Handle Peak Inrush Current of a BLDC Motor to protect the Power Supply

[Vatech]

TL;DR Summary

BLDC motors have a Peak current on startup which is 3x or more the rated current.
Because the motor will be powered by a SMPS i want to protect it and avoid the need to use a PS designed for Currents as much as motors Peak current because that would increase the cost of the device and the needs for space(bigger PS) . Current Limiters, Capacitors or other way , you are welcome to share your experience to handle that instant current

I have to use a BLDC motor combined with a BLDC motor driver (X-NUCLEO-IHM08M1)
The motor has a rated current of 7.3A. So i am planning to use a 36VDC 13.9A power supply (SMPS).
The problem is that the PS that i want to use has a "HICCUP mode" for overload protection and not a "constant current limiting protection". Most od the modern PS use Hiccup mode, which in this case is not ideal.
My problem is HOW TO HANDLE THE PEAK - INRUSH CURRENT of the motor on startup. From a search i found that it must be above 20A.
One way is to use current limiter (NTC) but my level on electronics is also limited to select and design the circuit.
An other way could be to use a Capacitor to handle the peak current that lasts ms, but same as above, i am not sure for my selection and if it will affect the PS if connected on parallel on output.
on link bellow you can check an Peak current example

So please, if you have experience or an idea how to handle it, you are more than welcome to share it with me and help me.
Thank you in advance
Motor used:
https://www.omc-stepperonline.com/download/57BLR110-36-01.pdf

 

[Joshy]

Sounds like your search isn't too far off. What parts or ideas you didn't like about the limiter or what was shown in the video?

I'm not sure about the shunt capacitor. The problem I would worry about the shunt capacitor is I think the inrush current is probably from the load capacitance. When you turn on something it's a step or fast change in voltage ($dV/dt$). The current through a capacitor is
$$i_C = C \frac{dV}{dt}$$
Shunt capacitor shouldn't it still have the same current going through the load and now additional current going through the shunt capacitor? That's why I'm worried.

I see it mentioned in the video I didn't look at the details, but I see a word on there it's a fancy way of saying there's a filter on there. That's not a bad option. What kind of circuit would do something like this :)? One of the challenges with that circuit is power requirement, and that is why it can become a little more elaborate like the ones he described in there.

I like the limiter too. It's a real cheap and easy work around with that power requirement. Its problem usually has to do with temperature and environment. Are you expecting your circuit to be in a harsh environment or have some stringent temperature requirement?

 

[Vatech]

I took the solution for using a capacitor after reading this post
https://electronics.stackexchange.com/questions/515340/proper-power-supply-for-bldc-motor
About the current limitter, No, due to its design , there will be room temperature. How do we use it? Just the element in series in +line?
Thank you for your time

 

[Baluncore]

You might consider an N-channel MOSFET in the negative supply rail. Use an RC LP filter on the gate so it turns on slowly.

 

[Vatech]

i would prefer to avoid creating a pcd, i am not an expert on electronics to calculate the elements value's, although if the values / elements were given i could do it using prototype pcb
https://www.ametherm.com/blog/inrush-current/dc-motor-inrush-current

 

[Vatech]

Based on my last posted link, i made the following calculationsRated current:7.3A

Inrush Current: 3*7.3= 21.9A

Inrush Duration: 200msE = Input Voltage * InrushCurrent * DurationOfInrush

E= 36*21.9*0.2

E=157.68 joules


MaxDesiredCurrent = 13.5A

Rmin= InputVoltage / MaxDesiredCurrent = 36/13.5= 2.66Ω

The question is what Current limiter should i use knowing this parameters?
https://gr.mouser.com/Search/Refine?N=18356455

could the following match our goal?
https://gr.mouser.com/ProductDetail/EPCOS-TDK/B57364S0259M051/?qs=Uha62PnlbFAlwtUb27gkGQ%3D%3D
Thank you

 

[Averagesupernova]

I did not look into the info on your motor driver, but is there a way to cause it to soft start? What's the application?

 

[Vatech]

I am using X-NUCLEO-IHM08M1 do drive it so i think i will be able to configure an acceleration, so yes, that is already on my list to do

 

[Tom.G]

Of course you could try contacting an Applications Engineer at the board manufacturer. STMicroelectronics is a major, world-wide supplier so Applications Engineers do exist, but you may not be able to get their attention for a low-volume sale.

If you can not change to a controller with Soft-Start capability, the Inrush Current Limiter suggested by @Baluncore is your best bet.

Another approach is to slow down the response time of the Over Current Protection (OCP) circuit on the controller. Realize though that this MAY cause the controller to self destruct rather than self protect when the output short circuits.

The straight forward way to do this is to increase the capacitor values in the OCP circuit. See the manual pg.17, fig.12, for the schematic. The capacitors are C124, C126, C128 and their value is 100nF. These are surface mount components, so solder a 500nF capacitor on to of each of them. This will extend the Over Current sensing delay to be 6 times the present value. The capacitors are in the Bill Of Material (BOM) on pg.20, item.1

Have someone that has worked on surface mount boards to do this work. Don't learn how on this project, it takes a soft touch and steady hand with the right soldering equipment.

Please keep us udated on your progress.

Cheers,
Tom

 

[Vatech]

Changing the capacitors as you suggested seems an easy solution but i do not have the equipment to do it correct, although i am familiar with gpu reballing etc(but not with correct equipment).

What is your opinion about that way-method suggested in the following article?
https://www.ametherm.com/blog/inrush-current/dc-motor-inrush-current

//Thank you very much for you willing to help

 

[Tom.G]

You are welcome.

Yes, the thermistor approach is valid, with one minor concern:
1) With the motor already running and the thermistor warmed up to its low-resistance state
2) The blade hits an obstacle and stalls

You then have no in-rush protection and the motor will draw the stalled-rotor current. The controller will probably sense the Over Current and either shut down or go into hiccup-mode current limiting. This may well be acceptable.

My personal opinion is it is worth a try and see if you, and the hardware, can live with it. You have already done most (all?) of the needed calculations. What remains is picking a thermistor with the closest chacteristics.

As for adding the capacitors to delay the Over Current response, it sounds like you have enough soldering experience and equipment to do the job; small tip, temperature controlled iron; tweezers; fine gauge low temperature solder (63/37 Sn/Pb works); maybe some liquid flux.

You use just enough heat to solder to the existing capacitors but not enough to melt the bond to the circuit board, if possible. That's probably easier if you have some solder paste, but it's not required.

For others that may read this: You may have lifted the Copper traces off the PC board on occassion. That is typically caused by the combination of high temperature and high force on the trace. If it is at soldering temperature, don't push on it!

Cheers,
Tom

 

[Vatech]

You are welcome.

Yes, the thermistor approach is valid, with one minor concern:
1) With the motor already running and the thermistor warmed up to its low-resistance state
2) The blade hits an obstacle and stalls

You then have no in-rush protection and the motor will draw the stalled-rotor current. The controller will probably sense the Over Current and either shut down or go into hiccup-mode current limiting. This may well be acceptable.

My personal opinion is it is worth a try and see if you, and the hardware, can live with it. You have already done most (all?) of the needed calculations. What remains is picking a thermistor with the closest chacteristics.

As for adding the capacitors to delay the Over Current response, it sounds like you have enough soldering experience and equipment to do the job; small tip, temperature controlled iron; tweezers; fine gauge low temperature solder (63/37 Sn/Pb works); maybe some liquid flux.

You use just enough heat to solder to the existing capacitors but not enough to melt the bond to the circuit board, if possible. That's probably easier if you have some solder paste, but it's not required.

For others that may read this: You may have lifted the Copper traces off the PC board on occassion. That is typically caused by the combination of high temperature and high force on the trace. If it is at soldering temperature, don't push on it!

Cheers,
Tom

I will follow your advice and stay on correct hardware configuration, i created a new post for that
https://www.physicsforums.com/threads/stm32-bldc-driver-advanced-configuration.1000096/

 

[Windadct]

ummm... A DC motor may see 2-3X inrush, but a BLDC with a motor controller ( controller + X-NUCLEO-IHM08M1) - will not. The driver/controller uses PWM to regulate the voltage applied, and there should be no inrush ( hard start). This driver NEEDS a uC or other controller to run the motor.

Or am I missing the point here completely?

 

[artis]

@Vatech maybe I am also missing something here but let me ask a few questions.

What model make etc is your "BLDC" motor?
Also from your description I get the impression that your motor unlike the typical PC- fan BLDC motors doesn't have a control/driver board integrated into the motor itself rather just wires coming out that you then attach to a driver board?

You see the motor itself is most likely a 3 phase stator with a permanent magnet rotor, but unless you give the specific model etc I'm guessing here, anyway , if I am correct that you have a plain old motor and the drive electronics is the X-NUCLEO-IHM08M1 then I think you don't have a problem here because from what I read the X-NUCLEO-IHM08M1 board is already loaded with everything you need , it has mosfets drive transistors an IC controller and it's output can be adjusted. I think it also must have a soft start/overcurrent protection built in.
So from what I understand it should be no problem powering this driver from your SMPS power supply.
Have you already tried it ?
It seems like all you need to match is the average power of your motor with the safe output power of your board, the inrush current is taken care of.
So if you want to drive a 12v 50w motor for example you logically need a 12v 50w power supply as power doesn;t grow on trees.

have you read the ST provided info PDF's?

Here is the application and setup of the board with explanations of jumpers and pin settings etc.
https://www.st.com/en/ecosystems/x-nucleo-ihm08m1.html#Take a look at the first PDF's namely, product specification and user manual

@Windadct is correct, because you have a driver/controller board between your power supply and your motor so that board from ST already takes care of inrush current as well as many other things, all you need to do is get a psu with appropriate power specs and drive your motor.

 

[Averagesupernova]

This could be sooooo simple. But we still haven't been told the application.

 

[Windadct]

There is no need for inrush protection here :

I was on my phone earlier and wanted to look more at the notes for the driver board - I thought I was missing somthing.

E1) It also has a motor profiling function built in - if you get the whole kit ( $35) :

 

[Vatech]

There is no need for inrush protection here :

I was on my phone earlier and wanted to look more at the notes for the driver board - I thought I was missing somthing.

E1) It also has a motor profiling function built in - if you get the whole kit ( $35) :

You are correct. I bought the whole kit, although the driver was much more expensive due to the fact that its availability is limited.
There is need for hardware configuration , but beside the jumper, there in no information on how to select and replace some capacitors values , or remove a capacitor as in posted video. In documentation is suggested to replace a specific capacitor if the startup current is low.
Its my first approach on BLDC motors and i would not like to damage the only board i got. Any advice?

 

[artis]

@Vatech Yes, learning is the advice. First use the board as is and see how it works, learn electronics fundamentals next, see how things are done , maybe try soldering etc, one really can't give any more specific advice for such a broad approach.
Maybe it would be good if you told us why you bought the kit in the first place, is it just for fun or is there a purpose ?
If one is a beginner it is easier to first buy a soldering iron and some flux and try soldering something , then maybe building a kit led blinking board with some crude timer etc, you know get a general feel and understanding. Controlling a 3 phase motor with a driver using N mosfets etc is not exactly the basics of this.

 

[Windadct]

Where was stock limited : Digikey is in stock and $35 : https://www.digikey.com/en/products/detail/stmicroelectronics/P-NUCLEO-IHM001/5415014

 

[Vatech]

@Vatech Yes, learning is the advice. First use the board as is and see how it works, learn electronics fundamentals next, see how things are done , maybe try soldering etc, one really can't give any more specific advice for such a broad approach.
Maybe it would be good if you told us why you bought the kit in the first place, is it just for fun or is there a purpose ?
If one is a beginner it is easier to first buy a soldering iron and some flux and try soldering something , then maybe building a kit led blinking board with some crude timer etc, you know get a general feel and understanding. Controlling a 3 phase motor with a driver using N mosfets etc is not exactly the basics of this.

Where was stock limited : Digikey is in stock and $35 : https://www.digikey.com/en/products/detail/stmicroelectronics/P-NUCLEO-IHM001/5415014

X-NUCLEO-IHM08M1 is the one i need
https://www.digikey.com/en/products/detail/stmicroelectronics/X-NUCLEO-IHM08M1/5873447

 

[Vatech]

@Vatech maybe I am also missing something here but let me ask a few questions.

What model make etc is your "BLDC" motor?
Also from your description I get the impression that your motor unlike the typical PC- fan BLDC motors doesn't have a control/driver board integrated into the motor itself rather just wires coming out that you then attach to a driver board?

You see the motor itself is most likely a 3 phase stator with a permanent magnet rotor, but unless you give the specific model etc I'm guessing here, anyway , if I am correct that you have a plain old motor and the drive electronics is the X-NUCLEO-IHM08M1 then I think you don't have a problem here because from what I read the X-NUCLEO-IHM08M1 board is already loaded with everything you need , it has mosfets drive transistors an IC controller and it's output can be adjusted. I think it also must have a soft start/overcurrent protection built in.
So from what I understand it should be no problem powering this driver from your SMPS power supply.
Have you already tried it ?
It seems like all you need to match is the average power of your motor with the safe output power of your board, the inrush current is taken care of.
So if you want to drive a 12v 50w motor for example you logically need a 12v 50w power supply as power doesn;t grow on trees.

have you read the ST provided info PDF's?

Here is the application and setup of the board with explanations of jumpers and pin settings etc.
https://www.st.com/en/ecosystems/x-nucleo-ihm08m1.html#Take a look at the first PDF's namely, product specification and user manual

@Windadct is correct, because you have a driver/controller board between your power supply and your motor so that board from ST already takes care of inrush current as well as many other things, all you need to do is get a psu with appropriate power specs and drive your motor.

From reading documentation i found that the recommended firmware for this board (x-cube-spn8) has 6-step trapezoidal driving mode. The board supports also FOC mode, based on STSW-STM32100. I think it would be better to go for FOC mode, what would you suggest? I am ready to configure the hardware for both options

 

[Vatech]

From reading documentation i found that the recommended firmware for this board (x-cube-spn8) has 6-step trapezoidal driving mode. The board supports also FOC mode, based on STSW-STM32100. I think it would be better to go for FOC mode, what would you suggest? I am ready to configure the hardware for both options

Thank you very much for your time and willing to help.
I am a Computer Engineer and as part of my university dissertation, i create an automation, which involves als BLDC driving for one device.
Bellow you can check the motor i am using.
https://www.omc-stepperonline.com/download/57BLR110-36-01.pdf
I have read the documentation and as i mentioned above i don't know if i should use FOC mode or 6-step/trapezoidal ( he recommended firmware for this board (x-cube-spn8) has 6-step trapezoidal driving mode. The board supports also FOC mode, based on STSW-STM32100. ).
While reading i found is also that X-NUCLEO-IHM08M1 is designed for sensorless driving. In this case my motor has Hall Sensor, can i use .
Currently , i only received my board, motor is under delivery.
I am ready to configure the hardware depending on mode (FOC or 6-step) which i did not yet decide, I would prefer FOC mode but there is no guide for using it with that mode.

//by the way, on video he desolders Resistor R181 which is not adviced anywere on hardware configuration manual .