Voltage and polarity of pre war Rovers

I *think* Rovers stayed with negative earth - even when others changed to positive. The only pre-war one I had dealing with was 12 volts. But surely this would be easy to ascertain by looking at a bulb etc if the battery is missing?

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. Mike.

Don't know many pre-war VW's. Quite a few small cars used 6v pre-war, but I would expect something the size and quality of a Rover (even the 10hp) to have been 12v and negative earth. In the absence of anything obvious to the contrary it should be reasonable to proceed on that assumption. Unless we are talking about an air-cooled flat twin 8hp of course.

Ron Robinson

"R N Robinson" wrote in message news:ga3thu$q11$ snipped-for-privacy@aioe.org...

The 1930s Rovers are 12volt. Not sure about the earthing though. No idea about the 8hp I'm afraid though I know someone who has one if we are desperate to know.

It is most certainly not true to say that most pre war cars are 12volt. All the Fords and I think Vauxhalls are 6 volt as well as the Morris 8.

Malcolm

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

Interesting - the sit up and beg post war Fords were 6 volt.

I reckon positive earth was a post war thingie. Said to extend plug and points life.

Pre-war Beetles?

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

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.

Jim

The message from "Mike G" contains these words:

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.

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.

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

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

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.

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.

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!)

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.