Old fashioned car battery charger technology

[Dave Plowman (News)]

I thought they used AC - hence the convoluted reversing system?

[clot]

Not my recollection, but it was a looong time agooo and I could be wrong!

[Bob Eager]

I don't remember any convoluted reversing system! But that would actually tend to reinforce my contention that we used DC mains for a while - my dad might have 'found' a car battery instead of getting a rotary converter, which would have had to output AC in that case. The later 'box' would have been just a transformer.

But say more...

[The Natural Philosopher]

Copper oxide recitfiers IIRC, and they usually did full.

[The Natural Philosopher]

Some had motors with field coils that ran on AC, and you shoved a HUGE DC pulse in them to flip a bistable relay to reverse the field coils, and teh loco..

[Andy Dingley]

Right back in the '30s they used a variable rheostat and a meter to control charging current carefully. By the '70s this had been abandoned in favour of more robust batteries and cruder chargers with no current control at all.

Not until the '90s did "retail" grade chargers start to see any sort of electronic intelligence, and even that was simplistic and far from universal.

[meow2222]

Sometimes, but more often a light bulb. Bulb chargers persisted for a fair time.

Neither of those is possible, and the latter not legal.

NT

[terry]

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Essentially two items inside a typical/conventional basic 'Battery Charger'.(For lead acid 'car' batteries).

1) Transformer; as the name suggests changes (steps down) the 240 volts mains to something a bit above 12 volts. 2) A device or devices called rectifiers; various types, selenium, copper oxide, mercury vapour as listed by other posters. These could be either half wave or full wave; or full wave bridge etc. depending on design. Different types of rectifiers introduce different voltage losses; these are allowed for in the overall design.

Didn't/doesn't much matter whether the rectification from alternating to direct voltage is full wave or half wave as long as sufficient energy is provided at the output of the charger . Charger could be very simple devices with no controls or provisions for adjustment. Just clip on the battery and away we go. Or more sophisticated with features such as 'Full charge', 'Finishing charge' and 'Trickle-Floating'.

Silicon and germanium just happen to be two of the more modern solid sate device materials used. The basic rectification process has essentially remained the same. For a very low voltage of 12 it would have been unlikely that vacuum tubes would have been used; except that mercury vapour (tungar) bulbs were available and recall seeing those in use in garages in the 1940s..

There were at one time 'wet/electrolytic' rectifiers (1920s and earlier?; before my time!) but not sure of their application.

However in more modern times we have seen the advent of 'switching power supplies', to supply computers etc. These, typically, supply plus and minus voltages of +12, minus 12, +5, minus 5 etc. Many of these can accept both 120 v AC @ 60 hz or 240 v AC @ 50 hz.

In some instances these can be converted to a battery charger or 12 volt power supply for a mobile or car type radio. We did this recently, converting a 10 to 15 year old scrapped computer PS to produce over 10 amps @12 volts to power an amateur radio rig.

Now we haven't even mention 'pulse charging' and other techniques for some very modern batteries; another whole subject.

[terry]

Andy: I first went on installation work in city of Gloucester in summer of 1953. DC mains were still fully in use in one part of that city where we were in digs (lodgings). Ironic cos I had built a radio to take with me using an ex Admiralty AC transformer! Other parts of Gloucester had 50 hertz AC. I'm not the least surprised that DC mains might have persisted in various parts of Britain for considerable time after that. Some things were still rationed in 1953 and later! Terry: Now in Newfoundland Canada with a nice comfortable 115/230 60 hertz 200 amp domestic service connection.

[tony sayer]

Was it as long ago as that?, ISTR that the old thompsons lane power station in Cambridge was supplying DC up the 1960's...

[zikkimalambo]

Sorry Bob, wasn't being rude, just wanted to know what a rotary converter was. Funny thing is whilst it meant nothing yesterday, before I read you explanation today I thought - Oh, he probably means a 240V motor driving a 12V gennie :=))

[zikkimalambo]

I had (have!) a controller which used to sit atop 3 batteries and I think it would have connected to all three and series-ed them (I suppose they were 4 volts each)

My dad modified this to run off the output of the transformer, which sounds very similar to yours, but I it never blew fuses, so I suspect it wasn't fused. The magnetic buzzy thing did trip if you put a penny across the (2) tracks though :=))

One time my brother set the track up and "forgot" to include the transformer in the circuit - The car didn't go very far :=((

Should've bought a soldering iron and some fuse wire :=))

[Bob Eager]

No problem! I think they were more commonly used to generate AC from DC....

[zikkimalambo]

I know my uncle built one once to convert between 240V and 120V.

It was for an electric fence in his Haunted House (he was a showman) If the local yoof got a bit excited and started thumping the cage that the exhibits were in, a nice belt of AC used to calm them down :=))

[mcbrien410]

Half wave is plenty.

I've always wanted to build but never made it yet is a mains motor driving a decent size, say 80amp, car alternator. After all that's what is normally used. In he US where they first had alternators on cars, Selenium stacks were used. I fitted some Silicon stud diodes to my Triumph 21 (350cc) back in the mid 60's. The first car alternator I used in the UK, again mid 60's used the big 30 amp push fit stud diodes made by Motorola. I have actually manged to push these out on odd occassions using about half inch rod and a mallet.

Copper Oxide diodes were used for moving coil instrument rectification.

Chris.

[Bob Mannix]

Yes, my dad had one for the car, 12V motor and little 240V alternator in the same package. Noisy and inefficient! Remeber my Triang TT gauge train set as well although we were always AC (being as , ahem, young as I am). One of my friends, having experienced the tingle you get if you put 6V battery terminals on your tongue decided to try the output of the Triang transformer set on his tongue. He didn't do it again. The best way he could find to describe it was it being like being struck simultaneously by torpedos on each side of his head. I decided not to follow suit!

[Andy Champ]

That serves me right for researching! Looks as if DC was around much later than I (and that website) thought.

Andy

[Andy Dingley]

Do you _ever_ post anything that isn't total rubbish?

When did you see a copper oxide rectifier with an adequate power rating for a battery charger?

Back in the days when transformers were relatively cheap compared to rectifiers, it was near universal to obtain full-wave recitified output from a pair of half-wave rectifiers and a centre-tapped transformer.

[Harry Bloomfield]

Dave Plowman (News) wrote on 13/09/2007 :

I had one too and from what I remember it was 12v DC for the trains fed via a reversing rheostat and a 15v AC supply for points. I seem to remember the rear of the unit had a 12 DC controlled output, 15v AC and a 12v DC uncontrolled output able to supply a second add-on rheostat control for another track.

The buzz from the trip button was caused by the raw DC passing through it. The AC supply would be used to feed a points switch lever, which energised one of two coils at the points - one pulling one way and the other the opposite way. Hold it at the energised position too long and the coils would overheat.

[Harry Bloomfield]

A predecessor for what we would now use an electronic inverter for - most common today would be 240v from a 12v car battery supply, but almost anything is possible with an inverter.

You used to be able to get hold of lots of rotary converters of various voltages at the ex-army electronics dealers. The cheapest ones were those designed for 400Hz aircraft supplies. I met one guy in the

1960's, who had an ex-MOD 12v to 240v rotary inverter under his car bonnet. He used it to supply his electric shaver when he was camping.