Blew up the capacitors on the L293D shield...

Hi everybody!

I'm trying to create a master clock for an old analogue slave clock. I've seen threads about this before and decided to buy an Arduino Uno with a L293D shield. The slave clock needs an impulse every minute with switched polarities, which is no problem with the H-bridge of the L293D shield.

Managed to program the shield but as the slave clock required 24V I had to put in an external power supply to the L293D shield. I connected the external power supply to the shield (without putting power to the Arduino Uno and the power supply jumper was off), the green LED on the shield turns on but a few seconds later two of the capacitors blew up. The clock was not connected to the shield and the Uno is still working.

The external power supply was a 24V/1A DC and the L293D is said to manage electric motors up to 36V. What could have caused this failure? Is the lack of power to the Arduino Uno when turning on the external power the cause?

I hope you guys could help me out on this one! Thanks!

The schematic diagram of an L293D motor shield shows two 16volt electrolytic buffer capacitors.
Shouldn't be too hard to replace them with >=25volt types.

Thank you for your reply.

Ok. I thought the capacitors would be able to withstand 24V as the maximum output to the engines is 36V according to the manufacturer.

The chips can handle 24volt, but the designer of the shield has decided to use lower voltage caps.
Assuming most people won't be using a higher than ~12volt motor supply.

Voltage rating is printed on the caps, like 100uF/16volt.
Just replace the two blown ones (on pin 8 of the chips) with 100uF/25volt (or higher) caps.
The others are for the 5volt supply, so should be fine.

Great! Will replace the blown one with new caps and try again! Thank you so much!

hello guys same i blown up my capasitor and ive replaced it but the motor now is not working.. some times it run slow then stop. did i broken something more than the capasitor?

Either something else is damaged, the capacitors haven't been replaced properly (wrong value, not soldered properly etc) or you didn't reconnect it properly when you put it back together after repairing it.

Welcome to the forum.

Please read the first post in any forum entitled how to use this forum.,148850.0.html .
Then look down to item #7 about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

What voltage are you using to power the motor.
Have you got the gnd of the motor controller connected to the gnd of the Arduino controller?

Thanks .. Tom... :slight_smile: