The message
from "Mike G" contains these words:

Pre-war Beetles?

Yes.
Pre war Beetles had a 6 volt system, which was retained in the
ones produced post war.

I thought that pre-war Beetles was a bit optimistic but a quick google
brought up the information that there were a few pre production
prototype Beetles made before war broke out. Production was actually
scheduled to begin in September 1939. I doubt very much whether any of
of the few prototypes would have made it to the UK before September 1939
though.

Memory fades but my faded memory tells me that 6 volt systems were
common back in 1962 when I bought my first car which, paradoxically, was
a 1939 Rover 12 with a 12 volt system.

--
Roger Chapman

Mike G wrote:

"JHB" wrote in message
...
Hi:

Does anyone off hand know the voltage and polarity of the pre war
Rover electrical systems?

AFAIR, most if not all prewar cars had 12v negative earths.
VW beetles were the only exception I know of that had a 6v system.

12v, insulated return:

Rover 10 1928-9
Standard 9 1929
Singer Senior 1929
Beardmore Taxicab 1929
Riley 9 1929
Citroen Swift

6v, insulated return:

Singer Junior 1929

6v, +ve earth
Ford 1929

6v, -ve earth:

Triumph 7 1929
Austin 7 1929
Citroen 1929
Essex 1929
Buick Light 6 1929
Trojan 1929 (fused between battery and earth)

and, while Mike G has stated categorically that Morris 8s were 12v, I'll
state, equally categorically, that they were 6v. Believe who you like.

Source for the detailed stuff above: "Motor Repair and Overhauling", Vol
II, George T Clarke, Newnes.

Also 6v, -ve earth:

MG Series M (source: Blower)

ICBA to look up any later cars at the moment.



--
Kevin Poole
****Use current date to reply (e.g. )****

Nope.
The Ford Y type I once owned, along with a Morris Series 1 and 2 and an E
type were certainly 12v.
Mike.


Then they must have been converted to 12 volt. My books show the Morris 8 up
to the Series E as 6 volt negative earth. People selling electrical spareas
for the Ford Y seem to think its 6 volt.

Malcolm

Jim Warren wrote:
JHB wrote:
Hi:

Does anyone off hand know the voltage and polarity of the pre war
Rover electrical systems?



I have just looked up Rover in my copy of "Modern Motor Cars" dated 1937.

Both the Rover 10 and the Rover 12 are shown as 12V Positive Earth.


And by 1940 (possibly sooner) so were the 14, 16, and 20hp Rovers

--
Kevin Poole
****Use current date to reply (e.g. )****

Hello John,
Pre-war Rovers used negative earth until part-way through the 1936 model
year, when they changed to positive earth. All models used conventional
earth return through the chassis.
Regards,
Richard Green
Tuesday 09/09/2008, 14:21

JHB wrote:
Hi:

Does anyone off hand know the voltage and polarity of the pre war
Rover electrical systems?


Thanks

John Baker

In article ,
Richard Green wrote:
Pre-war Rovers used negative earth until part-way through the 1936 model
year, when they changed to positive earth. All models used conventional
earth return through the chassis.

It's interesting that at least some of their models reverted to negative
earth long before electronics made this necessary. And of course Rolls
Royce stayed with negative earth.

--
*If at first you don't succeed, try management *

Dave Plowman London SW
To e-mail, change noise into sound.

Hello Dave,
I've never been clear whether car electronics are made with negative
earth because they have to be, or purely through convention, most cars
having negative earth when they were introduced. Certainly some of the
early radio/cassette players and accessory rev counters were switchable.
Regards,
Richard
Tuesday 09/09/2008, 16:18

Dave Plowman (News) wrote:
In article ,
Richard Green wrote:
Pre-war Rovers used negative earth until part-way through the 1936 model
year, when they changed to positive earth. All models used conventional
earth return through the chassis.

It's interesting that at least some of their models reverted to negative
earth long before electronics made this necessary. And of course Rolls
Royce stayed with negative earth.

On Tue, 09 Sep 2008 16:19:19 +0100, Richard Green
wrote:

Hello Dave,
I've never been clear whether car electronics are made with negative
earth because they have to be, or purely through convention, most cars
having negative earth when they were introduced. Certainly some of the
early radio/cassette players and accessory rev counters were switchable.
Regards,
Richard
Tuesday 09/09/2008, 16:18

Dave Plowman (News) wrote:
In article ,
Richard Green wrote:
Pre-war Rovers used negative earth until part-way through the 1936 model
year, when they changed to positive earth. All models used conventional
earth return through the chassis.

It's interesting that at least some of their models reverted to negative
earth long before electronics made this necessary. And of course Rolls
Royce stayed with negative earth.

I think it's largely convention - transistors can be made in either
polarity, though in the early days npn types were cheaper and there was
a greater range of them. No other component requires a connection to the
casing (most transistors don't either, but it was/is common with power
transistors for cooling) so there is no technical reason for either
earth polarity to be dominant.
--
Regards, Chris (Please take out my car to reply by plain text email)
------1967 Riley Elf------1978 Mini 1000------1971 Mini Clubman------
--1972 Mini Clubman estate--1979 Ford Capri--1984 VW Type 25 camper--

In article ,
Richard Green wrote:
I've never been clear whether car electronics are made with negative
earth because they have to be, or purely through convention, most cars
having negative earth when they were introduced. Certainly some of the
early radio/cassette players and accessory rev counters were switchable.

The first transistors were geranium and PNP so basically positive ground.
And very expensive. Silicon ones are NPN and negative ground - and they're
also very much cheaper to manufacture. Or were when they arrived.

Cars were all negative earth until some time in the mid '30s (according to
some here - I thought it was after WW2) and then some makes changed to
positive earth - but not in all countries. The change back did sort of
coincide with the arrival of cheaper electronics based round silicon
technology.

You can, of course, make any electronic device float - ie not connected to
the car ground, except at the battery. But this makes things much more
expensive than necessary - as well as introducing problems.

--
*Remember: First you pillage, then you burn.

Dave Plowman London SW
To e-mail, change noise into sound.

On Tue, 09 Sep 2008 18:49:43 +0100, "Dave Plowman (News)"
wrote:

In article ,
Richard Green wrote:
I've never been clear whether car electronics are made with negative
earth because they have to be, or purely through convention, most cars
having negative earth when they were introduced. Certainly some of the
early radio/cassette players and accessory rev counters were switchable.

The first transistors were geranium and PNP so basically positive ground.

Not all. When I was doing a lot of electronics in the 70s, one of the
most common transistors was the AC128 - an NPN germanium.
(FWIW they're now very sought-after by guitar fx builders!)

And very expensive. Silicon ones are NPN and negative ground - and they're
also very much cheaper to manufacture. Or were when they arrived.

But of course, apart from where heatsinking is required, there is no
need to connect any part of the transistor to ground. So an electronic
circuit board can be made with any polarity provided insulating mounts
are used.

So by and large it's convention.
--
Regards, Chris (Please take out my car to reply by plain text email)
------1967 Riley Elf------1978 Mini 1000------1971 Mini Clubman------
--1972 Mini Clubman estate--1979 Ford Capri--1984 VW Type 25 camper--