E.J. didn’t go into specifics as to how the “dim” option worked, however the Crouse-Hinds catalog is pretty detailed from what I’ve seen. Maybe they do?
One way to “dim” an arc lamp is to reverse the polarity feeding the lamp, works best when the two rods are of different material.
Starting in the 1920’s, there was a trend to using an M-G set to convert 600VDC to a lower voltage with a further advantage that the lower voltage could be regulated (i.e. doesn’t vary with trolley potential).
Don’t think this is a good idea with carbon arc, particularly if some of the pre-magnetite systems of regulation and automatic feeding are being used – all that reversing the polarity will do is cause the ‘other’ carbon to burn preferentially, and many of the feed mechanisms aren’t set up for that.
Does it matter in a modern short-arc envelope bulb which way the DC is applied? I did not think it did, but never thought about ways it might be designed to be ‘dimmed’ simply by reversing polarity.
If one rod is more refractory, then it should certainly be possible to diminish the luminosity of the arc as struck, and it would be interesting to see how this might be set up in practice for interurban ‘city’ use.
But you would not be using ‘stick’ arc lights with this in the first place – assuming that voltage control, and not current control, would affect the effective arc brightness at comparable maintenance, and that there were ‘enough’ low-voltage services on the car to warrant the expense of a motor-generator setup in the first place.
Of course, there are other ‘issues’ with a motor-generator setup. When I was inspecting the Liberty Liner in the Rockhill Trolley Museum, they pointed out the small incandescent bulb in the MG box that always had to be kept burning or else! Condensation moisture would accumulate in there … on the commutator and brushes … and you could find yourself in Flashover City, very very unhappy, without much advance warning. <
In most city cars the headlight was part of a string of bulbs. Depending on the reflector, a standard 56 watt streetcar bulb could be reasonably effective. Some systems used a higher-wattage bulb for the headlight in a string with lower-wattage bubs and dimmed it by cutting an additional bulbs into the string.
The dropping resistors used in the streetcars I have worked on are either cast segments similar to those used for motor control (but smaller), or nichrome wire on ceramic cores similar to electric heating units. Both would have been familiar to shop forces.
To run a 150 watt 120 volt bulb on 600 volts the dropping resistance required is 384 ohms, the equivalent of four more 150 watt bulbs. To dim the bulb, just add more resistance.
But note: (1) how much power you use in order to use the bulb in the first place, and (2) to dim it, you need to throw away even more power in the dropping resistors.
If you wondered where the money for the motor-generator setup would come from, any long-term analysis of this situation (once electricity costs ceased being “internal” to operations of utility companies and the like) I think this explains much.
I will have to dig ito the literature on the “Golden Glow” headlights to get the full story, but my recollection was that it used one copper electrode and one carbon electrode. IIRC, the copper electrode was negative in normal operation (i.e. emitting electrons) and the carbon electron was emtting light (electrons striking a crater in the carbon electrode was heating the crater to incandescense). In reverse polarity operation, the copper electrode would be emitting light, and would be running at a lower temperature and thus producing a “golden glow”.
N.B. I did find the source for reversing current to dim the arc - Electric Railway Engineering by Francis H. Doane published in 1915. The upper electrode was copper, lower electrode was magnetite in an iron tube. “High beam” o
Correct me if wrong, but I think most of the ‘Golden Glow’ secret sauce was in the reflector design, which I dimly recall may have involved “back-silvered” uranium glass. I thought most of those lights were using Mazda-type tungsten bulbs soon after those were commercialized (which coincided roughly with 1915…).
I wouldn’t be surprised to see the ‘golden’ reflector used with an arc source, but wouldn’t expect a non-carbon (I.e. non ‘flame’ arc) setup to produce other than a blue-white native light. On the other hand if copper is the ‘sacrificial’ electrode we have another strong possibility for where Quimby’s “green color” in the dimmed arc might come from.
PCC cars (even air-electric) have M-G sets and batteries. Many “standard” cars built in the 1920s and '30s have a battery charging circuit using the air compressor’s voltage drop.
An earlier example of using “voltage drop” to charge batteries was the 5,000V Grass Lake experiment, where the battery was in series with the traction motors.
M-G sets plus batteries have several advantages over series strings running off of 600VDC: Lights in parallel so one light burning doesn’t darken the whole string; safety as 32V is much less of a hazard than 600V; Lights running at constant brightness; 32V lights more rugged than 120V lights.
Third Avenue Rail System’s homebuilt lightweights had a belt-driven 24v generator running off the compressor shaft to charge batteries, used mostly for door controls as lights were still in 600v strings.
The lightweights were some of the last streetcars built that had 600 volts in the controllers (one each end) with K-type controllers (I think K-35), and a line-switch (crcuit-breaker) above on the ceiling. Even earlier cars, like the Brill 1931 Red Arrow cars, had low-voltage control systems controlling contactors for both resistancce insertion and removal and transition from series to parallel. In the traditional K-Type controller, this is all done manually by the controller handle and contact wipers and copper strips within the controller.
The lighting in the Broadway-42nd Street cars, 551-625, looked exactly like PCC lighting. These were the only Third Avenue cars with dropped celings, the others exposed the wood ceilings and had bare-bulb lighting just like the convertables and “box cars” (bowling-alley seating) they replaced. But the PCC-type glass diffusers were below the usual 32-volt bulbs arranged in a string for 600-volt operation. The streetcar 32-volt bulbs had a unique feature. When they failed, they shorted instead of opened. Thus, lighting would continue even before the single bulb was replaced. If more than one failed, then the added current and lower resistance would blow a fuse or circuit-breaker for the string.
The Third-Avenue foot brake is a complex story in inself, with push to the floor for release, and removing foot pressure to apply. Take your left foot off the pedal and emergency brakes apply and the front door opens. Creeping up to another car in the carbarn, you have your controller on the first point of power, maximum resistance in the motor circuit with all motors in series, and then depress and partially release the brakes with your left foot, inching up to the car ahead, as the automatic air-operated underfloor line-switch cuts in and out, out when any brake pressure is present. Fun cars to operate, and learned at age 15 in The Bronx.
Bringing this one back to life, we had a discussion going about arc lights. Were they dimmable, ot not?
Well, I found this interesting video. Now certainly it’s not a trolley headlight, it’s a carbon arc searchlight, but the starting process is interesting. It starts at a dim setting, then the operator reaches inside, throws a switch, and BOOM! The light goes to the max!
So it looks like that searchlight had a dimmable option. Here’s the vid…
https://www.youtube.com/watch?v=HWLmKcZtb-4
Been waiting three days to post this! Glad the Forum’s alive again!
The short answer is “no”. While it is possible to set an arc lamp to delver varying levels of light, the light level is set by the length of the arc. Ironically, a short arc, that produces less light, may actually consume more current.
On most electric railways where arc lights were used, they were used outside the city limits. An incandescent headlight, either built into the dash or hung on the headlight hanger beside the arc light, was used inside city limits.
What it appears you have is ‘brilliant’ and ‘incredibly brilliant’ more than what’s normally intended for 'dim’setting. There is minimum brightness imposed by the physics of the arc and its interaction with the carbon, still brilliant blue-white; I can’t tell whether there is a ‘starting’ current to establish the arc and then a switch to full amperage, or whether there is a setting of the carbon feed that adjusts the length.
A second consideration is that “dimmed” setting on many road vehicles also involves ‘dip’ – the original meaning of low vs. high beams. Some early locomotive headlights had the focus of the parabolic reflector aimed at a fairly close point on the track, as evidenced by early images; it is possible that this was adjustable by shifting the mirror relative to the fixed light source. It stands to reason – some reason at least – that a carbon-arc light could have its light lowered, and some sort of filter or gel interposed in the light path to reduce the glare.
But I doubt you’d dim the arc effectively by tinkering with current supply, and there would be unpleasant effects by trying to modulate the electricity supplied from the DC overhead wire.
Didn’t this turn into a fun discussion?
Continuing with the fun, how’s about an arc light “Death Ray?”
Wait for it…
https://www.youtube.com/watch?v=u8e_u_xqN30
I’ve got to get one of those things to mount of the front of the car. Then the next time I’m driving at night, and some oncoming idiot refuses to dim his high-beams, will I have a surprise for him! [}:)]
Problem is that the autoignition time for his paint and so forth is too long, a bit like using near-visible EM to make missiles fail.
What you want instead is something like the system Tom Clancy proposed to take down Japanese tanker aircraft. A very large capacitor bank discharging into a very large flash tube, mounted in a good front-surface reflector. Bet they get religion about high beams after that!
I’m a bit surprised something along these lines wasn’t used ‘back in the day’ for streamliner recognition, where a rotating vertical searchlight beam didn’t cause enough attention but periodic artificial lightning might have…