Measuring barrel connectors

[[email protected]]

First off, I know these are called "barrel connectors" but also go
under other names. So, I am referring to these:
http://www.surplustraders.net/a/mg584.gif
and these
http://media.digikey.com/Photos/Switchcraft Photos/S761KS17.JPG
They are often found on wall wart transformers. It seems they make
hundreds of sized of them. They are listed in metric sizes such as
5.5mm 25mm 72mm, etc.

Great, I suppose I could use a micrometer to measure the outside of
the connector, but what about the thickness of the center terminal
that goes in the hole on the connector. How do you measure them?
Worse yet, how do you measure the inside of the hole on the rear of a
device that needs one of these connectors? (such as on the rear of a
radio that needs a wall wart)?

Over the years, I have used the trial and error method. Take the
device to the store and begin plugging them in until one of them fits.
But these days, if I go to Radio Shack for example, they are all
packaged in sealed plastic and the store manager wont just let me open
all the packages. Worse yet, trying to order them online....

Is there any system or method to this madness of sizes? I was told
that they are sized according to voltage of the wart on the other end
of the cord. It does appear that the higher voltages have thicker and
larger connectors, but I have seen variances in the sizes for the same
voltage, such as 6 volt ones that may be 5.5mm or 8mm, or ?????
Sometimes the outer part will fit, but not the pin in the center.
More than once I have drilled out the center holes to make them fit.

This all seems like a jungle of chaos. Is there any way to easily
measure and determine what is needed (for both the male and the female
parts).

Thanks

 

[Don Y]

Great, I suppose I could use a micrometer to measure the outside of
the connector, but what about the thickness of the center terminal
that goes in the hole on the connector. How do you measure them?
Worse yet, how do you measure the inside of the hole on the rear of a
device that needs one of these connectors? (such as on the rear of a
radio that needs a wall wart)?

To measure the ID, a drill index comes in handy.

Personally, I took one of those "universal" power adapters
(i.e., the kind with a slew of interchangeable "plugs")
and use these to quickly identify the mate for a particular

Is there any system or method to this madness of sizes? I was told
that they are sized according to voltage of the wart on the other end
of the cord. It does appear that the higher voltages have thicker and
larger connectors, but I have seen variances in the sizes for the same
voltage, such as 6 volt ones that may be 5.5mm or 8mm, or ?????
Sometimes the outer part will fit, but not the pin in the center.
More than once I have drilled out the center holes to make them fit.

Some manufacturers try to color code the tips. But, this isn't
consistent. You will also notice that some devices require
*longer* barrels than what might otherwise be "typical".

My pet peeve is the crappy scheme adopted to identify the polarity
of the power. The tiny print is difficult to read and ink bleed
often makes the diagram of outer and inner conductors "--(O--"
difficult to read. I mark each wall wart/brick and device using
same with a circled '+' or '-' as I find them easier to read.

 

[[email protected]]

First off, I know these are called "barrel connectors" but also go
under other names. So, I am referring to these:
http://www.surplustraders.net/a/mg584.gif
and these
http://media.digikey.com/Photos/Switchcraft Photos/S761KS17.JPG
They are often found on wall wart transformers. It seems they make
hundreds of sized of them. They are listed in metric sizes such as
5.5mm 25mm 72mm, etc.

25mm? 72mm? I haven't seen one that's an inch around. Three?

The "standard size" is 5.5mm with a 1.27, 2.0mm, 2.1mm, or 2.5mm center post.
There is also a waterproof type that's a whole nuther kettle and completely
incompatible with the "standard" connectors. The best bet is to look them up
in the SwitchCraft catalog (online). Be careful, the numbering scheme is
crazy.

http://www.switchcraft.com/productsummary.aspx?Parent=479

Great, I suppose I could use a micrometer to measure the outside of
the connector, but what about the thickness of the center terminal
that goes in the hole on the connector. How do you measure them?
Worse yet, how do you measure the inside of the hole on the rear of a
device that needs one of these connectors? (such as on the rear of a
radio that needs a wall wart)?

Use calipers to measure the center hole. You can get close enough to identify
the model pretty easily. The length is a real problem, though. Having sample
mating connectors is the only way I've been able to keep these straight.

Over the years, I have used the trial and error method. Take the
device to the store and begin plugging them in until one of them fits.
But these days, if I go to Radio Shack for example, they are all
packaged in sealed plastic and the store manager wont just let me open
all the packages. Worse yet, trying to order them online....

Is there any system or method to this madness of sizes? I was told
that they are sized according to voltage of the wart on the other end
of the cord. It does appear that the higher voltages have thicker and
larger connectors, but I have seen variances in the sizes for the same
voltage, such as 6 volt ones that may be 5.5mm or 8mm, or ?????
Sometimes the outer part will fit, but not the pin in the center.
More than once I have drilled out the center holes to make them fit.

I keep a selection of the connectors for this purpose.

This all seems like a jungle of chaos. Is there any way to easily
measure and determine what is needed (for both the male and the female
parts).

It is. It's particularly frustrating matching the lengths from a catalog.

 

[Don Y]

Hi George,

Or just use a set of number drills (sets with #'s 1 to 60 are prettty
standard) get 'em cheap at harbour frieght perhaps. Stick 'em in
till you've bracketed the size... that should be close enough.

That was my point! Drill index conveniently labels the bits
(so you don't have to then mic' the actual stock) -- assuming you
keep yours in order ;-)

Use the non-business end of the bit, though. And recall that
the entry to the connector is often beveled. So, you want to
insert the bit until you are sure you are in the body of the
connector and not hung up on that "lip".

 

[Don Y]

Hi George,

Oh sorry Don, I thought the 'Drill index' was that flat piece of
steel I have with all the # size holes in it. Used to get the drill
back in the correct order.

Hmmm... I don't know what that's called. But, the little metal
box that holds my bits (in individually sized, LABELED "slots")
has "Drill Index" embossed on the front cover. :> (mine is
over 50 years old so I have no idea what the common practice is).

The problem with this approach is that you have to be extra
diligent to keep the bits in the right "slots". Otherwise,
the labeling on those slots is useless. (and, at the small
end of the index, the differences between bits are just too
hard to sort out casually)

[Note that the "card" you mentioned would be ideal for determining
the OD of the connectors!]

 

[mike]

First off, I know these are called "barrel connectors" but also go
under other names. So, I am referring to these:
http://www.surplustraders.net/a/mg584.gif
and these
http://media.digikey.com/Photos/Switchcraft Photos/S761KS17.JPG
They are often found on wall wart transformers. It seems they make
hundreds of sized of them. They are listed in metric sizes such as
5.5mm 25mm 72mm, etc.

Great, I suppose I could use a micrometer to measure the outside of
the connector, but what about the thickness of the center terminal
that goes in the hole on the connector. How do you measure them?
Worse yet, how do you measure the inside of the hole on the rear of a
device that needs one of these connectors? (such as on the rear of a
radio that needs a wall wart)?

Drill bits should get you close.
"Feeler gauges" like you used to set the points on your '55 Ford
come in round versions.
You can also make what you need from chunks of solid wire.
Go to the hobby store and buy some brass tubing. Calibrate the
inside diameter using your drill bits or feeler gauges.
Ditto for the outside diameter. You can also buy piano wire
in various sizes for the pin gauges.

You have to be a little careful about getting the outside connector diameter
too big. That won't let the plug offset in the hole far enough
to make reliable contact with the socket's inner pin...especially
when you can't buy exactly what you want and have to settle for a larger
inside hole. The opposite problem happens when the outside diameter is too
small to reliably disconnect whatever gets disconnected when you plug in
the charger.

Brass tubing comes in sizes that are a nice sliding fit from
tiny to large. Having a bunch of different sizes on hand comes
in handy for fixing stuff. Ditto for piano wire.

 

[josephkk]

Hi George,

Oh sorry Don, I thought the 'Drill index' was that flat piece of
steel I have with all the # size holes in it. Used to get the drill
back in the correct order.

Hmmm... I don't know what that's called. But, the little metal
box that holds my bits (in individually sized, LABELED "slots")
has "Drill Index" embossed on the front cover. :> (mine is
over 50 years old so I have no idea what the common practice is).

The problem with this approach is that you have to be extra
diligent to keep the bits in the right "slots". Otherwise,
the labeling on those slots is useless. (and, at the small
end of the index, the differences between bits are just too
hard to sort out casually)

[Note that the "card" you mentioned would be ideal for determining
the OD of the connectors!]

The little ('bout 2" by 3" to 3" by 4") steel plate ('bout 0.040 thick) is
called a "drill gauge".

?-)