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Motorshield V2.3 Burnout
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Please be positive and constructive with your questions and comments.

Motorshield V2.3 Burnout

by pharrell2 on Wed Dec 23, 2020 1:24 am

I'm working on a project to use a MotorShield V2.3 to control resistive heaters. On first powerup, the chip on the motorshield burned out when I activated the DC motor control. The only output in use (M1) was connected to an RCA port, with no short as far as I can tell post-mortem, and nothing connected.

Is there any reason the shield would burn out with an open connection across the power output?

Photos of the prototype setup attached. The damage to the chip adjacent to the M1/M2 header is visible (plus the smoke was a good indicator). Just want to understand the issue before I try to activate another channel.

Thanks!

EDIT:

Forgot to add:
The power input comes from a 12V/10A power supply to the power input header.
Attachments
PXL_20201223_050344655_1.jpg
PXL_20201223_050344655_1.jpg (237.88 KiB) Viewed 122 times

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Re: Motorshield V2.3 Burnout

by adafruit_support_bill on Wed Dec 23, 2020 7:07 am

What code was running on the board at the time?

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Re: Motorshield V2.3 Burnout

by pharrell2 on Wed Dec 23, 2020 11:35 am

I've attached the full code, but the parts which directly set the power output are quoted below. The heater power level is controlled by a touchscreen button, which when pressed cycles through 5 power levels (heater_power_list). It initializes at 0 power. I only saw the smoke start when I activated the heater to 100% (it goes from 0 -> 100% -> 75% and so on).

Code: Select all | TOGGLE FULL SIZE

heater = MotorKit(address = 0x60)
heater.motor1.throttle = 0
heater.motor2.throttle = 0
heater.motor3.throttle = 0
heater.motor4.throttle = 0

heater_power_list = [0, 0.25, 0.5, 0.75, 1.0]

heater_current = heater.motor1.throttle
i = heater_power_list.index(heater_current)
if i == 0:
      i = len(heater_power_list)-1
else:
      i = i - 1
heater_current = heater_power_list[i]
heater.motor1.throttle = heater_current
heater.motor2.throttle = heater_current
 
Attachments
code.py
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Re: Motorshield V2.3 Burnout

by adafruit_support_bill on Wed Dec 23, 2020 11:43 am

Can you link to a spec for the heating elements you are using?

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Re: Motorshield V2.3 Burnout

by pharrell2 on Wed Dec 23, 2020 11:56 am

adafruit_support_bill wrote:Can you link to a spec for the heating elements you are using?


It is designed to run a DN003 and DN005 as shown here: https://www.dew-not.com/specifications.htm. They draw 0.35A and 0.61A @ 12V respectively.

However, neither was connected at the time - the M1 and M2 outputs were connected to the RCA jacks that the heaters would connect to, and when I rechecked them after the smoke cleared, neither RCA connector appeared shorted.

One other note I forgot to mention: I'm powering the Metro M4 Express with 12V going into the DC jack. I know this is higher than the generally recommended 7-9V, but saw some comments elsewhere that it works as long as the current consumption is low enough, and was going to try it knowing may damage the Metro. I wouldn't think this would affect the MotorShield though.

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Re: Motorshield V2.3 Burnout

by adafruit_support_bill on Wed Dec 23, 2020 12:14 pm

12v should be OK for a lightly loaded Metro M4. But the voltage regulator will be running warm. It should have no effect on the shield with the VIN jumper disconnected as in your photo.

A smoked H-Bridge implies some sort of load - whether an intentional load or a short circuit. If there is no connectivity between the output legs of the bridge, there is no current flow through the chip.

Please post a photo showing the underside of the board.

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Re: Motorshield V2.3 Burnout

by pharrell2 on Wed Dec 23, 2020 12:48 pm

adafruit_support_bill wrote:12v should be OK for a lightly loaded Metro M4. But the voltage regulator will be running warm. It should have no effect on the shield with the VIN jumper disconnected as in your photo.

A smoked H-Bridge implies some sort of load - whether an intentional load or a short circuit. If there is no connectivity between the output legs of the bridge, there is no current flow through the chip.

Please post a photo showing the underside of the board.


Just spoke with a EE colleague and I think we found out the issue. While the +/- leads of each RCA jack aren't shorted, the negative leads of both were shorted together through the aluminum case, and I didn't realize that this would smoke the H bridge. I'm going to modify the case to isolate the case from the connector and try again tonight.

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Re: Motorshield V2.3 Burnout

by adafruit_support_bill on Wed Dec 23, 2020 1:06 pm

That would do it. The purpose of the H-Bridge is to allow you to reverse the current flow. So '+' and '-' have no fixed meaning with respect to the outputs of the bridge.

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Please be positive and constructive with your questions and comments.