Bigger BLDC Motor can not start it self (must rotate manually first)

Thread Starter

Iskhu

Joined Jun 10, 2019
11
Hi all,

sorry, I am newbie.
I made one circuit to control my BLDC motor,
using MC33035 and MC33039.
I attach both of Datasheet here.

I use circuit in Datasheet MC33035, figure 39.
For inverter part, I use IRF9530 for upper part, and IRF540PBF for lower part.
Please see the excel file and datasheet of these two parts.

I am using microchip microcontroller, but I will skip this part.

Using this combination, my circuit is working. I succeeded rotating my BLDC motor.
So, no problem in circuit, nor in programming part.

But when I change to bigger BLDC motor, then result is, it can not rotate this bigger BLDC motor.
I have to rotate by myself, then it will start to rotate.

In my understanding, bigger BLDC Motor must need bigger Torque, so it need bigger current (off course).
But when I tried to increase Current Source until around 7.5 A (I did not exactly remember, but around this amount), problem still happen (can not start to rotate by itself), then one of my Controller is burned.
Now, I am checking it using smaller current (max 2A), but still can not find the root cause.
Note: Voltage source is 24V.

My questions are:
1. Is my understanding correct: Need more Torque mean need more current source?
2. So in this problem, I have to increase more current, until this bigger BLDC start to rotate?
3. increasing current source to 7.5A burned my controlled, if I want to increase current amount (without burning my controller) which part should I change?
4. It seems the burned one is not the inverter, but logical part (Microcontroller).
Why this burn happen?
5. After I check, it seems that overcurrent signals many time become ON. So, voltage in RS is too big?
so, I need to change Rs value to lower one? is it safe?

Sorry for many questions, I really don't understand and need your support.

Thank you.














Definitely, this is because
 

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Thread Starter

Iskhu

Joined Jun 10, 2019
11
What model is this bigger BLDC?
The bigger one, I bought from AliExpress China: 8 inch 8inch double shafts brushless gear dc wheel hub scooter motor with tire phub-165
link already expired, I put its screenshot in attachment.

No info about Torque or others:(

but it can rotate, if I rotate it first.

The smaller one, I bought also from AliExpress China:
High Quality Racerstar 5065 BR5065 140KV 6-12S Brushless Motor With Gear For RC Motorcycle Multicopter Part
here is the link:
https://www.aliexpress.com/item/32834130958.html?spm=a2g0s.9042311.0.0.27424c4dxCXfln
Clearly, this smaller one is lighter, no load, only need smaller current.

For this smaller one, my controller can rotate it easily.
So, no problem in controller, both in Hardware, and also in software.
 

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Last edited:

AlbertHall

Joined Jun 4, 2014
11,504
Without any data for the motor you can only expect guesses.
My guess is that the motor requires more current than the power supply and/or controller can supply.
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
Without any data for the motor you can only expect guesses.
My guess is that the motor requires more current than the power supply and/or controller can supply.
Yes, that also my guess.

But my question is, how to increase level of max current in my circuit?
Which part should I change?

Because when I increase current, my controlled was burned.
I want to increase this level of burn, but how?
 

AlbertHall

Joined Jun 4, 2014
11,504
You can probably not modify the controller for more current - you will need a higher power controller but I have no idea how much power you will need.
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
You can probably not modify the controller for more current - you will need a higher power controller but I have no idea how much power you will need.
Can you give more explanation about "a higher power controller" ?
You mean, I have to put bigger Capacitor in my circuit?

Power voltage still 24V,
but let say, I want to increase current to 30A,
can you give advice to me what kind of circuit should I add?

For power source, currently I use Separate Source, and it can supply until 60V 17A,
but after finish, I want to try to use battery that can supply until 30A.
 
Last edited:

MrSalts

Joined Apr 2, 2020
534
My guess is that on the MC33035, Pin 22 is set for a 3-coil motor (120°) (the small one) and the big motor is likely a six coil (60°) - adjust as appropriate if the two motors have different number of coils.

also, read about current limiting on page 12 of the MC33035 datasheet. Pin 9 controls current limiting.
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
My guess is that on the MC33035, Pin 22 is set for a 3-coil motor (120°) (the small one) and the big motor is likely a six coil (60°) - adjust as appropriate if the two motors have different number of coils.

also, read about current limiting on page 12 of the MC33035 datasheet. Pin 9 controls current limiting.
for pin 22, I think it is correct.
When I change it using bigger BLDC motor, it didn't work.
So, current setting is OK, I think.

About pin 9 (current limiting), yes, now I am checking this.

This MC33035 also applies current limiting for every cycle, but I don't know, why for small current also this signal become ON?
Need to investigate again.

If you have any other advice, please let me know.
 

kaindub

Joined Oct 28, 2019
88
What EXACTLY are you using for a power supply
If the small motor is rated at 34A peak then the larger motor is going to be much hiigher rating
The power supply needs to be able to supply the watts of the larger motor.
I have found that starting current on BLDC motors and controllers needs a large stiff supply voltage.
Your bench power supply is not going to cut it
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
What EXACTLY are you using for a power supply
If the small motor is rated at 34A peak then the larger motor is going to be much hiigher rating
The power supply needs to be able to supply the watts of the larger motor.
I have found that starting current on BLDC motors and controllers needs a large stiff supply voltage.
Your bench power supply is not going to cut it
I use this for power supply:

https://www.amazon.com/CPS-6017-Updated-Adjustable-Regulators-Switching/dp/B01LZEV7PD

It can support until 60V 17A.

But I use 24V voltage, and when I raised current until 7.5A, then my controller is burned. This is for bigger BLDC motor.

For smaller BLDC motor, I used 24V 2A, it can rotate easily.

I think, problem is not in power supply side.

I still can raise it until 17A if needed, but maybe my controller will burn again.

What I need is, how to rotate bigger BLDC motor? If I have to increase current, how to prevent burn?
 

kaindub

Joined Oct 28, 2019
88
Why is the controller burning? What parts are burning? The controller chip does not actually carry any current. So is it the driver chips or the Mosfets?
You may need to put a cro across the current sense resistor and see what’s going on..
 

shortbus

Joined Sep 30, 2009
8,806

Thread Starter

Iskhu

Joined Jun 10, 2019
11
Why is the controller burning? What parts are burning? The controller chip does not actually carry any current. So is it the driver chips or the Mosfets?
You may need to put a cro across the current sense resistor and see what’s going on..
Ok, thanks.

I will try to investigate it.
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
That may be a big part of your problem. Switch mode power supplies are way less than ideal for motor power supplies. And probably even less for a BLDC power supply. You would be better off using a linear power supply- step down transformer, rectifier and capacitors.
I see.
I don't recognize this.
May I know why Switch Mode power supplies (SMPS) are not suitable for BLDC motor?
And why "Linear power supply- step down transformer, rectifier and capacitors" is better?

The reason is about "back EMF problem thay may damage power supply"?
In that case, if I use SMPS, can I prevent it by adding one Diode?
Changing one Diode is much more cheaper than buying new power supply.

But changing power supply is also ok for me, if really I need to buy it.

If I have to buy new Power Supply, can you give recommendation to me?
Maximum rate that I need is until 72V voltage, and current max 30A.

Last, in case of me, my controller was burn, it is also because I used "Switch Mode power supplies" ?
As long as I know, if power supply still able to supply the power, we can use any type of power supply.
Is it not correct?

Sorry for many questions.
If you can help, I will really appreciate it.
 

shortbus

Joined Sep 30, 2009
8,806
The big reason that SMPS(switch mode power supplies) are not suggested for DC motors of any real size is they lack what for lack of a better term(which I'm sure there is, but I don't know it) is "headroom". A linear power supply has a pretty large capacitor in it's output. This capacitor keeps the voltage and current up between when the AC input is going through zero volts. Small DC motors not under any real load will work fine with a SMPS, bigger motors or a few motors in something powered by a SMPS don't work so well.

A BLDC motor compounds this because it is also switching the power to the motors coils at a rate that may interact with the low spots/pulses of voltage coming from the SMPS. No machine that I'm aware of that uses a DC motor also uses a SMPS to power it because of the reasons they aren't so reliable for motors.

I also don't know about any one selling a linear power supply, since they are usually built by the person needing one. They are pretty simple, unlike building a SMPS.
 

MaxHeadRoom

Joined Jul 18, 2013
23,619
Over the years there has been a few linear DC supply manuf, one is GFC Global, now owned by Hammond, these had features such as regulation, SCR Crowbar fold-back, remote sensing etc.
But in reality, you do not need a regulated supply for motor control, and even the motor drive manuf. suggest avoiding SMPS.
And servo drives such as A-M-C etc that include a supply built in, use simple linear versions.
 

kaindub

Joined Oct 28, 2019
88
In the variable speed drive world, all manufacturers just rectify the mains voltage and filter with a large bank of capacitors. As MaxHeadRoom says regulation of the power supply for a speed drive is not necessary.
Remember the controller for your BLDC gets feedback from the hall sensors (to determine speed and magnetic phase angle) and a current sensor. This is what is used to regulate the speed of the motor.
Simplest and cheapest is a transformer , diode bridge and capacitor bank. youll need to do some calculations to make sure the transformer, diode bridge and capacitors are correctly size for the load. Also include a precharge circuit before the capacitors to save your diode bridge.
 

Thread Starter

Iskhu

Joined Jun 10, 2019
11
Over the years there has been a few linear DC supply manuf, one is GFC Global, now owned by Hammond, these had features such as regulation, SCR Crowbar fold-back, remote sensing etc.
But in reality, you do not need a regulated supply for motor control, and even the motor drive manuf. suggest avoiding SMPS.
And servo drives such as A-M-C etc that include a supply built in, use simple linear versions.
Thank you very much.
 
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