Barrel plug (electrical power) conventions?

[Sam Kaan]

You know those little barrel plug that normally comes with the electrical
wall adapter to power your cell phone
embedded computers etc? 5V, 9V, 12V etc.

Is there a convention as far as their polarities are concerned? I have a
board that I need to power using these
plugs. The board takes 5V to be supplied via a barrel plug connector. I
am unable to find the documentation
as to what polarity the plug should be wired up. Whether the outer barrel
is to be made negative while the inner
is positive and vice versa. I took a look at several Walmart adapter and
the likes, and notice that it doesn't follows
a set pattern, sometimes its one way and sometimes its the other way.

By the way, when you pick up an adapter/transform how can you tell if its
regulated or not? Does "For Indoor Use Only"
or "Class 2 Transformer" means anything in particular?

 

[Michael A. Terrell]

You know those little barrel plug that normally comes with the electrical
wall adapter to power your cell phone
embedded computers etc? 5V, 9V, 12V etc.

Is there a convention as far as their polarities are concerned? I have a
board that I need to power using these
plugs. The board takes 5V to be supplied via a barrel plug connector. I
am unable to find the documentation
as to what polarity the plug should be wired up. Whether the outer barrel
is to be made negative while the inner
is positive and vice versa. I took a look at several Walmart adapter and
the likes, and notice that it doesn't follows
a set pattern, sometimes its one way and sometimes its the other way.

Manufactures use whatever they want for those Coaxial power plugs. No
rhyme or reason. You need to determine which side is grounded to the
circuit before connecting the AC adapter. You may have to open the item,
but there may be a grounded connector for an earphone, antenna, or
similar that you can check with an ohm meter to find which part goes to
ground.

By the way, when you pick up an adapter/transform how can you tell if its
regulated or not?

Does it measure the rated voltage with no load? If it does, its
regulated.

Does "For Indoor Use Only"

This is rather obvious, isn't it? You can't use it outdoors where
rain can get into it, or across the AC power pins.

or "Class 2 Transformer" means anything in particular?

24 VAC or less, or less, and current limited to prevent a fire if
the output is shorted.


--
Merry Christmas!

Take care, and God bless.
Michael A. Terrell
Central Florida

 

[Sam Kaan]

Manufactures use whatever they want for those Coaxial power plugs. No
rhyme or reason. You need to determine which side is grounded to the
circuit before connecting the AC adapter. You may have to open the item,
but there may be a grounded connector for an earphone, antenna, or
similar that you can check with an ohm meter to find which part goes to
ground.




Does it measure the rated voltage with no load? If it does, its
regulated.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I see. So I just put my multimeter to such an adapter to my surprise it
measured
19V. While the adapter has labeled clearly on it 12V. So this is not
regulated right??

I supposed the regulated adapter would keep a constant 12V as the circuit
draws
various current loads from it.

 

[James Meyer]

Manufactures use whatever they want for those Coaxial power plugs. No
rhyme or reason.

Well, actually there is a *little* rhyme and reason.

Many coaxial plug sockets have three terminals. There's a connection to
the inner, one to the outer, and a third that forms a switch with (usually) the
outer connection. It's often a convenience when a device is to be powered from
either internal batteries or a wall plug to have the act of inserting the plug
automatically disconnect the batteries and let the wall power take over. The
third contact is used and then that determines whether the outer or inner
contact is one polarity or the other.

Jim

 

[Michael A. Terrell]

I see. So I just put my multimeter to such an adapter to my surprise it
measured
19V. While the adapter has labeled clearly on it 12V. So this is not
regulated right??

I supposed the regulated adapter would keep a constant 12V as the circuit
draws
various current loads from it.

Yes, that's what regulated means.

--
Merry Christmas!

Take care, and God bless.
Michael A. Terrell
Central Florida

 

[Michael A. Terrell]

Well, actually there is a *little* rhyme and reason.

Many coaxial plug sockets have three terminals. There's a connection to
the inner, one to the outer, and a third that forms a switch with (usually) the
outer connection. It's often a convenience when a device is to be powered from
either internal batteries or a wall plug to have the act of inserting the plug
automatically disconnect the batteries and let the wall power take over. The
third contact is used and then that determines whether the outer or inner
contact is one polarity or the other.

Jim

Jim, I agree it should make a difference, but I see quite a few
center negative connectors with a switch, and they use it to disconnect
the battery's ground to take it out of the circuit. It makes no logical
sense, and I think that is why its done. Anything to help obscure the
design, and to cause you to damage it when you plug in the more common
center positive power supplies. Walk into most places that sell
replacement wall warts. They want to start plugging in an adapter with
no idea of polarity. After all, if it doesn't work, they will try to
sell you another piece of junk.


--
Merry Christmas!

Take care, and God bless.
Michael A. Terrell
Central Florida

 

[Rich Grise]

If you have the luxury of selecting your own connector, pick one
that the outside is negative, if your circuit is "negarive ground."
If you have the further luxury of being able to add a regulator
to your device, then do that, and spec about a 9V wart.

Good Luck!
Rich

 

[Leon Heller]

You know those little barrel plug that normally comes with the electrical
wall adapter to power your cell phone
embedded computers etc? 5V, 9V, 12V etc.

Is there a convention as far as their polarities are concerned? I have a
board that I need to power using these
plugs. The board takes 5V to be supplied via a barrel plug connector. I
am unable to find the documentation
as to what polarity the plug should be wired up. Whether the outer barrel
is to be made negative while the inner
is positive and vice versa. I took a look at several Walmart adapter and
the likes, and notice that it doesn't follows
a set pattern, sometimes its one way and sometimes its the other way.

I always use a series diode on any equipment using this type of PS.

Leon

 

[John Woodgate]

I read in sci.electronics.design that Sam Kaan
bloor.is.net.cable.rogers.com>) about 'Barrel plug (electrical power)
conventions?', on Fri, 26 Dec 2003:

You know those little barrel plug that normally comes with the electrical
wall adapter to power your cell phone
embedded computers etc? 5V, 9V, 12V etc.

Is there a convention as far as their polarities are concerned?

There is supposed to be: the centre pin should be positive. This is in
an IEC standard for 'assessed quality' versions of the connector, which
are mostly dimensionally incompatible with the ones widely used.

But in the past, some manufacturers have used the opposite polarity. The
best thing to do is to put a diagram on the product, showing which
polarity it needs, AND put a protection diode in there to guard against
reversed polarity.

The diagram looks a but like this:
- +
-------Co------

The 'o' should be inside the 'C'.

 

[John Woodgate]

I read in sci.electronics.design that James Meyer <[email protected]>

Many coaxial plug sockets have three terminals. There's a connection to
the inner, one to the outer, and a third that forms a switch with (usually) the
outer connection. It's often a convenience when a device is to be powered from
either internal batteries or a wall plug to have the act of inserting the plug
automatically disconnect the batteries and let the wall power take over. The
third contact is used and then that determines whether the outer or inner
contact is one polarity or the other.

Not really: you can put the switch in either battery lead.

Keep the pin positive!

 

[Tim Shoppa]

You know those little barrel plug that normally comes with the electrical
wall adapter to power your cell phone
embedded computers etc? 5V, 9V, 12V etc.

Is there a convention as far as their polarities are concerned?

Even better than a convention, there are two conventions!

(I'm ignoring those AC-out-on-coaxial-plug adapters here, as they comply
with both of the above conventions, 60 times every second.)

The wonderful thing about standards is there are so many to choose from!

Tim.

 

[Tim Shoppa]

Jim, I agree it should make a difference, but I see quite a few
center negative connectors with a switch, and they use it to disconnect
the battery's ground to take it out of the circuit. It makes no logical
sense

Are you implying that it makes more sense to switch (+) as opposed to (-)?

I will admit that I always put a bridge rectifier after my DC power jacks.
(Put a filter capacitor there too and you can run the devices off of AC-out
adapters!)

Tim.

 

[N. Thornton]

I read in sci.electronics.design that Sam Kaan
bloor.is.net.cable.rogers.com>) about 'Barrel plug (electrical power)
conventions?', on Fri, 26 Dec 2003:

There is supposed to be: the centre pin should be positive. This is in
an IEC standard for 'assessed quality' versions of the connector, which
are mostly dimensionally incompatible with the ones widely used.

But in the past, some manufacturers have used the opposite polarity. The
best thing to do is to put a diagram on the product, showing which
polarity it needs, AND put a protection diode in there to guard against
reversed polarity.

The diagram looks a but like this:
- +
-------Co------

The 'o' should be inside the 'C'.

Even better is to use a full wave rectifier in your product, then you
can plug any of the 3 types of PSU in, centre -ve, centre +ve, or ac.


Regards, NT

 

[James Meyer]

Jim, I agree it should make a difference, but I see quite a few
center negative connectors with a switch, and they use it to disconnect
the battery's ground to take it out of the circuit. It makes no logical
sense, and I think that is why its done. Anything to help obscure the
design, and to cause you to damage it when you plug in the more common
center positive power supplies. Walk into most places that sell
replacement wall warts. They want to start plugging in an adapter with
no idea of polarity. After all, if it doesn't work, they will try to
sell you another piece of junk.

I've seen very few (no?) commercially produced devices that didn't
include a little picture, sometimes embossed into the case, that showed whether
the center pin is either plus or minus. It's a case of RTFM.

Jim

 

[James Meyer]

Are you implying that it makes more sense to switch (+) as opposed to (-)?

I will admit that I always put a bridge rectifier after my DC power jacks.
(Put a filter capacitor there too and you can run the devices off of AC-out
adapters!)

Tim.

A good idea if you don't mind losing 1.4 volts of input.

Jim

 

[Michael A. Terrell]

I've seen very few (no?) commercially produced devices that didn't
include a little picture, sometimes embossed into the case, that showed whether
the center pin is either plus or minus. It's a case of RTFM.

Jim

I do see items with no markings, or they had a sticker that dried out
and fell off. RTFM? Most things I see have no manuals. Last year I
scrapped over 30 junk cordless phones and only a couple were properly
marked. Some didn't even tell you what voltage, just the usual cryptic
warning to only use the proper power supply.

I do keep the manuals for anything I buy new.

I strip junk electronics for hardware and a few parts. There is a
local program in Ocala to teach people to solder so they can get low
paid assembly work. They use scrap boards in the class. Then, the boards
are sent to a refinery where the boards are burnt so the metals can be
recovered. If I could just find a place to take all the scrap plastic
cases there would be nothing left over for the landfill.
--
Merry Christmas!

Take care, and God bless.
Michael A. Terrell
Central Florida