results from small vfd driven 3 phase motors.

Spec rpm, range, desired power => vfd + small 3 phase is the best easiest sweet spot.
Really cheap.
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Re: Electric motors

Post by WJH »

hanermo wrote: Wed Oct 31, 2018 4:11 pm Mr ron ..
most motors apart from modern ac brushless servos have very low torque at low speeds, and usually high heat.

For traction apps like a train, you do not want a high rpm motor.
It is not hard to make a gearset to step down the speed, but it is VERY very very hard to make one able to deal with 10k+ revs, not be noisy, and last under any load over time.
Washing machines use a 1:11 transmission via a tiny flexible timing belt pulley, from 12.000 rpm to 1000 rpm. +/-.

You would probably get best results from small vfd driven 3 phase motors.

Spec rpm, range, desired power => vfd + small 3 phase is the best easiest sweet spot.
Really cheap.
Hey now, this is intriguing me. How would one do this? Large enough inverter that takes 48v DC, and makes it 220v single phase, to a VFD that powers a small 3 phase motor in the truck? Have two vfd's, one for each truck that drives one motor?
I don't know who makes the appropriate inverter, nor know which 3phase motors would fit inside the truck. I however think a VFD would be perfect for driving a locomotive with ramp up, ramp down, and dynamic braking with an external power resistor like the real thing.
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