[tempest345]

Around 6.3V was a standard voltage for vacuum tube heater pins (the part that emitted free electrons via thermal emission inside the tube to be available for the electrical fields to accelerate).

My guess would be that historically 6.3V supplies made forvacumee tubes where commonly available when transistor based electronics where created so it made sense to utilize them. Works quite nicely for the typical 5V circuits as a "rough" input voltage to be feed through a LDO regulator, for example. And so it just stuck.

[adammunich]

6.3V is the standard voltage of a farm tractor battery --these vacuum tube heaters were designed to use them.

12.6V is two farm tractor batteries (one car battery), which is why our computer industry uses 12V for motherboards (12 volts - 0.6V reverse protection diode).

Early computer power supplies used voltage regulators that were designed for car radios, originally.

[madaxe_again]

That’s because you get ~2.1v out of a single charged lead acid cell, and an old tractor battery contains three. Your car battery has six.

So the real answer to “why” is because of the electrochemistry of lead.

Kinda similar to how a lot of our world is structured around the dimensions of two horses side by side.

[foobarbecue]

Also the electrochemistry of sulfuric acid (the other half-cell)

[psychphysic]

It'd be very hitchhiker-esque if OP got the answer because 3x(1.69 - -0.36) ~ 6.3

[bluGill]

Farm tractors and cars switched from 6 volt to 12 volt at about the same time, and for the same reasons. However the old 6 volt farm tractors are still around and used for framing, while 6 volt cars are rare collectors items (even though there were more of them).

[gary_0]

Some people in the auto industry want to double the voltage again (for efficiency and to reduce the weight/complexity requirements for all the wiring, especially in EVs) but the 12 volt standard is pretty entrenched.

(Note that I'm talking about the voltage used for everything outside of the internal engine/li-ion electrical systems, which already use higher voltages as needed.)

[madaxe_again]

What’s old is new again. Military land rovers from as far back as the 1950s are all 24v.

[namdnay]

I think bikes are 6V, as well as stuff like quads, jet skis etc

[sidewndr46]

not even close. I'm not aware of a single vehicle still in production with a 6 volt battery system.

Many kick-start and pull-start engines do not have a specific voltage but may use an alternator wound with a number of different coils to produce different voltages.

[stmpjmpr]

Marine batteries are commonly 6v.

[K0balt]

….As part of a bank of batteries producing a higher voltage. I haven’t seen any 6v equipment manufactured for any engine based equipment larger than a couple of KW for a very, very long time (mid 1960s). Lower voltage means higher amperage means more weight, more cost, more heat, more failures. Objectively, the world would be a significantly better place if we had fully transitioned to 24v or higher (up to 48v anyway) much sooner than later.

Interestingly, micro-miniaturization has reversed the trend of higher voltage = higher efficiency, at least for computing.

[bluGill]

Often used in series for more than 6 volts. At least in the applications i've seen, though i'm a long ways from a sea and lakes may be different.

[sidewndr46]

yes, because the underlying cell voltage is much lower than that. Many 6 volt batteries still exist because they are used in series to make the desired voltage. They are easier to move around and transport when they aren't build as all the cells in one unit.

[tiedieconderoga]

But don't 12V lead-acid batteries have a wide voltage range between charged (~14.5V) and discharged (~10V)? I don't think they would provide exactly 12.6V very often, or for very long.

[humanpotato]

They are not 14.5V charged. They need about 14V to charge.

https://footprinthero.com/wp-content/uploads/2022/05/Lead-Ac...

[ddalex]

But is the SBR the width of two horses asses ?

[CoastalCoder]

Horses don't "have" asses. They're both individual contributors.

[dghlsakjg]

That's why its pluralized

[downvotetruth]

The adjective form of nouns that refer to animals is usually singular when acting as adjectives (goose liver, dog food, rat race). So, it would be two horse asses. The preference for singular is likely to avoid confusion with the possessive form, which in this case would be missing an apostrophe or of for possession: two horses' asses or the asses of [those (specific / in context)] two horses.

[ChrisRR]

Are you sure about that? Many computers used ±12V in the 80s/90s when LDOs weren't common at all

[rrobukef]

I think the cause and effect was switched. 12V was used because of 12.6V is two batteries, LDO's are used nowadays because 6V, 12V was standard.

[ShadowBanThis01]

Cool info, thanks!

[eimrine]

That was my immediate thought also, but vacuum tubes I know commonly use 6.3V AC.

[makomk]

The filaments will run off either AC or DC because they're basically just heaters. AC became the norm in mains-powered devices after electrification took off, but a lot of the early radios were powered by DC from batteries - initially this was seperate, possibly rechargable, low voltage battery for the filament supply and a disposable high-voltage battery, with the second battery being replaced by step-up devices using vibrators and transformers fairly early on.

[h2odragon]

https://en.wikipedia.org/wiki/Vacuum_tube_battery

Up to 120VDC early on

[jacquesm]

Not necessarily, they would run just fine of lead acid cells, 3 of which produce... 6.3V DC.