why would anyone do it the other way around ? - Page 1
Forum section: electronics / general

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 03, 2012, 04:25:05 pm
content: i think this should be made an industry standard . what you think ?

author: deephaven
author_rank: Frequent Contributor
timestamp: February 03, 2012, 04:28:59 pm
content: 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!

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 03, 2012, 04:33:13 pm
content: i have an old casio pocket t.v. thats minus in the centre ?

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 03, 2012, 04:38:38 pm
content: set of "time" pc speakers the other way around.wierd i tell yah

author: 8086
author_rank: Super Contributor
timestamp: February 03, 2012, 04:41:18 pm
content: A lot of guitar equipment has negative centre, no idea why. It's almost got me a few times

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 03, 2012, 04:48:59 pm
content: just looked at my zoom 50511 fx pedal never looked before as use batteries in it.it's weong as well

author: Short Circuit
author_rank: Frequent Contributor
timestamp: February 03, 2012, 05:08:53 pm
content: 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...

author: G7PSK
author_rank: Super Contributor
timestamp: February 03, 2012, 05:15:12 pm
content: 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.

author: siliconmix
author_rank: Frequent Contributor
timestamp: February 03, 2012, 05:23:42 pm
content: Quote from: Short Circuit on February 03, 2012, 05:08:53 pmhmm 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.

author: Simon
author_rank: Unknown
timestamp: February 03, 2012, 05:29:03 pm
content: 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.

author: Zero999
author_rank: Super Contributor
timestamp: February 03, 2012, 06:31:40 pm
content: 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.

author: Simon
author_rank: Unknown
timestamp: February 03, 2012, 06:43:41 pm
content: 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

author: ivan747
author_rank: Super Contributor
timestamp: February 03, 2012, 06:56:40 pm
content: Quote from: 8086 on February 03, 2012, 04:41:18 pmThat'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.

author: Simon
author_rank: Unknown
timestamp: February 03, 2012, 07:17:02 pm
content: Quote from: ivan747 on February 03, 2012, 06:56:40 pmI 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

author: ciccio
author_rank: Frequent Contributor
timestamp: February 03, 2012, 08:25:06 pm
content: 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!

author: PStevenson
author_rank: Regular Contributor
timestamp: February 03, 2012, 11:04:19 pm
content: 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

author: MarkS
author_rank: Unknown
timestamp: February 03, 2012, 11:08:46 pm
content: Quote from: PStevenson on February 03, 2012, 11:04:19 pmThat's not a bad idea!

author: Unknown
author_rank: Unknown
timestamp: February 03, 2012, 11:54:35 pm
content: 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.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 04, 2012, 12:09:16 am
content: 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

author: gregariz
author_rank: Frequent Contributor
timestamp: February 04, 2012, 01:13:10 am
content: 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/

author: Jimmy
author_rank: Regular Contributor
timestamp: February 04, 2012, 02:43:47 am
content: The thing with standards is there is so many to choose from

author: ivan747
author_rank: Super Contributor
timestamp: February 04, 2012, 02:46:46 am
content: This is the reality of standards:

author: electrode
author_rank: Regular Contributor
timestamp: February 04, 2012, 05:06:37 am
content: 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 drainGND to gatesource of MOSFET becomes the +ve supply for circuitIf you connect it backwards, it simply doesn't turn on. No messing with fuses and no wasting voltage with diodes.

author: PStevenson
author_rank: Regular Contributor
timestamp: February 04, 2012, 10:24:37 am
content: 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 becauseI 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 thanhaving to piss about looking for the right plug pack of which I'm sure we all have bloody draws full of, I know I domy time loss is more critical than a volt loss

author: rr100
author_rank: Frequent Contributor
timestamp: February 05, 2012, 08:40:07 am
content: 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!

author: SeanB
author_rank: Super Contributor
timestamp: February 05, 2012, 12:01:16 pm
content: 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.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: February 05, 2012, 06:47:31 pm
content: Quote from: PStevenson on February 03, 2012, 11:04:19 pmThis 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!

author: Bored@Work
author_rank: Super Contributor
timestamp: February 05, 2012, 08:01:04 pm
content: 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.

author: PStevenson
author_rank: Regular Contributor
timestamp: February 05, 2012, 11:43:01 pm
content: Quote from: BoredAtWork on February 05, 2012, 08:01:04 pmnothing 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!

author: electrode
author_rank: Regular Contributor
timestamp: February 05, 2012, 11:47:57 pm
content: Quote from: PStevenson on February 05, 2012, 11:43:01 pmIs this with unregulated plugpacks?