Mains plugs for 12V DC

"David L. Jones"

** I believe it is totally illegal to use a 240 volt plug or socket for any other purpose than as a mains connector.

Back when I was a keen model power boat racer, one of the club members showed up at the lakeside with a new 12V starter motor fitted with a standard 3 pin mains plug. He had also fitted a double power point to his tool box to allow connection to the 12 volt battery he kept inside. The other socket allowed him to plug in a 12V fuel pump.

Thing is, the guy made his living as an electrician !!!

Besides being ludicrously DANGEROUS the idea will not work reliably as the brass plug pins and female socket parts are very prone to tarnishing and when thick enough this tarnish will fully insulate at 12 volts.

One of the reasons why the earth pin has to be nickel plated nowadays.

..... Phil

When all you have is a hammer, everything looks like a nail I guess!

Yup. Silly, dangerous, and a poor choice.

So what would other people use as a bench 12V connector for gear? First thing that springs to mind for me would be XLR connectors. Easy to mount a strip of those on a panel, and 16A types are readily available. Get a 4 way type and double up on the pins.

Dave.

"David L. Jones" "Phil Allison"

** I have used 4 pin " CB mic " connectors ( DSE cat P1834) for a bench PSU that outputs +/-15 volts regulated DC to connect up various audio test items I made to run from that voltage.

Good for a couple of amps.

Nice and cheap at $ 2.49 each - even less at WES.

.... Phil

Aren't there mains style clipsal/hpm or whatever plugs/sockets with two pins arranged in a "T" configuration that are intended for DC applications? Maybe my memory is faulty.

"Den"

**This what you mean ?

** 32 volt, 15 amp AC only it says.

Same issues with tarnishing if used at a lower voltage plus a NASTY arcing issue if used for high current DC.

..... Phil

I used to use those back in the 1970s. I think they're called 'ELV' (Extra Low Voltage) connectors and are for 32V maximum if I remember correctly. Dunno if they're still around ... too busy to go searching.

I used the 2 pin .093" MOLEX connectors on my benches about 25 years ago. They were rated to 10 amps per pin, and held up well for the 10 tears I used them. A simple rectangular notch in a piece of angle aluminum made a nice mounting bracket. Best o all, they were cheap, and always in stock, since I used them on some job sites.

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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.

Yep those are them - also at

I think they were used by Telecom in the 70s & 80s in vehicles, trucks, 4wds etc for running accessories in the field.

as

and

And yet strangely all the slot car tracks 30 years ago used 240V sockets for the 12V hand controllers. I have no idea if the remaining ones still do.

Most people use the car cigarette lighter plug/sockets, or the smaller "merit" versions. Neither is ideal, but at least most people will instantly recognise what to expect.

pins

Maybe

Nope, your memory is fine, that's what my enlarger (12v halogen) uses. They were rated to 32V from memory.

MrT.

A local radio ham with who I have "foxhunted" uses RCS plugs. They're not terribly strong, but there's heaps of contact area and they won't come unplugged by themselves. Audio gear always has DC isolation to 12V at least, so though inadvertent mis-connection might make some nasty noises, no smoke.

Clifford Heath.

On Thu, 25 Sep 2008 20:22:05 -0700 (PDT), "David L. Jones" put finger to keyboard and composed:

An old friend did something like that for his radio gear, only he used DC sockets to supply 240VAC.

He blew up at least one radio that I know of.

- Franc Zabkar

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On Thu, 25 Sep 2008 20:22:05 -0700 (PDT), "David L. Jones" put finger to keyboard and composed:

I remember an Iranian friend telling me that for a while Iran used the same wall sockets for AC mains as for telephones. People would sometimes plug a telephone into the mains. The phone would ring, presumably at the mains frequency, and then die.

This Wikipedia article shows one plug style as CEE 7/17 Euro 2 pin:

This article shows that the CEE 7/16 2-pin plug was used in older installations:

- Franc Zabkar

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"Franc Zabkar" <

** I'm sure I remember a story in EA magazine, maybe in the servicemen column, about a man who used 3 pin mains plugs to connect a big woofer cabinet to an amplifier.

One day, his wife unplugged the woofer to do the vacuuming and then ....

BIG bang - no more woof.

..... Phil

"Franc Zabkar"

** The common 4mm " double banana" plug and the mating dual 4mm binding post terminals in 19 mm spacing are BANNED in the EU for use on any sort of audio or entertainment equipment.

Why ????

Cos it plugs straight into this:

Ouch !!!

.... Phil

I agree. However, this page promotes them as "Suitable for most DC applicacations" (their typo - not mine) and "ultra reliable". I don't think so..........

Andy

Yes, got quite a shock seeing that, however in times gone by I have seen mains fittings used for car to trailer connectors, as connectors for "slot car" hand controllers (for public use) in an amusement centre, and even as speaker connectors when I was in school (cant remember if it was the 240 type or the 2 pin US type). Fortunately now there are many more "correct" low voltage plugs and sockets available to the hobbyist via Auto suppliers, dick smith and similar stores, this probably wasn't the case prior to the 1970s, and people would use what was commonly available - household fittings.

I can only assume that SC did this in order to provide an example of HOW NOT to do something.

If he ABSOLUTELY HAD TO use this system, he should have at least used the neutral and earth as the + and - connectors, and sawn off the active pin. At least then, there would be much less risk of danger if it was plugged into a 240v socket mistakenly.

The other problem with his system is that Mains fittings are clearly labelled "AC ONLY" and are probably not designed to be used with 10A DC, especially if there are switches involved. You are also limited to 10amps (via the CB in the power board he used) which kind of defeats the purpose a bit if you want to connect higher current equipment.

SC should have pointed out that for low voltage use, (32v lighting plants?) there is a plug and socket available - similar to the 240v unit, but with the pins arranged in a " T " configuration. Dick smith had these, and no doubt Haymans etc would be able to get them for you.

Alternately, go to Super Cheap or Autobarn, and check out the connectors etc that they use for the high wattage sound system installs. These would be far superior in current handling to any mains plugs.

Also this Reminded me of another article in either EA or ETI some 25 years back showing where some fool had decided to convert his Telecom phone system to a mains plug and socket arrangement so he could carry the phone around his house and plug it in anywhere he wanted. (at that time it probably was near impossible to buy the proper "Telecom" type sockets for the average hobbyist?)

"kreed"

The other problem with his system is that Mains fittings are clearly labelled "AC ONLY" and are probably not designed to be used with 10A DC, especially if there are switches involved.

** The "AC ONLY" prohibition relates to use with a 240 volt DC circuit - where arcing is a MAJOR hazard.

Generally, if a switch will reliably break 240 volts AC at some amp rating, it will also be OK at 12 volts DC and probably 24 volts DC at that same max current. Nearly all switches and relay contacts have such dual ratings.

However, if like mains plugs and switches, the metal parts are made of un-plated brass, then they cannot be relied on to *make* in a circuit at low voltages like 12 volts.

..... Phil

Ugh, that should have been "RCA" plugs, sorry.

Or maybe not. The PMG once used 4 pin sockets for portable/relocateable phones that did look similar to the standard "bakelite" mains sockets used at the time, at least to a casual observer anyway. That was a lot more than

25 years ago however, and the Aus standard 6 pin plug/sockets have been readily available for a lot longer than that too.

MrT.