ESC (electronic speed controller) with bldc motor

[Vraj]

first thing i need is less RPM .

https://www.amazon.com/Toro-Beast-520KV-Brushless-Motor/dp/B00WIM7BMI?ie=UTF8&*Version*=1&*entries*=0


i found that bldc motor has rating on kv. which means if i give 2v to 520kv motor , it's RPM will be 1040.

so for achieving low rpm, i have to apply low voltage and high current. i also need high discharing rated batteries.
but minimum voltage for ESC is 7.4v. can i get maximum power at this minimum voltage?
i can't reduce RPM by mechanical gears. because the is no space left.

i need low rpm for more torque.so maximum power of bldc is required.

 

[chuckey]

" i need low rpm for more torque.", The torque from a motor is only dependent on the current through it not its speed. The speed at which the torque is delivered means that at high speed the output power increases. If you really want more torque then either a gearbox or more current is required. Running a motor slowly can cause them to overheat as the cooling fan will not operate properly.
Frank

 

[Vraj]

https://www.hobbypartz.com/96m802-4074-2150kv.html

this motor tells 2600 watts is this possible?
it is still 1:8 !!!

 

[chuckey]

This is input watts, not output power. They claim 95% efficiency (?), so thats 5 % X 2600 ~ 130W in a non fanned metal unit 75mm long. Should last 10 minutes before it over heats.
On another forum, people have been discussing these motors for real engineering jobs, boring, milling, grinding. Because 2600W is over 3 Hp which is correct for a medium sized machine. The consensus is that they have a short life and require a large step down ratio to be off any use. See :- https://www.model-engineer.co.uk/forums/postings.asp?th=119035
Frank

 

[Vraj]

i think also there is power dissipation at ESC . you don't think overall brushed motor is more efficient? ; )

 

[chuckey]

The concept of ESC is that you need a variable speed control. In real computer controlled machining centres they use a 15 KW ESC motor for the main tool rotating device. This is so the tool can be braked to a standstill for changing and then rotated at its maximum speed for cutting. There is a efficiency penalty, but not a convenience of use penalty.
One thing worth remembering about ESC motors is that the speed must always be ramped up from zero, so the rotor can lock onto the rotating magnetic field.
Frank

 

[Vraj]

if the bldc motor is rated 90% efficient and 2000kw power(input) that means the output power is 1800w?
i think it is not correct!

 

[c_mitra]

You need to go through the comments in the thread below:

https://electronics.stackexchange.com/questions/175861/bldc-max-speed-kv-or-hz

It is messy but not difficult

 

[FvM]

if the bldc motor is rated 90% efficient and 2000kw power(input) that means the output power is 1800w?
i think it is not correct!

Surely not, because you are mixing up watt and kilowatt.

Apart from this trivial error I wonder what your actual question is?

 

[Vraj]

yes it is 2000w not 200kw

- - - Updated - - -

i mean 2000w not 2000kw

 

[c_mitra]

i mean 2000w not 2000kw

The power an electric motor can deliver depends on several factors:

1. RPM; we shall ignore this and consider only the energy output per revolution

2. current in the motor coils- and the magnetic fields interactions. They depend on the copper and iron. Both are lossy.

A given winding can carry a max current that is defined by the losses. A given mass of iron will produce a max magnetization.

You can increase the output power by increasing the RPM. Perhaps you can have a BLDC motor running at 50,000 RPM with a 2kW power output. The same motor at 5000 RPM will produce a fraction of the rated power.

 

[FvM]

O.K. 2000 W * 90% = 1800 W is correct. It says that the motor is delivering 1800 W of mechanical power when supplied with 2000 W electrical input. But the specification is only valid for a specific operation point, most likely full speed. It also doesn't necessary tell about continuous motor rating.

As far as I understand, you want to operate the BLDC motor at a small percentage of rated speed, so the advertising specifications aren't of much worth.

Perhaps you can manage to clarify your question?

I agree with c_mitra that you expect in a first order speed independent maximum motor current and respective torque. Maximum power will be scaled down linearly with speed.

Previous posts mentioned possible current reduction at low speed due to reduced cooling. I believe the effect won't be very strong with BLDC motors that don't have a fan.

 

[Vraj]

i cant found bldc motor rated less than 520kv. so let suppose, it is the final motor.
i need more TORQUE.

for a ESC i found, that it has minimum input voltage is ~7v.

can i get less than 520*7 rpm? by controlling this current from ESC?
i cant compromise with the torque.

 

[c_mitra]

i for a ESC i found, that it has minimum input voltage is ~7v.
.

You need to study the detailed specs for the ESC. If it has been optimized for a given application (some ESCs are) then you are out of luck.

 

[FvM]

Looking quite a bit into the Toro-Beast specification reveals that it's sensorless BLDC motor without electronics. It has to be supplemented by an external 3-phase inverter ("ESC"). Parameters like minimum speed are mainly set by the inverter properties, specific speed/V and torque/I are however defined by the motor hardware. Like all sensorless AC motors, it has problems to run at low speed with maximal torque, but a good sensorless vector controller can still do a lot. Or you may add an external resolver.

Achievable kV range respectively rated speed of brushless DC motors is somehow restricted by physical law. You can run a motor at lower speed but the power will reduce respectively.

The speed range of the usual ESC models is however defined by the application as c_mitra mentioned. RC vehicles don't need low speed. Other technical applications like servo drives are utilizing BLDC motors over a larger speed range. Means you either need to design your own ESC or find a more versatile one.

 

[Vraj]

can i use stepper motor instead of bldc?
can stepper motor used for constant speed and single direction? (clock or anti-clock)

 

[FvM]

You can use a stepper motor but the torque will be considerably smaller than that of a intelligently controlled BLDC.

 

[c_mitra]

I suggest you consider a BLDC motor with sensors (typically Hall sensors) and invest in a good controller. Perhaps you will be able to get your torque-rpm combination.