NodeMCU power external power

Community General Discussion
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I've seen a similar topic about the Node MCU being discussed here but the replies weren't enough to answer my question.

I have an external power supply that is based on a charging system and because of RPM fluctuations, I can have voltage output from 4.2v to 4.9 with a spike that can be made to happen that's about 5.1v

Will the Node MCU input pin (Vin) which is usually powered by 5v be fine to connect to a lesser voltage as shown and still function? I know it's internally regulated to 3.3v, which I think is the internal operating voltage anyhow, but wonder about input that low on a pin that might expect 5v.

Make sense?

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If you look at the datasheet for the SPX3819 its dropout voltage could be as high at 700mV under a 500mA load. That's 4V for a 3.3V regulator. 4.2V doesn't leave much margin, but then again the NodeMCU probably doesn't consume 500mA.

I'm less sanguine about those voltage spikes though. I'd be thinking about some very robust filtering on that power line.

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The voltage spike is something I'm trying to find the source to. I'm not sure at which stage the power spike happens. It might even be just the readout on my testing unit spiking the reading rather than the voltage actually spiking.
I'll be testing with a different meter in the future.
As for the voltage drop, it sounds like I'll probably be OK since the draw should be very minimal. I'm only driving an output signal. Not trying to power any LEDs or other devices.

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For reference, at 50mA the dropout voltage is only 250mV.

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If you are going to condition the voltage look at a SEPIC (Buck Boost) converter. That will give you a much bigger range and has the needed filtering. By chance is this a vehicle system?

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The intent is to develop a system that will accept many different voltage inputs based on the need of the output.
Yes, vehicles would be one of these applications but not specifically for vehicles.

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VUSB feeds an onboard 3V3 regulator, an "LDO".
It's probably good down to 4V in.

1 Like
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Here is some reading that will help in the future:
There is a good app note AN2689 by ST on automotive electronics. reading it will help you a lot.
https://www.st.com/resource/en/application_note/cd00181783-protection-of-automotive-electronics-from-electrical-hazards-guidelines-for-design-and-component-selection-stmicroelectronics.pdf

Also take a look at this: Distilled Automotive Electronics Design | Analog Devices

Arduinos were originally designed for and are are intended for experimentation and learning, often with breadboards and loose wires that eventually break if vibrated. Most important, the boards are not protected against harsh, dirty or electrically noisy environments found in industrial, automotive and other commercial applications.

There are some protected boards available and they are much more expensive for good reason.

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