why would anyone do it the other way around ?

[siliconmix]

i think this should be made an industry standard . what you think ?

[deephaven]

That is the usual way round. I have seen battery connections to broadcast TV cameras which have it the other way round. Don't ask me why!

[siliconmix]

i have an old casio pocket t.v. thats minus in the centre ?

[siliconmix]

set of "time" pc speakers the other way around.wierd i tell yah

[8086]

A lot of guitar equipment has negative centre, no idea why. It's almost got me a few times

[siliconmix]

just looked at my zoom 50511 fx pedal never looked before as use batteries in it.it's weong as well

[Short Circuit]

The socket usually have switching contact on the outter ring. So thinking straightforward and having a battery to disable with adapter plugged in, it makes sense to put positive on the outside and common negative on the center contact. Having a few dozens of different sizes around, I don't think standardizing this would be of much help...

[G7PSK]

In a lot of older equipment the negative is center, I think that this was to do with cars being positive earth so equipment that could plug into a car had to be the same now its the other way round, so if you get a new positive outer plug its most like just so you have to use the adapter sold by the same equipment maker.

[siliconmix]

The socket usually have switching contact on the outter ring. So thinking straightforward and having a battery to disable with adapter plugged in, it makes sense to put positive on the outside and common negative on the center contact. Having a few dozens of different sizes around, I don't think standardizing this would be of much help...

hmm maybe.but the connectors are power/ headphone/line in /line out.anyway.i wish someone would decide on a way and stick to it.we could have a vote.

[Simon]

about as anoying as the GB plugs or rather wallwarts with wires coming out the wrong side. I guess it is about making sure they sell you another adapter when it breaks or you loose it.

[Zero999]

The only reason I can think of for doing it the other way round would be in the case of a positive earth but most DC supplies are floating so it's irrelevant.

I think there should be a standard for DC connectors which should be keyed so it's impossible to get the voltage or polarity wrong and for AC non-polarised connectors could be used.

[Simon]

yes i agree, we have the mobile phone charger saga and then a parallel saga of all the other different types of power adapters, silly voltages and a myriad of connectors, not good in a "green" world where we could use standardized power adapters

[ivan747]

A lot of guitar equipment has negative centre, no idea why. It's almost got me a few times

That's because the barrel jack connector has a normally closed switch (closed when nothing is plugged into the jack) on the outer contact. That can be used to switch to another power source when the power brick is disconnected. I suppose guitar equipment designers want to switch the positive rail over to a battery, rather than the negative but I don't know the reason for this.

Or maybe they it's just a convention used by guitar equipment designers. I hope they use diodes.

[Simon]

I hope they use diodes.

I bet they don't, having the user at fault for blowing up their equipment makes more sales. After all not using the original adapter invalidates warranty bla bla

[ciccio]

This type of plug is manufactured in many sizes (Maplin stores about 15 types: http://www.maplin.co.uk/dc-power-plugs-43084).
I'm not sure if there is a standard, but most of the times I see the larger one (2.5 mm pin diameter) with negative outer shell and the mid-size one (2.1 mm pin diameter) with positive outer shell.
I don't remember how is for the smaller ones (i see them only occasionally).
Sometimes they are used for ac power, such as in many modems and routers. and so they will work with  ac or with both dc polarity.... no more problems!

[PStevenson]

to be honest whenever I design anything, I put a bridge rectifier on the DC input so it automatically corrects the polarity at the cost of a volt, cause I'm sick of getting people emailing me to say "I blew it up with my powerpack" so yeah I would love a standard

[MarkS]

to be honest whenever I design anything, I put a bridge rectifier on the DC input so it automatically corrects the polarity at the cost of a volt, cause I'm sick of getting people emailing me to say "I blew it up with my powerpack" so yeah I would love a standard

That's not a bad idea!

[alm]

Diodes drop voltage, which is not always an option. Of course they also add another $0.001 or so to the BOM . A fuse plus crowbar diode is another option, and I believe Bob Pease also published a circuit with two MOSFETs for reverse polarity protection without voltage drop.

[vk6zgo]

That's what all your outlandishly expensive DMMs are for----check first,plug in later!!
But seriously,you've got a history of manufacturers going their own way for around 40 years with these connectors,I don't think you'll get them to change their ways now!

By the way,have you notice that some barrel connectors have thinner centre pins than others?
They sort of fit,then at the worst possible moment lose contact!

VK6ZGO

[gregariz]

I've got an old wavetek signal generator with a PH-163 connector. With those connectors, some manufactures wired live and neutral one way and others did it the opposite.

http://richardhess.com/notes/2006/03/15/round-pin-power-cords-for-older-equipment-using-ph-163-connector/

[Jimmy]

The thing with standards is there is so many to choose from

[ivan747]

This is the reality of standards:

[electrode]

It's easy to use a P-channel MOSFET for reverse polarity protection - much better than a diode too, as forward voltage drop is maybe 0.1 V instead of 0.7 V (eg. Fairchild FQP17P06).

Connect as follows:
+ve of power supply to MOSFET drain
GND to gate
source of MOSFET becomes the +ve supply for circuit

If you connect it backwards, it simply doesn't turn on. No messing with fuses and no wasting voltage with diodes.

[PStevenson]

the reason I chose the bridge just to correct polarity rather than a method that only works when you plug the right thing in is because
I don't design things which are voltage critical in that way, I'd rather have the thing work with whatever you plug into it rather than
having to piss about looking for the right plug pack of which I'm sure we all have bloody draws full of, I know I do

my time loss is more critical than a volt loss

[rr100]

Funny thing I have a special "kit" with 16 of those small plugs (apart from ones salvaged from dead wall-warts, universal wall-warts, etc). They've been invaluable when one or other router, external hdd or something else dies (as they usually do - I tend to keep a lot of equipment around even from 1990's).
HOWEVER just after I bought the kit I instantly found that at least two sizes were missing!!! One was the "large" Nokia type! What the heck, how many different mechanically incompatible hollow cylinders can you design in half a centimeter or so of space!

[SeanB]

Bought from the Fong kong store ( actually the store is called Wan Long Wholesalers.........) a 12 in one USB charger kit. Cost a whole $5, and has a nasty 12V USB converter and a mains version. As well a lead with 12 different points on it, from a tiny little barrel to a proprietary one for a certain computer company that uses a 30 pin connector for everything. Bought as I wanted a spare phone charger for the car, and it will do all the phones I have, after cutting off all the unused connectors.

[Jon Chandler]

to be honest whenever I design anything, I put a bridge rectifier on the DC input so it automatically corrects the polarity at the cost of a volt, cause I'm sick of getting people emailing me to say "I blew it up with my powerpack" so yeah I would love a standard

This of course works, but in at least one case, led to a lot of frustration.  I had a device with a coaxial jack marked "12 VDC" but no polarity.  Not wanting to blow the thing up, I disassembled it to figure out what polarity it needed.  Many screws later, I can finally see the circuit board: JACK - BRIDGE RECTIFIER - REGULATOR, etc.  Geez, yes, using the rectifier should have made it foolproof, but not marking the polarity made it much more difficult!

[Bored@Work]

A bridge rectifier lifts your device's ground. If you power multiple devices from the same power supply, and you happen to have other ground connections between the devices these ground connections short out one diode in the rectifier (non-destructive). This in turn raises the output of the rectifier in the device by one diode drop.

Depending on how much current the device uses and what signals you have this can be rather undesirable.

[PStevenson]

A bridge rectifier lifts your device's ground. If you power multiple devices from the same power supply, and you happen to have other ground connections between the devices these ground connections short out one diode in the rectifier (non-destructive). This in turn raises the output of the rectifier in the device by one diode drop.

Depending on how much current the device uses and what signals you have this can be rather undesirable.

nothing too sensitive, usually just 9 volt guitar effects and stuff like that, with those a lot of users prefer the ground to be lifted so using the bridge has another function.
it's good to know that though cheers.

@Jon I had a similar experience so I always mark things I use them in "use any polarity at x volts" one of my friends just recklessly plugs anything into anything and it's always okay but on the odd occasion I have done it, catastrophic failure!

[electrode]

[...]one of my friends just recklessly plugs anything into anything and it's always okay but on the odd occasion I have done it, catastrophic failure!

Is this with unregulated plugpacks?