Will stalling DC motor blow any fuses?

Thread Starter

GoatJames

Joined Aug 8, 2020
9
I have a wall plug that supplies 12 volts and is rated for 2 amps, and I want to use it to supply power to this DC motor.
The motor's spec sheet indicates its idle current is 0.6 amps, which is perfectly in range. However, the stall current is 14 amps. Do I have to worry about blowing any fuses if the stall current is reached (i.e. either the circuit breaker in my house is tripped or the wall plug catches on fire), or does the wall plug handle this (i.e. 2 amps is the max output, and the motor cannot draw more than that)?

For more context, in my project, the stall current should never really be reached. I plan on attaching a flywheel to the DC motor to shoot out ping pong balls periodically, so there will be brief spikes in current required by the motor.
 

drc_567

Joined Dec 29, 2008
1,152
You might want to devise some method to ramp up the motor, from zero RPM to the normal operating speed. An adjustable potentiometer, in a shunt configuration, could be placed in series with the motor, in order to provide some degree of series current control.
 

Thread Starter

GoatJames

Joined Aug 8, 2020
9
Wall plug = SMPS ? PS will probably shut down. One or 2 motors or just 2 flywheels ?
My wall plug is similar to this cheap thing from Amazon. Not sure what a SMPS is, or if that sort of wall plug would qualify. The current setup is the wall plug is the power source to 1 motor with a tiny flywheel attached onto the shaft (and throw in a flyback diode).

Picture:
 

Thread Starter

GoatJames

Joined Aug 8, 2020
9
You might want to devise some method to ramp up the motor, from zero RPM to the normal operating speed. An adjustable potentiometer, in a shunt configuration, could be placed in series with the motor, in order to provide some degree of series current control.
In most circumstances, using a potentiometer to control the voltage and limiting the current that way would make sense, but the motor will have to exert varying amounts of torque in my case. For a brief amount of time, every few seconds or so, the motor will have to exert more torque when the flywheel makes contact with a ping pong ball. This spike is the main issue - the motor will draw more current for this brief moment (I could probably measure this somehow), and I wanted to know if this would cause any problems in my setup.
 

drc_567

Joined Dec 29, 2008
1,152
In most circumstances, using a potentiometer to control the voltage and limiting the current that way would make sense, but the motor will have to exert varying amounts of torque in my case. For a brief amount of time, every few seconds or so, the motor will have to exert more torque when the flywheel makes contact with a ping pong ball. This spike is the main issue - the motor will draw more current for this brief moment (I could probably measure this somehow), and I wanted to know if this would cause any problems in my setup.
The potentiometer method is intended only to get past the stalled motor current that will occur at start-up. Any subsequent current spikes will have to be within the power supply and motor tolerances.
The potentiometer should have sufficient wattage capability to withstand the maximum power demand for a few seconds at least, after which it will be zeroed and essentially out of the circuit.
 

crutschow

Joined Mar 14, 2008
27,696
You could also add a 2-transistor current-limiter to the circuit.

LTspice simulation of example circuit shown below for 2A limit with load varying from 1Ω to 20Ω.

Note that the MOSFET power dissipation is low for normal running but will be up to 24W if the output is shorted or the motor is stalled, and will thus need an appropriate heatsink if those conditions occur for more than a second or so.

1604472955857.png
 
Last edited:

Alec_t

Joined Sep 17, 2013
12,197
in my project, the stall current should never really be reached.
Start-up current is the same as stall current, so whenever you switch the motor on the 2A supply will be severely stressed. Whether or not it limits its output accordingly, or simply dies, will depend on the design and quality of the supply.
I wouldn't consider using a potentiometer alone as a current-limiter. Finding one to handle 14A, albeit briefly, could be difficult and expensive. Crutschow's solution would be better, and automatic.
 

Delta Prime

Joined Nov 15, 2019
1,147
This spike is the main issue - the motor will draw more current for this brief moment (I could probably measure this somehow), and I wanted to know if this would cause any problems in my setup
Hello there
:) Starting torque is the maximum torque that can be produced by a motor in order to start rotational movement of the load. Stall torque is the maximum torque that can be applied to the shaft and cause the motor to stop rotating. When there is no rotation in the motor, the wound coils are acting as a fixed resistance. Ohm’s Law states that current is equal to the supplied voltage divided by the resistance. This would be the starting/stall current. If the motor’s torque constant (Kt) is known you can take Kt* the current and determine the starting/stall torque.
Remember that torque is proportional to the current. You need to make sure that you can supply enough current to reach the torque required to start the load:)
 

MaxHeadRoom

Joined Jul 18, 2013
23,595
The stall current is shown a 14a, this will occur momentarily on start up, providing the supply can deliver this amount of current.
Max.
 

BobaMosfet

Joined Jul 1, 2009
1,848
I have a wall plug that supplies 12 volts and is rated for 2 amps, and I want to use it to supply power to this DC motor.
The motor's spec sheet indicates its idle current is 0.6 amps, which is perfectly in range. However, the stall current is 14 amps. Do I have to worry about blowing any fuses if the stall current is reached (i.e. either the circuit breaker in my house is tripped or the wall plug catches on fire), or does the wall plug handle this (i.e. 2 amps is the max output, and the motor cannot draw more than that)?

For more context, in my project, the stall current should never really be reached. I plan on attaching a flywheel to the DC motor to shoot out ping pong balls periodically, so there will be brief spikes in current required by the motor.
Stall = SHORT.

If you are in the USA, your wiring inside your walls is usually rated for about 7A. 15-20A for oven/stove. Which means your breakers for average circuits are usually also rated at about 7A. So, 14A will throw a breaker.

Having said that, if you are using a WalWart for your power, then the maximum amount of power deliverable to the motor is governed by the max current the Walwart can deliver, not the MAINS.
 

Bernard

Joined Aug 7, 2008
5,788
I would just add a 5 ohm R in series with motor. Need more inf. on flywheel. Motor shaft of 2 mm makes me nervous. SMPS = switch mode power supply which is what you have. PB launch-2 00000.png Could not bring up
picture so will provide mine.
 

MaxHeadRoom

Joined Jul 18, 2013
23,595
Stall is not a dead short, it is the minimum armature resistance, this can be discovered by a current measurement with locked rotor, using a DC L.V. supply and an ammeter.
Test using various positions and take the highest current to calculate.
Max.
 

Tonyr1084

Joined Sep 24, 2015
6,243
-14 Amp Stall Current: For a motor that small (2mm Shaft size) that's a lot of current. I would suspect the data is inaccurate.
-Ideal Voltage 11.1 Volts: OK; 12V should be no problem.
-Shaft size: 2mm (smooth): You're not going to get much work out of a motor this small.

-35000 RPM
-410 G CM Stall Torque
-130 Form Factor
 

Tonyr1084

Joined Sep 24, 2015
6,243
I would just add a 5 ohm R in series with motor. Need more inf. on flywheel. Motor shaft of 2 mm makes me nervous. SMPS = switch mode power supply which is what you have. View attachment 221454 Could not bring up
picture so will provide mine.
Those motors are substantially larger than the TS choice.

Actually, I can't see his/her tiny little motor drawing more than a few amps when dead stalled. But without testing - - - .
 

Thread Starter

GoatJames

Joined Aug 8, 2020
9
-14 Amp Stall Current: For a motor that small (2mm Shaft size) that's a lot of current. I would suspect the data is inaccurate.
The motor I listed was designed to be used in Nerf Guns, where they expect a LiPo battery as a power supply, which can easily supply the 14 amps at stall. I believe the data is probably accurate.

For clarification, the motor I had pictured in one of the earlier posts in this thread is not said motor. I want to switch over to the nerf-model motors for better performance and because they were specifically designed with flywheels in mind. I had wanted to avoid using a LiPo battery if possible (didn't want to sink ~$50 for battery and charger), but I probably will have to if I want to upgrade my motor or avoid some of the creative solutions in this thread.
 

sparky 1

Joined Nov 3, 2018
576
When an electrolytic capacitor is stressed by running it beyond it's rated capacity you might hear a hissss
because it developed a small hole in the dielectric. A flat tire you can patch when capacitor's dielectric damaged it is toast)

With electric motors the enamel on the wires must to be satisfactory.
When there is a stall condition a fault mechanism should shut down the motor before the heat and stress increased vibration and burns
the motor's vital dielectric. The motor now a useless char broiled piece of junk. It has a distinctive electrical burning smell. Any heat damage will lessen the motor's service life and weaken it's reliability.

We are always trying to avoid overheating it is no surprise that long lasting motors run smoother and cooler than what harbor freight sells.
 
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shortbus

Joined Sep 30, 2009
8,797
If you are in the USA, your wiring inside your walls is usually rated for about 7A. 15-20A for oven/stove.
What part of the USA do you live in???? Those numbers may have been normal back in the 1940's or 1950's
But not today. Most new or rewired homes use 20A wiring and breakers for common circuits, and 30A or higher on stoves and driers.
 
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