DC Farm supply in USA, why 32V ?

[60 oldjohn]

32v dc seems an odd voltage, and not multiples of 12v or 6v lead acid tractor batteries. Was it anything to do with aircraft surplus stock after WW11 ?

John.

[Herald1360]

Wasn't it considered to be the highest voltage that was safe under all conditions?

[G6Tanuki]

Most of the 32V farm-systems predated WWII by a couple of decades.


http://www.doctordelco.com/Dr._Delco...lco-Light.html
http://en.wikipedia.org/wiki/Rural_e...#United_States
http://antiqueradios.com/forums/view...179415&start=0
http://www.powerstream.com/1922/batt.../chapter17.htm

"Rural Electrification" projects to replace the old "Delco-light" generators/wind-turbines/batteries and similar 32V systems by connection to proper mains-power were actually a big part of the 1930s make-work schemes put in place during the Great Depression (also, the Hoover Dam).

Why 32V though seems to be ill-defined. People mention that railroads used 32V.

[broadgage]

Several reasons seem probable and have been suggested.
About the highest voltage that is safe except under very improbable conditions.
Already in use for railway coaches, yachts and boats.

Although not a multiple of 6, 32 volts is a multiple of both 4 and 8. In years gone by, 4 volt and 8 volt batteries were common.

Another advantage of 32 volts is that very cheap mass produced "bus bulbs" may be used for domestic lighting and give a good compromise between lamp life and light output.
Although by convention "bus bulbs" are called 24 volt, they are in fact designed for 28 volts, this being the voltage present in a bus when the engine is running and the 24 volt battery is on float charge.
In a home lighting plant with the battery being discharged, it would probably deliver about 31 volts at the battery and about 29/30 volts at the lamps.
Running 28 volt lamps at 29 or 30 volts would give an improved light output, and an acceptable life, especially as the lamps would not be subjected to the vibrations on an early motor bus.

[60 oldjohn]

Interesting, I thought it was a supply cobbled together by the farmers. I didn't know they were not tractor batteries, but dedicated cells. Never heard of 4v & 8v batteries. The idea is lot older than I had imagined.

John.

[AC/HL]

We think of battery valves as 2 volts, but they were available as 4 or 6 volts for a time at least. It's mentioned on a Cossor Melody Maker plan.

[turretslug]

I'm sure I heard of a class of (valve) radios that were intended to run from nominal 32VDC farm supplies without resort to vibrators, dynamotors etc., I suppose even adapted "midget" sets would have served as a basis, though volume wouldn't have been stunning. The odd little 28D7 probably featured in a few, perhaps even the likes of the 25L6? The military BC1206, a direct-use 28VDC beacon receiver proved that it wasn't a flakey concept.

[broadgage]

8 volt lead acid batteries are readily available today in the USA, often used several in series to power electric golf carts and other lightweight electric vehicles. 4 such batteries in series are used by enthusiasts who keep in working order vintage 32 volt lighting sets.

4 volt batteries are less popular these days but are still made by at least one manufacturer in very large sizes for off grid homes.

32 volt equipment was never very popular in the UK, more of a USA thing.

[broadgage]

At least 3 different technologies were used to operate a valve radio from the 32 volts.

The heaters were invariably series connected with a dropper or sometimes just one or two dial lamps.

Some sets simply used the 32 volts for HT, this worked to an extent but give limited volume unless special and expensive valves were used.

Another approach was to use an external battery in series with the 32 volt supply to provide HT. This would be of lower voltage and therefore cost than if providing the whole of the HT voltage from batteries.
Back in the day, large dry battery handlamps that used 6 volt batteries with screw terminals were very popular. When too run down to light a 500ma bulb, these batteries could be used several in series at effectively zero cost, to supplement the 32 volt supply.
Or a purchased, relatively low voltage HT battery could be used, perhaps 45 volts.

The large 32 volt battery bank would not last forever of course. When replacement was needed, some people kept the old bank and used this in series with new main battery bank to give 64 volts nominal for HT.

Very large premises might have 2 independent 32 volt lighting plants, in which case one could earth the negative of one system and the positive of the other, and thereby obtain 64 volts HT between the 2 systems.

Other sets simply used a vibrator unit as in vehicle radio practice.

[G6Tanuki]

Originally Posted by turretslug

I'm sure I heard of a class of (valve) radios that were intended to run from nominal 32VDC farm supplies without resort to vibrators, dynamotors etc., I suppose even adapted "midget" sets would have served as a basis, though volume wouldn't have been stunning. The odd little 28D7 probably featured in a few, perhaps even the likes of the 25L6? The military BC1206, a direct-use 28VDC beacon receiver proved that it wasn't a flakey concept.

32V-HT was a problem when it came to audio power stages: I recall seeing the circuit of one such farm-radio that used six directly-heated triodes in zero-bias push-pull-parallel with 32V on the anodes. A seventh such triode was used as the transformer-coupled driver stage.

I gather also that some of the early 32V radios had difficulties with the local-oscillator being unreliable, particularly on short-wave.

[AC/HL]

Please keep on topic, problems running valve radios on low voltages.
Cars, Steam Locomotives and Aircraft are not really relevant here.