ESP8266 Community Forum

- Thu Oct 22, 2020 11:43 pm #89171 Hi guys,

So you've read it right. I had a capacitor designated 106J explode on my NODEMCU. It is this one:



Basically what I was trying to do is rotate a SG90 servo motor through my NODEMCU when it happened. The circuit is very simple. LiPo battery is connected to a step-up converter to bring 3.7V to 8V, which is then connected to the NODEMCU VIN and GND pins. Additionally, there is a 5V LDO hooked up after that step-up converter to provide 5V for the SG90. And there is a electrolytic 2200uF capacitor next to NODEMCU's VIN and GND. This capacitor is meant to smooth out the current for the NODEMCU due to the whole setup using single LiPo cell.

So, I hooked up the LiPo for the first time (previously I tested with a PSU), and noticed that the LiPo disengages immediately, because the 2200uF capacitor is too damn hungry, and exceeds the current that LiPo can supply in such a short time. So for the time being, I un-soldered the capacitor until I could figure it out. Without capacitor, LiPo was okay, and NODEMCU booted up nicely. So I gave it a command to run that SG90. And that when it happened. A LOUD, bright explosion. A burst of flame at least 5 centimeters long. Left flashes in my eyes for at least 10 minutes.

Upon inspecting the NODEMCU, I saw that the small 10uF capacitor designated 106J is now black and has massive holes on both sides of it. I replaced that 106J by scrapping another bricked NODEMCU, and now my primary NODEMCU is running fine again.

My question is, why did this happen? Did removing that 2200uF capacitor from the circuit cause some kind of an overload or a voltage spike that caused that little capacitor on the NODEMCU to explode? Again, I wasn't powering my SG90 directly from NODEMCU - I know that one should never do that - it was powered in parallel from LiPo, as I described earlier. So I can't understand how that SG90 could have caused damage to NODEMCU.

Do you have any ideas why this happened, and how to protect against it? Do I need some flyback diode or something?

- Fri Oct 23, 2020 5:36 am #89172 What is the voltage rating on that capacitor?

This capacitor type seems to vary between different NodeMCU models, e.g. 1uF 20V on some models.

It is possible this 10uF capacitor has a 6.3V rating which is fine for a 5V external input but not with your 8V input.

In general it is not great to feed a linear regulator with too high an input. 7.2V will mean nearly 4V drop across the regulator leading to more power dissipation in the regulator. It will probably be OK as the average current will be ~100mA.

I would have considered boosting the battery to 5V to feed both the board and the servo. There is no harm in using this for both purposes; the servo does not draw much current.

- Fri Oct 23, 2020 9:34 am #89173

What is the voltage rating on that capacitor?

This capacitor type seems to vary between different NodeMCU models, e.g. 1uF 20V on some models.

It is possible this 10uF capacitor has a 6.3V rating which is fine for a 5V external input but not with your 8V input.

In general it is not great to feed a linear regulator with too high an input. 7.2V will mean nearly 4V drop across the regulator leading to more power dissipation in the regulator. It will probably be OK as the average current will be ~100mA.

I would have considered boosting the battery to 5V to feed both the board and the servo. There is no harm in using this for both purposes; the servo does not draw much current.

I have no idea what the voltage rating is on that cap. All I have is that general designation 106J written on it, which means it is 10uF, but gives no indication to it's voltage rating. In any case, NODEMCU is supposed to be fed 7-12V on the VIN pin, because it has an internal regulator that brings it down to 3.3V for the chip. I chose 8V to have a small reserve over the minimum input voltage, just in case. So in any case, by specifications, that capacitor should be able to handle up to 12V. I guess it is a 20V capacitor.

The LDO that I have installed to drop that 8V to 5V for the servo should be able to easily handle it. It is rated for 2A I think, it is very large (large area for heat dissipation) and it is not even getting warm. I am not using another boost because boost modules are very large compared to LDOs, and I there are size restrictions to this projects.

So why would have that onboard NODEMCU capacitor exploded when I removed the big 2200uF capacitor from my circuit? The loads in this circuit are well below the limits of every component in it.

- Fri Oct 23, 2020 9:49 am #89174 The capacitor maximum voltage marking is this J in 106J, and it means that it is 6.3V ( https://www.electronics-notes.com/artic ... rkings.php )...