Arduino Forum

Using Arduino => General Electronics => Topic started by: he3r0 on Jan 05, 2013, 01:26 pm

Title: Mega Power source
Post by: he3r0 on Jan 05, 2013, 01:26 pm
I have Arduino Mega 2560, and few of the 12V baateries like this
(http://www.atlasgentech.co.nz/images/Security/Products/_Accessories_Misc/Batteries/50204_Battery-7Amp_Large.jpg)

Can i connect it directly to the power socket on the mega? or do i have to add something else in between?
Title: Re: Mega Power source
Post by: retrolefty on Jan 05, 2013, 04:06 pm
Yes that can be plugged directly into the external DC power connector on the mega board.

Lefty
Title: Re: Mega Power source
Post by: Jantje on Jan 05, 2013, 04:44 pm

Yes that can be plugged directly into the external DC power connector on the mega board.

Lefty

Even though this is true I would add a note based on personal experience.
The recommended voltage for Arduino Mega is 7-12V. A fully charged Lead acid battery holds 14.4V.
The input voltage limits are 6-20V.
This is not taking into account additional hardware attached to your arduino. So if you just have a mega running to see the led flash you are 200% OK. If you add an ethernet shield and some motorshields you may run into troubles.

In other words. Yes you can run from a 12 volt led acid battery. But when you have lots of power consuming shields or power consuming additional electronics the Mega may get overheated. In this case make sure your mega gets enough cooling (no closed box or walls around the mega, have it ly down on its long side, use a ventilator) or better use a switching regulator and power with a modified USB cable. The last option will make your solution run 2 times longer.
Note that it is the power converter on the board that gets (to?) hot. 

Practically. Use the battery and have a feel from time to time to verify whether your power consumption is sustainable.

Best regards
Jantje
Title: Re: Mega Power source
Post by: he3r0 on Jan 06, 2013, 12:32 am
Awesome, thank you guys for answers.
At This stage My projects Don't go further than simple LCD with ethernet Shield, and perhaps Some servos.  But im having feeling that Separate Circuit for 5v and 3.3v from battery To devices mighg Be a good idea. So i'll look Into that as well.
Once more, thank you guys.
Title: Re: Mega Power source
Post by: MAS3 on Jan 06, 2013, 01:19 am
If you're thinking about a mobile setup with motors, have a look at BEC speedcontrollers as used in RC models.
These often have a regulated power output to the RC receiver, and if i remember correctly, these are supposed to be at 4,8 or 6 volts.
Might be worth to have a look at these.
Title: Re: Mega Power source
Post by: Zapro on Jan 06, 2013, 02:51 am

If you're thinking about a mobile setup with motors, have a look at BEC speedcontrollers as used in RC models.
These often have a regulated power output to the RC receiver, and if i remember correctly, these are supposed to be at 4,8 or 6 volts.
Might be worth to have a look at these.


Why use a ESC with BEC to power the 'Duino when OP does not need to use a brushless motor ?

You can get standalone BEC's

To OP: I would recommend a board like this anytime when powering the 'Duino from a voltage higher than 5,5V

http://goo.gl/xnJJz

Much more effecient, no extra heat!

// Per.
Title: Re: Mega Power source
Post by: retrolefty on Jan 06, 2013, 02:57 am
Quote
To OP: I would recommend a board like this anytime when powering the 'Duino from a voltage higher than 5,5V

http://goo.gl/xnJJz

Much more effecient, no extra heat!

// Per.


I'm a big fan of those Asian switching regulators, they are so useful and would be perfect for using 12v battery power with the switching regulator adjusted to 7.5 vdc output. I found them even cheaper (free shipping!) and bought five of them:

http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Lefty
Title: Re: Mega Power source
Post by: lemming on Jan 06, 2013, 03:07 am
Quote
http://goo.gl/xnJJz


I like the line halfway down the page where it says:

"Maybe it like this? only ?5.72 ?kick the picture?"
Title: Re: Mega Power source
Post by: Zapro on Jan 06, 2013, 04:27 am

Quote
To OP: I would recommend a board like this anytime when powering the 'Duino from a voltage higher than 5,5V

http://goo.gl/xnJJz

Much more effecient, no extra heat!

// Per.


I'm a big fan of those Asian switching regulators, they are so useful and would be perfect for using 12v battery power with the switching regulator adjusted to 7.5 vdc output. I found them even cheaper (free shipping!) and bought five of them:


And why would you adjust them for 7,5V and burn off extra power in the Voltage regulator ? Why no set it to 5V and power the Arduino from the 5V-pin... ?

// Per.
Title: Re: Mega Power source
Post by: zoomkat on Jan 06, 2013, 04:30 am
Be advised when using the external power regulator with a higher external voltage to check the actual voltage on the arduino 5v pin.
Title: Re: Mega Power source
Post by: retrolefty on Jan 06, 2013, 04:43 am


Quote
To OP: I would recommend a board like this anytime when powering the 'Duino from a voltage higher than 5,5V

http://goo.gl/xnJJz

Much more effecient, no extra heat!

// Per.


I'm a big fan of those Asian switching regulators, they are so useful and would be perfect for using 12v battery power with the switching regulator adjusted to 7.5 vdc output. I found them even cheaper (free shipping!) and bought five of them:


And why would you adjust them for 7,5V and burn off extra power in the Voltage regulator ? Why no set it to 5V and power the Arduino from the 5V-pin... ?

// Per.


Because the arduino folks advice against wiring +5vdc into the 5V pin.

Quote
5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.


Lefty
Title: Re: Mega Power source
Post by: cr0sh on Jan 06, 2013, 07:06 am

Because the arduino folks advice against wiring +5vdc into the 5V pin.


Provided the voltage supplied to the 5V pin is a well-regulated 5 volts DC (by whatever means) - there shouldn't be any problem.
Title: Re: Mega Power source
Post by: retrolefty on Jan 06, 2013, 10:57 am


Because the arduino folks advice against wiring +5vdc into the 5V pin.


Provided the voltage supplied to the 5V pin is a well-regulated 5 volts DC (by whatever means) - there shouldn't be any problem.


Then why the explicit warning on the arduino Uno product page? The older arduino Duemilanove that most of us started with did explicity state that one COULD do this. The latest Uno product page explicity recommends NOT doing it. CrossRoads thinks it's the change of +5vdc regulator device in the Uno that doesn't like or sensitive to having voltage applied it's output terminal while it has no voltage on it's input terminal.

Anyway here is the pin 5V definition in the Duemilanove product description:

Quote
5V. The regulated power supply used to power the microcontroller and other components on the board. This can come either from VIN via an on-board regulator, or be supplied by USB or another regulated 5V supply.


Here is the pin 5V definition in the latest Uno product description:

Quote
5V.This pin outputs a regulated 5V from the regulator on the board. The board can be supplied with power either from the DC power jack (7 - 12V), the USB connector (5V), or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses the regulator, and can damage your board. We don't advise it.


So don't be too quick to dismiss this issue. We may not have a definitive answer or explanation yet (or ever) but I for one when wanting to power an arduino board with external regulated +5vdc, go through the USB connector rather then the 5V pin, as that is how the Uno is operating when it's on USB power only, however don't dare ask me how that is any different electrically from the perspective of the on-board +5 volt regulator because I don't see a difference.   :D

Lefty
Title: Re: Mega Power source
Post by: Zapro on Jan 06, 2013, 11:04 am
Every sensible design with a linear voltage regulator has a diode wired from the output to the input, if this is not the case on the 'Duino Mega, one should add a 1n4148 and there is no problems.

Usually you only run into the problem if you have a large cap at the secondary of the Vreg (1000 uF or more) or some kind of H-bridge with a motor attached that acts like a generator if it's running and the power is cut. There is very little possibility of destroying the Vreg from "Normal" use of an Ardunio.

I power my Uno's and Mega's from the 5V connection all the time, never had a problem. There are literaly thousands of 3D printers out there with their Mega powered from the 5V pin, never a problem.

// Per.
Title: Re: Mega Power source
Post by: retrolefty on Jan 06, 2013, 11:10 am

Every sensible design with a linear voltage regulator has a diode wired from the output to the input, if this is not the case on the 'Duino Mega, one should add a 1n4148 and there is no problems.

There is no such diode across the on-board 5vdc regulator on any of the arduino boards ever released to the best of my knowledge and memory of reading the various schematics. CrossRoads thinks that is also the correct 'solution'. But alas that doesn't help newcomers to the arduino world with there brand new Uno board.

Usually you only run into the problem if you have a large cap at the secondary of the Vreg (1000 uF or more) or some kind of H-bridge with a motor attached that acts like a generator if it's running and the power is cut. There is very little possibility of destroying the Vreg from "Normal" use of an Ardunio.

I power my Uno's and Mega's from the 5V connection all the time, never had a problem. There are literaly thousands of 3D printers out there with their Mega powered from the 5V pin, never a problem.

Yes we know that, but have not received an explanation from the arduino designers on why they now explicitly recommend not to power the board via the 5V pin on the current Uno and Mega boards. Do you know why they added that caution? As I showed it was a added change from their prior definition for the 5V pin on both prior 328p based boards and the mega boards. The changed words didn't happen by accident I suspect?
Lefty

// Per.
Title: Re: Mega Power source
Post by: Zapro on Jan 06, 2013, 11:19 am

Yes we know that, but have not received an explanation from the arduino designers on why that explicitly recommend not to power the board via the 5V pin. Do you know why they added the caution?
Lefty


Probably because one time or another people forgets it's the 5V pin and applies more than 5V and destroy the board....

The datasheet for the Regulator on the UNO says this:
(http://img805.imageshack.us/img805/1216/screenshot20130106at111.png)

So it's only a possible problem if you power it from the 5V pin and Crowbar the input pin of the Vreg - You cannot crowbar the 'Duino from the DC-jack since a diode is wired in series with the input.

// Per.
Title: Re: Mega Power source
Post by: retrolefty on Jan 06, 2013, 11:23 am
Quote
Probably because one time or another people forgets it's the 5V pin and applies more than 5V and destroy the board....


Ok, we will put you down for that guess.

Lefty
Title: Re: Mega Power source
Post by: Jantje on Jan 06, 2013, 07:44 pm
I used to power the Arduino on the 5 volt pin. I strongly advice against doing so now.
Why?
First of All I did have problems. I guess they were engine related which drove the voltage up but I never had a decent explanation.
More importantly though
If you supply power on the 5 volt and you plug in the USB or power the jack you (can?) get into problems.
That is why I advice to power with a modified USB cable. This way you have to remove the USB power plug to plug your USB cable in.

... or better use a switching regulator and power with a modified USB cable. The last option will make your solution run 2 times longer.

It costs an USB cable but it can save your arduino and your shields. So I think it is worth it.

Best regards
Jantje
Title: Re: Mega Power source
Post by: he3r0 on Jan 06, 2013, 11:22 pm
Thanks guys! Plenty of good ideas :)
Actually I have a few Esc's with built-in bec's spares from my planes and helis, so atm it could be the easiest solution.
However, since i    have few of Those batteries, (just found also one 6v like that) then external power connector will be my power delivery method atm.and with this, another question, im assuming that I'm safe to supply my mega with external power through the jack (either from my battery of wall-wart power adapter) and having usb from pc connected to it? (Im an user of ardupilot based on mega, and there were some issues with that if i remember correctly - also ardupilo was a reason for me diving deeper into arduino,did not wanted to be a user only.)