How did battery chargers rectify AC to DC before solid state diodes?

[Stray Electron]

I know about selenium and mercury rectifiers, but rechargeable batteries have been around a long time. How did people charge batteries from AC without resorting to such expensive rectifiers?

Selenium and copper oxide rectifiers, both crude forms of semiconductor diodes, were cheap.They performed poorly compared to modern silicon rectifiers, but they did a perfectly serviceable job in their day.

   Nails it!

[Connecteur]

What about the vibrating rectifier? The AC causes a relay to invert the inverted power, converting it to DC.

[coppice]

What about the vibrating rectifier? The AC causes a relay to invert the inverted power, converting it to DC.

I covered that one earlier in this thread.

[TimFox]

At the other end of the voltage range in years gone by, Shimadzu (the first Japanese x-ray equipment manufacturer) brought a century-old museum piece to their exhibit at RSNA a few years ago that featured a mechanical rectifier to rectify the high-voltage transformer output.  A rotating spark gap, driven by a synchronous motor, rectified the voltage applied to the x-ray tube by commutation.  Probably wouldn't pass modern EMI regulations.

[Gyro]

Most mercury rectifiers were of the pool + arc type. They were common in the 1950s, but pretty much gone by the end of 1960s, because silicon rectifiers developed so fast and outclassed them. British Rail introduced trains running from 25kV AC at the beginning of the 1960s, using mercury arc rectifiers in the trains, and they were a disaster. Those rectifiers worked well in fixed locations, but very poorly with the mercury sloshing about on the move. Luckily, silicon rectifiers came to the rescue in the nick of time, and the trains ended up working well.

UK suburban services (the 600 / 750V 3rd rail ones) used stationary mercury rectifiers for a very long time. Likewise the London Underground train supply.

[coppice]

Most mercury rectifiers were of the pool + arc type. They were common in the 1950s, but pretty much gone by the end of 1960s, because silicon rectifiers developed so fast and outclassed them. British Rail introduced trains running from 25kV AC at the beginning of the 1960s, using mercury arc rectifiers in the trains, and they were a disaster. Those rectifiers worked well in fixed locations, but very poorly with the mercury sloshing about on the move. Luckily, silicon rectifiers came to the rescue in the nick of time, and the trains ended up working well.

UK suburban services (the 600 / 750V 3rd rail ones) used stationary mercury rectifiers for a very long time. Likewise the London Underground train supply.

Yep, the stationary ones work well. I saw some monster ones in industrial applications in the 80s, where they worked well enough there was no point in replacing them with superior silicon rectifiers until they failed.

[edpalmer42]

Another early non-solidstate rectifier was the Exide Rectifier.

https://www.americanradiohistory.com/hd2/IDX-Service-%26-Sales-IDX/Archive-Radio-Retailing-IDX/IDX/20s/Radio-Retailing-1925-02-OCR-Page-0089.pdf

One terminal was lead, the other was aluminum.  Add water and a packet of powdered chemicals and it formed a rectifier.  I saw a description in a 1930 book about storage batteries.

[Renate]

UK suburban services (the 600 / 750V 3rd rail ones) used stationary mercury rectifiers for a very long time. Likewise the London Underground train supply.

Not to get too tangential...
I remember the "Green" subway line in Boston in years gone by had lighting int the tunnels
that consisted of a foot square piece of plywood with five household lightbulbs in an "X" pattern.
5 x 120 V = 600 V, AC or DC, it's all the same.

[BrianHG]

Here is a restoration of a 1920's rare battery charger.  Before skipping to the end to see it working, see if you can figure out how it gets DC from the AC source:

[tooki]

How did people charge batteries from AC without resorting to such expensive rectifiers?

using 20 cents rectifier ic like this... https://lcsc.com/product-detail/Bridge-Rectifiers_DIOTEC-S380_C212805.html why bring up or even consider semi conductor from jurassic age?

It's like someone asking how Roman chariots were built, and you tell them why even consider an ancient chariot, just go and buy a cheap bicycle 

read again the OP.. he asked how to build a roman chariot, without using expensive roman chariot.

Uhhh, nope. OP did not ask for advice on how to do it. They asked how it was done in the past.

Don’t tell other people to read when you’ve demonstrated your inability and/or unwillingness to do so yourself.

[bdunham7]

ditto!... whats the purpose of placing solid state diodes afterward anyway? if its already rectified to DC? just to drop few multiples of 0.3V? to avoid over voltage trickle charge level? i havent seen that kind of trick recently done by factories... except with my own very crude and unintelligent charger ymmv.

Perhaps there is a linguistic or idiomatic barrier here?  Nobody suggested an alternator--I suggested a DC generator--and 'before solid state diodes' in this case means 'in the time preceding the invention of silicon power rectifiers'.   It's not a bad question, AC power and rechargeable batteries predate silicon rectifiers by more than 50 years. 

[bdunham7]

Here is a restoration of a 1920's rare battery charger.  Before skipping to the end to see it working, see if you can figure out how it gets DC from the AC source:

It uses vibranium!  That's an interesting core on that transformer. 

[Robert Smith Eco Warrior]

I am not that good with history but I think a lot of equipment avoided AC entirely.
I have a 1940 Lister generating set that is 3kW 110v DC and was used to power a large house.
I also lived in a cottage that was part of an estate belonging to a big house. The big house, not he same one my generator was from, had a room with rows of glass tanks about 2 feet wide, deep and tall and about an inch thick glass. These tanks were big flooded lead acid batteries for powering that big house. The lead had been taken for scrap years before just leaving the big glass tanks.

[james_s]

Perhaps there is a linguistic or idiomatic barrier here?  Nobody suggested an alternator--I suggested a DC generator--and 'before solid state diodes' in this case means 'in the time preceding the invention of silicon power rectifiers'.   It's not a bad question, AC power and rechargeable batteries predate silicon rectifiers by more than 50 years.

Maybe that's it, that didn't occur to me. In this case "before" clearly means back in an earlier time, prior to the invention of solid state diodes. Not placed before a diode in a circuit. There was a time before silicon diodes existed, and the OP is asking what methods were used back in that time. Totally reasonable question.

[janoc]

It seems that nobody has posted this here yet:
https://en.wikipedia.org/wiki/Rotary_converter

These were pretty common for powering trams, railways, metros and such.

Still in operation in 1996:

https://www.nycsubway.org/wiki/IRT_Substation_21

And a video of it running:



And startup with explanation:

[BrianHG]

Here is a restoration of a 1920's rare battery charger.  Before skipping to the end to see it working, see if you can figure out how it gets DC from the AC source:

It uses vibranium!  That's an interesting core on that transformer.

LOL, Literally...

[coppice]

It seems that nobody has posted this here yet:
https://en.wikipedia.org/wiki/Rotary_converter

These were pretty common for powering trams, railways, metros and such.

Still in operation in 1996:

You could still find mainframe computers in the late 80s running from rotary converters, although most of those were used to convert 50/60Hz AC to 440Hz 3 phase AC, to simplify the power supplies.

[TimFox]

Nomenclature detail:  strictly, "generators" make DC and "alternators" make AC.
A motor-generator set has a motor driving a "generator", which strictly means a DC generator.  Dynamotors (common field with separate armature windings on a single rotor) were used in WWII military radios to produce high-voltage DC for the plate supply from a low-voltage source (e.g., 200 or 250 VDC from a 28 VDC vehicle battery).
A rotary converter has an AC motor driving an "alternator", which generates AC.  These are commonly used to change frequency, as in the 400 Hz case above and electrified railways (e.g., the Swiss railways that use 16-2/3 Hz AC, a subharmonic of the 50 Hz commercial mains).

[bdunham7]

Nomenclature detail:  strictly, "generators" make DC and "alternators" make AC.

'Alternator' certainly seems to imply AC, at least internally, but 'generator' is a more generic term and the term is widely used that way.  It could be generating AC, DC or smoke.  Do you have a style guide somewhere that specifies that the term 'generator' can only apply to DC?  Perhaps you are thinking of 'dynamo'?

[TimFox]

The term “generator” is now generic, including DC, AC, noise, RF, etc.
I remember when alternators (with solid-state rectifiers) replaced generators in automobiles, and that was the distinction.
“Dynamo” is still restricted to mechanical generators with a commutator to produce DC.

[coppice]

Nomenclature detail:  strictly, "generators" make DC and "alternators" make AC.

A generator is something that generates something. Its a very generic term. An alternator is merely something that alternates, although in electrical terms we have a fairly clear idea what that means. I don't remember the big generators in power stations being referred to as anything but generators or generating sets.

[bdunham7]

I remember when alternators (with solid-state rectifiers) replaced generators in automobiles, and that was the distinction.
“Dynamo” is still restricted to mechanical generators with a commutator to produce DC.

I don't know if Westinghouse used the term to distinguish his generators during the AC/DC wars, but Chrysler used the term in advertising to distinguish their product and it stuck.  Years later, the SAE standardized terms and now it is 'officially' referred to as a generator in modern day service and parts manuals.  I guess that's the metric equivalent of an alternator.  I would point out that all of the devices mentioned so far actually produce AC at their core, the automotive alternator using rectifiers to produce DC while the dynamo is actually a many-phased AC generator that uses mechanical rectification--the commutator.  The only mechanical true DC generator I can think of would be a Van de Graaf type.

[Zero999]

The only mechanical true DC generator I can think of would be a Van de Graaf type.

Look up the homopolar generator.
https://en.wikipedia.org/wiki/Homopolar_generator

[Gyro]

It's sad that Faraday never thought to try cutting some radial slots in the disc. I remember trying the one in the Science Museum in South Kensington (when you were allowed to do such things). It was a bugger to turn at any significant speed!

[janoc]

Nomenclature detail:  strictly, "generators" make DC and "alternators" make AC.
A motor-generator set has a motor driving a "generator", which strictly means a DC generator.

That's not true. You have plenty of diesel-powered generator sets that generate AC:
https://www.survivalcenter.com/Diesel%20Generators.html

I would even argue that AC generators are way more common because they are simpler and more useful (most appliances meant to run from mains need AC) than DC which would require an inverter.

Or even electrically powered sets:
https://www.horlick.com/products/motor-generators/

A rotary converter has an AC motor driving an "alternator", which generates AC.  These are commonly used to change frequency, as in the 400 Hz case above and electrified railways (e.g., the Swiss railways that use 16-2/3 Hz AC, a subharmonic of the 50 Hz commercial mains).

That's not quite true either or rather it is not the only type. Read the articles I have posted and watch the video. They explicitly talk about rotary converters with DC output. That's from New York subway which was converting 25Hz ("cycle") AC to 625V DC used for the third rail.

These actually predate the use of the frequency converting types by a lot - the substation with the converter from New York was built and operating roughly 10 years before Switzerland has even adopted that 16 2/3Hz for railways and 2 years before the first line electrified by this type of system (at 16Hz) by Siemens started to operate in Bavaria.

Also, rotary converter is not a "motor driving a generator" (i.e. implying two machines connected by some shaft, belt or gears), even though the function principle is the same. The two machines actually share the same armature and field coils, making the whole assembly smaller, lighter and more efficient than having two units connected only mechanically, as is common in motor-generators.