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Topic: Surprised at voltage drop, is it normal? (Read 692 times) previous topic - next topic

WaitSome

Hi all,

I have been having some issues with a sensor Node on our IoT stuff. Measuring voltages I was surprised to find a voltage drop when checking just a bare Nano with blank (empty) sketch that does nothing. I then dragged out 3 other Nanos and a 2 Unos.

Using a 5vdc power bank, a bench power supply, I am getting a voltage drop. is this normal?

Nano 5.11v input via USB and power bank shows 4.37 to 4.41v at the "5v" pin.
Nano 5.00v input via USB and bench supply shows 4.47 to 4.42v at the "5v" pin.

Uno 5.11v input via USB and power bank shows 4.58 to 4.71v at the "5v" pin.
Uno 5.00v input via USB and bench supply shows 4.60 to 4.74v at the "5v" pin.

While I am pretty sure the voltage is not an issue with my Node problem, I am just surprised at the drop and wondered why, is it normal and OK?

Thanks

jremington

#1
Jul 04, 2019, 06:01 pm Last Edit: Jul 04, 2019, 06:03 pm by jremington
The schematic diagrams are available. Assuming that you are measuring the voltages correctly, there must be components between wherever you are measuring the input voltage and the "5V pin".

WaitSome

Assuming that you are measuring the voltages correctly
I assume I am, I tried 3 meters  and 2 usb-inline testers for the incoming voltage. The meter set to 20vdc range. Black probe to "Gnd" on the nano and red probe to the "5v," pin.

there must be components between wherever you are measuring the input voltage and the "5V pin".
Umm, bare Nano nothing plugged in to any pins just sitting on the bench just as it had arrived fom Amazon. I'd be interested if you were to check some or one of yours. I have several different brands and they all drop around the same levels.

I am wondering if it is worth buying a genuine Arduino Nano at 20-bucks. I'd hate to spend that to find it is no different to the clones at a 1/8th the price.

johnerrington

There is a 5V regulator from Vin to the 5V pin.

https://www.st.com/resource/en/datasheet/l78m.pdf

it can not provide regulation with less than about 2V headroom, so you need a supply of about 7V at vin.

That is why you are seeing a drop.

alternatively you can power directly from usb or 5v pin


srnet

Nano 5.00v input via USB and bench supply shows 4.47 to 4.42v at the "5v" pin.
Completly unclear what you are doing here.

What is this 'and bench supply', where is it connected and what voltage is it ?
http://www.50dollarsat.info/
http://www.loratracker.uk/

jremington

Quote
There is a 5V regulator from Vin to the 5V pin.
Power from the USB port does not go through Vin.

jremington

#6
Jul 04, 2019, 10:10 pm Last Edit: Jul 04, 2019, 10:10 pm by jremington
Since it is apparently too much trouble to google the Nano schematic, I did it for you.

Does this portion of the official schematic for Nano Rev 3.2 suggest anything to you?


MarkT

That SS1P3L is a schottky diode, so will drop 0.3 or so depending on the current level drawn, however the observed drop is significantly larger for the Nano, which suggests its not a schottky on your Nanos?
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

WaitSome

What is this 'and bench supply', where is it connected and what voltage is it ?
Seriously? Think it through. Take a USB cable and cut off the big connector end and find the red and black wires. Connect those to the red and black posts of a bench power supply like this ( https://www.amazon.com/Siglent-Technologies-SPD3303X-Triple-Output/dp/B01410O424) dial up 5v and 2A and plug the Mini-usb into the Nano.

The 3 or 4 Nanos I tested had voltages ranging between those 4.xx numbers.

WaitSome

Since it is apparently too much trouble to google the Nano schematic, I did it for you.
Let me repeat, think it through. IF I knew how to read a schematic there could be some sense in looking for one. Since I do not, that image means nothing to me.

Also, IF I could read and understand a schematic I would most likely NOT need to be asking here.

Damn it is hard to get ACTUAL answers to the original questions on newsgroups. Half the people here have to chest thump with how much more they know than the OP.

It's a HELP forum folk.

Having said that, thanks to the very-few here that actually were helpful.

jremington

Good tutorial on reading schematics. Very handy skill if you plan to continue with this hobby!

Southpark

Let me repeat, think it through.
Show clearly the situation. Your opening post did not clearly show everything that you did. For example, you used the power bank ----- need to show how this power bank was connected to the nano.

Also, your description below is confusing for readers.

Quote
Nano 5.11v input via USB and power bank shows 4.37 to 4.41v at the "5v" pin.
Nano 5.00v input via USB and bench supply shows 4.47 to 4.42v at the "5v" pin.
For example, in the above, you mention that USB supplies 5.11 volt, and the power bank shows approx 4.4 volt at the '5V' pin. So what does this mean exactly? Does this mean that you're supplying the NANO with both USB and PowerBank power at the same time? And what is the meaning of 'the powerbank shows  4.4 v at the 5V pin'? A power bank is not a voltage measurement device.....so it's not designed to show voltage measurement results at the '5V' pin.

And also --- make sure to read instructions on using/powering the Nano. You did read some instructions in the past, right? For example, on the internet - some information says "The Arduino Nano accepts the 7-12 volt input power not from the USB port, but from the Vin pin (pin30)". Now, it's possible that 10 to 12 volt applied to the Vin pin could make the regulator run hot. So 7 to 8 volt might be nicer on the regulator.

Here's an example of how you should describe what you're doing ----- Supply USB power to the Nano, and used a multimeter to measure 5.11 volt at the '5V' pin. Then removed USB power from the Nano, then used bench power supply to supply X volt at the Vin pin, and used multimeter to measure the voltage at the '5V' pin, and the measured voltage at the '5V' pin was 4.4 volt.

When describing something ---- it needs to be clear, or clear enough. Otherwise, people might misunderstand something, or not able to understand what you're trying to convey.

wvmarle

The diode in the schematic (which uses the symbol of a regular diode rather than a Schottky) has a 0.35-0.38V drop according to its datasheet.

But maybe OP has a cheap clone - and they used a regular diode instead of a Schottky type to shave a few fen of the BOM? The voltage drop strongly suggests a regular diode there.

Seriously? Think it through. Take a USB cable and cut off the big connector end and find the red and black wires.
That is info you should have spelled out in the OP if you want us to know that's exactly what you have done.

You're here long enough (>140 posts) to know this. We ONLY know about your project what YOU tell us. Now don't start complaining about us filling in gaps in YOUR information because YOU failed to provide sufficiently detailed information or use coherent and unambiguous sentences.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

TomGeorge

I assume I am, I tried 3 meters  and 2 usb-inline testers for the incoming voltage. The meter set to 20vdc range. Black probe to "Gnd" on the nano and red probe to the "5v," pin.

Did you use the DMM to measure the USB 5V line and not rely on the inline tester reading?
Please redo the  test again, using the same DMM for ALL measurements.
I have three of those mongrel USB testers and they are not accurate.
So please measure at the controller USB input and 5V pins with respect to the same gnd, with the same DMM.
Thanks.. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

jremington

#14
Jul 05, 2019, 06:47 pm Last Edit: Jul 05, 2019, 06:48 pm by jremington
Yes, the voltage drop is "normal".

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