Hi collectors,

I own two carbon arc lamps, a 1910's manual-feed magic lantern projector and a 1905's Siemens Liliput lamp.
I know almost nothing about electricity and I feel a bit scared by these lamps (while I'm used to flame lighting and feel confident to light acetylene lamps that people often consider as potential bombs!). So I need some advice before trying them  



About the magic lantern:

The magic lantern comes with its resistor (i.e. a coil around a porcelain cylinder) and I read somewhere that this kind of small projector used a 4A rheostat.

I tried the resistor by plugging it in series with a 500W bulb (I live in Canada so I use 110-120V). The bulb brights dimmer and I feel some heat from the coil:

1) I assume this is the normal behaviour so I can use this resistor, right?

2) I measured 3.15A (with the resistor and the bulb in series): I'm not familiar at all with amperage/voltage/parallel/series notions (I read a few basic tutorials but can't extrapolate to "real life"), so can this measurement allow me to know which amperage applies to my resistor? Or should I plug the resistor directly on 110V with only my ammeter in series, and read the value?

3) Now if I want to try my projector, is the following procedure correct? I install the lantern in series with the coil (as I did with the bulb), then I "strike" the carbons by turning the wheel to bring them together and immediately separate them? Is there a risk of short circuit etc.? Did someone here try this? I feel a bit stressed  

4) The carbon rods are left bare behind the lantern (as shown on this picture, which is not mine but comparable to my projector) as well as the contacts. It seems very dangerous to me! Is the risk of electrocution high or will the coil and carbon resistance make an accidental contact not too painful?

5) I know I MUST always protect my eye from direct lighting (the carbons are enclosed and there's a small red window to see the arc).


About the Siemens Liliput

This lamp was intended to be used indoors indoors and has automatic rod adjustment. Carbons and shade are missing on mine. I didn't find any piece of information about current, voltage, etc. (I contacted the author of this video but he never replied).

1) I was told that I could use carbon-zing cell rods: does it work? I assume this is not the best but remains better than nothing.

2) I assume the black coil thing I see on top of the lamp is the electromagnetic feed mechanism, so I need an extra resistor. Should I guess that it used a 1A resistor? Can I use a 100W bulb (in series) as a resistor?

3) Is there a risk of making everything burning or do these 1900's electromagnetic mechanisms still work well 100 years later?  

4) Because of UVs I have to find a shade. I guess standard electric or gas shades don't filter UVs, so I have to find something specific.

Sorry for making it long, but I prefer to ask you precise questions rather than just asking "Please help me"  
Thanks a lot

It's difficult to advise you what resistance values you might need for your old lamps, because we don't know what supply voltage they were intended for.  A good start however would be to put a fairly small incandescent lamp in series with your setup and test it.  The resistance of the filament will protect your arc lamp circuit fairly well and should still allow you to strike a small arc.  Then repeat with progressively bigger incandescent lamps and keep an eye each time on your resistor.  If at any time it starts to glow even slightly, then you're running it too hard and you should go back to a smaller lamp in series.  You may find however that if your arc lamp is designed for 110-120V that in the end you can use a very large incandescent lamp in series which provides effectively no current limitation, and then know that its safe to simply use the resistance in your arc lamp connected directly to the mains with no protective lamp in series.

You shouldn't feel reluctant to touch the carbons together to start the arc.  I did this many times and it works well!  The volt drop across the arc is in any case usually quite low and the current flow during normal use is not so much lower than simply shorting the carbons, which in any case have their own fairly high resistance.  Again if you wish you can experiment first by putting smaller incandescent lamps in series and check for the difference in current flow with shorted carbons and when the arc is burning.

If you also have regular discharge lamp control gear, you can experiment first with this.  A good start is something like a 175W mercury lamp ballast wired in series with the mains and your two carbons.  Just touch them together and then separate and the arc will strike directly and burn well up to a few mm arc gap.

Wearing safety glasses to block the UV is crucial.  When I was about 12yrs old and experimenting with this kind of setup, I quickly learned what arc eye was!  Beware especially of modern carbons.  Until the 1970s some companies made these for UV therapeutic lamps having iron-doped carbons, which boosts dramatically the UV output and the risk of eye and skin burns.  Best is to find pure carbon high density rods of the type used as tools by glassblowers.

For the regulating lamp, it can be more complex.  Apparently even a century ago they were not always very reliable and difficult to regulate properly.  I have never seen a self-regulating one before which was still in good enough condition to work, but years ago did know another collector who apparently restored some and managed to get them operational.  First you might need to give yours a good mechanical overhaul and ensure that the mechanisms are all able to move freely.

Good luck, and be sure to post some photos here if you get them working!

James.

Thanks for your very detailed reply -- it helps a lot!

I guess my magic lantern was for 110V, but I'll follow your advice and plug a bulb in parallel with the rest: the worst I can do should be... lighting the bulb

I've lived in Canada for a few years so 110-120V is somewhat new to me compared to 220V (I still feel uncomfortable with warm plugs!), so the bare carbons and wire contacts make me feel stressed (in addition to striking electric arc). But, well, this is 1900's safety rules and I'm supposed to wear gloves to handle glass slides.

The carbon rods I own are for projection so they shouldn't emit more UVs than standard carbons (I didn't know that sun lamps used specific carbons).

The carbon rods of the magic lantern are enclosed (there's only a dark red window) and I prefer not wearing protection glasses because of the bare electric contacts. When I try the other lamp, I will wear some for sure (about regulation, the one in the video seems to regulate pretty well).

110-120V is less dangerous than 220-240V. However, as you've suggested, it's equally important to take precautions as no shock is likely to be pleasant!

I too would love to see a photo of it working.


BG

To act as ballast (current limiting) the incandescent must o in series wth the arc not in parallel

120v is less of a shock hazard but more of a fire hazard, since all currents are double of those in a 240v circuit of the same power. If a moerately bad connection with 5A can silently heat in a 240v circuit and just melt some plastic, you'd possibly get fire with such connection on 120v where there are 10A going through it (which mean 4 times the power dissipation)

To act as ballast (current limiting) the incandescent must o in series wth the arc not in parallel

Oops, I meant "in series" not "in parallel"  
(As I did to test the coil.)

120v is less of a shock hazard but more of a fire hazard, since all currents are double of those in a 240v circuit of the same power. If a moerately bad connection with 5A can silently heat in a 240v circuit and just melt some plastic, you'd possibly get fire with such connection on 120v where there are 10A going through it (which mean 4 times the power dissipation)

When I arrived in Canada, I discovered that people weren't stressed by warm plugs, while I wasn't used to it with 220V and lower amperages.  

Warm plugs are sign of trouble. They are not supposed to be warm in any voltage

Now if people try to get 15A through a plug rated to 15A, thats a whole other problem. Our Israeli plugs are rated to 16A and you'll get a pool of plastic if you load them more than 10A. Probably we are not the only ones with too high ratings on plugs

Many devices in the U.S. come with cords that are running at their current limit (12A vacuum with 16 AWG wire, for example) so warm plugs are much more common than they should be. If they feel too warm to me, I replace the cord with a heavier gauge.

Sounds like our electric kettles. 10A on 0.75mm^2 - its only ok since it does not work for very long each time....

0.75mm² on a kettle ?! surely not

Ours have thick cables .. sounds like your kettles wouldn't last long in my aunt's house


BG

Hi,

You asked me photos... Here's the video :

http://www.youtube.com/watch?v=RaCXTmfG76k  

I tried different combinations as a ballast:
- 500W bulb + original coil: a few sparks when striking but can't create an arc;
- 500W bulb: you get an arc but not very powerful;
- original coil: works better!

The sound is not pleasant and there are sometimes a few sparks coming from one of a carbon rod... I guess a lot of people preferred the 400W Mazda-Edison incandescent bulb model!

Edit: I added a few slides to the video.

Nice video!