Positive ground electrical systems?

[aussiblue]

I expected to see pictures of three men in primitive copper power-suits shooting electricity out of their hands at each other

Well one of Tesla's dinner party tricks that apparently nobody has been able to replicate was to carry balls of blue lightening around in his hand.

[aussiblue]

And here is a somewhat bizarre and less than serious but nonetheless humorous description of the current wars: http://monsterrebellion.wordpress.com/2009/07/

[Grum]

Originally Posted by Big Damo

We've been taught at school current flows from negative terminal to the positive terminal, not the other way around.

'Conventional current'

A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention for the direction of current which is independent of the type of charge carriers is needed. The direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges.

In metals, which make up the wires and other conductors in most electrical circuits, the positive charges are immobile, and the charge carriers are electrons. Because the electron carries negative charge, the electron motion in a metal conductor is in the direction opposite to that of conventional (or electric) current.

http://en.wikipedia.org/wiki/Electric_current

[zilo]

Originally Posted by au3xr6

nothing to do with returning to actual earth it is due to electrolisys, the positive earth system encourages rust due to electrolosys

I am well versed in electronics.

Please explain that statement and don't hold back on the details...?

[Sprint]

Originally Posted by Ugg

I am well versed in electronics.

Please explain that statement and don't hold back on the details...?

Tafe will teach you current flows from + to neg "conventual flow"

But they should also explain the oposite theory to you.

electron flow.

http://www.electro-tech-online.com/g...tron-flow.html

[zilo]

Originally Posted by Sprint

Tafe will teach you current flows from + to neg "conventual flow"

But they should also explain the oposite theory to you.

electron flow.

http://www.electro-tech-online.com/g...tron-flow.html

How does that link prove that positive earth cars corrode more than negative earth ones?

[Sprint]

oh that i cannot prove.

[Mr Hardware]

So the phone systems running at about 50v, how many amps would they provide?

[cs123]

Originally Posted by Mr Hardware

So the phone systems running at about 50v, how many amps would they provide?

Internally. Lots of amps. The TE I use to work in had battery rooms bigger than your average house. Each battery bank had 24x 2 volt cells. Each cell stood around 3 foot high. 5 banks of batteries powered the TE.

[Olbucko]

Originally Posted by Mr Hardware

So the phone systems running at about 50v, how many amps would they provide?

If you shorted out the the large battery banks in a telephone exchange or electrical sub station the current flow would be in the order of hundreds of thousands of amps, enough to cause a serious explosion and fire. Might only be 50 volts but potentially very dangerous. In an electrical substation the battery room can be as dangerous a place to be as the high voltage areas

Even a car battery is good for a few thousand amps if you short it out with something like a spanner

[Mr Hardware]

What about to premises?

[foxtrot3]

Originally Posted by Ugg

How does that link prove that positive earth cars corrode more than negative earth ones?

Hi. I dont think it makes much difference, When I first got my licence I had a rusty 15 year old car that I fixed up and it was a + earth car and at 15 years of age both my XE and my parents XE were rust buckets and they were - earth. Cheers MD

[Itsme]

Originally Posted by Olbucko

Even a car battery is good for a few thousand amps if you short it out with something like a spanner

A battery with a few thousand amps!!! Where can I buy one?

[cs123]

Originally Posted by Mr Hardware

What about to premises?

The DC loop is milliamps, you can short out the wires to your house without any issues and this is used with decadic (rotary) dialling to the exchange. It is timed make/break on the circuit.

The line circuits in the TE have over current protection too.

The TE sends AC to signal an incoming call, to ring the bell. That will give you a tickle up if you touch it but is not lethal.

[cs123]

Originally Posted by trublu

A battery with a few thousand amps!!! Where can I buy one?

You might have trouble fitting them into your car.

This is a pic I found on a website.

There are 2 batteries in the pic. Each battery has 24 2volt cells. The apprentice tech use to have to check these things regularly... oh the memories....

[Franco Cozzo]

Originally Posted by trublu

A battery with a few thousand amps!!! Where can I buy one?

Get an N200P, I can get one in stock for you no problem ;)

[Itsme]

I think both of you missed my sarcasm remark in regards to a normal car battery.....

Not to say there are special batteries with high capacity amps.

[Silver Ghia]

The MGTD I fully restored from ground up some years ago now did not seem to worry that the current was going the other way, but then there was no radio installed. The main reason for all cars going to negative earth in the late '60's and early '70's was because of the radios and cassette players coming on the market at the time, which were all negative earthed for reasons given below.

Here's an interesting article from the Davies Craig website, about positive and negative earthed cars, which helps explains things:

I have long wondered why my 1937 MG has positive earth whilst my 1936 Bentley has negative earth. Many cars constructed before about 1950 were positive earth with later cars reverting to negative earth. The following is a Lucas reply to a similar question regarding positive and negative earth put in 1966.


“Electrical equipment will only function with current flow which requires a return path for the current that has passed through the component. Originally most vehicle manufacturers utilised either a special wire or the chassis for a return path. To distinguish between the two wiring systems, the type that used special wire return was designated ‘insulated return or I.R’. and the chassis return as ‘earth return or E.R’.

Earth return would be dangerous where high voltages are used, but earth return is quite safe for low voltages between 6 and 12 volts, but any leakage between wiring and chassis causes corrosion at the leaky point.

Pre-war insulating material was usually basically wood, rubber, ebonite, glass or later bakelite. All but glass had tendencies to exhibit minute leakage, which over a period of time encouraged corrosion of the terminals. Battery connections were most prone to corrosion because of the added effect of the acid. Earth return is only effective if the battery has one terminal connected to the chassis, and for certain chemical reasons less corrosion occurs if the positive earth terminal is earthed.

It was because of the advantages of earth return that by about 1935 nearly all manufacturers were using this system and to reduce corrosion the positive battery terminal was earthed. An additional advantage of positive earth was that a sparking plug sparks better with the earth electrode positive.

Since the war, plastic insulation has been used extensively, and because of this the leakage current no longer prevails. As there is no leakage to bother about, it does not matter which battery terminal is earthed from a corrosion point of view. Sparking plugs still operate more effectively with a positive earth electrode but now that ignition coils can be made which reverse the earthing potential of the power flowing through them, it is possible to use a negative earth battery and still obtain positive earth high tension. In theory the last few facts are a little more complicated than stated but in practice the effects are still the same.

Post war negative earthing has many factors in its favour, and the most predominant are given below: -
Television interference is easier to suppress with negative earth, and of course this was no bother before the war. Electrical equipment is now being used as standard in more cars additional to the radio (probably the first electronic devise used in a British car)

It is characteristic of all electrical apparatus, as opposed to electric, to be polarity conscious, that is affected by which supply terminal is earthed. If a transistor is connected the wrong way round it will be immediately irreparably damaged. Universal negative earthling would ensure that all power supplies to electronic gear were to the same earth and therefore reversed connections impossible. Electrical components like bulbs etc are not affected by which terminal is earthed, therefore these can be unchanged and universal in their application.

To help avoid any confusion which may arise in the difficult in-between changeover period, when vehicles of both types of earthing are produced, components are being marked + and -. To consider an ignition coil, for instance with positive earth,+ is earth, so this is for distributor contacts and – is live, so this is the ignition feed. The same coil when used with negative earthing would be earth at – and so this is for the contact breaker, and live at +, making this the ignition feed.

Thus to summarise, Positive earth gives a better spark and less corrosion when insulators leak current. Negative earth interference is easier to suppress and electronic components are less likely to be damaged."

.

[GTpilot]

Originally Posted by Big Damo

We've been taught at school current flows from negative terminal to the positive terminal, not the other way around.

Electron flow is neg to pos
Conventional current flow is pos to neg.

[GTpilot]

Originally Posted by cs123

You might have trouble fitting them into your car.

This is a pic I found on a website.

There are 2 batteries in the pic. Each battery has 24 2volt cells. The apprentice tech use to have to check these things regularly... oh the memories....


image

And that was only once you finished cleaning all the contacts!

[aussiblue]

As per Grom Quote I think Wikipedia covers it pretty well http://en.wikipedia.org/wiki/Electri...nce_direction:

A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention for the direction of current which is independent of the type of charge carriers is needed. The direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges.

In metals, which make up the wires and other conductors in most electrical circuits, the positive charges are immobile, and the charge carriers are electrons. Because the electron carries negative charge, the electron motion in a metal conductor is in the direction opposite to that of conventional (or electric) current.

[edit] Reference directionWhen analyzing electrical circuits, the actual direction of current through a specific circuit element is usually unknown. Consequently, each circuit element is assigned a current variable with an arbitrarily chosen reference direction. When the circuit is solved, the circuit element currents may have positive or negative values. A negative value means that the actual direction of current through that circuit element is opposite that of the chosen reference direction. In electronic circuits the reference current directions are usually chosen so that all currents flow toward ground. This often matches conventional current direction, because in many circuits the power supply voltage is positive with respect to ground.

[Olbucko]

Originally Posted by Olbucko

Even a car battery is good for a few thousand amps if you short it out with something like a spanner

The current flow might be several thousand amps however the spanner would become red hot and may melt, the battery would be flattened, permanently damaged, and may even explode. It would be all over in a few seconds.

Don't try this at home!

[zilo]

Originally Posted by Silver Ghia

The MGTD I fully restored from ground up some years ago now did not seem to worry that the current was going the other way, but then there was no radio installed. The main reason for all cars going to negative earth in the late '60's and early '70's was because of the radios and cassette players coming on the market at the time, which were all negative earthed for reasons given below.

Here's an interesting article from the Davies Craig website, about positive and negative earthed cars, which helps explains things:

.

Thanks for the website link, most of it is sensible , but his claim of corrosion is just rhetoric without any proof or reason.