Mark Hooper wrote:
Can somebody tell me what the rational was behind the change from
Positive
to Negative grounding.
Randall Young replied:
You'll get almost as many opinions on that topic as on what fluif to
use in
dashpots !
Snip
There were numerous rationales given at the time why companies like
Triumph
and Mack didn't switch, but IMO they were just excuses.
But eventually, especially with the increasing popularity of
electronic
devices that were polarity sensitive, it made more sense to use the
same
polarity as everyone else. Again IMO, the main impetus for Triumphs
switching was a cost-cutting measure by Leyland (although perhaps it
was
indirect, in the form of pressure on Lucas to lower costs).
Perhaps this will clarify?
1. Most if not all British cars were positive earth for many years.
Standard Triumph were no exception to this rule.
2. The change from positive to negative earth appears to have been
brought about by no less an organisation than 'old Joe' being
pro-active rather tan re-active. Herewith an extract of a engineering
paper dated March 1962 which I turned up in the Gaydo archive today.
It runs to about six pages, is substantially technical and I've taken
only a few key points from the summary:
QUOTE
* Ever greater demands are being placed on vehicle electrical systems.
* Vehicle manufacturers are offering production fitted options whose
electrical requirements place substantial discharge rates on batteries
and charging systems. These are higher than hitherto and seem more
likely to continue than to diminish..
* As part of its overall product development programme, Joseph Lucas
Limited feels it is important to advise manufacturers of its longer
term intentions regarding product evolution applicable to new vehicles
that are likely to become effective within the next five years.
* Conventional dynamos are unable to meet anticipated discharge rates.
Higher output dynamos can be designed and manufactured but this brings
additional size, weight and cost penalties that vehicle manufacturers
are likely to find unattractive.
* The alternator has already proved from research that it is capable
of providing greatly enhanced electrical performance and at rotational
speeds significantly lower than establised direct current dynamos.
* An alternator will meet the electrical demands placed on the
charging system where loads that ten years ago would have been
determined as abnormal are now common. Broadly, these can be
summarised as the simultaneous operation of radio, headlights,
windscreen wipers, heater blower and embedded-element rear window
heaters in heavy and/or slow moving traffic conditions with engine
speeds frequently at idle or marginally above idle.
*Sustained use of such equipment in conditions where the vehicle is
not driven in a manner that allows the charging system to replenish
depleted energy, will discharge batteries to a level where cold
starting in winter will cause operational difficulties.
* Joseph Lucas Limited is already well advanced in the developmment of
improved charging systems and higher capacity, lighter weight
batteries On the longer term, the company is confident that it will
be able to provide manufacturers wit greatly enhanced products to
complement an increased range of electrical accessories and equipment.
Low Maintenance and Maintenance Free batteries will be a reality
within ten years and thereafter will soon establish themselves as the
preferred option in O.E. and aftermarket situations.
*Coincident with this resolve, is the requirement for vehicles that
historically have had positive earth systems to realign to negative
earth. While there is no intrinsic difficulty with a Positive earth
system, there is ample evidence that in some world markets, a negative
earth system is an accepted standard. Joseph Lucas Limited feels that
to continue with an earthing standard that does not recognise this
convention could lead to normal maintenance and repair procedures
being compromised by those who are technically unaware of specific
system differences.
* Manufacturers of electrical accessories for OE or aftermarket
applications are clearly favouring either a switchable earth concept -
likely to be a short-lived phenomenon - or negative earth only
* This new product development is an issue to which Joseph Lucas
Limited is committed to follow. However, this does not mean or imply
that existing products, whether new or reconditioned are at risk of
early discontinuation. The company is determined to ensure their ready
availability and supply for as long as a demand is proven to exist"
UNQUOTE
Jonmac
1950 Ferguson TED20 152318
(fitted this last week with the exact same type Lucas dynamo (NEW) as
fitted OE in 1950)
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