Why does the Honeywell Tilt-a-mite flash have a capacitor?

Discussion in 'Lighting' started by skorpiius, Jul 12, 2016.

  1. skorpiius

    skorpiius Subscriber

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    Probably receiving a replacement cap today and it occurred to me that my other flash guns, like one on a Hawkeye Brownie or on my Polaroid land simply has a battery to ignite the flashbulb.

    Any idea why the tilt-a-mite has a cap? esp since it uses a 15 volt battery you'd think it wouldn't be needed.

    Pic for reference

    [​IMG] https://c2.staticflickr.com/6/5058/5424747977_47f718fee4_b.jpg

    [​IMG]

    Maybe to try to eliminate as much delay as possible?
     
  2. wiltw

    wiltw Subscriber
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    Could it be simply that your Tilt-a-Mite capacitor is VISIBLE to you, whereas the other flash units have it internal within the case and not visible to you?!
     
  3. AgX

    AgX Member

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    The internal resistance of a battery, which is growing over it's life, limits its maximum current. A high current though is necessary for the incandescant firing feature.

    Thus for firing the battery is "substituted" by a capacitator in parallel to the battery. The capacitator can deliver high currency as long as it is charged.
    And that can be done even with a weak battery (though then with reduced voltage).


    wiltw, there are indeed bulb flashes without capacitator.
     
    Last edited: Jul 12, 2016
  4. wiltw

    wiltw Subscriber
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    So with these flashes, as the battery gets weak the bulb firing becomes impossible sooner?
    I know non-BC flashes existed.

    In the case of the Polaroid flash, it is called a 'Polaroid BC flash model 281' -- for Bulb-Capacitor

    [​IMG]
    So OP, are you thinking about a different Polaroi flash than the one I mention?
     
    Last edited: Jul 12, 2016
  5. AgX

    AgX Member

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    Yes. We all know that exhausted batteries take longer, up to very long to charge an electronic flash. Because their current dropped over time.
    And it is this current that in a bulb flash may not longer be strong enogh to get the firing wire hot enough.
     
  6. OP
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    skorpiius

    skorpiius Subscriber

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    268. Inside there is just a place for a AA battery. Maybe a capacitor in the camera body?
    [​IMG]
     
  7. OP
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    skorpiius

    skorpiius Subscriber

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    This is a good point, with a capacitor the flash delay would be much more consistent. So perhaps flashgun with capacitor = more professional/accurate
     
  8. AgX

    AgX Member

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    If I remember right I got one myself; never opened it.

    Sometimes with bulb flashes with capacitator, the capacitator is visible in the batteries compartment, sometimes it is hidde in thr rest of the flash.
    I even got one model where the capacitator is spring fastened similar to the battery.
     
  9. AgX

    AgX Member

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    That is another aspect. Worth considering.

    The vast majority of my bulb flashes got a capacitator. It got kind of standard by time. The cost factor seems minimal anyway: one capacitor, one resistor, four additional soldering points. (But I have to find out what a small capacitator cost back then. Might be more then we think today.)
     
  10. frank

    frank Member
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    I thought all flashes had capacitors.
     
  11. Prof_Pixel

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    'BC' usually means 'battery-capacitor'


    When Polaroid brought out their 3000 speed film in the late 1950's, they actually did use a fill light that was a small lightbulb fired by a BC flash unit. They called it a 'wink light'.
     
  12. wiltw

    wiltw Subscriber
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    Thanks for the correction, my brain knew that -- but my fingers typed 'bulb' simply because 'BC flash' pertained to flashbulb flash units!
     
  13. BrianShaw

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    Nope. One of the most classic flash handles, Graflite, was battery only. Graflex offered a B-C module as an option but the basic flash used by countless press photographers was D-cell powered.
     
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  15. frank

    frank Member
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    Learn something everyday. Thanks Brian!
     
  16. DWThomas

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    I believe the battery/capacitor arrangement was to cut overall size. A flashbulb takes a very short burst (~millisecond) of relatively high current to fire. Early flash guns used two or three 'C' or 'D' cells which can provide several amperes of current. A b-c flash gun can charge the capacitor from a much smaller lower current battery and the capacitor then supplies the short burst of high current. (Electrolytic capacitors have relatively low internal resistance and supply a very high current, but of short duration.)

    My mid-1950s Argus C3 flash has no cap but takes two C cells.
     
  17. Jim Jones

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    Dave, the pre-war UniveX Mercury camera pioneered a hot shoe flash which used two AA cells in most versions. The slightly different post-war flash also used two AA cells. Such small batteries must have been reliable in triggering flash bulbs for them to be retained for so long. Their light weight probably seemed desirable in a hot shoe flash before we discovered that heavier modern hot shoe flashes with plastic feet would also work.
     
  18. ronnie_retro

    ronnie_retro Member

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    The Tilt-a-mite provided a smaller, more lightweight alternative to the massive flash units that loaded 'C' or 'D' size cells. It's actually a very elegant solution, simple though it is. I'll go through some simplified math to show you why, or you can skip to the end of this post.

    Amazingly, the capacitor on mine is still good and measures 400uF. Now, the energy stored in a capacitor is (1/2)*C*V^2, or in our case (1/2)*(400x10^-6)*15^2, or 0.045 Joule.

    The original 15V Eveready 504 battery was rated at 60 mAHr. So the rated stored energy of the battery is (15)*(.06)*(60)*(60), or 3240 Watt seconds, which is also 3240 Joules.

    The real world deliverable capacity is probably about 1/2 that, since we still need about 12 V at end of life and there will be loss due to aging. Even so, the battery can be expected to deliver 1620 J.

    Now, the simple resistor charging method has an efficiency of 50%, so we use

    (2)*(.045) = 0.09 J every time the capacitor needs to be charged.

    And, we'll fire the test lamp before each picture to be sure we'll get the shot, so we charge the capacitor twice for each bulb fire. (0.09)*2 = 0.18 J

    We use 0.18 Joule for each fired bulb. We have 1620 J available in the battery, so, finally,



    *1620/0.18 = 9000 flashbulb fires, an incredible *750 dozen*!!!*



    Now, an M3 flashbulb has a resistance of about 1 ohm. Even though the capacitor takes just a tiny sip from the battery, I measured, using the original ancient capacitor, a peak current through a 1 ohm resistor (for just several microseconds, of course) of 11A. So the system can deliver an instantaneous power of 11^2 * 1, or over *100 Watts* - nearly as surprising (to me, anyway).

    Back in the day, a hobbyist with some money to burn and who went through a couple dozen flashbulbs a week could expect the battery to hold out for seven years - longer than the shelf life of a carbon zinc battery.

    I was really surprised when I worked it out. A superbly designed system. BTW, the complete opposite of the Polaroid flash, which was a crude hack job by comparison. It didn't even supply the minimum rated voltage for flashbulbs, which has been at least 3V for everyone I've seen.

    One thing to keep in mind, if anyone has one of these gizmos, is that they need to be stored with the flashbulb removed so the small leakage current through the capacitor won't discharge the battery over time.

    Cheers!
     
  19. cobbu2

    cobbu2 Member
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    I just discovered this interesting thread and it just so happens I have a Tilt-a-Mite unit and a 15V battery that still shows relavely strong with a voltmeter. After installing the battery, the test light does not illuminate, so I’m guessing it’s the capacitor.

    Should I just leave the battery in the unit for a while as was mentioned above and maybe the capacitor will reform (I assume with no bulb in the unit)?

    Is it possible for the unit to function without the capacitor if it turns out I can’t reform it, by then just running a wire between the capacitor terminals inside the unit?

    Thanks in advance.
     
  20. AgX

    AgX Member

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    No.
    In a battery-capacitator flash you got two different circuits, though both are coupled via the lamp (bulb):
    One includes the bulb, the capacitator and the syncro-switch, the other the bulb, battery, capacitator and resistor.
    You would have to rewire the whole shebang.

    My sample of the Tilt-a-Mite lacks the capacitator. I shall substitute it with an off the shelf type.
     
  21. Sirius Glass

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    The capacitor is part of a R-C circuit and provides timing and power discharge.
     
  22. AgX

    AgX Member

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    There is no "RC circuit" in a bulb flash. At least not in its common meaning which is being a resonator in an high-frequency circuit.
    Also the capacitor in a bulb flash has hardly a timing function. That is served by the burning material in the bulb and its burning characteristic.
    One could argue that a battery with its internal resistance and limited current will take longer to ignite the explosive in the bulb, than a capacitator would do and thus giving it a timing character, but I consider that academic. Also there is no hint on that in any bulb data sheet I know.
    As explained above the idea of a capacitator in a bulbflash is to get more ignitions out of a battery.
     
  23. cobbu2

    cobbu2 Member
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    Thanks for the responses! So with that, what is the best and/or easiest method to reform the capacitor, or can a replacement be found?
     
  24. AgX

    AgX Member

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    Read my post.
     
  25. DWThomas

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    I suspect a drop-in replacement capacitor falls between ultra-rare and non-existent. Since improved manufacturing processes over the intervening decades have typically shrunk the size of such capacitors, the trick is probably to buy an axial lead unit somewhat smaller physically and then do whatever has to be done to make an adapter to stick it in the Tilt-a-Mite. Places like Mouser and Digi-Key are where I would start a search. I would want a voltage rating more than 15 volts -- perhaps 18 to 25 -- to minimize potential (electrical) leakage. And someone upthread said the original is 400 uf, I suspect anything from around 270 to 500 would be a candidate.

    Many axial lead units are actually an aluminum can with the negative lead spotwelded to the end of the can. Don't know what form factors may exist today, but with luck one might snip the negative lead flush and improvise some sort of button on the positive end to make it a drop-in replacement. Please note that reversing the capacitor polarity will ruin it. Trying to use a Tilt-a-Mite on a modern electronic camera is likely a bad idea also (open circuit voltage and firing current issues).

    (Gad, the way the world is going there's probably a Facebook Tilt-a-Mite group where some entrepreneur offers replacements from his basement workshop!)

    I own a Tilt-a-Mite, but can't feel any urge to start popping flashbulbs. Several years back when this topic came up the Eveready 504 15 volt batteries were still available from online specialty stores, although IIRC they were about a dollar per volt. I have the two C cell flashgun for my Argus C3 if I absolutely must zap a bulb!
     
    Last edited: Dec 8, 2018
  26. AgX

    AgX Member

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    It does not need to be 15V.
     
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