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Topic: Powering Arduino (Read 266 times) previous topic - next topic

Mikkoe

Hello!

I'm  trying to understand the basics of powering Arduino in different ways. I read this article which is a good source.

https://www.open-electronics.org/the-power-of-arduino-this-unknown/

For example, if I'm trying to power two of these servos (link below) with Arduino, If I understand correctly, it would require 2 x 170mA for the servos and 200mA for the Arduino. Regarding the voltage, I think 5 V should be enough?

http://www.towerpro.com.tw/product/mg945/

Because it's possible to get only 500mA trough USB, I think I'll have to use an external voltage. I have some questions.

If I power Arduino from external 9V Battery, does it go trough a voltage regulator or just trough the diode? What would be the voltage then if using the 9V battery and the Vin-pin as an output with servos? What about the total current?

Here it says (link below) that voltage from the external source is regulated to be 5 V. If that's the case, is it impossible to get more than 5 V from Vin when connecting Arduino to e.g. 9 V battery?

https://learn.adafruit.com/ladyadas-learn-arduino-lesson-number-0/power-jack-and-supply

Servos didn't operate so well with this setting so there isn't enough current I think. That's why I started to wonder what's the logic behind voltage/current when using external voltage and vin as output.

Thank you for your help!

Budvar10

#1
Mar 12, 2018, 02:10 pm Last Edit: Mar 12, 2018, 03:19 pm by Budvar10
Quote
Because it's possible to get only 500mA trough USB, I think I'll have to use an external voltage. I have some questions.
Definitely use an external power. Generally it is not good idea to power high current consumption devices, like servos are, from the USB.

Quote
What would be the voltage then if using the 9V battery and the Vin-pin as an output with servos? What about the total current?
You mean 9v to the barell jack, right? Then, the voltage drops about 0,7V. There is a diode in the path. Vin can be used for additional devices, but not for several servos. Current should be a problem. Max. forward current through the diode is 1A. Just one servo can exceed this under some conditions.

Quote
Here it says (link below) that voltage from the external source is regulated to be 5 V. If that's the case, is it impossible to get more than 5 V from Vin when connecting Arduino to e.g. 9 V battery?
No, as I wrote above, if there is 9V on the barre jack Vin should be about 8.3V. Vin is not regulated. It is input for Arduino on-board 5V regulator.

I am recommending to use an extra branch for servos, directly from battery like in "High power consumption 5 V circuit plan" (https://www.open-electronics.org/the-power-of-arduino-this-unknown/).
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

Mikkoe

Thank you for your help!

Quote
You mean 9v to the barell jack, right?
Yes, I meant it.

Quote
I am recommending to use an extra branch for servos, directly from battery like in "High power consumption 5 V circuit plan" (ttps://www.open-electronics.org/the-power-of-arduino-this-unknown/).
Could you resend the link? I didn't get it to open and am very interested in how to power 2 servos because even with 9V battery to barrell jack, the current isn't enough.

I was also wondering whether is possible to connect the battery to servos voltage directly trough breadboard. Maybe not the most safe alternative...




Budvar10

#3
Mar 12, 2018, 03:25 pm Last Edit: Mar 12, 2018, 03:27 pm by Budvar10
The link is corrected. It is same as you have sent.

9V is too much for these servos. They wrote 4.8-6.6V. You will need the regulator. I will go to some switching regulator instead of the 78xx from schematics.
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

Mikkoe

Thank you!

What about powering two servos directly with 4 x 1,5 V (AAA) battery, connected in series? In this way the voltage would be 6 V.

Is there a possibility that the voltage source would provide "too much current" for the components or is the total current in a circuit just the current that the components draw from a battery etc.?

simonbiton

The link is corrected. It is same as you have sent.

9V is too much for these servos. They wrote 4.8-6.6V. You will need the regulator. I will go to some switching regulator instead of the 78xx from schematics.
78XX are not switching as I remember- they are linear.
What you probably mean for DC-stepDOWN VR ( recommended and I use them a lot ) is:
"Step down buck  Voltage regulator LM"
Look it up at ebay
the best tutorial for it is:
https://www.youtube.com/watch?v=77vxOF2V-xU

Budvar10

@Mikkoe
In any case you should use the regulator. Yes, the batteries in series provide 6V, but do not forget that the voltage is not stable and constant. Fully charged battery has voltage higher than nominal and the voltage falling down as the battery is discharged.

@simonbiton
Yes, the 78xx is not switching regulator. I meant "use switching instead of 78xx".
Arduino clone with ATmega1284P   http://forum.arduino.cc/index.php?topic=277260.0

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