Big Easy Driver: actual max current output?

Robotics
1

Hi folks,

I’m trying to drive my [stepper rated for 1.5 A per winding in full step.

I started to be worry when I saw this sentence on the arduino forum:

“Contrary to the advertising, the Big Easy Driver unfortunately cannot handle 2 A/winding current. A4988 based drivers like the BED can handle only about 1A/phase without extra cooling.”

https://forum.arduino.cc/index.php?topi … msg4266946

Is there any truth in this?

After investing on the Allegro A4988 Datasheet I discovered that in full-step it power both winding by using 70.71% of ItripMax current value.

On the other hand, the Brian Schmalz manual reports this sibylline/ambiguos sentence at page 4:

If your BED uses .11 ohm sense resistors (all v1.2 and above BEDs): The range of the
pot produces maximum motor currents from around 0mA (fully clockwise) to 5A (fully
counterclockwise). Now, the driver can’t supply 5A, so the full range of the pot won’t be
used. A Vref of 1.76V will result in a motor current of 2A.

What exactly means “a motor current of 2A”? 2A per winding, or max 2A as total current output?

In the first case the BED should be enough to power my 1.5A stepper, since 0.71 x 2A = 1.42 A

P.S.

In what above I don’t care about cooling problems. In my application I need to provide the max current only for 5 or 6 seconds.](https://www.orientalmotor.de/Products/Stepper_motors/Stepper_motors/high_torque_2phase_motors_pkp/?arid=23564)

2

I made some tests today with two different PSU unit but I got the same result: seems that the max current output of the BED is 1.35 A per winding.

This is quite different from the 2A advertised in the shop… :cry:

I have made a little video with my cheap and old Panasonis fotocamera. I will try to post here the link ASAP.

3

According to the [manufacturer the maximum current is 2 amps but you need a heatsink to achieve that level of current.

Capture.JPG
Capture.JPG923×303 42.5 KB
](https://www.allegromicro.com/)

4

No No.

It stops at 1.35 Amps before it gets too hot and start switching on and off because of heat-protection.

I’ve measured 55 °C with the pot completely turned to max. No way to get more then 1.35 A. After some time it gets hot and start switching.

Please be patient. I’m still working on the first video of my life! It will be ready in one hour.

5

Here the video of my test (sorry for the poor resolution):

https://youtu.be/85l6LqA0dNg

6

I think what TS-Chris is saying is that if you want maximum current, you have to keep the chip cool to get it.

7

Yes, I understood that. And I repeat that this is not what is limiting the current.

P.S.

I think I’ve discovered the reason for the current to not going up to the max value, but I’ve to go to my lab to verify my idea. Unfortunately my wife is not so happy with that during the weekend… :slight_smile:

8

Hello, here below my video explaining why I was not observing the max current declared for the BED.

The reason is inside the Allegro A4988 datasheet:

https://youtu.be/7dbgjjJmxfQ

P.S.

This is the second video of my life. I used the free OpenShot video-editor. Funny experience.

9

You can expect at most about 1 Ampere/winding from the A4988 driver, unless you supply plenty of extra cooling. For more current, buy a heavier duty stepper driver.

Pololu has by far the best selection.

10

Yes, the BED is not so “BAD”. I think that with a decent heatsink I could use it for my needs (max 1,5 A/Phase).

Anyway, I’m already looking at the TB67S249FTG from Pololu to stay on the safe side. Probably I will keep the BED just to make experiments and tests.