Author Topic: Is there a standard (or common) spec on DC power jacks?  (Read 2734 times)

0 Members and 1 Guest are viewing this topic.

Offline elroyTopic starter

  • Regular Contributor
  • *
  • Posts: 89
  • Country: us
Is there a standard (or common) spec on DC power jacks?
« on: December 14, 2017, 08:09:15 pm »
Recently I bought and assembled one of these simple function generator boards:

https://www.amazon.com/gp/product/B01HM70CMY

The board has a jack for DC power in what appeared to me to be a size I'd seen fairly often. I figured it would be handy to have a supply of jacks and plugs so that I could swap around power supplies while working on various projects, so I bought this assortment:

https://www.amazon.com/gp/product/B00N8C49OA

Unfortunately, I found that some plugs and jacks that appear to me to be reasonable fits don't result in an electrical connection. I don't think any of them are necessarily defective, there just must be be slight size differences.

So, if I wanted to stock up on some jacks and plugs that would run the best chances of fitting kits and so on, is there a particular size that tends to be used most frequently these days?

 

Offline tooki

  • Super Contributor
  • ***
  • Posts: 11342
  • Country: ch
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #1 on: December 14, 2017, 08:25:57 pm »
The 5.5mm outer diameter, 2.1mm inner diameter is probably the most common, and 9V DC, center negative positive is probably the most common configuration. But these vary wildly.

The most common almost-but-not-quite fit is the 5.5 outer/2.5 inner plug. It will fit a 5.5/2.1mm jack, but will make at best an intermittent connection.
« Last Edit: December 15, 2017, 06:11:44 pm by tooki »
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #2 on: December 14, 2017, 08:42:00 pm »
Unfortunately there is no standard, though the 2.5mm center pin is frequently used on adapters that put out AC voltage while 2.1mm is the most common with DC voltage but this is by no means absolute. Then occasionally you find something that uses the center pin as negative instead of positive. I have no idea why none of this was ever standardized.
 

Online Jeroen3

  • Super Contributor
  • ***
  • Posts: 4068
  • Country: nl
  • Embedded Engineer
    • jeroen3.nl
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #3 on: December 14, 2017, 08:45:07 pm »
No. There is no standard.
You buy the plugs and sockets with the outer radius and the pin diameter.
2.5mm/5.5mm is common though.

 

Offline suicidaleggroll

  • Super Contributor
  • ***
  • Posts: 1453
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #4 on: December 14, 2017, 09:21:35 pm »
The 5.5mm outer diameter, 2.1mm inner diameter is probably the most common
Definitely

and 9V DC
I see far more 5 and 12, but 9 is somewhat common

center negative
Never in my life have I seen a barrel plug DC supply with negative on the center
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #5 on: December 14, 2017, 09:28:28 pm »
Never in my life have I seen a barrel plug DC supply with negative on the center

It's very common on musical gear. Samplers, keyboards, sequencers, etc. I also have a scanner radio that uses 9V center negative on a barrel connector. It's not nearly as common as center positive but I wouldn't call it rare either.
 

Offline Kjelt

  • Super Contributor
  • ***
  • Posts: 6459
  • Country: nl
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #6 on: December 14, 2017, 10:03:20 pm »
Lots of stuff before 2000 had negative center.
Luckily now it looks like + on center is standard, now only the pin diameters  :(
BTW I hate these connectors since they have no lock, every week or so a connector of my usb hubs or ip switches will be out of the chassis, i started to hot glue them stuck.
 

Offline chrisl

  • Regular Contributor
  • *
  • Posts: 90
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #7 on: December 14, 2017, 11:34:10 pm »
I have seen a lot keyboards with negative center pin.
 

Offline bitseeker

  • Super Contributor
  • ***
  • Posts: 9057
  • Country: us
  • Lots of engineer-tweakable parts inside!
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #8 on: December 15, 2017, 01:22:41 am »
Center positive is much more common nowadays than it used to be. Center negative is often found on devices that use the jack as a switch (e.g., disconnect onboard battery when barrel plug is inserted).
TEA is the way. | TEA Time channel
 

Offline tooki

  • Super Contributor
  • ***
  • Posts: 11342
  • Country: ch
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #9 on: December 15, 2017, 06:10:28 pm »
Ack, my brain meant to write center positive, but I wrote negative instead!
 

Offline tooki

  • Super Contributor
  • ***
  • Posts: 11342
  • Country: ch
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #10 on: December 15, 2017, 06:12:45 pm »
You buy the plugs and sockets with the outer radius and the pin diameter.
2.5mm/5.5mm is common though.
Err, you mean outer diameter and inner (pin) diameter, don’t you? And that’d be 5.5/2.5mm, then. ;) But the 2.1mm inner is actually more common, I think.
 

Offline Gyro

  • Super Contributor
  • ***
  • Posts: 9410
  • Country: gb
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #11 on: December 15, 2017, 07:10:37 pm »
...
BTW I hate these connectors since they have no lock, every week or so a connector of my usb hubs or ip switches will be out of the chassis, i started to hot glue them stuck.

Although some connectors have smooth barrels and others have a reduced diameter 'ring' near the tip. These, in combination with the right socket, do provide a positive retention. It often doesn't work out in practice though (after-market adapters etc.).
Best Regards, Chris
 

Offline BBBbbb

  • Supporter
  • ****
  • Posts: 289
  • Country: nl
Is there a standard (or common) spec on DC power jacks?
« Reply #12 on: December 15, 2017, 08:14:24 pm »
5.5/2.1mm with (+) in the middle is by far the most common.

Something like this is useful to have on hand:
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F232022657600
 

Offline Macbeth

  • Super Contributor
  • ***
  • Posts: 2571
  • Country: gb
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #13 on: December 15, 2017, 10:23:03 pm »
center negative
Never in my life have I seen a barrel plug DC supply with negative on the center
You haven't lived! Just recently I found a modernish Dymo label printer with its own custom wallwart running that same scam.

But it appears there is a good reason behind '80s battery products with external power after all...

 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #14 on: December 15, 2017, 11:53:40 pm »
Maybe I'm a bit tired but wouldn't the same thing work with center positive? You'd just disconnect the negative battery wire instead of the positive wire when external power is supplied. The battery is an isolated source anyway so that wouldn't make any difference.
 

Offline Macbeth

  • Super Contributor
  • ***
  • Posts: 2571
  • Country: gb
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #15 on: December 16, 2017, 12:02:20 am »
Maybe I'm a bit tired but wouldn't the same thing work with center positive? You'd just disconnect the negative battery wire instead of the positive wire when external power is supplied. The battery is an isolated source anyway so that wouldn't make any difference.

Because the DC jack socket doesn't have a SPDT switch to the centre, it does have one to the outside barrel - for obvious mechanical reasons. Think about it. @3:33
« Last Edit: December 16, 2017, 12:06:58 am by Macbeth »
 

Offline james_s

  • Super Contributor
  • ***
  • Posts: 21611
  • Country: us
Re: Is there a standard (or common) spec on DC power jacks?
« Reply #16 on: December 16, 2017, 01:08:40 am »
Because the DC jack socket doesn't have a SPDT switch to the centre, it does have one to the outside barrel - for obvious mechanical reasons. Think about it. @3:33

Sure but what difference does it make? Tie both the battery positive and the device positive to the center pin, when you plug in the external adapter the negative side of the battery is disconnected and negative is supplied by the external adapter instead. Sure convention is to switch the positive side but what difference does it make? The electrons don't care, old cars had positive ground systems, aside from convention it doesn't really matter.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf