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Author Topic: Cigarette lighter adapter to M plug polarity?  (Read 4685 times)
K7JG
Member

Posts: 40




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« on: February 12, 2013, 08:32:38 PM »

Are cigarette lighter adapters and M plugs usually wired center pin to center pin and barrel to barrel to deliver 12V DC or is the polarity reversed by convention?

Thanks and 73,
John K7JG
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KB5ZSM
Member

Posts: 70




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« Reply #1 on: February 12, 2013, 10:32:25 PM »

Hey John,
         In the 45 years of electronics work I've done, I've never heard of an 'M' connector and I doubt most of us here have ever heard of one either. If you could give a better description of this connector, I'm sure we could help you.
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KB5ZSM
Member

Posts: 70




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« Reply #2 on: February 12, 2013, 11:13:44 PM »

I can't help but wonder if your talking about a D.C. power connector used allot on wall warts (those ugly little transformers you plug in to the wall) that looks like a small barrel with a hole in the end. If so, there is no standard. The center (hole) could be either positive or negative in respect to the barrel. The most common is positive but not always the case. Usually the device that you plug it in to will have a marking near it that will indicate the polarity or it may tell you in the booklet that came with the item your powering. If your device came with a wall wart, look at the wall wart as it should be marked on it (in most cases anyway). Also make sure the device can handle the 13.8 volts you will be supplying to it.
I'm sure these connectors have a proper name but I haven't seen it. I have seen them referred to as: DC power connectors or Barrel connectors and they come in may sizes.
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K7JG
Member

Posts: 40




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« Reply #3 on: February 13, 2013, 02:46:08 AM »

Yes, that is what I was referring to. The local Radio Shack personnel referred to it as an M plug and their equivalent part is labelled "Size M: Coaxial DC Power Plug."

When I connect a manufactured plug with wire already on it, provided by the manufacturer of the device I'm trying to power up, to an Enercell "Car Power Adapter", lined wire to lined wire, the outside barrel of the small plug is connected to the center pin of the adapter and the device doesn't power up. If I reverse the wires, it does. According to the manufacturer, the device has a reversed polarity protection diode but they neglected to indicate the polarity it requires.

Thanks and 73,
John K7JG


 
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AA4HA
Member

Posts: 1481




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« Reply #4 on: February 13, 2013, 05:01:35 AM »

Yea, Rat-Shack trying to make a barrel plug connector into some special sizing.

What they call "size M" is one of the most common barrel connector dimensions for DC power apps.

Tip size: 5.5mm O.D. x 2.1mm I.D.

There is a larger barrel connector that Radio Shack calls "size N" that has a fatter center pin;

Tip size: 5.5mm O.D. x 2.5mm I.D.

And there are bunch more with a smaller body and smaller center pin. That goes all the way down to things that are practically microscopic.

Polarity (DC) seems to be non-standard but manufacturers that do not go positive-center-pin should be beaten with sticks. Also you have manufacturers who will put AC on there and it all comes in a variety of voltages.

Most everything I have is positive center pin except for a few portable SW receivers. Getting tired of forgetting what supply to use on those I put in a tiny bridge rectifier inside of the portable and now it does not matter if I use a positive or negative center pin supply on those devices. They work just fine as the bridge rectifier takes care of the transition.
« Last Edit: February 13, 2013, 06:00:11 AM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
NR4C
Member

Posts: 308




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« Reply #5 on: February 15, 2013, 06:55:34 AM »

If you're t rying to connect your radio to the Cigar lighter, save yourself a lot of heartache, and just DON'T.  The power is often not very clean, and may be fused a lot lower than you want.  Save time, get a proper power cable run from the battery, fuse it properly and use it.

...bill   nr4c
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W0FM
Member

Posts: 2056




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« Reply #6 on: February 15, 2013, 12:32:36 PM »

Most manufacturers of the DC connector that you are referring to call them "coaxial" connectors.  As they connect "coaxially".  More people will recognize what you are referring to if you use that term.

73,

Terry, WØFM
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WA3SKN
Member

Posts: 5493




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« Reply #7 on: February 19, 2013, 12:21:21 PM »

There is no "standard" for those small power connectors... they are used for AC and for both DC polarities and various voltages.  I have never heard them referred to as M connectors.  However, the male PL259 (as we know it) is referred to as a M connector over in Japan. So you can see the possible confusion to your reference.
73s.

-Mike.
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N6AJR
Member

Posts: 9910




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« Reply #8 on: February 20, 2013, 09:08:45 AM »

buy a cheepo  multi meter  so you can check  the output for pos or neg center and continuity chaek  for which pin goes where.  those rat shack connector can revers power polairty by turning the connector over.  and buy the way almost any movement will cause the connector to loosen.  you can buy a nice little yellow  multimeter form hi serria for like 5 or 6 bucks.

http://www.hamcq.com/
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