Film-Tech Forum ARCHIVE: Low intensity carbon arc rods

This is topic Low intensity carbon arc rods in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Sigurd Wik (Member # 6131) on 08-10-2016, 11:36 AM:

I'm planning screenings of, and lecture on, very early films. The films will be screened on 35mm on an Ernemann IV with low intensity carbon arc lamphouse, which should be fun. I seem to remember (but I'm not quite sure) that the rod diameter that goes together with 14mm is 9mm. Anyone know if this is right? The reason I ask is that I have a lot of 14mm rods, some 11mm, some 9mm and almost nothing else.

Also, if 9mm is indeed the right diameter, does anyone have any of these? I'm in need of more than I have right now.

Please note that this is the low intensity (LI) version, not the high intensity (HI). Many HI rods are for sale on the bay, but few LI.

Posted by Monte L Fullmer (Member # 2797) on 08-10-2016, 03:20 PM:

Good Luck with this project.

LI rods were not copper coated-a little FYI.

Posted by Jim Cassedy (Member # 4115) on 08-10-2016, 04:16 PM:

The diameter of the carbon rods you need is usually related to the amount of
voltage & amperage your rectifiers and lamphouse were set up for.

You can probably still find some old carbon size charts from National Carbon,
or somesuch other company online somewhere. I know have some charts in
some old projection books I have. But without having some idea of what voltage
& current your lamphouse was set up for, it's difficult to say exactly what the 'proper'
size carbons are. And, as you point out, carbons of any size or type are getting pretty
hard to find. Last time I checked, I think there was still some company in the Soviet
Union making them ("Soviet-Union Carbide?" hahaha) but you you could only buy
them by the pallet-load. There was some US company that was buying them like
that and re-selling them in single box quantities, but as I recall, the price was pretty
exorbitant.

Posted by Sigurd Wik (Member # 6131) on 08-10-2016, 04:37 PM:

Thanks for info! As far as I can remember the rectifier I use deliver 6A, and I'm on 230V. I have used this rectifier/lamphouse setup once before, and I am sure I used the 14mm positive rod for acceptable result on a pretty small screen, but can't remember the diameter of the negative one.

I will check some more online for info.

EDIT: I just found out I asked this question here five years ago! Completely forgot. I got some nice tips there, and 14/10mm is one of them. I'll aslo check some of the carbon rod suppliers listed there.

Posted by Scott Norwood (Member # 30) on 08-10-2016, 09:08 PM:

So, are the carbons actually different for low-intensity lamps? And is there an actual difference between a "negative" carbon rod and a "positive" one, other than the length and diameter?

Posted by Jim Cassedy (Member # 4115) on 08-10-2016, 10:59 PM:

quote: Scott Norwood
..is there an actual difference between a "negative" carbon
rod and a "positive" one, other than the length and diameter?

Aside from the diameter, the positive carbons were shipped with a slight
crater pre-formed on one end, & the the negative carbons had a pre-formed
pointed tip, since these were the natural shapes the carbons were going to
form as they burned down anyway. If the ends of the new carbons were
simply flat (perpendicular) to each other, the light would be somewhat
unsteady for a few minutes or so until the crater & core formed naturally.

Also, as I recall, low intensity lamps ALWAYS used 'cored' positives in
which the center of the carbon rod was composed of a 'softer' grade of
carbon than the outer 'shell'. I think there was also some sort of mineral
salts or chemicals added to the core to either improve burning or color
temperature. (or both) As I recall, the negative carbons were always
'solid' (not cored), but I could be wrong about that.

Posted by Monte L Fullmer (Member # 2797) on 08-11-2016, 03:08 PM:

True. The core for both Li and Hi positives was made from a rare earth material that burns away with superb brightness, but real quickly. Thus, the outer shell was constructed to be a harder base to resist rapid burning as with the core.

Why you have the crater with positive rods.

As for the negative, the LI were solid just to stabilize the burn, but when HI carbons came out, they added a lot smaller, rare earth core to aid in with the current flow and to stabilize the arc, but the outer core burnt away faster than the core, why you have the cone.

Hi needed the copper coating, whereas the larger, rotating ones didn't need the copper coating since the DC current contacts were inches away from the tip of the rod.

I do remember striking up 13.6mm rotator positives with 1/2" negatives, and with over 200 DC amps at your disposal on contact, there was almost like an explosion in the lamphouse with you touched the negative into the positive on striking.

Dang, xenon took our fun away.

- Monte

Posted by Stephan Shelley (Member # 8587) on 08-11-2016, 03:27 PM:

I might have some of what you need. Not sure the size and if I even have the negatives. They have not been stored in ideally. They are in an outdoor metal shed. I would bake them to dry them out. Should have somewhere between 6-12 sticks.

Posted by Sigurd Wik (Member # 6131) on 08-11-2016, 04:23 PM:

Got some news since last post. I'm running on 45V/24A DC. I got a tip that 14mm might be too large for the negative rod, but not certain. Also awaiting answer from CinemaCarbons.com.

I also got this from Dick Prather five years ago on this forum, but none of the V fit within what I have got. Don't know what means for my rod diameter needs, maybe I should ideally have 12/8?

16-20 A, 54-57 V - 10mm pos, 7mm neg
21-32 A, 54-57 V - 12mm pos, 8mm neg
32-42 A, 54-57 V - 13mm pos, 9mm neg
42.52 A, 54-57 V - 14mm pos, 10mm neg

Stephan: That's great. Just to let you know, I'm in some hurry, as the screening is Aug 24. The reason for this is that I was clumsy and a packet of 9mm rods fell to the floor and most of them broke. But I can ship express if necessary.

Posted by Will Kutler (Member # 770) on 08-12-2016, 12:37 PM:

Unsure of what specific make or model lamphouse you are using. However, here is some advice regarding Magnarcs.

1: Find a copy of the operation instruction and parts books.

2: Look for specific electrical information on the lamphouse data tag (back door).

3: Magnarc books have carbon charts that state the specific negative-positive diameter selections per specific current ranges and arc voltage ranges. The chart also specifies consumption rates @ inches/hr.

4: There may be different part numbers for both the negative and positive carbon holders and carbon guides. The mechanical differences in these parts correlate to specific carbon diameters.

Posted by Rick Raskin (Member # 1561) on 08-12-2016, 06:10 PM:

The National Carbon manual (in the miscellaneous section) of the manuals in the warehouse has charts for LI carbon pairings.

Posted by Marin Zorica (Member # 1716) on 08-12-2016, 06:46 PM:

Hi! I am just reading from old book, data on german Ringsdorff low intensity carbon's, and it goes like this:

10/7......15-20A
11/8......18-24A
12/9......22-28A
13/10.....26-32A
14/11.....30-40A

in firast column are diameter positive in mm and than negative in mm, than current in ampere A.

I am having ernemann IV projector still in my warehouse, it did use low intensity carbon arc lamphouse also with something like 250mm diameter reflector.

Posted by Sigurd Wik (Member # 6131) on 08-13-2016, 01:35 PM:

Thanks for nice tips! I will check the lamphouse for info. The neg holder seem to accomodate 8 and 9mm, while the pos seem to accomodate a wide range as it is variable.

With the info I have so far (lamphouse excluded) the 12/9 combo seems to be the most ideal. Interesting that the National Carbon bulletin states that there is both solid and cored neg rods, probably to enhance light output, as mentioned above.

Will also post on the classified section on this forum.

Posted by Louis Bornwasser (Member # 3063) on 08-13-2016, 06:35 PM:

See Rick Raskin's post above. Complete scan of National Carbon manual under Miscellaneous in Manuals section. More than you would ever want to know about L.I.carbon trims.