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I'm working on a device that controls three stepper motor actuators, one servo motor and a DC motor/encoder. The stepper motors and DC motor are run at 6V and are controlled by an Arduino Nano's GPIO pins, connected to four L293D half-bridge motor drivers.

Arduino and L293D U3

L293D U4 and U5

L293D U6, L4940V5, OKR-t/3-W12-C

In the above schematic, U6 is connected to the DC motor. U5 and U4 both control stepper motors and share GPIO connects as they are expected to operate in sync on an axis. U3 also controls a stepper motor, but on another axis.

I've been running into a problem where one particular L293D (U3) overheats and burns out, forcing me to replace it. The other L293Ds do feel warm when I'm testing (possibly uncomfortably so, I haven't burned myself yet), but it doesn't feel like they're getting nearly as hot as U3 does.

I'm considering replacing the L293D with a different motor driver, but I don't want to make such a big change without determining as best I can why U3 in particular keeps overheating like this. I'm still gathering information, but if anyone sees something already, I'd be glad to hear it.

Update: Okay, I've been able to do some more testing, and it seems that U4 &5 are also getting hotter than I expected. I'm still pretty sure that U3 is getting hotter at a more rapid pace than U4 & U5, but its still all uncomfortable temperatures that could burn if left alone. I still don't know why U3 is the one that keeps actually breaking, but I think it's fair to say that all three L293Ds connected to the steppers are at least in danger of burning out. That said, this doesn't seem to be common to all the boards I'm working with. I'm working on getting some proper current measurements to go with this.

E.HP.S
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    @Andyaka Are these ones more to your liking? – E.HP.S Jun 26 '23 at 15:54
  • [Problems with L293, L298 and SN754410 H-bridge drivers on a low voltage supply](https://electronics.stackexchange.com/questions/108686/problems-with-l293-l298-and-sn754410-h-bridge-drivers-on-a-low-voltage-supply) – Andy aka Jun 26 '23 at 16:05
  • Is the motor attached to U3 the same as the others? Disconnect them and measure the winding resistance to verify. – rdtsc Jun 26 '23 at 16:26
  • Is U3 physically located between some other devices which are heating it? – Andrew Morton Jun 26 '23 at 16:29
  • @rdtsc Yeah, I checked the winding resistance against the other two. It matches. I'm wondering if it's a PCB problem. – E.HP.S Jun 26 '23 at 16:32
  • @AndrewMorton All four of the L293Ds are in relatively close proximity, but U3 is at the edge of the board. I will add that all of them are using 16-DIP connectors rather than being fully attached to the board. Would that effect heat transfer to the ground pour for heat dispersal? – E.HP.S Jun 26 '23 at 16:36
  • @E.HP.S A DIP socket will definitely impede the heat transfer. I couldn't quickly find any figures for the thermal resistance. However, if you think they're all in the same thermal environment, then it appears that something else is the problem. Is the stepper motor controlled by U3 doing more work? – Andrew Morton Jun 26 '23 at 16:53
  • @E.HP.S I couldn't find information, but user Spehro Pefhany has a link to useful information in [this answer](https://electronics.stackexchange.com/a/346527/36731). – Andrew Morton Jun 26 '23 at 16:57
  • @AndrewMorton In the full setup, sort of? U3 is moving a load along an x-axis, while U4 and U5 move U3 and its attachment up and down a z-axis. However, I was testing this without anything attached at all (stepper motors all just lying on a table) and U3 still felt noticeably hotter than U4 and U5. – E.HP.S Jun 26 '23 at 16:57

1 Answers1

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  1. you may use glued heat sinkers (ex 7x7x6 mm on ali: https://www.aliexpress.com/item/1005004214087361.html?spm=a2g0o.order_list.order_list_main.21.21ef1802Qh3lMA)
  2. the heating could be caused by improper timings/operation by the MCU, for example currents may still flow via motor windings even then motor is not rotating in this time.
Pinus
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  • Neither of your two points address the asked question why the chip overheats. – Justme Jun 26 '23 at 15:49
  • If a timing problem was the case, couldn't I expect to also see the other two stepper motors burning up? At the moment, it's just U3 getting to the point of not working. The other two get warm, but not painful (so far as I've encountered) – E.HP.S Jun 26 '23 at 16:40
  • @E.HP.S, the signals could differ (all depends of the firmware in MCU), also you may check if the motor itself is heating higher then others two – Pinus Jun 26 '23 at 16:54