MKR Motor Carrier just burst into FLAMES

OK,

This is the second Motor Carrier board I’ve had, and the second to fail! :slightly_frowning_face:

I’m just really lucky I caught this in time as it was a proper fire inside a droid I’m building.

The first board that blew up went short circuit, and I couldn’t figure out why, I was running from a 12V bench PSU, and when it happened the PSU was clamped at 2 amps, so it caught the issue and switched back the supply. So no noticeable damage on the MKR shield but it was now short circuit on the Vin rail.

This time I had my full system sat on the bench in front of me, I had been running it for about a week.

The MKR Motor Shield is powered by a 12V, 10amp Dc-Dc converter powered by a 12V NiMh battery fused at 8Amps. The system was switched on but in standby mode, e.g. my code was running all the motors were switched off (zero duty ) so basically nothing was happening. I was just tweaking some code and the board burst into flames!

Looks like the mosfet power switch section!

Seeing as this is the second time this has happened, I’m sure this is a defect in the design. I contacted Arduino tech support the first time it happened but have had no solution or replacement.

So, having posted this else where the following has been pointed out:

Looking at the schematic and in particular the two P-Channel MOSFET chips for switching the power. These devices are AON7407 devices and they have a VGS rating of +/- 8V Abs Max.

This means that in the circuit when connected to a 12V battery the VGS voltage is 4 volts over their rated capacity as you have the gate pin tied to ground on Q1 and switched to ground on Q3.

With this configuration the maximum battery input voltage would be 8V. It is stated in the specifications to be 12.6V or a 11.1V LiPo battery.

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Your topic is welcome BTW.

Bob

Ok no problem. I just want to make sure anyone else using this shield is a aware of this potentially dangerous situation.. mine was very close to a full blown fire. Hence posting this information to someone else asking about the shields capabilities.

Matt