Can a 12 VDC barrel jack/socket (female) that receives power (inlet) also be used to provide power (outlet)?

Question

EE Experience: apprentice

Application:

There are two devices: Main device #1 contains a 12V DC (2.1A) pump powered by an AC 100/240V to DC 12V (10A) main power supply; secondary device #2 contains a 5V DC (2.1A) LED strip and a 12V DC to 5V DC buck converter. Device #1 will provide power to device #2 via an 8" detachable 2 conductor 20 AWG cable with tinned copper strands.

Question: What is the best (most practical) way to do this?

My first thought is to use an 8" male to male cable.

And use two female panel mount DC connectors.

Note: those Digikey connectors are listed under "power connectors" which leads me to believe that they can be used either as a powered (provide power) or a non-powered (receive power) connector in contrast to typical usage whereby the female jack/socket is almost always used in a device to receive power via it's corresponding male plug.

As I'm looking at both the standard DC male barrel plug and female barrel jack/socket, it looks like a human finger has about the same chance of touching the positive center pin (in my case) on either the male or female DC barrel plug which leads a novice such as myself to believe that I can use the female jack/socket to provide power.

IMPORATNT UPDATE! I spoke with Digikey tech support. They said in contrast to popular belief, a DC barrel jack/socket can in fact be used to provide power in contrast to its typical usage to receive power; the reason we see devices using the barrel jack/socket to receive power is for design preference because the female barrel jack/socket is flush with the surface of the device in contrast to the male barrel jack plug.

Answer 1

I'm confused by your question. What do you mean by "without power" in one instance and then "with power" in another? (Do you mean "providing" and "receiving" power?)

You say you have a "12 VDC panel mount outlet": from what? Do you have a power supply with a female DC jack for output? Although unusual, that configuration is often found in, for example, guitar pedal power supplies where a male-to-male plug cable is used to connect between the supply and the pedal. (Those are typically 9 V DC.)

Later on, you mention two things that I think need clarification:

• The chance of touching the positive center pin with a finger
• That female connectors are typically used as 'non-powered' connectors

Both of these statements betray some possible misconceptions.

Barrel jack usage

Barrel jacks are frequently used as DC power connectors, so much so that they are often called "DC barrel jacks." There's no rules or standards that dictate what these connectors can be used for, so you might encounter one that is used for data or something else, but it would be somewhat unusual.

Generally speaking, power supplies (wall warts, desktop adapters, etc.) have male plugs while devices have female jacks. But as I mentioned earlier, that certainly is not a standard.

When repairing or replacing existing supplies/connectors, you have to be diligent and consider polarity, voltage, pin and outer diameter, etc. (More details here.) If you are designing from scratch, the voltage, polarity, and diameter of these connectors are completely up to you.

Low voltage/safety

Although DC barrel jacks are designed so that the middle pin is tucked away "safely" this is by no means primarily a safety consideration. In many cases it is merely a convenience for aligning the connector, or to connect ground before positive. (Though since opposite polarity is a thing, that's not necessarily a reason.)

With voltages under ~48 V you needn't worry much about the possibility of touching the positive pin.* If this consideration is driving some of your design choices, you may want to move it to the "don't worry about it" column.

Practicality

Without knowing more about your power supply, it's difficult to say what the most practical way of connecting your LED strip is. Based on your question, you mention adding a buck converter to achieve 5 V. That suggests to me the most practical way might be to change the power supply altogether, and get one that supplies 5 V with a male plug of the correct size and polarity.

Failing that, a male-to-male cable should work just fine. Just ensure that everything can support the current draw of the LED strip (supply, wires, connectors, and buck converter).

_{*These low voltages are at little risk of giving you an electric shock, but if you try hard enough you can make anything dangerous.}

Answer 2

Sure you can use but if you think it why it might be a bad idea you don't really want to.

Because most power producing devices already have plugs and power consuming devices have sockets, that's the current de facto usage and infrastructure you live in.

If you do make a socket as an outlet, it allows you to make incorrect connections and damage something.

If you connect the power supply to your inlet because the connectors are near each other, will it damage something? If you accidentally plug in incorrect plug and you parallel two power supplies, will they damage?

Also there are not that many cables wth DC plugs on both ends that you can buy. That's because usually you don't have the need to connect two devices together from their sockets.

It isn't that mind-boggling at all. And we have many questions if it is a good idea to use standard connector X for custom purpose Y, and most of the time it isn't.

You can use any connector in any way you want, there is no rule or law against it, except common sense to limit use to the de facto usage.

If you use the DC jack to provide power, it allows accidentally damaging something.

Much like you decided it is a good idea to transfer mains power to a bike shed with a cable that has mains plugs on both ends.

Same goes for using USB connectors for non-USB usage. Not a good idea. You or someone else will damage a standard USB device like PC or mobile phone if accidentally plugged in, just because a matching cable looks to be free to use for charging.

There are already too many different and incompatible uses for connectors like 8P8C modular jacks (some people call them RJ45), XLR connectors, TRS plugs and jacks, DIN connectors, D-Sub connectors etc. You can't expect devices to work or even survive without damage when plugged in, even if they have matching connectors.

There are many standards that have mandated which connector to use and how. Some standards (like DMX512, AES/EBU, MIDI, RS-232) have defined to use existing connectors used also for other purposes. Some standards define their own connector (USB, HDMI, DisplayPort) that have not been previously used for any purposes, which guarantees they are used by engineers as per the standard, and there is the assumption it is not used incorrectly to incompatible non-standard purposes.

Some receptacles like HDMI and DisplayPort are identical on monitors and PCs, and the assumption is, you will use a cable with identical plugs on both ends to connect a monitor to a PC, as you would know from the context that it makes no sense to connect two monitors or two PCs together even if the connectors allow it, and the interfaces are designed to not damage if accidentally connected incorrectly.

With USB Type-A and Type-B, standard mandates what kind of connectors are used on hosts and devices, and what kind of cables are defined to be used between them. So as hosts have Type-A sockets and devices have Type-B sockets, you know you only need cables with Type-A plug and Type-B plugs, and it alone prevents from making invalid connections that do damage, as you have no cables to connect two hosts or two devices together.

USB Type-C is different. All your devices have same receptacle, much like HDMI or DisplayPort. Cables can have same Type-C plug on both ends. The standard requires that even before power or data wires are activated on the receptacle, the devices must negotiate their power and data role. For example you can plug in two laptops together, but likely it makes no sense during the negotiation process and nothing happens. Some laptops may allow to start charging the other laptop. But any invalid combination or unsupported role on a device will just do nothing.

That does not apply to your DC plug. 99.99% of the devices are built with the assumption plugs provide power into a receptacle, and cables with plugs on both ends are not needed for that reason.

DC plugs are already a hazard as same plug and receptacle is used for different incompatible voltages and currents. It's already a pain to make sure you are not plugging in a 12V supply into a 5V device, or 12V supply into a 12V device which expects different DC polarity.

So while you can use a receptacle to output power, nobody expects it, and there is no existing infrastructure to support that, such as cables with DC plugs on both ends.

Answer 3

In general, electrical power connectors are designated as 'male' and 'female'.

The terms 'plug' and 'socket' are also used instead of 'male' and 'female' respectively.

The female connector or socket is a receptacle that receives and holds the male plug.

Here's a barrel plug on a cable that plugs into the PCB-mounted barrel socket, shown alongside,

or into the barrel socket on a cable, shown below.

It is standard practice to have the barrel plug feed power from the source to the barrel socket on the device.

This ensures safety and proper functionality and prevents unsafe or non-functional configurations that could result in interconnection of two power sources or two devices.

Image Credits:

Emerging Technologies
Quartz Components