DC power jack design decision: 2.1mm ID or 2.5mm ID?????

Hello all,  I just received this great reply directly in email, so I thought I would share it with everyone...

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Steve,

   I couldn't find a way to reply to your post so I'll just email you. Regarding the dilemna about DC power jacks, after I designed in a 2.5 MM jack to use some of the power supplies that I though were so common I found myself making many adapters from 2.5 to 2.1 mm. I would suggest that you design in center positive 2.1 MM jacks as this seems to be the most common wall adapter available for 12VDC. If I ever do it again I will make sure that I do the same. Hope this helps, Lloyd Carver Austin Electronics austinelex.com

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Thank you Lloyd Carver!!

So, why is no one else answering this question?  After talking with Emerson Network Power they said that they had done the research and have determined that 2.5mm is the most popular, so therefore they are hopping on that bandwagon.  You can see that its true here...

http://www.powerconversion.com/products/websheet/414/DA4-US

http://www.powerconversion.com/products/websheet/400/DA12-M-Medical

http://www.powerconversion.com/products/websheet/146/DA16

http://www.powerconversion.com/products/websheet/431/DA18-M-Medical

They are all 2.5mm except the 12w model, which offers both 2.5mm and 2.1mm.  So, I have gotten definitely contradicting opinions from people and yet you viewers remain silent.  We are getting ready to launch a family of consumer widgets and it would be nice to confidently move ahead with the right solution.....oh wait, this is engineering...there is no such thing as a right solution!!!

Thank you for any suggestions!!.... changing after we make several thousand will be much more difficult!

Hi Steve, It's an interesting question, one which I have wondered about myself.  2.5mm is about 1/10 inch and I wonder if this is a clue?  It maybe market dependant perhaps? - markets in locations that tend to imperial measurements might prefer 2.5mm, being the equalivant of 1/10".  Having said that it doesn't make much sense that markets that tend towards metric would prefer 2.1mm.  Nice lighting effects on your website!  I use to work for a company, here in New Zealand, that manufactured all the LED lighting products for Hella  for world wide distribution.  Regards, Chris

I don't think you will have any issues whichever you choose, they have both been around for years and will continue to do so. From my own research I settled on 2.1mm as looking at catalogues to ensure second and third source options it seemed to be the size I could most easily find several manufacturers and suppliers covering in the same footprint.

A change in supplier for the power-supply, will only make a little change in production necessary

Using the smaller pin on the target device allows both sizes of wall wart connector to be used in a pinch. The bigger pin can only be used with the proper mate.

The bigger pin seems a bit sturdier and should have higher retention force.

Be a bit careful with that idea.  I have come across many 2.1mm sockets that don't connect well with the 2.5mm plug.  The 2.1mm pin doesn't always contact the 2.5mm hole properly.  You wouldn't think it possible, but it's bitten me lots of times.

Here is the solution, a dual 21./2.5 socket:

http://au.element14.com/webapp/wcs/stores/servlet/Search?catalogId=15001&langId=43&storeId=10184&categoryName=All%20Categories&selectedCategoryId=&gs=true&st=FC681465

The 2.1mm-vs-2.5mm dilemma strikes me as kind of a blood type scenario. Where some people can give blood to anybody, others can receive from anybody:

A 2.1mm receptacle:

• Will be able to have both types of plugs plug into it.
• Although some 2.5mm plugs have very springy inner contacts (so that they can make a solid contact with a 2.1mm pin), others do not, and, hence, can lose contact if the plug gets wiggled. But, at the very least, if all you have is a 2.5mm plug, you can get your device powered... but you may have to ensure that it doesn't get bumped or moved. Probably the choice when you prefer user-friendliness over solid reliability.

A 2.5mm receptacle:

• Will not be able to receive a 2.1mm plug. This removes all doubt about which type of connector the user needs. They can only plug in the "correct" size. This could force your user to forestall using your device for a day or two as they shop for the proper power supply.

But your question was about which one was more common/standard. I try to make a habit of trying a 2.1mm plug on every new coaxial-powered device I get, to find out for sure. Lately, it seems like everything I use has a 2.1mm pin on the receptacle.

This may be of little help but I would suggest 2.1mm.

The Arduino Uno sports a 2.1mm power connector. Your first thought may be, what the heck does Arduino's have to do with my product. The Arduino microcontroller doesn't but the power supply requirement do. I suspect there are some makers catering to that 2.1mm market demand. The Ardunio Uno and your product can use the same power supply.

I know this is a very, very old thread resurrected but bizarrely I was looking into this question myself on Saturday.  I think 2.1mm and 2.5mm is very common.  What you need to be aware of is the voltage and current specs on available jacks (female sockets):

• 2.1mm with 12V capable jacks, even up to 5A, are as common as hydrogen molecules.  Try finding one that takes 15V though - hen’s teeth.  I was looking for a 2.1mm jack to take 15V, 0.5A.  No chance, not on Farnell, CPC, RS components.
• 2.5mm can go to higher voltages with jacks but are more expensive for some reason. 

Note that the jacks are not defined by power, i.e. a 12V 5A is not a 60VA socket so that 15V 0.5A is acceptable: the two specs are separate.  The current spec defines the power handling capability based on the connector resistance (typically <50mOhm); the voltage spec defines the insulation capability.

TBH I don’t think there would be a problem with 15V 0.5A in a 12V 5A jack but the latter isn’t specced for it.  If you are looking to build your own board connector solution, check that you can get the right plug and socket combination.