0

9v power supply, 2.1mm jack
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

9v power supply, 2.1mm jack

by scooterx3 on Wed Aug 25, 2010 11:46 pm

I want to order either the 'budget' starter kit, or the regular starter kit that comes with a 9v power supply. The only thing that the decision depends upon is whether or not I already have a 9v power supply. The description for that supply says that it's got a 2.1mm jack. 2.1mm is pretty small, and I wonder - is that the outside diameter of the jack? I know this may be a dumb question, but can anyone shed some light on this subject for me? Thanks!
scooterx3
 
Posts: 4
Joined: Wed Aug 25, 2010 11:43 pm

Re: 9v power supply, 2.1mm jack

by jdl2001 on Thu Aug 26, 2010 12:31 am

5.5mm outside diameter, 2.1mm is the center hole diameter. Make sure your power supply is center positive or you'll have to cut the cord and modify it (simply splice the wires in the alternative method). It's always a good idea to verify the polarity of a power supply in any case.

Good luck.
jdl2001
 
Posts: 86
Joined: Sun Mar 08, 2009 12:53 pm

Re: 9v power supply, 2.1mm jack

by scooterx3 on Thu Aug 26, 2010 1:40 am

Sweet deal, thanks for that. And especially about the polarity. It'd really suck if I accidentally messed up my first arduino right out of the box...
scooterx3
 
Posts: 4
Joined: Wed Aug 25, 2010 11:43 pm

Re: 9v power supply, 2.1mm jack

by scooterx3 on Thu Aug 26, 2010 3:50 am

Dang, it says 9v, it's a 2.1mm jack, but I went to find out the polarity with my meter, and I read 13v. Seems that the power supply is messed up. Guess I'll have to order one.
scooterx3
 
Posts: 4
Joined: Wed Aug 25, 2010 11:43 pm

Re: 9v power supply, 2.1mm jack

by adafruit_support_bill on Thu Aug 26, 2010 5:56 am

I read 13v. Seems that the power supply is messed up.

It is typical for an inexpensive unregulated 'wall'wart' to read high with no load. You would be better off with a regulated supply like the ones in the Adafruit shop. It's a great little supply for the money. http://www.adafruit.com/index.php?main_page=product_info&cPath=38&products_id=63

adafruit_support_bill
 
Posts: 75758
Joined: Sat Feb 07, 2009 10:11 am

Re: 9v power supply, 2.1mm jack

by Entropy on Thu Aug 26, 2010 10:08 am

scooterx3 wrote:Dang, it says 9v, it's a 2.1mm jack, but I went to find out the polarity with my meter, and I read 13v. Seems that the power supply is messed up. Guess I'll have to order one.

The 7805 used by most Arduinos/Boarduinos is rated to something like 20-30 volts.

It's just that the higher the input voltage you give it, the less current you can draw without overheating the regulator. The wattage dissipated by the regulator is I*(Vin-5) - So the higher the Vin, the higher the wattage.
Entropy
 
Posts: 472
Joined: Tue Jan 08, 2008 12:43 am
Location: Owego, NY USA

Re: 9v power supply, 2.1mm jack

by scooterx3 on Thu Aug 26, 2010 12:15 pm

Well this one came with an old Palm Pilot cradle, but still.

So for my basic projects, it'd probably be just fine. But if I'm running some crazy huge circuit that's trying to figure out how to cure cancer and drawing too many amps, I'm more likely to burn out the regulator (if the processor doesn't go first that is). :lol:

Thanks for the info.
scooterx3
 
Posts: 4
Joined: Wed Aug 25, 2010 11:43 pm

Re: 9v power supply, 2.1mm jack

by adafruit_support_bill on Thu Aug 26, 2010 12:29 pm

You will likely see that 13v drop pretty quickly as soon as you put a load on it. If you are not doing anything that involves motors or other high-current devices it will probably work just fine for you.

adafruit_support_bill
 
Posts: 75758
Joined: Sat Feb 07, 2009 10:11 am

Re: 9v power supply, 2.1mm jack

by Entropy on Tue Aug 31, 2010 11:20 am

scooterx3 wrote:Well this one came with an old Palm Pilot cradle, but still.

So for my basic projects, it'd probably be just fine. But if I'm running some crazy huge circuit that's trying to figure out how to cure cancer and drawing too many amps, I'm more likely to burn out the regulator (if the processor doesn't go first that is). :lol:

Thanks for the info.

It's more along the lines of milliamps, but still - it depends on how much is being drawn from that 5v rail.

At 12v, the regulator starts getting VERY hot when feeding 8 or so LEDs at 20 mA each. Even with a small heatsink it was too hot. Running from 9v almost halves the regulator dissipation (dropping 4v instead of 7).

I just bypassed the 7805 in the end - I cannibalized a 1A car power supply for mini-USB devices (e.g. a BlackBerry car charger) that had a damaged connector. I removed the power jumper from my Boarduino, connected the input of the charger to one of the Vin pins, the ground of the charger to ground, and the output to one of the +5v pins. Now I can run 15 LEDs at 20 mA each and the switcher barely gets warm. :)
Entropy
 
Posts: 472
Joined: Tue Jan 08, 2008 12:43 am
Location: Owego, NY USA

Please be positive and constructive with your questions and comments.