Accumulators

[G6Tanuki]

Originally Posted by Herald1360

Wasn't the rather odd 6.3V rating for valve heaters derived from the fully charged voltage of a 6V car battery anyway? Or maybe it's the midpoint voltage between the "on charge" and rated end of discharge voltages. For ac transformer operation it would have been an odd choice of value.

Yes, 6.3V was first adopted (primarily in the US) because it was the 'right' filament-voltage for car-radio applications running off a 6V battery (back then 6V was the standard car-electrical voltage, and car-radios were much more rapidly adopted in the 1930s US than elsewhere).

When 6V became insufficient to start more-modern high-compression engines, cars switched to 12V and the radios moved to 12.6V filaments to match. 12.6V was also used as the 'HT' on a range of designed-for-car-radio-applications valves in the 1950s, often in association with a single big power-transistor (OC16 or similar) as a Class-A audio-amp.

25.2V was the next step-up for filament voltage, based on the 24V electrical system used in trucks. There were also valves designed to run with 27-28V filament-power because that had become the standard in aviation applications.

32 Volts was also used widely in 'farm radios' in the US (the power coming from batteries charged either by a windmill-powered generator or an engine, which often also powered a well-pump). I've never seen 32V-filament valves, farm-radios generally used lower-voltage-filament valves wired in series - one I recall had *six* triodes in its output, three in each side of a push-pull Class-B output stage, you needed to do that in order to get enough audio 'oomph' when you only had 32V of HT available!

[turretslug]

The oddball 28D7 is illustrative of just how inefficient trying to get decent output power from HT of around 28V was when comparing required heater current/power vs. HT ditto and actual output power!

http://www.r-type.org/exhib/aaa0899.htm

[G6Tanuki]

Originally Posted by turretslug

The oddball 28D7 is illustrative of just how inefficient trying to get decent output power from HT of around 28V was when comparing required heater current/power vs. HT ditto and actual output power!

http://www.r-type.org/exhib/aaa0899.htm

Yes, in terms of audio-output-power vs heater-power-consumption the 28D7 must qualify as a serious under-achiever in the world of audio power application.

[The only place I've ever seen a 28D7 in real-world use it had both halves strapped in parallel and was used as a DC-amplifier to activate a relay which in turn activated a lamp on the pilot's instrument-panel at a crucial stage of approach]

[broadgage]

Regarding the farm radios for 32 volt supply, some sets used an external battery in series with the 32 volt supply in order to obtain a higher HT voltage.
An old vehicle battery was one option, or a couple of 6 volt dry batteries. Handlamps that used a 991 6 volt battery were popular, and such batteries when too run down to give a good light, could still supply HT in series with the 32 volt supply.

[Heatercathodeshort]

This contraption allowed you to charge 2V accumulators from your DC lighting mains. The lamp acted as ballast according to it's wattage. The meter showing the charge together with the lamp ballast was in series with the accumulator leads. [Dragged off dump years ago]
Another bodge if you had a DC supply was connect the battery across the light switch itself. With the switch off the accumulator would charge at a rate determined by the wattage of the lamp.
It's all so easy now! John.

[Richard_FM]

My Dad had a book on the development of buses out from the library once, & a photo of the interior of a bus from the 1930s-40s there was a sign stating that carrying wireless accumulators on board was forbidden.

[broadgage]

I believe that most bus companies prohibited the carrying of accumulators on their vehicles, presumably for fear of acid spillage.
In urban areas, an accumulator charging shop was generally within walking or cycling distance.
In more rural locations, the local radio shop offered collection and delivery service.

There was little demand for charging services once mains electricity became available.

[turretslug]

There was probably a fair amount of anecdotal awareness that charged accumulators with chunky exposed terminals could be dangerous in careless hands, even if the consequences weren't always as serious as this tragic tale;

https://www.bbc.co.uk/news/uk-scotland-50502446

I'm sure we've all heard the legion tales involving metal tea-trays and submarines, too- even if fanciful, it goes to show that there was awareness of the potential (!) hazards.

[TonyDuell]

Originally Posted by broadgage

I believe that most bus companies prohibited the carrying of accumulators on their vehicles, presumably for fear of acid spillage.

When I was in Bristol about 30 years ago you could not carry a car battery on the buses. I assume that was due to the risk of leaking acid (I did carry a sealed lead-acid battery ('Gel-Cell') from Maplin on the bus a couple of times)

[AC/HL]

To be honest, I can't imagine that coming as a surprise to anyone, then or now!

[G6Tanuki]

Public transport has traditionally not-liked anything risky: my local busco bans the carriage of tins of paint, and some decades ago a friend was refused entry to a bus because he was carrying two ferrets and ten dead rabbits.

Old-style 'open top' glass-jar accumulators I can understand being a significant acid-goes-everywhere-if-you-hit-a-big-bump risk, but by the early-1930s there were plenty of "spillproof" accumulators which had a labyrinth in the vent-plugs to stop the escape of acid if they were tipped over. I remember in the late-60s buying some 2V 16AmpHour new-but-ex-Military accumulators made by "Pritchett and Gold and EPS" which had robust pitch-impregnated-fibre cases and labyrinth-seal vents. 1944 manufacture-dates embossed on the cases. I believe these were originally used to power short-range "WS17" superregenerative VHF transceivers during WWII searchlight operations. They were cheap, and I suspect that the spongy-lead had deteriorated with age because even after being introduced to fresh electrolyte at the recommended specific-gravity they didn't really survive more than 20 or 30 charge/discharge cycles.

[broadgage]

Bus companies, past and present, often prohibit the carriage of "unwrapped glass" which would preclude glass cased accumulators even if not specifically noted.
I have seen a bus conductor decline to accept a portable TV set due to the "no unwrapped glass" rule.
Likewise glass bottles of drink, even lemonade or other soft drink are often banned. It is the glass that is the problem, not alcohol.

[bobsterkent]

I believe that most bus companies prohibited the carrying of accumulators on their vehicles, presumably for fear of acid spillage.

Maidstone and District certainly had this in its 'terms of carriage', however as a newbie conductor found out in the 60's it was often ignored as the tiny hamlets out past Teynham were still not on the grid and the residents had to carry them in to Faversham for charging.

[AC/HL]

I think we've got the idea that accumulators weren't welcome on buses, also by extension other forms of transport, for well understood reasons. When contemporary, businesses offering the service were widespread.
The OP was asking about the accumulators themselves.

[broadgage]

Once motor cars became popular, some people charged wireless accumulators from the car battery, either whilst driving the vehicle, or overnight in the garage.
Others simply purchased a spare car battery, and used one indoors for the wireless and maybe some minimal lighting.
It was a simple matter to swap the batteries over when the indoor one was discharged. Most cars in those days had cranking handles.

With reasonable knowledge, a wireless intended for a 2 volt accumulator could be modified to use a 6 or 12 volt battery.
Options included a dropper resistance in series with each heater, or replacement valves with 6 volt heaters, or re-connecting the heaters in series.
Some people also derived the HT from a car battery, as in a vehicle radio by means of a vibrator.