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Christian S. Hansen
Prolific User
Username: enquiring_mind

Post Number: 125
Registered: 4-2015
Posted on Saturday, 23 January, 2016 - 01:49 pm:   Edit PostDelete PostView Post/Check IP

My 1955 Silver Dawn SUJ128 is positive ground. I wonder, first, if there was any particular reason why positive as opposed to negative ground was chosen. Secondly, what are the pros and cons regarding converting to negative ground? Is it a good idea or not? I recall reading somewhere that there were problems encountered with positive ground systems...something about coolant electrolysis or whatever?...that was reason to consider the switch. Thirdly, what is involved in making that switch? Are there any downsides to going to negative ground?
Any input on the subject will be appreciated. Thank you.
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David Gore
Moderator
Username: david_gore

Post Number: 1895
Registered: 4-2003
Posted on Saturday, 23 January, 2016 - 07:26 pm:   Edit PostDelete PostView Post/Check IP

Christian,

The following forum thread and incorporated links will be of interest to you:

http://au.rrforums.net/forum/messages/17004/331.html

http://rroc.org.au/library/polarity_change.html
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Christian S. Hansen
Prolific User
Username: enquiring_mind

Post Number: 126
Registered: 4-2015
Posted on Sunday, 24 January, 2016 - 08:45 am:   Edit PostDelete PostView Post/Check IP

David...
Thanks for the links. Prior to posting the question I attempted a search but used "positive ground" rather than "polarity" and found little of relevance. Anyway, it would seem that there are no compelling reasons to make the change away from positive. Placing a tag near the battery regarding the positive earth is a prudent suggestion though. Thanks again.
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ChristopherCarnley
Unregistered guest
Posted From: 86.147.219.159
Posted on Saturday, 23 January, 2016 - 08:30 pm:   Edit PostDelete PostView Post/Check IP

Christian,
You have opened a can of worms here, and there are many theories, most of them false.
Tony Ward in the online library tells you how to do it, and the only downside is that the ammeter reads backwards.
It was discovered that the post war, industry wide change to positive earth encouraged the corrosion of copper wiring, which should always be of the multi-strand type,and more importantly the corrosion of steel bodies, and the silting up of radiators.
Some questions were asked about the poor dielectric strength of Empire tape wrapped rubber cable sheathing, prior to the use of PVC.
There was some concern regarding television suppression, and the awareness that electrons flow to the positive terminal, and may it be better, positive earth? Post war transistors of the germanium type were positive ground, unlike the later flood of Japanese silicon negative earthed types.
Electrons don,t care if the earth return switching is plus or minus.
So take your pick of the post war "Brave New World" ideas, and then consider the corrosion question, and the world wide use of negative earthed on board entertainment/communication systems

(Message approved by david_gore)
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Christian S. Hansen
Prolific User
Username: enquiring_mind

Post Number: 127
Registered: 4-2015
Posted on Sunday, 24 January, 2016 - 09:39 am:   Edit PostDelete PostView Post/Check IP

Christopher...
Thanks for your input, especially the corrosion issue. In that regard, I guess that my questions are, "Where is the corrosion manifested?" and "How can one observe on a car that is now 60 years old, whether or not there actually is evidence of that corrosion?"
As a novice in this respect, I would imagine that if corrosion were indeed a genuine issue, that significant damage would have by now manifested and would be readily observable. That is, if no corrosion can be found, perhaps its relevance is overstated. Is there any relevance in these questions?
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John Rowney
New User
Username: johnrowney

Post Number: 10
Registered: 2-2015
Posted on Sunday, 24 January, 2016 - 10:13 am:   Edit PostDelete PostView Post/Check IP

I have a 1938 Wraith WXA68 with negative earth and there is no apparent corrosion - not too bad after nearly 78 years. My 1951 Bentley Mk VI special B25KL had its positive earth altered to negative earth done in the early 80s when it was rebodied by Roger Fry. My guess it would have been to accommodate a modern radio/cassette of the day. The main benefit to changing would seem to be the polarity for entertainment systems is correct without problems and the polarity for all our common devices running off the cigarette lighter is also correct.
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1070
Registered: 5-2012
Posted on Monday, 25 January, 2016 - 06:25 am:   Edit PostDelete PostView Post/Check IP

Purely by coincidence I came across an article describing how to swap the polarity on older cars.

The components it mentioned that are not polarity sensitive and therefore do not require changing are the starter motor and regulator.

It advised to switch the connections on the coil so that the spark jumps from the hot middle electrode to the cooler side electrode. Not doing this can result in difficulty in hot starting.

Most SU fuel pumps are ok but some fuel pumps require the connections to be reversed.

Heater fans will blow backwards if the connections are not reversed.

Dynamos need to be re-polarized.

The ammeter connections will need to be reversed.

Electronic tachos need to be replaced.

If anyone would like a copy of this article, pm me with your email address.

Geoff
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ChristopherCarnley
Unregistered guest
Posted From: 86.138.60.22
Posted on Sunday, 24 January, 2016 - 08:26 pm:   Edit PostDelete PostView Post/Check IP

Christian,
For corrosion of carbon containing iron to occur, there has to be a corrosive medium,slightly acid (salty)water either directly or in the form of condensation,being the principal one. If your car has spent the whole of its life in a dry atmosphere, corrosion will be negligible, as we are finding in Australian re-imports into the UK.
The multi element sills go first, along with the front and rear wheel arches.
Cars exported from the UK after a few years in our climate are always rusted to some degree.
There is plenty of learned literature on all typed of corrosion, stress corrosion in aluminium alloys being of particular interest, when used in aircraft.
Regarding the post from John,R, there was also some concern in the changes of steel making during the post war years, in that the furnace linings of pre-war steel works were "acid" in nature, but change to "basic" during and after WW2, and it became clear that the rimming steels so produced had a greater tendency to corrode.
It is now clear that a 1% increase in the oxygen content of the atmosphere will result in the immediate corrosion of iron back to haematite.

(Message approved by david_gore)
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Christian S. Hansen
Prolific User
Username: enquiring_mind

Post Number: 130
Registered: 4-2015
Posted on Monday, 25 January, 2016 - 07:44 pm:   Edit PostDelete PostView Post/Check IP

Can of worms, yes. Forgive me if I seem to be persistently confused but isn't the body panel corrosion Christopher is referring to caused more by environment conditions as opposed to the alleged elecrolysis degradation caused by polarity issues? ...OR... is it the inference that the environmental corrosion is exacerbated by the positive polarity and will be minimized by a negative polarity?? ...OR... are the two issues apples and oranges???
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ChristopherCarnley
Unregistered guest
Posted From: 5.80.16.30
Posted on Monday, 25 January, 2016 - 10:39 pm:   Edit PostDelete PostView Post/Check IP

The S1 and Silver Cloud series with negative earth,rust just as badly as the MK VI family,as corrosion has no respect for "pedigree".
As I said above, most of the theories were wrong.

(Message approved by david_gore)
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Christian S. Hansen
Prolific User
Username: enquiring_mind

Post Number: 131
Registered: 4-2015
Posted on Tuesday, 26 January, 2016 - 06:04 pm:   Edit PostDelete PostView Post/Check IP

So...in summary and after setting aside the historic discussions...it would seem that since there are no certain problems or dire consequences caused by positive gounding, and the only advantage of negative grounding has to do with the use of "modern" audio equipment, it would seem that converting polarity requires considerable effort simply to have "tunes" onboard.

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