capacitors and flashbulbs?

[John_4185]

I have a 1953 military bulb-flash unit for bay or screw-type bulbs that uses two 22.5V batteries plus a capacitor. So that's 45 volts with a capacitor. It makes no sense to me. Why would it be designed like that when two D cells will easily fire the bulb?

[Jim Rhoades]

I'll be interested to see the correct answer. O.Winston link invented some pretty heavy duty battery and capacitor systems to fire all the flashbulbs to light trains. Maybe it was designed to fire multiple flashbulbs hooked in series.

[medform-norm]

JJ,
I know you are going to think this is a worthless reply, but I'll give it anyway. The answer lies in your question: why would it by designed like that? Because it was designed by/for the military! Better be safe than sorry and so forth.
Norm

[Donald Qualls]

"Modern" flashbulbs (those made in the 1960s and 1970s) would and will fire on as little as 1.5 volts with no capacitor required, using modern batteries.

The same is not true of the screw base bulbs and old technology carbon-zinc batteries available in the 1940s; a modern alkaline D cell can deliver as much as 10 times the current of a 1940s cell the same size, and has as much as 20 times the total capacity. The capacitor was present to deliver the large jolt of current needed to ignite early flashbulbs. The high voltage (45 V with fresh batteries, probably as low as 25 V when the battery was nearly dead) was needed to push that current through the bulbs.

Where a 1970s production AG-1 bulb will ignite on 50 mA, it took the better part of an amp to ignite a screw-base bulb of the kind used in WWII era flash photography (and military cameras in 1953 would still have been made for screw base, even if they had an adapter for bayonet bulbs). There were no dry cell batteries available prior to the early 1960s that could deliver an amp in D size; carbon-zinc batteries were once made in special "photoflash" type that gave up capacity to be able to deliver larger pulses of current, but those didn't come along until M2 and M3 were the standard bulbs.

So, to simplify, the flash you have is designed to use 45 V and a good sized capacitor because that was what it took to fire some of the flashbulbs it was made to use. BTW, a side benefit of this (if you were to recap the flash and find some bulbs) is that the battery life is very long because the flash will still work when there's just a whisper of life in the batteries (kind of like modern TV remote controls, which will run for a year on batteries that will barely raise a flicker from my Mini-Maglite).

[John_4185]

Donald Qualls [...]carbon-zinc batteries were once made in special "photoflash" type that gave up capacity to be able to deliver larger pulses of current, [...]

Ah, thanks so much for the memory jog, Donald! Yes, now I remember "photoflash" batteries. Med-form, you are also apparently correct; they suffered no compromise. This is a "combat" rangefinder 70mm Graflex. (I've the IR bulbs, too.)

FWIW, the batteries I mentioned are still available, and I presume (perhaps in error) that they are made of modern materials. They are Eveready #412, 22.5V, intended to support those very few who use vintage equipment, largely old portable radios. I just got two from Radio Shack.

[Ernest Purdum]

Capacitor flash units weren't just military. They were common and popular shortly before flashbulbs were going out of use.

That 70mm Combat Graflex is an impressive camera.

[John_4185]

That 70mm Combat Graflex is an impressive camera.

It really is - like a supersized Contax, but with more features. The lens lube is so stiff I can barely focus either lens. Gee, stiff after sitting for only fifty years. :) If I can find the courage, I'll take it to a camera repair expert - if I can find someone old enough to know and respect it.

(To the rest, sorry for drifting OT.)

[Donald Qualls]

FWIW, the batteries I mentioned are still available, and I presume (perhaps in error) that they are made of modern materials. They are Eveready #412, 22.5V, intended to support those very few who use vintage equipment, largely old portable radios. I just got two from Radio Shack.



Nope, sorry to say, those are still carbon-zinc construction (you can tell by the red outer cover; Everready alkalines are always silvery, carbon-zinc always red, the latter for the past 60 years or more). They're probably better than the ones that would have been available in 1953, but nowhere near an alkaline for current sourcing or total life. OTOH, with the capacitor in there, they don't need to be anything else; the battery is good for 100 mA, but the capacitor can easily drop 25 Amps if necessary to ignite the bulb. BTW, you can also still get the similarly sized 15 V batteries used in many smaller flash units, if you should happen to have or find one (I have one for my Minolta 16 MG); same reasoning, they're used in some tiny tube radios and similar low-drain applications.

[John_4185]

So it seems that I would be just as well off adapting a modern alkaline 9V battery, and bypassing the capacitor would not hurt. I'm almost sorry I bought the red batteries.

Your nudge reminded me that I've many memories of leaking batteries from back then. The smell, the goo, the ruined equipment.

[Donald Qualls]

Actually, JJ, I'd suggest you first try reforming the capacitor (load batteries and leave the flash for a week or two, then test, ideally with a test bulb instead of a live magnesium bulb, though some flashes required a bulb to be loaded before they'd charge the capacitor -- to prevent draining a battery if the 1940s technology capacitor leaked a bit), or look into replacing it, and use the original batteries. Failure to flash became a big issue when people started trying to fire bulbs from batteries without capacitors, because manufacturers were trying to cut costs and the spec sheets said a pair of AA or C cells would do the job -- and they would, as long as every contact in the entire circuit was clean and tight. 45V will cut through stuff that stops 3V cold...

BTW, if you take the bayonet adapter to the local auto parts store, you can probably find a single filament clearance light bulb that will fit the socket and match the bayonet, and 45 V in a short pulse won't burn out a 12V turn signal or parking light bulb (i.e. it'll last many dozens, if not thousands of flashes in a test application). Use that as a test bulb, if the flash didn't include one...

[Mike Kovacs]

Is it any wonder, since the Contax designer, Hubert Nerwin, also designed the Combat Graphic ;) I have and enjoy many of his Zeiss Ikon camera designs - browsing the page below, I suppose I should add a Tenax II to round out the collection.

http://www.zeisshistorica.org/Nerwin.html

[Mike Kovacs]

list includes - Contax II/III, Tenax II, folding Contessa, Contax IIA/IIIA, Contax S (worlds first pentaprism SLR), etc etc. Man was a genius.

[John_4185]

I will do what you suggest, Don. Thanks. I have test lamps, and am just plain lucky to have cases of real flashbulbs. In turn for your help, and in the original spirit of the net, let me know if I can send you some. My address is under the 'jj' above.

Mike, that's a great link! Others might look to www.zeisshistorica.org/Nerwin%20cameras.html (http://www.zeisshistorica.org/Nerwin%20cameras.html) (scroll down) or jump to the camera in question via www.zeisshistorica.org/Images/combatgraphic.jpg (http://www.zeisshistorica.org/Images/combatgraphic.jpg)

What is not apparent there is how very large the camera is. If this were a MF forum, I would post an illustration that better shows scale.

Thank you, everyone.

[Donald Qualls]

JJ, the only flash I own that uses screw base bulbs fits an Ansco Pioneer 620; I wouldn't *dream* of burning one of those huge bulbs for that camera. Even bayonet bulbs are far more light than I need for any reasonable purpose; I do fine with AG-1 and M2/M3. Thanks for the offer though -- I would be interested in seeing results if you ever manage to use the camera (perfed 70 mm is getting hard to find, I hear, and cassettes more so). My e-mail is linked from my name, too.

Yeah, scale is tricky, you just have to remember it's like a Contax blown up 2x for the 70 mm film. That'd make it bigger than my Moskva-5, more like a fixed-lens version of a 2x3 Speed...

[John_4185]

http://elearning.winona.edu/staff_o/jjs/cb.jpg

To put the off-topic thing in scale, Mr. Qualls. Howzat for a rangefinder?