Measuring barrel connectors

First off, I know these are called "barrel connectors" but also go under other names. So, I am referring to these:

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and these
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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

Reply to
jw
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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 connection. Then, order .

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.

Reply to
Don Y

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.

George H.

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Reply to
George Herold

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.

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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.

I keep a selection of the connectors for this purpose.

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

Reply to
krw

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".

Reply to
Don Y

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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.

George H.

Reply to
George Herold

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!]
Reply to
Don Y

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.

Reply to
mike

prettty

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

?-)

Reply to
josephkk

To measure a center hole, it would be useful to have a set of drill bits or gage wires that can be fished into position, then you just have to know how much force is 'normal fit' for the contact. To measure a center pin, however (if you have only one sex of the connector in question) my best approach is to press a bit of form-fitting material (Handi-Tak is available at Big Lots...) into the pin, then pull it off and examine under a good magnifier with a fine ruler, or with a measuring microscope. If, that is, you HAVE a measuring microscope (really just a calibrated translation stage, and microscope with crosshairs reticle eyepiece).

The press-in-then-measure trick also gives the diameter of the surrounding aperture around that center pin, which has to allow the socket's insulator to pass.

The trouble I have, is that matching the connector dimensions doesn't always work with short-form catalog data, you really need the full engineering drawing of the connector. So, I usually rummage for a matching connector on a wallwart I don't use, and lop it off, leaving enough of a pigtail of wire for a good splice.

Reply to
whit3rd

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