Motor Selection for minature Hoist

Thread Starter

EDANN

Joined Oct 24, 2016
24
Hello
I want to make a circuit that uses a a motor to work hoist and lift an object up. When this object is lifted, i will shut off my motor, and i want to drop the object and spin the motor backwards (making it a generator) and try to create electricity that i could try to store. Firstly i am wondering what type of motor would be best suited for this application. The motor must have a relatively low voltage (12VDC maybe), and will be powered from the wall, with some sort of power adapter in-between to supply the correct power. I know a little about motors, and so far i am leaning towards a small brushless DC motor, i am just unsure if i could generate electricity spinning in reverse. Any advice or guidance is welcome.
Thanks
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
A DC brushed motor would probably be the best, a BLDC will generate 3ph AC when back fed, so would need a 3 phase rectifier.
Max.
 

Alec_t

Joined Sep 17, 2013
11,513
A BLDC with internal commutation electronics is unlikely to be suitable as a generator.
i want to drop the object and spin the motor backwards (making it a generator) and try to create electricity that i could try to store.
Are you aware this would be a very inefficient process? The energy used to raise the object will be much greater than the energy put into the store.
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
A BLDC with internal commutation electronics is unlikely to be suitable as a generator.
.
A BLDC motor is essentially identical to a 3ph sinusoidal P.M. motor, and when back fed or rotated produces a perfect 3 phase wave form, the BLDC commutation when used as a motor is completely different.
The commutation components are not connected to the 3 phase armature (stator).
Max.
 
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Thread Starter

EDANN

Joined Oct 24, 2016
24
Thanks for the replys,
yes i am aware this is an inefficient process, 30% eff maybe, however, that is still energy i can capture.
I was looking at those small gear motors before, they seem to fit my application.
Now, lets say i use that gear motor, what will i need to capture this energy that the motor (generator now) creates when it spins in reverse?
Lets say i have a 12V battery as my energy storage device. Will i need some kind of buck boost converter to charge my battery?, how does that exactly work?, any limitations?
Any input is welcomed, thanks
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
The generated voltage at a particular rpm is close to equivalent to the voltage need to be applied to make it rotate at that same rpm.
So if it is rotating at a certain rpm when 12 volts is applied, that rpm will be needed , or above to produce a generated 12v.
Spinning in reverse is a reverse generated voltage, so you would need a diode 'steering' bridge to feedback the same polarity.
Max.
 

Thread Starter

EDANN

Joined Oct 24, 2016
24
Now i am wondering, would it be hard to spin a gear motor in reverse by using the weight of a mass on a string attached to the shaft, due to all the gears.
Would it be easier to use a normal brushed dc motor with a high rpm to lift my mass, and just use PWM to control the speed. Then it would be easier to lower i think?
Just a thought
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
If you eliminate the gearing, it will obviously require a larger motor, equal to the increased torque advantage when gearing is used.
Also you have a problem of the braking effect when placing a capture load on the motor, this then reduces the voltage you may require to capture, a bit of a catch 22.
Max.
 

tranzz4md

Joined Apr 10, 2015
310
Your mechanical and conversion losses (particularly on the generation side) will be much higher with gearing. I doubt you could reach 30% efficiency, let alone losses on that type of falling weight forces cycle.

It'd be fun to try,,, and tweak on. That said, you may end up with something much different than what you start with.

We'd like to hear of your experiments and results. This is a very unusual generation cycle, because the mechanisms necessary to acquire useful generation with efficiencies that could ever even pay for the equipment, typically affect the lifting equipment enough that even the added losses of efficiency in the lift cycle can more than offset the generation products.
 
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Alec_t

Joined Sep 17, 2013
11,513
How much energy are you hoping to store? Have you done the maths?
If, for example, you raise a 1kg weight 1 metre then it has gained 9.8 Joules of potential energy. Allowing for inefficiencies you would be unlikely to recover more than about 3 Joules of that.
 

Thread Starter

EDANN

Joined Oct 24, 2016
24
I don't plan on storing much energy, i just want to demonstrate it is possible for a large scale operation.
Hey guys, i got another question ya'll might be able to answer. I'm new to electrical engineering so i don't know everything about motors.
https://www.teknic.com/model-info/CPM-MCVC-3441P-RLN/
This motor here fits my need for a position control system problem. It is way bigger than what i need but it doesn't matter (i don't think). It meets my torque needs, size, voltage etc. It a brushless dc motor from my understanding. I think there are two possible ways i can 'extract' energy from this motor.
One would be the regenerative breaking it features
Two would be when i use a mass (torque) to spin the shaft in reverse
Both of these powers would come in different forms i think? Two would be 3 phase, and one would be reverse dc power? Any ideas?
Thanks
 

Kermit2

Joined Feb 5, 2010
4,162
Any motor like the brushless DC one you mentioned that require a driver circuit to run, will be unlikely to provide generator action when the driver is cut off and the rotor is turned backwards.
To easily switch between motor action and generator action use a permanent magnet type DC motor.
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
Evidently the motor linked to has a built in controller, otherwise the average BLDC that has external drive, has the capability to generate 3 ph AC.
Max.
 

Kermit2

Joined Feb 5, 2010
4,162
Doesn't it have to remain energized in order to generate? Or does it have magnets in it??? If it is a wound rotor and the field remains energized then it would become a generator. Are there driver chips that include the option for generating from a brushless motor installation? Hell. Now I have to Google away my lunch hour. :)
 

MaxHeadRoom

Joined Jul 18, 2013
21,200
The majority of BLDC and AC sinusoidal motors now have P.M. rotors, very rare to see a wound field now in DC brushed or AC Motion control motors.
This .PDF shows the 3ph waveform as a result of a back fed (rotated) BLDC motor.
Max.
 

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ronv

Joined Nov 12, 2008
3,770
I don't plan on storing much energy, i just want to demonstrate it is possible for a large scale operation.
Hey guys, i got another question ya'll might be able to answer. I'm new to electrical engineering so i don't know everything about motors.
https://www.teknic.com/model-info/CPM-MCVC-3441P-RLN/
This motor here fits my need for a position control system problem. It is way bigger than what i need but it doesn't matter (i don't think). It meets my torque needs, size, voltage etc. It a brushless dc motor from my understanding. I think there are two possible ways i can 'extract' energy from this motor.
One would be the regenerative breaking it features
Two would be when i use a mass (torque) to spin the shaft in reverse
Both of these powers would come in different forms i think? Two would be 3 phase, and one would be reverse dc power? Any ideas?
Thanks
It's going to be very tricky. To get it to be slow enough you will need lots of gears so friction. This has to be overcome when you try to drop the load. My guess is it won't fall.
 
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