BLDC Motor Controllers

[PICmonster]

Dear All,

I am back engineering a BLDC Motor Controller, I have found that the Motor has a rated voltage of 36V and can be found hear:-
https://www.kocodcmotion.com/fileadmin/user_upload/pdf/products/bldc-motors/Brushless_DC_Motors_DC_MOTION_datasheet-21.pdf

The motor has hall sensor and the BLDC driver has hall sensor inputs for finer control, it is driven from the conventional 3 phase MOSFET driver using 6 MOSFET all ok so far, I am however confused about why it is powered from a 48V@4A DC supply, would this not over voltage the motor I was thinking since the motor has a rated voltage of 36V?

I then thought since the 3 phase's are PWM then this would limit the overall voltage to the motor?

Can anyone more familiar with this subject please offer an explanation?

Best Regards

Jim

[beanflying]

You are dealing with DC motors so drop your some of your AC mains based concepts. Also unless you need extra torque at low speeds (traction type use) typically the sensors have been done away with in ESC designs. Even though fitted you don't need to use them!

As a metric in model aircraft or buggy motors we tend to talk kv (not kVolts) which is RPM/VOLT so a 1000kv would at no load produce 1000 RPM nominal for each Volt applied to the ESC. The motor series you linked to is 5200RPM @ 36V NL getting you 144.44kv so at 48V NL you will simply see it spin up to around 6933 RPM this is a fairly linear function. Even though this is then higher than the rated speed it is still fairly low for a 57mm diameter motor. Depending on the internals and bearings 10-20000 RPM is quite typical for motors of this diameter.

The Motor limit tends to be Current and to a degree Power/Efficiency not voltage so providing you keep it under the rated current or power or at reasonable efficiency you will be fine. If you push the power up (due to increasing voltage on a fixed load) it tends to push the motor beyond best efficiency point and generate some extra heat and can run into magnet and insulation issues if it becomes to extreme. I have motors of that size in the order of 1000-2500 Watts for peak bursts so I suggest to you it is very conservatively rated on that data sheet.

If you are going to roll your own ESC don't skimp on the current lest the smoke come out and in particular if you watch out for back emf hitting the FET's depending on you application as they will smoke.

What is the application for the motor? The above is a quick general idea with little info from you.

[PICmonster]

Thank's for your help, you are very informative.

One more question, the BLDC controller I am going to use for testing is this :-

http://grauonline.de/wordpress/?page_id=3122

This BLDC Controller is rated for use with a maximum 36V supply so it says but the MOSFETs used (NCE6690) on it have an absolute Vds of 69V, so what would happen if you run it with a 48V supply?

I want to use the 48V supply so it is the same as the product I am back engineering, is it the back EMF that is the problem here not the 48V supply?  if so changing these MOSFETs to 150V (IRFI4321PbF) with similar Id would be a good way to go so it can then be operated from 48V supply with less likelihood of any problems due to back EMF?

Thanks in advance.

[beanflying]

Depending on your load and how it behaves on shutdown it can create issues with the ESC FETS. I have landed a few aircraft trailing smoke over the years when it goes wrong.

Instead of modding a fairly average and likely inefficient ESC have you considered adding a DC converter to your supply? 200W 60V rated buck converters are cheap and not that large eBay auction: #123374633095

If you bring the supply back to say 12V it opens up a vast number of different motor and ESC's from the Model area instead of narrowing the range by going up in voltage.

[Circlotron]

One more question, the BLDC controller I am going to use for testing is this :-

http://grauonline.de/wordpress/?page_id=3122

This BLDC Controller is rated for use with a maximum 36V supply so it says but the MOSFETs used (NCE6690) on it have an absolute Vds of 69V, so what would happen if you run it with a 48V supply?

I've got one of those motor controllers.
The supply voltage also goes to an LM317 voltage regulator and I think 36 volts is the max input for it. If you could limit the input voltage to LM317 you could likely run the mosfets at a higher voltage.