Inrush current

Thread Starter

Harrynotpotter

Joined Feb 5, 2021
9
Hi all,

I should probably preface this by saying I’m not an electrical engineer and I am very much learning at this point. I think that will be obvious but thought I’d mention it.

I am currently trying to make a steering wheel for my racing simulator games. I have a stm32 micro controller, a Chinese servo motor (Mige 130st-10010), its driver and since it requires 220v, I have a 2kw transformer to step up US voltage. -I am a student so I can’t install a 220v line in my accommodation. I did at first try a circuit combiner but that tripped a gfci outlet that I was using, hence the change to a transformer.

The problem I am having I believe is inrush current, whenever I try to give the motor a command to move it trips a breaker. (It is a 20A gfci outlet).

I can’t change the breakers for ones that can handle more inrush current, I must change my set up. So I believe I need to add a resistor to the circuit, but I have no idea where to start with selecting one. I’m not sure if a thermistor will work aa I believe the servo motor will constantly be turning on and off while playing the games. -If that isn’t the case please let me know. So I think a safe bet is just a standard resistor, but what value, how much current should it be rated for to be safe and where to I put it in the circuit? Before the transformer or after?

Any help at all would be greatly appreciated!
Many thanks,
Harry
 

Tonyr1084

Joined Sep 24, 2015
5,966
First, welcome to AAC.
Second, many of us are not Electrical Engineers.
Third, honestly I don't exactly know the answer to your question but I believe if you try to mess with the circuitry you could be headed for danger and trouble. I'm thinking you may have an AFCB (Arc Fault Circuit Breaker) and not a GFCI. There's a difference. And with an AFCB inrush can be a problem.

But be assured there ARE people who know how to answer your question. I'm just not sure it's allowed. Guidelines prohibit mains power topics that are directly related to manipulation of mains power. While many circuits may be run from mains through a transformer or a SMPS (Switch Mode Power Supply), those circuits are allowed. Seeing that you're a new member, and we're happy to have you, if there's a problem with the topic a moderator will be kind enough to explain why.
 

BobaMosfet

Joined Jul 1, 2009
1,767
Hi all,

I should probably preface this by saying I’m not an electrical engineer and I am very much learning at this point. I think that will be obvious but thought I’d mention it.

I am currently trying to make a steering wheel for my racing simulator games. I have a stm32 micro controller, a Chinese servo motor (Mige 130st-10010), its driver and since it requires 220v, I have a 2kw transformer to step up US voltage. -I am a student so I can’t install a 220v line in my accommodation. I did at first try a circuit combiner but that tripped a gfci outlet that I was using, hence the change to a transformer.

The problem I am having I believe is inrush current, whenever I try to give the motor a command to move it trips a breaker. (It is a 20A gfci outlet).

I can’t change the breakers for ones that can handle more inrush current, I must change my set up. So I believe I need to add a resistor to the circuit, but I have no idea where to start with selecting one. I’m not sure if a thermistor will work aa I believe the servo motor will constantly be turning on and off while playing the games. -If that isn’t the case please let me know. So I think a safe bet is just a standard resistor, but what value, how much current should it be rated for to be safe and where to I put it in the circuit? Before the transformer or after?

Any help at all would be greatly appreciated!
Many thanks,
Harry
What you are looking for is called a Thermistor. It is a thermally regulated resistor. Meaning, inrushing current will make it hot and it will resist, limiting the current until the surge has passed.
 

MaxHeadRoom

Joined Jul 18, 2013
23,085
What is the servo driver you are using?
A resistor is not going to cure your problem, and is counter-intuitive to a servo application.
If you have a servo driver, then you need a linear supply rated for the applicable voltage.
The whole idea of a servo is you control the current in order that it does not exceed the continuos rated current of the motor.
Max.
 

Audioguru again

Joined Oct 21, 2019
3,172
Your link has hundreds of motors. Which one?
A big motor is heavy and has inertia so it takes a high current to start it running. If you reduce the starting current then it might not start or it will take some time to get up to speed.
 

wayneh

Joined Sep 9, 2010
17,152
You may want a “soft start” circuit for the motor. These are popular for tablesaw motors and such. It reduces the surge and is probably a bit safer for power tools as well. You can get these as add-on units.
 

MisterBill2

Joined Jan 23, 2018
8,723
I was going to ask the same question. Tripping a 20 amp breaker takes a load of over 2000 watts. And a steering simulator should not need anything near that much power. So for starters we need a much more detailed description of the system, and of what the load on the servo motor is.
Otherwise you can't get anything better than random guesses.
 

MaxHeadRoom

Joined Jul 18, 2013
23,085
For a low rate of rpm control, if it were a case of a large load, the answer would be to use a much smaller motor and suitable gearing, have you taken a simple torque test requirement for the steering action?
It can be done very simply with a spring scale etc.
Max.
 

MaxHeadRoom

Joined Jul 18, 2013
23,085
IT does not appear to the power up inrush but when a motor command is issued, which a thermistor will not solve.
The problem I am having I believe is inrush current, whenever I try to give the motor a command to move it trips a breaker. (It is a 20A gfci outlet).
 

Audioguru again

Joined Oct 21, 2019
3,172
Whenever an electric motor is suddenly started to move quickly, it draws a very high current until it gets going.
A motor used for steering draws a high current when you try to turn a wheel but the tire sticks to the ground before the car begins moving. Try it in a car that does not have power steering and the extra force needed might break your arm.
 

Thread Starter

Harrynotpotter

Joined Feb 5, 2021
9
So I’m playing around with it now. When I put in a test rpm of 1000 it spins for a second and trips the gfci. But when I try 150rpm it spins for maybe 30 seconds before tripping it.
 

MaxHeadRoom

Joined Jul 18, 2013
23,085
Whenever an electric motor is suddenly started to move quickly, it draws a very high current until it gets going.
A motor used for steering draws a high current when you try to turn a wheel but the tire sticks to the ground before the car begins moving. Try it in a car that does not have power steering and the extra force needed might break your arm.
But not if it is operated as a servo, the initial current can be controlled.
I repeat my previous question, why is a 2hp motor needed? Have you measure the torque required?
Max.
 
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