Arduino Vcc=3 when batteries supply 4.8V

Using Arduino General Electronics
#1

I've got four 1.2V rechargeable batteries connected in series to a

TP4056 5V 1A Micro USB 18650 Lithium Battery Charger Module Board X9U4

recharger. The voltage these batteries are supplying when not connected to the Arduino Uno is 4.94V https://drive.google.com/file/d/1E1grrS053dxGHd95uC2tAJg9UiayX--H/view?usp=sharing but the Uno's Vcc is only 3.1V https://drive.google.com/file/d/1fkOOJW46HXQy9OB9MEbbra9qgUpaslw0/view?usp=sharing

why is my voltage drop so bad? the batteries are 1.2V AA rechargeable 3000mAh. they're all identical from the same brand new package and fully charged.

what's going on here? is this the Uno's voltage regulator making my life difficult?

#2

Are you connecting to the Vin pin or the 5V pin? Hint: connect 4.94V to the 5V pin. The 5V regulator needs 7V to its input to regulate properly.

#3

A circuit diagram might be helpful because at the moment I can't work out why you are using a LITHIUM charger board with batteries which at 1.2V each are NiMH not lithium. Where does the Lithium battery come in? What is powering the TP4056?

Steve

#4

ok. I had it connected to the 7V-12V jack as that worked fine when I had a 9V square battery powering my project(hadn't actually looked at the pinout that pointed this voltage range out before now).

so, with your suggestion in mind I had a look at this pinout and determined that Vin was probably appropriate. Maybe you're right about 5V pin but the pinout diagram I'm looking at describes that pin as not only 5V but actually explicitly states V*out*.

I've got it connected to V*in* and its working fine running an MG995 power-hog servo and a few LEDs to drain the battery and test the charger. 2 hours on and my batteries are still at 4.48V and doing fine.

thanks for your input. Christ

#5

slipstick: A circuit diagram might be helpful because at the moment I can't work out why you are using a LITHIUM charger board with batteries which at 1.2V each are NiMH not lithium. Where does the Lithium battery come in? What is powering the TP4056?

Steve

thank you for your input, I did post two images of my project and I don't know why they're not visible. I have the charger in parallel with the Uno(and its power switch). I hadn't considered whether rechargeable NiMH batteries would work with this charger but as I'm draining the batteries now to test if it does, I'll let you know in a few hours.

Christ

#6

I drained my batteries and recharged them, that's good. No problem there. however ... I have them connected to V*in* and they're pushing 4.54V but the Vcc voltage is 3.19V ... that would be all fine and good except I can't see the LCD screen. When I plug it into a USB port every works great. I have a power supply issue. my batteries are 1.2V batteries connected in series to make up 4.8V when fully charged. I had those batteries pumping an M995 Servo for about 3hours this morning and they won't work at such a low voltage. when I unplug everything and measure the voltage there's still a drop from 4.5V at V*in* to 3.19V at Vcc (5V pins)

so how is that happening?

#7

That's because, despite what you think, the batteries should be connected to the 5V pin. What you're seeing is the expected volt drop across the internal regulator. Vin needs at least 6.5V to work reliably.

Steve

#8

slipstick: That's because, despite what you think, the batteries should be connected to the 5V pin. What you're seeing is the expected volt drop across the internal regulator. Vin needs at least 6.5V to work reliably.

Steve

great.

thanks. 5V it is...

#9

This is what the power scheme looks like on your Arduino Uno board.

Note how the Pwr Supply and Vin points are upstream of the onboard regulator and the 5 volt pin is downstream. Anything upstream of the regulator will require about 2 volts above regulation so we get a minimum of 7 volts and consider the forward drop of D1. Applying 5 volts on the 5 volt pin will work just fine and is a good way to go.

Ron

Arduino UNO %V Reg.png
Arduino UNO %V Reg.png945×352 45.3 KB

#10

groundFungus: Are you connecting to the Vin pin or the 5V pin? Hint: connect 4.94V to the 5V pin. The 5V regulator needs 7V to its input to regulate properly.

yea... that was it all along! thanks.

#11

slipstick: A circuit diagram might be helpful because at the moment I can't work out why you are using a LITHIUM charger board with batteries which at 1.2V each are NiMH not lithium. Where does the Lithium battery come in? What is powering the TP4056?

Steve

hmmm... about that. it seems I have a problem. my batteries are discharging at hypersonic speed rendering my project's internal power supply utterly useless.

so...? I have the wrong batteries?

.. also, I added a wire from my batteries to an analog pin and used it to get a read on my voltage and it keeps telling me that its full power when its obviously (and factually) not. so, I'm guessing the analogRead(pinVoltage) returns a value from 0 to 1024 relative to the input voltage and that's why its always 'full' ?

#12

There is a way to read your voltage using a resistive voltage divider and the internal analog reference voltage source. Sorry but I don't know the details of how to do this but the details have been published on the internet. Without doing anything like this, you are comparing to the Arduino power supply voltage. Reading the Arduino power supply voltage with an analog pin (without doing anything else) will always give you the maximum reading.

Basically, you need to turn on the reference source and use a voltage divider that divides your maximum input voltage down to that of the reference.

#13

I don't know about "the wrong batteries" but you certainly have a mismatch between your charger and your batteries. Charge current, voltage and charge method are all wrong.

Whether you change charger or batteries is up to you and probably depends on what it is that you're trying to power, for how long, what is powering the charger etc. That's why a circuit diagram and details of ALL your components are needed to give useful advice.

Steve

#14

slipstick:
I don’t know about “the wrong batteries” but you certainly have a mismatch between your charger and your batteries. Charge current, voltage and charge method are all wrong.

Whether you change charger or batteries is up to you and probably depends on what it is that you’re trying to power, for how long, what is powering the charger etc. That’s why a circuit diagram and details of ALL your components are needed to give useful advice.

Steve

I wrote an article about my project “sans-rechargeable batteries” at the CodePorject

Code Project Article : Reps Counter

#15

after recharging my not-lithium batteries in a proper wall-plugged battery charger the sum of 4 1.2V batteries is 5.57Volts. If I connect these to the UNO's 5V pin (by-passing the voltage regulator) is this going to damage the Arduino that operates at 5Volts?

#16

The maximum voltage to the Vcc and AVcc pins is 5.5V. That spec is in the processor data sheet.

#17

I changed the img tags to url tags, the links to your google drive images appear now.

I think img tags only work when the file ends in .jpg. The google drive stuff does not.

#18

Does it damage the Arduino when you power it via USB? That also bypasses the regulator. You could use a USB cable and power the board thru the USB port.

#19

thanks.

CrossRoads: Does it damage the Arduino when you power it via USB? That also bypasses the regulator. You could use a USB cable and power the board thru the USB port.

no. the USB port doesn't damage it... probably for a good reason. but I was worried about my 4x1.2V batteries in series pushing out 5.5V when I measured it with my volt-meter since I'm plugging them in the 5V output pin, bypassing the voltage regulator.

thanks for you post

#20