Need help in driving brushless C6374 KV170

[Vasily]

Sorry for my bad english, I'm trying to do my best
I'm going to make an electric catamaran with combined solar + accumulator power supply. Continuous power level is expected to be at 500-600 watts, and I decided to use C6374 KV170 brushless motor. It has rated power more than 3KW, so i assume there will not be any problem with motor heating at my power level.
As I absolutely new to brushless motors, I need some help with its speed control.
The main question is what should I have to make a simplest speed regulator? There is no need in radio-control for me. How can I use ESC without receiver?
Can anybody recommend ESC for 100-120A and 24-28V? (I'm going to use two automotive accumulator battery in serial).

Another question is about motor efficiency. At 24v this motor will go with no load at around 4000 RPM. Maximum efficiency should be at around 2800-3000 RPM. If I'll drive it at 1000-1500 RPM, what would it be? 90%? 80%?

 

[Vasily]

Further reading gave me an answer to one of my questions. There is a simple way to drive brushless motor without receiver and transmitter. Instead of using receiver, ESC should be connected to servo tester - very cheap thing which costs about 5-10$. Hope it will work.
Whether I chose right combination?
C6374 Kv170 rated 100A + 120A ESC suitable for 2-7 LiPo or 6-20 NiMH + CCPM Master Checker 3 CH 4.8-6V

 

[Miles]

Vasily,

This is the motor you have in mind?
http://www.aeolianmotor.net/Aeolian-Motor/Aeolian-Motor-C6374-KV170-brushless-RC-motor-for-RC-airplane

 

[Hillhater]

... At 24v this motor will go with no load at around 4000 RPM. Maximum efficiency should be at around 2800-3000 RPM. If I'll drive it at 1000-1500 RPM, what would it be? 90%? 80%?

If you are using a 24v supply and using the ESC to restrict the rpm down to 1000-1500... i suspect your efficiency will be much lower than you hope for.
And the ESC's do not like to run at part throttle with high power loads, but your 600w may not cause a problem.?
If efficiency is critical to you, you might consider a reduction drive so that you can run the motor at optimum rpm ? .. but of course any reduction will have losses also.
I Assume you will use a marine ESC with water cooling ?
http://www.hobbyking.com/hobbyking/store/__8946__Turnigy_Marine_120A_Brushless_Boat_ESC.html

 

[spinningmagnets]

If you use an inexpensive Servo-Tester as a throttle, the input to the ST requires 5V. I have seen several ways to accomplish this.

1) Make sure to select an ESC that has a built-in 5V wire (called a BEC/Battery Elimination Circuit)

2) If your desired ESC does not have a 5V BEC (it will be labeled as needing an additional UBEC/Universal-BEC), you can use a generic 4-cell pack that holds 4 rechargeable NiMH cells that are AA or AAA-sized. (Thanks EVTodd!)

3) Add a small Voltage-Regulator (VR), that will drop your pack voltage (often 36V-48V) down to 5V for the throttle.

4) There are probably other ways I don't know about...

 

[Vasily]

Thank you all for your answers.

Miles, you are right, it is the motor I have in mind.

Hillhater, actually I decided to use this ESC: http://www.himodel.com/electric/HiM..._Speed_Controller_W_BEC_Type_GX-125A-BEC.html
Do you think water cooling is necessary for me? If motor will run at 600W, how much heat would generate ESC? I think tens of watt of heating power is not a problem. Am I right?

About efficiency. AFAIK, belt reduction drive will consume not so much, about 3-4% of transmitted power. If motor efficiency decline at 1000-1500 prm will exceed 10%, it is a reason for me to use reduction drive. But how should I choose reduction ratio? The thing that I don't know is what RPM would get my motor with full throttle at 600W load? No load RPM is about 4000 for 24 volts.

Another question about efficiency is preferred voltage level. I can make 18V power supply, with lower RPM and reduction ratio, but higher amperage at 600W. And I can make 24V or even 30V power supply, with higher PRM and reduction ratio, but with lower amperage at 600W. Does anybody know what would be better for overall system efficiency?

spinningmagnets, ESC I chose already have a 5V BEC. Does BEC consume considerable power to operate? May be ESC w/o BEC together with 4-cell NiMH pack would be more efficient?

 

[Lebowski]

Typicalle engine speed depends on the Kv and the effective motor voltage. The
effective motor voltage is the power supply (battery) voltage minus the current times the motor resistance.

At 600 W / 24 V your current will be 25 Amps.
With the specified motor resistance of 56 mOhm your effective voltage will be
24 - 25*0.056 = 22.6 V

With a Kv of 170 you will get 3824 rpm.

 

[Miles]

This is based on the data that they give (I've assumed that the no load amps is at 14.8V)

 

[spinningmagnets]

RC model airplanes and boats have a rudder (among other devices that move by using a servo) and since operators want the model to run a very long time on the main battery, the models sometimes have a small separate battery to power the moving parts, which normally operate with 5V.

The servo-tester allows you to test and adjust these components while the model is in your shop. Some models do not have many devices to operate at 5V, so some ESCs have a tiny internal voltage regulated power supply. Since these have their own built-in 5V supply, the separate 5V battery is not needed, and that is the battery that is eliminated, by having a Battery Elimination Circuit (BEC).

Your ESC will be fine, using a servo-tester as a throttle will draw very little amps.

 

[Vasily]

With a Kv of 170 you will get 3824 rpm.

Thank you!
So, if I want to get 1000 RPM I need to make about 1:4 belt reduction drive. One thing than I worry about is belt speed. I read a book about belt reduction drives, and there was said that typical belt speed does not exceed dozens of m/s. But I'm not sure this book is up-to-date. If my faster shaft will go 3800 RPM and be even just 1" in diameter, belt speed will be about 300 m/s. Is it possible? Will such a belt drive operate successful, or belt will be damaged after hours or minutes of work?

Miles, great graph, thank you! So, max efficiency is 83% at a load of about 550W. Sounds pretty good for me. But why do they write 98% efficiency in the motor description? Is it a kind of false advertising or such a high efficiency will be achievable at higher voltage?

 

[Miles]

But why do they write 98% efficiency in the motor description? Is it a kind of false advertising or such a high efficiency will be achievable at higher voltage?

It's complete BS....

 

[Lebowski]

With a Kv of 170 you will get 3824 rpm.

Thank you!
So, if I want to get 1000 RPM I need to make about 1:4 belt reduction drive. One thing than I worry about is belt speed. I read a book about belt reduction drives, and there was said that typical belt speed does not exceed dozens of m/s. But I'm not sure this book is up-to-date. If my faster shaft will go 3800 RPM and be even just 1" in diameter, belt speed will be about 300 m/s. Is it possible? Will such a belt drive operate successful, or belt will be damaged after hours or minutes of work?

Miles, great graph, thank you! So, max efficiency is 83% at a load of about 550W. Sounds pretty good for me. But why do they write 98% efficiency in the motor description? Is it a kind of false advertising or such a high efficiency will be achievable at higher voltage?

I think you got an error in your calculations... an inch of diameter gives you around 10 cm of belt
per revolution. 3800 rpMINUTE is 64 rotations per second @ 10 cm is 6.4 meter of belt / sec.
This is less than dozens of m/s so should be ok...

 

[Vasily]

Your ESC will be fine, using a servo-tester as a throttle will draw very little amps.

Ok, NiMH 4-cell pack idea is eliminated

 

[Vasily]

3800 rpMINUTE is 64 rotations per second @ 10 cm is 6.4 meter of belt / sec.

Sure you are right! I've forgot to change PRM to RPS Yes, it seems to be ok.

 

[Vasily]

Miles, your graph is calculated with assumption on constant full throttle and variable load, isn't it? But what will happen, if I use this motor to direct drive a prop which draw 600 watt of power at 400 RPM? AFAIK, such prop will draw much more than 3 kW at 3800 RPM, so with full throttle my motor will be hardly overloaded. But if I regulate it just to 400 RPM @ 600W, what efficiency can I account on? And what will happen, if I use 1:3 timing belt system and 1200 RPM @ 600W?
May be you have links to DC brushless motor main equations, I think I could do some calculations by myself.

 

[Miles]

Vasily,

Motor efficiency relates directly to torque/amps drawn (square of current).

Peak efficiency is the point where available torque is at parity with parasitic torque.

Max. possible power is at half no-load speed at an efficiency of 50%.

 

[Vasily]

Thanks for your answer!

 

[Miles]

http://www.innovatia.com/Design_Center/Motor_Efficiency_3.htm

 

[Vasily]

http://www.innovatia.com/Design_Center/ ... ency_3.htm

Oh, this one is extremely useful! Especially "A Short-Course on Motor Theory for Electronics Designers" section. Why don't you put it in "PMDC Motor theory - formulae etc." or "How Motors Work - some educational links" thread?

 

[Miles]

Done.