postive ground nonsense... io!

[Quackzed]

i'm sorry, but the whole positive ground idea really bugs me. it seems needlessly complicated and backwards... why can't ground be ground?!? and any voltage source just be +9v OR in the case of pnp stuff -9v or whatever and leave ground alone!!!  i just don't get it...

[Quackzed]

ok, so looking again, it looks like that IS how its done? ground stays ground? and battery and polarized caps are reversed to reflect a negative source?!? oi' i'm just confusing myself now... but maybee i was just thinking about it from the wrong perspective? i does now look like what i described...  well at least i think i get it...

[merlinb]

I agree that caling it 'positive ground' is needlessly confusing. God knows how it started in the first place. It is more straightforward to call a circuit  'positive supply voltage' or 'negative supply voltage'. Ground is the notional reference to which everything else can conveniently be called 'positive' or 'negative'. A 'positive ground' circuit is simply one which uses a negative supply rail such as -9V.

[Keppy]

Exactly. It's been commented that instead of positive ground/negative ground, we should refer to negative supply/positive supply, since ground remains the same, just as you said.

One way of thinking about it is rather than "ground is positive," think "positive end of supply voltage tied to ground."

EDIT: Merlin beat me to it.

[R.G.]

God knows how it started in the first place.

I believe it started with either the telegraph, then telephone industries, or possibly the automotive industry, where the battery + or - could be connected to the chassis.

One can speculate that the descriptive term might have been "positive side grounded" or "negative side grounded" or some such. There is some evidence that the central office batteries may have had their positive sides connected to the earthing/grounding rods to lessen corrosion on the lines between stations.

There were both positive-side-grounded and negative-side-grounded autos at one time. In fact, I believe that most British auto industry cars up through the mid 1960s were positive ground while the rest of the planet used negative ground cars. I have read that some auto enthusiast/techies think that positive-ground cars corrode less, for some reason, perhaps a carryover from the mythos of the tele-whatsit industry.

Here's a readable sendup of the topic: http://mgaguru.com/mgtech/electric/et098.htm

[Quackzed]

well, at least i'm not the only one  . thanks for the support guys! interesting history as well, the idea of having positive connected to earth to keep voltages below earth to reduce corrosion, makes some sense i guess...
any i definately have a better understanding of 'positive ground'  pedals, having realized my 'solution' is already implemented    , other than the confusing nameing convention... i took a confusing/frustrating road to get here, but i think i'm on solid ground again...

[boppy100]

In fact, I believe that most British auto industry cars up through the mid 1960s were positive ground while the rest of the planet used negative ground cars. I have read that some auto enthusiast/techies think that positive-ground cars corrode less, for some reason, perhaps a carryover from the mythos of the tele-whatsit industry.

Here's a readable sendup of the topic: http://mgaguru.com/mgtech/electric/et098.htm

So that's why MGs and Triumphs "last so long".  Does it also explain digi2t's can of Lucas wiring harness smoke?

[bluebunny]

i'm just confusing myself now...

I think it was Mark Hammer who painted a nice de-confusing picture.  Consider that the world outside of stompboxes uses bipolar power supplies all over the place (and over-simplification, but stick with it...).  Our tiny little stompy circuits just use half of that bipolar supply - usually the "top" half.  But a few use the "bottom" half.  The ground is always ground and sits in the "middle".

[antonis]

So that's why MGs and Triumphs "last so long". 

Propably you're kidding...

Positive ground was THE reason for coachwork's electrolytic corrosion and rust...

[digi2t]

Lucas.

The Prince of Darkness. 

[dennism]

Not just British automobiles either.   My 1929 Model A Ford is positive ground.

[Digital Larry]

I'm afraid to order pasta and antipasto at the same time.  Who knows what could happen.

[R.G.]

So that's why MGs and Triumphs "last so long".  Does it also explain digi2t's can of Lucas wiring harness smoke?

They last as long as they do because you have to re-sync and tune the @&^*$@!^ side-draft carburetors every few minutes.  I went through an assortment of MGs, and at one point could remove the engine and transmission from a Sprite by myself in four hours.  I considered putting push/pull cables and knobs into the dash so I could tweak the carburetor alignment as I drove.

[digi2t]

So that's why MGs and Triumphs "last so long".  Does it also explain digi2t's can of Lucas wiring harness smoke?

They last as long as they do because you have to re-sync and tune the @&^*$@!^ side-draft carburetors every few minutes.  I went through an assortment of MGs, and at one point could remove the engine and transmission from a Sprite by myself in four hours.  I considered putting push/pull cables and knobs into the dash so I could tweak the carburetor alignment as I drove.

My first car, a Triumph TR-6.

My first street bike, a Honda CBX.

Obviously, I was a glutton for punishment where side draft carburetors were concerned. 

I must admit though, the 6 carbs on the CBX held their tune better than the 2 carb on the TR-6 ever could. 

[PRR]

> possibly the automotive industry

That's probably where most hackers started.

The designation "to ground" may make sense in a car because there's a lot of wires fanning out from the hot terminal, but the other terminal often has ONE wire going directly to frame or block, easier to trace.

In a pre-1950 car, it really hardly matters which side of the battery is bonded to the frame. That's why both car-battery terminals are (stupidly) the SAME size. And in that period, both wires were black. (Good colored insulation is mostly a post-WWII thing.)

The incandescent lights and cigar lighter sure do not care. If you've used toy motors you think that you reverse polarity to reverse rotation, but car motors and generators are (were) all Field Coil instead of Permanent Magnet. Reverse the polarity, both rotor and field reverse, rotation stays the same. Gas gauges usually go by heat, are not polarity sensitive. They said the spark was a little better if the electrons jumped off the arm electrode, but the difference was small, and spark coils did have interchangable + and - marks which you could go by after you knew the battery polarity.

Radios were uncommon but deserve a look. The 6V heaters do not care. The high volt was got by vibrating to AC and then rectifying. With a conventional rectifier, the HV polarity was sure to be right; however the rectifier heater was an issue (both gas-rects and insulated cathodes were used). There was also a self-rectifying vibrator which *was* polarity critical; it seems to be un-common and the uncertain polarity of many cars may be the reason.

IIRC, about 70% of US cars in this period came from the factory Positive to Ground. I know a 1941 Plymouth is. This could be changed, by mistake or deliberately; there was a recurring article in the transition decade.

The idea that Positive Ground is less corrosion is bogus on a car because car "ground" is NOT dirt ground (a real issue in power and phone work), it sits on insulating tyres. Internal corrosion between wires and frame "could" make a difference, except they supposed to be well insulated and even when not, corrosion on either side is bad. Corrosion control by polarity works when you have sacrificial anodes OR you are diverting corrosion from your wires to the streetcar tracks (make it someone else's problem).

US cars changed in the 1950s to all negative ground (positive hot). There are several reasons and I am not sure anybody really thought it through. Generators were replaced by alternators, which have rectifiers (built-in absolute polarity), and the early rectifiers *may* have been a buck cheaper if the negative stud were bolted to big metal for cooling (however usually they ended up with an insulated cooling plate so no difference). Transistor radios were on the horizon, but early-on PNP was cheaper than NPN so you would think positive ground was logical. But between tube and transistor radios there was a year of small tubes run on low voltage and one big transistor for the power output. These tubes were rigged for negative ground (altho they could have been rigged the other way).

In the US this all overlapped with the change from 6V to 12V (apparently the UK was mostly 12V all along). And while they talked about hi-compression starters and quad headlights, I bet the real reason was the significant voltage-drop in the rectifiers in the new alternators. That's good for 10%-20% improvement in efficiency (output per dollar of dynamo cost) which is about the gross difference between a generator and an alternator (so the alternator-pushers needed that last buck). There's added savings in less-fat starter wire and wire generally, due to same power at lower current at higher voltage. (Using modern starter cable on the 1941 Plymouth is a summer-only fix; winter starting demands fatter copper than modern 12V cars ever need.)

> at least i'm not the only one

I once had the radio station's main console on the bench for a month because they used an unconventional pos/neg convention, and I would *not* see my screw-up.