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wanted: DC socket with pigtail, not 5.5x2.x

today we had a customer on the other side of the world plug a 12V supply into a microcontroller that was expecting 5v. bad stuff happened.

We send some equipemnt with a 12V supply and some with a 5V supply. the 12V stuff has screw terminals and we attach a 5.5mmx2.1mm socket pigtail so they can easily test it before installing

Unfortunately the emicrocontroller has a 5.5x2.1mm socket for the 5V supply. the customer plugged the 12V into the microcontrooler and a few seconds later the TVS quit. game over.

we can stick a different plug on the 12V supply, but then I cant find a suitable interface to the screw terminals.

we're using a 12V wall-wart with interchangable DC heads and use hot glue to ensure correct polarity. se we've got

5.5.2.5mm (which is no good as it'll fit the microcontroller badly) 5.5x2.1mm (which fits the microcontroller perfectly: therfore no good), 3.5x1.7mm (commonly used for 5V into usb hubs - probably not a good choice). 5.5x1.7mm, (preferred) 3.5mm phone (acceptable) 2.5mm phone (acceptable)

So, does anyone know where I can get socket pigtails that fit one of the acceptable sizes. 12V, 300mA

preferably MOQ

Reply to
Jasen Betts
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You might want to check out Tyco PolyZens. One of those would have survived fine, and protected the board. Good medicine.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

We're buying the boards off the shelf. I've asked the maker if they can substitute a 3.5x1.35mm DC socket. like USB hubs use.

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umop apisdn
Reply to
Jasen Betts

Can you hot-glue the 12 V wall-wart plug to the pigtail? Or does this risk them damaging the wall-wart plug when they cut it apart to install the 12 V wall-wart in the final system?

I'm not sure about the 5.5x1.7 mm spec. Some places talk about a 5x1.7 and Digi-Key has cables with a 4.75x1.7 mm socket.

If 4.75x1.7 mm works, Digi-Key has 6' for $2.70/1 and $2.10/100, and

3' for $2.78/1 and $2.22/100 . (Yes, the shorter cable is more expensive.)
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Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

Much becomes clear.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

Yup that's what we did... well made our own with a 5.6V zener and poly fuse.

George H.

Reply to
George Herold

Cheap insurance against whatever- that's what I usually do (TVS rather than zener though).

Reply to
Spehro Pefhany

Spehro, What's the advantage of a TVS over a zener? Do you choose it by the minimum break down voltage? One nice feature of the zener is that you get reverse polarity protection for free. The few TVS I looked at on DK, all had forward voltage drops of 3.3V (~5V TVS)

George H.

Reply to
George Herold

The TVS units are rated for extremely high fault currents and built to survive them (or fail short). You can pick a bipolar or a unipolar TVS- the unipolar type may give you reverse protection, but in both cases you have to look at how much voltage can exist with the fault condition present and see what that might do to your circuit. Protection against Vbe breakdown is easy- but a forward biased junction might not survive.

The old backwards MOSFET method works nicely for reverse voltage protection if you protect the gate. I've also used circuits that open up a series MOSFET if moderate overvoltage (up to the rating of the MOSFET) is applied.

Reply to
Spehro Pefhany

The beauty of the PolyZen is that the zener dissipation speeds up the polyfuse, which protects the zener. I've started using them in everything with a user-accessible power connector.

Cheers

Phil Hobbs

Reply to
Phil Hobbs

Thanks, I was protecting against the wrong ~12W wall wart, about 1 amp max. Though you never know what someone will plug in.

The poly fuses I looked at aged in the right way... they blew at smaller and smaller currents. (with age measured in number or time in fault condition.)

George H.

Reply to
George Herold

even easier, I could just cut the plug off the cord and hard-wire the wallwart

The plug is marked 5.5x1.7 and appears to be the same outside diameter as the other 5.5mm OD plugs supplied (+/- 2%) possibly this was due to a mis-reading at the manufacturer. I guess I could substitute a third-party tip, if I could find one-

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seems kind of expensive and jaycar NZ is out of stock, does digikey have those

I see they also do 3.5x1.35, but we occasionally ship USB hubs with that calibre of DC connector, so and that combination could also prove expensive in the wrong hands.

OTOH I could butcher some audio cables and use phone plugs for

12V, if someones's i-thing is mis-plugged and explodes it's not so much my problem, but probably not a good look. 
--
umop apisdn
Reply to
Jasen Betts

Sure. I thought perhaps the 12 V wall-wart you ship is required in the finished installation; if they get their 12 V elsewhere and the wall- wart is only for testing, running the wall-wart straight into the board seems reasonable.

The Jaycar tip is apparently 4.75 x 1.75 mm.

Digi-Key has a *4.0* by 1.7 mm tip. Not sure if it's compatible with the two-pin socket you have, but most of these I've seen in the wild are pretty similar. Check the drawing to be sure:

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$2.05/1, $1.60/100. 97 in stock.

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Standard disclaimers apply: I don't get money or other consideration from any companies mentioned.

Matt Roberds

Reply to
mroberds

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