I don't think a voltmeter is going to tell me much... [Δαφνη Ευτυχια Αρθουρος]

Still feeling run down (sleep helped, but I probably need more) and am now battling a headache. Looking around to see what I can get done without pushing myself too hard.

I was recently given an old photoflash. One that takes flashbulbs. (I've wanted one for a while -- some of my older cameras have an "FP" connector, so once I rig an adaptor and find slow-burning flashbulbs, I'll be able to shoot with flash at any shutter speed as long as I'm using an old enough camera.) I popped it open to see whether the "Kodak 'C' Photoflash" batteries described on the sticker on the back of the reflector were just ordinary C cells. I was surprised to see that there were batteries still inside. They're the size of modern C cells, labelled "Bright Star Photo-Flash Battery", but have no voltage marked ... I'm guessing they're just C flashlight batteries labelled for sale in camera stores. But that's not what amused me enough to write about them. What got my attention was that they have an expiration date on them like the name brands have started doing recently. They're marked, "FOR BEST SERVICE USE BEFORE 3-57".

There's surprisingly little corrosion, for something that's had batteries in it for nearly half a century.

(The electrical connection is a pair of posts sticking out the side of the unit. They're spaced the same as the holes on the side of my Argus rangefinder (which, because it uses a leaf shutter, should be able to shoot flash at any shutter speed anyhow), but one post is threaded and extends all the way through the device to a knob on the other side, and the threaded part is too wide to fit into the hole on the Argus. Anyhow, my plan is to use the cable from a broken PC-hotshoe adaptor and connect the wires to the studs with alligator clips to start with and do something more permanent later. That's the easy part. Slightly harder (but not by much) will be the mechanical mod to attach it to an SLR (I'd prefer not to simply stretch rubber bands around camera and flash). I've got a few ideas for that.)

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I believe they're the same voltage but they're designed to produce a higher initial current than ordinary C cells. (See also: why cars use non-gelled lead-acid batteries, and why (IIRC) some(?) propellor airplanes use heated NiCd batteries, both for starting their engines.)

That said, we're talking about 1957 battery technology; I have no idea what the appropriate modern battery would be.

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An alkaline battery probably puts out more current than a '50s photo flash battery. A NiCad would put out much more.

Many flashes had a capacitor to handle the peak current demand, so the battery is less critical.

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I suspected as much, but didn't want to commit to it. :)

I would actually suspect most modern batteries would work fairly well; the issue back then wasn't so much the peak current but how quickly the battery recovered afterward and how long it could continue to deliver current with that usage model (most batteries being designed to produce a steady current over a longer time, whereas flash wants a high initial current and doesn't care much about how long the current can be sustained). Battery technology being much better these days, it's entirely possible that even ordinary zinc cells would do — although their lifespan would undoubtedly be fairly short.

"whereas flash wants a high initial current and doesn't care much about how long the current can be sustained"

*nod* As soon as the magnesium ignites it becomes an open circuit anyhow, eh?

No capacitor in this one, just springy metal bent to form a battery holder and a flashbulb holder and connect tht two. But I'll keep that in mind for a modification if I ever decide it's a problem.

Wow, historical ephemera. I wonder how many batteries from the 1950s there are just kicking around. Seems to me that most of those would be in landfills by now.

Glenn, I have to disagree. You've been run down so much lately, that I think you should immediately find a voltmeter and measure the potential difference among various parts of your body. Has a really good chance of locating the source of the "I'm out of energy today" problem.

First reaction: Pbbbbbbbt!!

Second reaction: "Wait, where did I leave the voltmeter; it'd be terribly silly to find out there was something to measure..."

The photoflash batteries are made with relatively large plate area and less plate thickness, so they can maintain a low impedance (and therefore source a large initial- and peak current for a fairly short time) even after repeated flash cycles compared to standard batteries. The tradeoff is a Much shorter life and a tendency to fade more rapidly at high(er) temperatures. This is very similar to the tradeoffs between vehicle starter batteries and marine deep-discharge batteries.

Compared to the ~state-of-the-art in 1957, modern alkalines should handily run that flash. If they turn out to die ~young, you Can still get photoflash batteries at better camera stores last I checked (~2001?).

Note that capacitors come in ~regular and photoflash varieties as well and for the same reasons. If you're building something that needs a fast, high current pulse, the photoflash caps (or 'laser discharge' caps as the larger and higher-rated units are often labelled) are well worth the premium. Regular capacitors can Easily be driven so hard by flash type circuits that they explode. Having build a few things of that sort, I have seen it happen ... ;-S Switching power supplies also require such low-ESR* capacitors and one of their major failure modes is the caps exploding in a series of high-voltage arcs.

* ESR => Effective Series Resistance or Equivalent Series Resistance depending on the source you look at.

Wow, didn't know photoflash batteries were still around -- useful information.

But first, to remember on which machine (and in which browser) I bookmarked the site where I can still buy flashbulbs...

The photoflash capacitors he's referring to are for xenon strobes. For dumping pulses
into flashbulbs, any old capacitor should do fine. Note that you should probably have
a snubber network of some sort, more to protect the camera contacts than the capacitor.

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I don't think a voltmeter is going to tell me much...

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