• Why 64 Volts?

  • General discussion about locomotives, rolling stock, and equipment
General discussion about locomotives, rolling stock, and equipment

Moderator: John_Perkowski

  by RMFLinton
:-D I'm sure this question has been asked in the past, but I've been unable to locate a post to answer it...

Why do locomotives use a nominal 64 volt battery system? I've always assumed it was to limit the size and current to the start motors, but that's just an assumption. Does anyone know the origin of 64 volts, and why it wasn't something different? (ex: why not 48, 60, 68, etc). I've heard other theories to the origin in the past, ranging from making it impossible to use railroad batteries on "non-railroad" uses, the maximum output of steam dynamos for lighting, and being able to use 120 volt AC power through simple rectifiers to power loco systems and maintain batteries. I suppose all could be plausible, so I'm curious to hear the other members input on the background.

  by DutchRailnut
The max voltage allowed has to do with electric code, as not allowing a voltage over xx volt to ground or certified electricians need be used.
The locomotive voltage is actually 72 volt as that is charging voltage for a 64 volt battery.
  by JimBoylan
Many steam locomotives, some smaller Diesels, passenger cars, and rural farmhouses used 32 volts Direct Current batteries and/or generators. Baldwin Locomotive Works made Diesels for the Copper Range RR in Upper Michigan with 112 volts of battery, to be charged at 128.8 volts. That's 2.3 volts per 2 volt battery cell.
  by CN Sparky
...and that 64 volts is made up of eight 8-volt batteries connected in series to make up the 64 volts. Or two 32-volt batteries on some of the big boys.

Most of the road units I see running are putting out around 74 volts, not 72. Though the yard engines can be all over the place... whoever decided regular maintenance of these things wasn't necessary, I'll never understand...
  by DutchRailnut
The output you see is charging voltage, not the battery voltage.
And the charging voltage varies, as the charger will raise the voltage to put more current in battery.
A trickle charge will be around 69 volts and a heavy charge can go as high as 76 volt.
  by farecard
Didn't cars go from 32 to 64 [nominal]? I recalling being told years ago that to do so, they went from single-ended 32 to center-tapped 64; i.e both + & - legs above a centertap.

  by Owen S. Paulsen
This is In 1924-1925 ALCo Boxcabs Diesel-Electric Switcher Locomotive.
And in 1928 ALCo Diesel-Electric passenger Locomotive for New York Central.
You do not have the required permissions to view the files attached to this post.
  by Owen S. Paulsen
This is continued fron the first post
You do not have the required permissions to view the files attached to this post.
  by Owen S. Paulsen
This is continued from the second post
You do not have the required permissions to view the files attached to this post.
  by Owen S. Paulsen
This is continued from the third and final post

This is from American Technical Society Copyright 1905,1906,1909,1911,1913,1914,and 1916.

This idea for a Locomotive in Steam era on loco engine was was 64 Volt plus charge a 72
Volt I belive the is way the first Diesel have 64 Volt so to reason:
It Shop the battery for it 64 Volt.
The size 4 cell for battery as at equalling in size old for train lite.
In 1924-1925 ALCo Boxcabs Diesel-Electric Switcher Locomotive.
And in 1928 ALCo Diesel-Electric passenger Locomotive for New York Central.
You do not have the required permissions to view the files attached to this post.
  by Pneudyne
Some years back I did look for “hard” information as to the origins of the 74/64-volt standard for North American diesel locomotives. I did not find very much, but this item from the Simmons-Boardman 1954 publication, “Diesel-Electrics..How to Keep ’Em Rolling” (LCC 54-10911) was useful:

“Early diesel-electric locomotives had 16-cell batteries, like railroad car lighting systems. As the diesel engines got bigger, this was not enough voltage to give the heavy cranking currents required. So the battery was doubled, giving the present 32-cell, 64-volt system”.
Simmons-Boardman DE p.112.jpg
That book essentially addressed Alco-GE electrical practice of the time, and was written by GE staffers. Given that GE was “in at the beginning”, as it were, then the above commentary reasonably could be taken as being authentic.

Of course, that “answer” simply moves the question back to why was 32 volts chosen for railroad car lighting. That seems to be less clear. 32 volts was also widely used for farm powerplants and industrial safety applications, and also for some road vehicle applications, but these may all have postdated the railroad case. The safety aspect may have been in mind when railroad car lighting was first visualized.

As already outpointed, some care is needed in interpreting nominal voltage numbers, as practice is not consistent, either amongst industries or even within them. Sometimes the battery voltage is quoted, based upon 2 volts per lead-acid cell. At other times the generator charging voltage is quoted, and the basis for this is not always consistent.

To quote again from the above-mentioned book:

“To charge this [64-volt] battery you have to set the voltage regulator for 32 x 2.32 volts, or 74 volts. This may vary some according to the weather. In cold weather, you may have to set it up a bit. Since the locomotive charging system works at all engine speeds, - even idling – you never have to change the setting much. You seldom will go below 72 volts and never above 76 volts.”

So within the railroad industry it had been common practice to refer to “32-volt” systems (nominal battery voltage) for car lighting and small locomotives, and to “74-volt” systems (nominal generator voltage) for larger locomotives. That said, the auxiliary electrical system of the PRR E2b AC electric locomotive was described as being fed by a 37.5-volt DC generator; one assumes that the battery was 32 volts.

Some further information on generator voltages is available from the battery-maker data sheets included in the GE 70-tonner maintenance manual, attached.
Exide 4843 p.03.jpg
Gould 751B p.03.jpg

Exide stated that the generator voltages should be 74 volts for 32-cell batteries and 130 volts for 56-cell batteries. The corresponding numbers from Gould were 74 volts and 129 volts.

The 56-cell case would, I think, have referred to the “125-volt” auxiliary electrical systems used by Baldwin and Fairbanks Morse on some of their diesel-electric locomotives of the late 1940s. Given that the generator voltage was 129 or 130 volts, and the nominal battery voltage was 56 x 2 = 112 volts, the “125-volt” number may be seen as some kind of weighted average of the two. That is more evidence of inconsistency in the way that locomotive auxiliary electrical systems are specified.

Worldwide, practice has varied somewhat. In the UK, British Rail in 1955 adopted 110 volts as the standard for its line-service diesel locomotives, although other voltages were used for some switchers and EMUs and DMUs. (Car lighting in the UK and other British-influenced countries was usually 24 volts; 12- lead-acid cells.) This 110-volt number, amongst others, had previously been used by all of the major UK electric equipment makers. I suspect that it was adopted in part because 110 volts DC was an established marine and industrial standard, for which switchgear designs, etc., were readily available. It was based upon the use of a 48-cell lead-acid battery, which implies a charging voltage of 2.29 volts per cell. 110 volts was also the norm for British export locomotives from the early 1950s.

The French mostly used what were described as “72-volt” systems on both domestic and export diesel-electric and electric locomotives, and usually with alkaline batteries. Generator voltages and battery cell counts seemed to have varied a little, but one example was 78 volts and 54 (alkaline) cells. In practice this 72-volt standard was probably not materially different to the American 74-volt standard.

Many JNR (Japan) locomotives were described as having “100-volt” auxiliary electrical systems (although some early AC electric locomotives were “52-volts”.) On the face of it, this looks like yet another standard, but in fact it was not. A description for the 1950s DD50 and DF50 diesel-electric locomotives shows that they had 48-cell lead-acid batteries, and that for the DF50 at least, the auxiliary generator voltage was kept in the range 95 to 110 volts. So the “100-volt” number was again a weighted average of some kind. Possibly it was chosen because Japanese domestic electricity supplies are 100 volts. Thus Japanese export locomotives that went to railway systems who specified or accepted 110-volt auxiliary electrical systems did not require anything different to what was used for domestic practice.

You do not have the required permissions to view the files attached to this post.
  by ex Budd man
Great info, I'm always asked by newbies "is it 64volts or 72 volts?" If you 'do the math' battery voltage is 64vDC, but charging voltage must be higher thus 72-74vDC.Just as with an automobile battery/charging system where a fully charged battery is 12.5vDC and the alternator output is 14.5vDC.