# VNH5019 : Problem with the power supply

Hello,

As indicated in my last topic, I am back because I’ve met a really annoying problem.

I do not know why but sometimes the VNH5019 cuts its power supply suddenly.

I never met this problem before but since 4 days it happens often.

It often happens after the calling of the calling of `void setM1Speed(int speed)` with a negative value of speed.

And I should disconnect / reconnect the power supply every time.

I am using it for industrial applications so it could be really annoying if it happens often.

Could someone help me to solve this problem ?

I am using four 24DC/7.5Amps motors. (I have 2 VNH5019).

Many thanks.

If you rapidly reverse the direction of a DC motor, it briefly draws up to TWICE the stall current.
It sounds like you are overloading the driver and/or the power supply and it is shutting down.

What is the voltage of the power supply, the stall current of the motor at that voltage and what is the maximum current that the power supply can deliver?

Hello.

In addition to answering Jim’s questions, could you measure the DIAG pins (either with your Arduino or with a multimeter) to see if the drivers are reporting any motor faults when the power turns off? Could you also post your code and pictures of your entire setup?

- Jeremy

[quote=“Jim Remington”]
What is the voltage of the power supply, the stall current of the motor at that voltage and what is the maximum current that the power supply can deliver?[/quote]
The voltage of the power supply is 24V and it can deliver 31.3Amps. I use this power supply because in my application I got 4 DC/motors 7.5Amps, therefore 4x7.5=30Amps.
I don’t really know the stall current of the motor, in the datasheet of the motor it is not indicated, I have just 24V/7.5Amps.

Sorry for this late answer, I am in France and with the time difference it’s not easy.

Assuming that the 7.5 amperes is the normal current under typical load conditions, the stall current is most likely in the 20 to 50 ampere range, but could be even higher than 50. It is not surprising that the power supply is overloaded. Also, the VNH5019 driver may not be adequate for these motors.

For design and reliable operation of high power equipment, it is absolutely essential to know the detailed characteristics of the important components and plan accordingly. That certainly includes knowing the stall current of the motors, which the manufacturer can provide.

You can mitigate the present problem by avoiding sudden direction reversals. Stop the motor completely before starting it up in the other direction. But you should expect other failures in the long run.

[quote=“Jim Remington”]Assuming that the 7.5 amperes is the normal current under typical load conditions, the stall current is most likely in the 20 to 50 ampere range, but could be even higher than 50. It is not surprising that the power supply is overloaded. Also, the VNH5019 driver may not be adequate for these motors.
[/quote]

What happens if a motor reaches its stall current ?
If this component (“Pololu Dual VNH5019 Motor Driver”) respects the caracteristics indicated in its datasheet ,i-e : 5.5V to 24V and 12Amps per motor,
I think it should be adequate for these motors.
I met a new problem this afternoon, when I connect the power supply the 2 LED (green and red) near the motor connections blink at the same time and my motor do not run at all. And I have a motor fault when I call the fonction “void stopIfFault()”.
Do you know other motor driver for Arduino which could be adequate for these motors ?

Many thanks

Clearly, not if the motor draws more than 12 amperes, which is almost certainly the case. Furthermore, it is dangerous to use the VNH5019 with a power supply voltage equal to the maximum rated (24V), because motors induce voltage spikes into the circuitry.

It appears that you don’t understand the (variable) current draw of a motor – it is roughly proportional to the mechanical load, or torque drawn by the attached machinery.

The manufacturer’s claim of 7.5 amperes is meaningless unless the load is specified. Unless you have fully characterized the motor current draw in your application and it agrees with the manufacturer’s load recommendation, it is a mistake to rely on the manufacturer’s claims.

I strongly recommend that you get a complete data sheet for the motor, and post a link or let us know what it says.

[quote=“Jim Remington”][quote]
I strongly recommend that you get a complete data sheet for the motor, and post a link or let us know what it says.[/quote][/quote]
I will give you more details of these motors when I’ll get them.
What I know about them are its torque, its nominal voltage and current.
The torque is : 250Nm ; Voltage/Current : 24V/7.5A
The “Dual VNH5019 Motor Driver” sounds like very flexible and seemed (for me) a really high-performance component that is why I went for this.
I will use 7.5A fuses to prevent that the motor draws more than 7.5A but I’d like the whole works normally with this motor driver because I’ve finished all the code of my application, it took me 1 month …

Every time the motor starts, it briefly draws the stall current.

Could I use peripheral components to reduce this stall current ? Or to ensure that this stall current does not affect the VNH5019 ?

Thanks

Find out what the stall current is before making plans.

I contacted the manufacturer and he cannot give me an exact value of the stall current.
These motor are used for pool covers and are manufactured in a “cottage” way.
Their speed do not exceed 6rpm.
I tried to measure the current when the motor starts and it doesn’t exceed 9A.

I did some tests with the motor loaded (about 150kg) and in reverse direction my motor doesn’t stop when I call the brake function provided in the library.
I think that the motor brake is defective and because the motor doesn’t stop it could generate current which is absorbed by the VNH motor driver.

Another question, do you think that the length of motor wires could affected the power of the motor or not ? The wires length is about 20m.

You can get an estimate of the stall current in two ways.

1. Measure it directly with the motor shaft locked, but with a much lower voltage on the motor (say 3 volts). Multiply by 8 for a 24 V power supply.

2. Measure the winding resistance with a multimeter, while very slowly rotating the motor shaft. Take the lowest value in Ohms and divide that into 24V.

The brake function is probably not defective. If it were, the motor driver wouldn’t work. It may not be functioning the way you expect, though.

Whether the motor leads affect the motor output power depends on their total resistance, which will create a voltage drop along the wire. Measure the voltage at the power supply and compare that to the voltage across the motor terminals to see if the difference is significant.

I will measure that asap and will post it soon.
Just a note regarding the default library provided by Pololu, the function “setM2Speed” doesn’t work with the default pins configuration.
Thanks.

Which Arduino are you using? Could you post pictures of your setup?

- Jeremy

I am using an Arduino Mega 2560.
I will post it tomorrow (in France).
I purchased 4 VNH5019 motor driver and 3 of them are not functioning normally.
I met a real problem, since the day that the shield turned off itself when I tried to stop the motor with the brake function while the motor was load (about 150kg), the shield caused a malfunction of my Arduinos, my 3 Arduino Mega don’t function and are not yet recognized by Windows.
I got this message: “Unknown Device” when I plug one of the 3 Arduinos.
I foresaw to change the shield and to purchase others Arduinos to go on my tests, so I think I will buy a “RoboClaw 2x15A”. I hope it will be more suitable for my motors and it will not caused any damage to the Arduino.
Many thanks for all …

I am still awaiting your photos.

[quote=“Jim Remington”]You can get an estimate of the stall current in two ways.

1. Measure it directly with the motor shaft locked, but with a much lower voltage on the motor (say 3 volts). Multiply by 8 for a 24 V power supply.

2. Measure the winding resistance with a multimeter, while very slowly rotating the motor shaft. Take the lowest value in Ohms and divide that into 24V.
[/quote]
Also, did you ever get a chance to measure this or get additional information about the motor?

- Jeremy

[quote=“JeremyT”]I am still awaiting your photos.

[quote=“Jim Remington”]You can get an estimate of the stall current in two ways.

1. Measure it directly with the motor shaft locked, but with a much lower voltage on the motor (say 3 volts). Multiply by 8 for a 24 V power supply.

2. Measure the winding resistance with a multimeter, while very slowly rotating the motor shaft. Take the lowest value in Ohms and divide that into 24V.
[/quote]
Also, did you ever get a chance to measure this or get additional information about the motor?

• Jeremy[/quote]

Hello,

I think the stall current is approximately 16.5A because the winding resistance is “1.45 Ohms”.
That is why the shield did not support this.
Coud you advise me a new shield which could bear the caracteristics of these motors?

Kind regards

A stall current of 16.5A is within the current capabilities of the VNH5019 shield; however, as mentioned before, changing the direction of a DC motor rapidly can cause it to draw up to TWICE the stall current and might be more than what your power supply could handle.

The VNH5019 dual motor driver shield is our highest power motor driver shield. For a more powerful motor driver, you might consider our high-power motor drivers. They do not stack on top of an Arduino like a shield, but you should be able to control it with your Arduino using the logic connections. Alternatively, you might consider configuring the VNH5019 shield into single-channel mode. In single-channel mode, the shield can deliver up to a continuous 24A. You can read more about this in the “Using the Driver in Single-Channel Mode” section of the VNH5019 shield user’s guide.

Before changing to a different motor driver, it might be good to make sure there is not anything else going on in your setup that could be causing problems. You still have not posted photos of your setup or your code. If you post them, I would be happy to take a look.

- Jeremy

[quote=“JeremyT”]

Before changing to a different motor driver, it might be good to make sure there is not anything else going on in your setup that could be causing problems. You still have not posted photos of your setup or your code. If you post them, I would be happy to take a look.

• Jeremy[/quote]
Thanks a lot,

I will post the whole ASAP in purpose to have your point of view.

Many thanks again