On 13 Sep, 16:18, "Bob Eager" wrote:
On Thu, 13 Sep 2007 11:47:27 UTC, wrote:
Hi all,

Just an academic question.

What used to be used in Car Battery charger to convert the AC - DC
before silicon diodes/bridge rectifiers came along?

Supplementary:

What used to be used in car battery chargers to convery 240v to 12v when
the mains was DC?

(my train set used a small rotary converter)

Explain please

Thinking about it, I think I still have the "Transformer" that my
parents bought for the family train set in my loft C 1966 or so, and I
remember it having bugger all in it apart from a transformer and some
kind of overcurrent trip. I wonder what is in there?

I did have a look at the wikipaedia article mentioed earlier and also
followed the link to Bridge Rectifiers and the later link to vibrators
(electrical). Fascinating stuff!

I think my friend's late uncle's battery charger probably had a centre
tapped transformer and a couple of metal diodes (centre tapped so as
to get full wave rectification with just of two diodes) thus saving
the cost of two diodes. I suppose this made sense in the olden days
when diodes were relatively expensive compared with an extra tapping
on the transformer.