DC connector standards / best practices - Page 1
Forum section: electronics / projects

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 10, 2014, 06:12:59 pm
content: DC connectors are a pretty insane world. The arbitrary DIN connectors of old electronic devices have been supplanted by arbitrary coaxial connectors, sometimes vaguely standardized, sometimes completely random...USB power is a great development for 5V... I'm wondering, what do you guys consider good practice for cases where you need 12V, 24V, or current levels higher than the USB standard allows. If you go with barrel connectors, is there a clear preference in barrel connector sizes? There are so many different kinds out there.The EIAJ standard seems relatively strict, and semi-widely adopted, but for example Mouser doesn't have any sockets for EIAJ-4 (3.3x5.5) even listed, let alone stocked.

author: Falcon69
author_rank: Super Contributor
timestamp: December 10, 2014, 07:31:08 pm
content: I really dislike barrel connectors for one reason.one day:I had my laptop, and an external harddrive.Unfortunately, both power connectors had the same size barrel for input. My laptop is 19volts, the external harddrive was 5volts. I did not realize I had accidentally hooked up the laptop power supply to the external harddrive, and the external harddrive power to the laptop. When I switched them on, the Laptop did not turn on (not enough voltage) and the external drive had magic smoke. I fried the protection Diode in the external harddrive, luckily, fixing it, saved the harddrive and no information was lost.The standard size for a barrel connector that most manufactures use is 5.5mm outer, 2.5mm inner (or sometimes 2.1mm), because of this, mistakes like the one mentioned above occur.I still use barrel jacks, because they are a quick connection, however, if I am selling or designing multiple projects that are used together in the same lab or household, I'll use a different size barrel connector for each unit. That way, they can't be plugged into each other, possibly destroying them.

author: ajb
author_rank: Super Contributor
timestamp: December 10, 2014, 08:57:05 pm
content: The other problem with barrel jacks is that many combinations of plug and jack are close enough to sometimes sort-of intermate, leading to intermittent connections.I just had a call today with an onsite tech working on some of our equipment that uses an external plug pack. One unit wasn't working because it had a plug pack with a not-quote-right connector that was only connecting intermittently, and another wasn't working because the end user had connected a 3V pack instead of the required 5V. Who knows what happened to the plug packs that were supplied originally.We've switched to using a screw-lock barrel connecter on that device, which on top of being more secure to start with should hopefully discourage end users from trying to use whatever plug pack they having lying around that happens to look about right. Fortunately it's the only thing we sell that has a low voltage input, everything else has mains input via IEC or PowerCON.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 11, 2014, 02:39:00 am
content: Tell me about it. I have already killed two cheap Chinese power packs by overloading them... Once there was the WIFI router, with a 12V/2A pack, and the cable modem, with a 12V/0.5A pack. Well, plugged in in reverse. Nothing bad happened to the router or the modem thankfully, but the .5A power pack got fried.(And, to make matters even more dangerous, Arduinos and Beaglebones use the 5.5/2.5mm barrel plug... for 5V! That's just a recipe for disaster.)Anyway, it's quite clear that barrel plugs are horrible, but is there an alternative? USB power covers only a rather narrow slice of all the various use-cases, and while there is protocol extension for higher voltages and currents, those require negotiation (obviously), to avoid frying unprepared devices.

author: Falcon69
author_rank: Super Contributor
timestamp: December 11, 2014, 02:56:27 am
content: You could do something completely different, and use a DIN connector instead. My new external Harddrive cases have them. No more problems accidentally plugging in the laptop power supply.Here's one for example.http://www.ebay.com/itm/5pc-Mini-DIN-Jack-Connector-Socket-Female-3pin-3P-PCB-pin-KMD11-3-2008-3-/130413516909?pt=LH_DefaultDomain_0&hash=item1e5d40586d

author: SL4P
author_rank: Super Contributor
timestamp: December 11, 2014, 03:10:17 am
content: Yes.We've had a previous discussion on the 'merits' ofDeutsche Industrie Normconnectors.Very happy they all but disappeared in the late 80sFar too many reason they should never come back!

author: Someone
author_rank: Super Contributor
timestamp: December 11, 2014, 04:08:38 am
content: Quote from: Sigmoid on December 11, 2014, 02:39:00 amThere is nothing available thats as cost effective as the barrels, unless you are apple and can order millions of your new connector. Its a catch 22, you want something cheap (which is produced in huge quantities to make it cheap) but you want something unique.Rugged equipment will abuse various XLR variants, or Lemo connectors. Even then you still protect against reverse polarity and over voltage to 48V or more.

author: SL4P
author_rank: Super Contributor
timestamp: December 11, 2014, 04:40:55 am
content: This thread raises an interesting product possibility.A low-cost, keyed / multi-pole connector series that is small, robust and suitable for production or one-off assemblies. Panel or in-line, hermaphrodite style that can be implemented to 'standard' in seconds. Releasable snap-in pins for reconfiguration or repair.Somethinglike USB size/form factor, that is keyed to allow multiple/different signals or voltages on a single 3-8 pin connector body - thatmechanically inhibitsincorrect polarity or voltage connections by configuration at the time of assembly.Alternate mating types (crimp, solder, screw, spade, coax, gold/plated/tinned etc)I know these already exist in the premium 'MOQ 1,000pcs' category - with a price to match...I have a box full with gold mating sets, a bit larger than typical hobbyist project connectors) - great... but not what 90% of prototypes and projects need.Even if they came in a 10-pairs kit, I'm sure a lot of people would rush out to buy sets for their bench. 10 bodies, 10 shells, 20 pins, 20-sockets, etc.. in all variations. $2-$4 a bag, so a typical connector pair comes in at 5 bags = $10 a pair (with plenty of spare pieces leftover). Next pair of connectors may cost $3-$4 and so-on as you use the overlapping parts plus new bags to top-up your bench stock.And they would beindustry definedwith pin-out and pairing standards - e.g. supply on femaie shrouded bodies etc. Long pin-1 mates first...(Sigh - I'm getting excitedat the thought of it! )

author: GreyWoolfe
author_rank: Unknown
timestamp: December 11, 2014, 12:52:11 pm
content: Why not Anderson powerpoles? They come free standing for wire to wire and panel mount. They can be assembled to be electrically correct, clearly show positive(red) and negative(black) with no other color choice and can't be plugged in wrong. They are a little pricey but for one offs or low production and the crimp tool is also a bit pricey but they are a good solution and they can handle high currents-25-35 Amps.

author: SL4P
author_rank: Super Contributor
timestamp: December 11, 2014, 03:39:51 pm
content: Maybe a bit chunky for a handheld device 4-6 pole connector for ground, a couple of voltages @ 1A + signals.http://www.andersonpower.com/products/singlepole-connectors.htmlCertainly nice reliable connectors for fixed devices (not sure about number of insertion cycles)

author: Kjelt
author_rank: Super Contributor
timestamp: December 11, 2014, 04:15:44 pm
content: The DC connectors used in PC's are good for internal connections.I love but rarely use the (expensive) elmo connectors.What I hate from most DC connectors is that they are not lockable, eg they snapp out if you even pull softly on them, so you have a risk of bad contacts if it is half in.I always want lockable connectors for critical applications.So what I do use, esp. with currents over 2Amps are the CA connectors.Made by multiple manufacturers and available with multiple poles to connect AC or DC to 10 Amps. see datasheet as example.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 11, 2014, 05:26:38 pm
content: Those Anderson poles are lovely.That said, some reading did make it clear that weird nonstandard usage is just as widespread as with barrel plugs.According to the Anderson code, 12V is yellow and 24V is red. However, almost ALL HAM clubs use red for 12V. Lol... I'm like, "way to go, guys".

author: German_EE
author_rank: Super Contributor
timestamp: December 11, 2014, 07:36:42 pm
content: 10/10 for the Powerpoles, and if you want to avoid plugging 19V power into a 5V device then rotate one of the Powerpoles by 90 degrees before forming your 19V connector set.