# Arduino Forum

## Using Arduino => Motors, Mechanics, and Power => Topic started by: fux on Aug 25, 2011, 06:25 pm

Title: max ampere for VIN pin
Post by: fux on Aug 25, 2011, 06:25 pm
Hi there,

what is the maximum ampere the VIN pin of the Arduino UNO can handle when using an external power supply via the power jack.
Is there any limitation?

thanks,

Andreas
Title: Re: max ampere for VIN pin
Post by: retrolefty on Aug 25, 2011, 06:35 pm

Hi there,

what is the maximum ampere the VIN pin of the Arduino UNO can handle when using an external power supply via the power jack.
Is there any limitation?

thanks,

Andreas

Yes, there is a series polarity protection diode wired between the external power connector + to the Vin pin, this is I believe a nominal 1 amp maximum forward current rated diode.

Lefty
Title: Re: max ampere for VIN pin
Post by: fux on Aug 25, 2011, 06:40 pm
Thanks!
Title: Re: max ampere for VIN pin
Post by: MarkT on Aug 25, 2011, 06:56 pm
Also the on-board regulator can overheat if it dissipates too much power (it should just shutdown if this happens).  The heat in the regulator depends on the (Vin - 5)*current.  In general any high current 5V devices should not be powered from the Arduino 5V output via the regulator - they should have their own power supply arrangements.
Title: Re: max ampere for VIN pin
Post by: Grumpy_Mike on Aug 25, 2011, 07:27 pm
The actual current available out of the on board regulator depends on the exact voltage you put in. This is because of power dissipation and heat sinking capacities. See here for some calculations:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html (http://www.thebox.myzen.co.uk/Tutorial/Power_Examples.html)
Title: Re: max ampere for VIN pin
Post by: retrolefty on Aug 25, 2011, 07:54 pm
Yes, of course. However the original question was how much Vin current could the OP draw from the Vin pin to power external componets. So the on-board +5vdc regulator is really only related in that it too draws from the total external power current limit imposed by the series diode.

Lefty

Title: Re: max ampere for VIN pin
Post by: Grumpy_Mike on Aug 25, 2011, 11:55 pm
Yes that is what he said, but was that what he meant?
Title: Re: max ampere for VIN pin
Post by: retrolefty on Aug 26, 2011, 05:14 am

Yes that is what he said, but was that what he meant?

Why do you say that? If he using an external +12vdc power source plugged into the arduino external power plug and wants to then power some external devices that requires +12vdc, say a solenoid or relay using the +12vdc avalible at the Vin pin, then it's a very logical question to ask how much current can one safely draw from the Vin pin. The limit is the current rating of the external power source or one amp, whichever is less (minus whatever current the on-board regulator is drawing). No ?

Lefty

Title: Re: max ampere for VIN pin
Post by: fux on Aug 26, 2011, 10:11 am
Lefty you got it.
Normally I power parts like a MOSFET plus solonoid with its own power supply and not through the VIN pin.
I was just curious what is the limitation of the VIN pin.

Thanks again.
Title: Re: max ampere for VIN pin
Post by: Grumpy_Mike on Aug 26, 2011, 08:26 pm
Quote
Lefty you got it.

Well done.  :)
Title: Re: max ampere for VIN pin
Post by: drone on Aug 26, 2011, 08:49 pm
It's worth noting that I have about a thousand devices in the field drawing from 1.25A to 2A @12V through the Arduino Vin pin (to a shield), and none of them have burned out any traces or melted any pins in the Arduino =)

The biggest concern I had originally, was the trace size from the dc plug to the Vin pin, which seems fairly small, and AFAIK the Arduino boards use 1oz pours.  (My shield uses 20 mil traces for the biggest consuming paths, and 2oz pours.)  However, this has not proven out to be an issue.  However, I still have some serious concerns in the long run, considering a lot of the female headers I see out there are rated @ 2A through each contact.  I don't know the specific P/N of the headers used in the Arduino, but I'd bet money on them being around the same.

!c

Title: Re: max ampere for VIN pin
Post by: retrolefty on Aug 26, 2011, 09:26 pm
Quote
It's worth noting that I have about a thousand devices in the field drawing from 1.25A to 2A @12V through the Arduino Vin pin (to a shield), and none of them have burned out any traces or melted any pins in the Arduino =)

Well the issue (and limit) is the maximum continuous forward current rating of the series polarity protection diode wired between the external power connector and the Vin pin. This diode will pass all current supplied to the board and any current consumed off board via the Vin pin. Does anyone one know the actual diode part number used and it's max forward current rating? I have no doubt one can draw more then it's safe rating but it's not an accepted good engineering practice to do so. I always assumed it was a bog standard 1 amp diode?

Lefty
Title: Re: max ampere for VIN pin
Post by: drone on Aug 27, 2011, 12:11 am

Well the issue (and limit) is the maximum continuous forward current rating of the series polarity protection diode wired between the external power connector and the Vin pin. This diode will pass all current supplied to the board and any current consumed off board via the Vin pin. Does anyone one know the actual diode part number used and it's max forward current rating? I have no doubt one can draw more then it's safe rating but it's not an accepted good engineering practice to do so. I always assumed it was a bog standard 1 amp diode?

You know, now I feel like an Idiot with a capital I.

No matter how many times I've looked at that schematic, I've blocked D1 out of my mind until this moment.

Now I'm nervous, hah. (Well, not really... But now I just have to know!)  I'm going to take a look when I get home and see if I can discern anything...

!c
Title: Re: max ampere for VIN pin
Post by: drone on Aug 30, 2011, 02:39 am
My duemilanove in front of me has a 4007 diode.  Meaning, 1A max continuous.

!c
Title: Re: max ampere for VIN pin
Post by: retrolefty on Aug 30, 2011, 02:46 am

My duemilanove in front of me has a 4007 diode.  Meaning, 1A max continuous.

!c

Yea, but I've had a 5 amp transistor blow up to protect a 2 amp fuse.  :D
Title: Re: max ampere for VIN pin
Post by: drone on Sep 05, 2011, 05:12 pm

Yea, but I've had a 5 amp transistor blow up to protect a 2 amp fuse.  :D

Yeah, pretty much every 4N007 has a 30A "spike" current, and "spikes" can be loosely defined, in my example, I'm doing lots of PWM, so those "spikes" are very short, but very often =)

!c
Title: Re: max ampere for VIN pin
Post by: Gitternmaker on Aug 14, 2013, 12:37 am
Just a thought - it's quite easy to solder a wire (or a 1-pin socket) to the back of the input jack on an Uno. That way, you can take off the input voltage before it goes through D1. I'm using that method to breadboard a multi-servo system. The servos are powered by a separate regulator, but it saves having two power supplies.
Title: Re: max ampere for VIN pin
Post by: terryking228 on Feb 08, 2015, 03:08 am
FYI The UNO uses a "M7" Diode.. 1A continuous.

See: http://www.kingtronics.com/pdf/M7-diode.pdf

See this and much more about Arduino power capabilities and limitations  HERE: (http://arduino-info.wikispaces.com/QuickRef)