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How to use current chopping properly

Hi, I’m confused about how to use the current chopping/limiting setting on my motor driver.
(This is the specific motor driver I’m using g2 24v13 Pololu G2 High-Power Motor Driver 24v13)

The motor driver page says: “The G2 driver has the ability to limit the motor current through current chopping: once the motor drive current reaches a set threshold, the driver goes into brake mode (slow decay) for about 25 µs before applying power to drive the motor again. This makes it more practical to use the driver with a motor that might only draw a few amps while running but can draw many times that amount (tens of amps) when starting.
The current limiting threshold is set to about 30 A by default.”

Since my motors (GR-WM4 24V DC High Torque Low Noise 35rpm Worm Gear Motor - Gimson Robotics | The linear actuator and electric motor specialist) have a 15A stall current while taking 4A normally, should I lower this current limit to the 4A value or the 15A? Do I need to limit the current at all in this way?
What happens if I don’t adjust the threshold and leave it at the default value? Would the motor driver get damaged?

Hi.

The 24v13 G2 high-power motor driver should have no trouble handling quick bursts of 15A, so lowering the current limit of your drivers is probably not necessary. If you want to be extra cautious or there is a chance your motors might stall for prolonged periods, you could lower the limit. If you choose to lower the limit, you should leave plenty of room above your 4 typical draw so the limit does not interfere with normal operation. Something between 10-13A might be good.

-Claire

I’m not sure I understand when it’s required to lower the limit.
If you leave it at the default threshold, then there shouldn’t be any problems right?

If my motors stall for prolonged periods, then wouldn’t I want to keep the limit higher? Since if I lower the limit, then the motors won’t be able to draw enough current when stalling?
(My understanding of this is probably wrong, so please correct me)

Stalling a brushed DC motor is generally not good practice and can damage the motor quickly (sometimes instantaneously). So, in my example, I was considering the stall condition a failure of the system that you might want to protect the driver or other electronics from.

-Claire

Ok right that makes sense.
This is probably a dumb question, but is it okay to only give the motor, say, 6A, instead of the total 15A it’s trying to draw? Would it harm the motor in any way if it can’t get as much current as it would like?

Hi, if I’m using the 24v13 driver, Pololu G2 High-Power Motor Driver 24v13, on a motor that has a 15A stall current, is that okay?
The driver is only rated for 13A max, so would this damage the driver?

What if I used the current chopping/limiting functionality built into the board? If I set the chopping threshold to 6A, then could the motor still draw 15A eventually and still break my board, or would doing this be enough to protect it?

I moved one of your other posts to this thread since it is close to the question you already asked here.

As I mentioned above, I do not expect the 15A stall current of your motor to be an issue, but if you want to be extra cautious, you could lower the current limit to something between 10-13A. Once the current limit is set the driver will prevent the motor from drawing any current above that limit. Limiting the current the motor can draw in this way will not damage the motor, but it will limit the torque the motor can produce.

-Claire

Hi I’m using two 24v13 drivers Pololu G2 High-Power Motor Driver 24v13
and I can connect a resistor to their VREF pins in order to control the current limiting level.

Since I want to set their current limits to the same level, can I connect both their VREF pins to the same resistor which is connected a ground pin on my arduino?
Or do I need to connect each VREF to its own resistor and then to ground?

I moved your post to yoru thread abotu the 24v13 high-power motor driver’s current limiting.

You should use separate VREF resistors for each driver.

-Claire

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Ok thanks, could you tell me how you know you’re supposed to use separate resistors?

The reference voltage the driver IC reads to determine the current limit is set by a voltage divider on the board. When you connect a VREF resistor it works in parallel with the pull-down side of that divider to change the reference voltage. Connecting two drivers to a single VREF resistor would also connect the drivers’ voltage dividers and throw off the calculations given on the product page for figuring out what VREF resistance to use for a desired current limit.

-Claire

1 Like