Plastic capacitor for camera flash tube?

[Dontspam]

I'd like to experiment with a camera flash tube but cannot easily
obtain a proper photoflash capacitor, not even one from an old
flash gun. It's not for photography and I need only a fairly low
flash energy - a few microfarads worth, and the interval between
flashes will generally be minutes, although it may occasionally
be as short as 10 seconds. Will a plastic capacitor - like MKP or
MKT type - be suitable? If so, will an AC x2 cap be more suitable
than a DC cap? Thanks in advance.

[Baron]

Dontspam Inscribed thus:

Go grab a used disposable camera ! If you ask one of the D&P shops
nicely they might give you one for free to play with.

--
Best Regards:
Baron.

[Dontspam]

Unfortunately, I don't live in a place where they give, sell or
rent out disposable cameras. But you've given me an idea. I'll
see if I can get my hands on an old box film camera with a flash.
In any case, I'd still like to know if plastic capacitors are
suitable for the purpose.

[Cydrome Leader]

Dontspam <dont...@invalid.invalid> wrote:
> Baron wrote:
>> Dontspam Inscribed thus:
>>
>>> I'd like to experiment with a camera flash tube but cannot
>>> easily
>>> obtain a proper photoflash capacitor, not even one from an old
>>> flash gun. It's not for photography and I need only a fairly
>>> low
>>> flash energy - a few microfarads worth, and the interval
>>> between
>>> flashes will generally be minutes, although it may
>>> occasionally
>>> be as short as 10 seconds. Will a plastic capacitor - like MKP
>>> or
>>> MKT type - be suitable? If so, will an AC x2 cap be more
>>> suitable
>>> than a DC cap? Thanks in advance.
>>
>> Go grab a used disposable camera ! If you ask one of the D&P
>> shops
>> nicely they might give you one for free to play with.
>
> Unfortunately, I don't live in a place where they give, sell or
> rent out disposable cameras. But you've given me an idea. I'll

where are you located?

> see if I can get my hands on an old box film camera with a flash.
> In any case, I'd still like to know if plastic capacitors are
> suitable for the purpose.

in short, no. they're too small, unless you can get some giant film caps
in metal cans. Giant means you need two hands to lift and carry the thing.

[Dontspam]

In an isolated corner of a developing country where online shops
are still mostly a joke.

>
>
>> see if I can get my hands on an old box film camera with a
>> flash.
>> In any case, I'd still like to know if plastic capacitors are
>> suitable for the purpose.
>
> in short, no. they're too small, unless you can get some giant
> film
> caps in metal cans. Giant means you need two hands to lift and
> carry
> the thing.

Would you mind explaining the 'too small' part? I do have some
film caps of a few microfarads rated up to 630VDC and some 275V
AC ones. I thought the joule capacity was sufficient for what I
want to do and was more concerned about the caps' ESR and their
ability to withstand repeated high-current discharge.

[John Fields]

---
If you're just fooling around, any old thing you stick in there which
will stand off the charge voltage and not blow up the flash tube will
work.

Is there anything special about your experiments which would dictate
the choice of capacitor?

--
JF

[Dontspam]

I don't have any specific application for it at the moment but
may do so in the future. A few years ago, I built a unit with
ordinary Al caps for charge storage and the result was
disappointing, though not really unexpected.

I suppose I could just go ahead and set up another one except for
a couple of things: 1. I can't think of a simple method of
measuring or estimating the efficiency of the output. The
efficiency may be important for some future application and is
also of academic interest to me. 2. I'd like to have some prior
idea of how well the capacitor will stand up to repeated
high-current discharges.

[Charles]

I suppose I could just go ahead and set up another one except for
a couple of things: 1. I can't think of a simple method of
measuring or estimating the efficiency of the output. The
efficiency may be important for some future application and is
also of academic interest to me. 2. I'd like to have some prior
idea of how well the capacitor will stand up to repeated
high-current discharges.

As to measuring output energy, a high-speed op-amp integrator might work.
Use an appropriate voltage divider and current sensor and it might be
doable.

I guess it depends on how serious you are about your efficiency
investigation.

[Phil Allison]

"Dontspam"

>
> I'd like to experiment with a camera flash tube but cannot easily obtain a
> proper photoflash capacitor, not even one from an old flash gun. It's not
> for photography and I need only a fairly low flash energy - a few
> microfarads worth, and the interval between flashes will generally be
> minutes, although it may occasionally be as short as 10 seconds. Will a
> plastic capacitor - like MKP or MKT type - be suitable?

** Yep, they will work fine.

> If so, will an AC x2 cap be more suitable than a DC cap?

** X2 caps are regularly used in party strobes etc.


... Phil

[John Larkin]

On Wed, 3 Oct 2012 23:58:14 +0530, "Dontspam"
<dont...@invalid.invalid> wrote:

A film cap will work fine. Mylars have pretty good energy density. For
high-power, short-pulse flashing, it was sort of traditional to use an
oil-filled paper cap at fairly high voltage, a kilovolt or so.

I used to fire military surplus coiled-tube flashtubes (used to be
runway lights) at 5 KV or so from a few uF of oil cap. At 6-7 KV, they
would fire without a trigger. Short linear tubes, like from a camera,
will self-fire at lower voltages.

Can you use an LED instead?


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

[Dontspam]

Charles wrote:
> I suppose I could just go ahead and set up another one except
> for
> a couple of things: 1. I can't think of a simple method of
> measuring or estimating the efficiency of the output. The
> efficiency may be important for some future application and is
> also of academic interest to me. 2. I'd like to have some prior
> idea of how well the capacitor will stand up to repeated
> high-current discharges.
>
> As to measuring output energy, a high-speed op-amp integrator
> might
> work. Use an appropriate voltage divider and current sensor and
> it
> might be doable.

That gives me a starting point. Thanks.

>
> I guess it depends on how serious you are about your efficiency
> investigation.

Not too serious at the moment, but it may become more so. I have
some vague ideas floating around in my mind about possible
practical applications.

[Dontspam]

Thanks. I take it that that means film caps can be expected to
produce better results than ordinary Al electrolytics, and that
they will not degrade quickly with repeated discharges.

[bw]

"Dontspam" <dont...@invalid.invalid> wrote in message
news:k4khii$l2i$1...@dont-email.me...
> Phil Allison wrote:
>> "Dontspam"

>> ** Yep, they will work fine.
>>
>>> If so, will an AC x2 cap be more suitable than a DC cap?
>>
>> ** X2 caps are regularly used in party strobes etc.
>
>
> Thanks. I take it that that means film caps can be expected to produce
> better results than ordinary Al electrolytics, and that they will not
> degrade quickly with repeated discharges.
>

Your local thrift store will have boxes full of old flash cameras selling
for pennys. Buy a few, take them apart.
Any cheap 35mm from the 1980s is ok, but look for really old polaroid
cameras. They have simple, easily understood circuits.
http://donklipstein.com/donflash.html has all the info you want on flash
circuits

[Dontspam]

Thanks for your interest, but there are no thrift shops where I
live, at least not the kind that sells such stuff.

[YD]

Late at night, by candle light, "Dontspam" <dont...@invalid.invalid>
penned this immortal opus:

Can you get an old microwave oven? They have a large HV cap inside.

- YD.

--
Remove HAT if replying by mail.

[Phil Allison]

"Dontspam"

>
>> ** Yep, they will work fine.
>>
>>> If so, will an AC x2 cap be more suitable than a DC cap?
>>
>> ** X2 caps are regularly used in party strobes etc.
>
>
> Thanks. I take it that that means film caps can be expected to produce
> better results than ordinary Al electrolytics,

** There is NO comparison.

Electros of a " few microfarads " will not be suitable at all.

Their internal resistance (or ESR) is way too high.


.... Phil

[David Eather]

On Fri, 05 Oct 2012 21:29:48 +1000, David Eather <eat...@tpg.com.au> wrote:

> No. It means X2 caps won't catastrophically self destruct if anything
> goes wrong. Something that is important with HV

[Phil Allison]

"David Eather"

>
>> No. It means X2 caps won't catastrophically self destruct if anything
>> goes wrong.

** Complete nonsense.

An X2 cap may develop an internal short our and smoke and burn if mistreated
or at the end of its life.



.... Phil

[John Fields]

On Fri, 5 Oct 2012 01:20:44 +0530, "Dontspam"
<dont...@invalid.invalid> wrote:

>bw wrote:
>> "Dontspam" <dont...@invalid.invalid> wrote in message
>> news:k4khii$l2i$1...@dont-email.me...
>>> Phil Allison wrote:
>>>> "Dontspam"
>>>> ** Yep, they will work fine.
>>>>
>>>>> If so, will an AC x2 cap be more suitable than a DC cap?
>>>>
>>>> ** X2 caps are regularly used in party strobes etc.
>>>
>>>
>>> Thanks. I take it that that means film caps can be expected to
>>> produce better results than ordinary Al electrolytics, and
>>> that they
>>> will not degrade quickly with repeated discharges.

---
That's right.

The problem with electrolytic capacitors is that their ESR is higher
than that of film caps, causing them to heat up more than a film cap
would for the same output pulse.

Another caveat is that electrolytics can, and do fail catastrophically
when an internal short occurs between foil layers.

The foil in film caps is much thinner and if contact is made between
the film layers the foil will just vaporize, clearing the short and
"healing" the cap.

http://www.illinoiscapacitor.com/pdf/Papers/introduction_to_film.pdf

--
JF

[John Fields]

On Fri, 5 Oct 2012 01:20:44 +0530, "Dontspam"
<dont...@invalid.invalid> wrote:

>Thanks for your interest, but there are no thrift shops where I
>live, at least not the kind that sells such stuff.

---
I have a nice assortment of polyester (Mylar) caps and if you'd email
me a physical address I can send then to, and what voltages and
capacitances you'd like, I'll see what I can do.

--
JF

[tuinkabouter]

Ever connected an electrolytic capacitor revere on a 48 volt battery?

I can tel you that is gives a big bang (and a lot of dirt).

--
pim.

[Dontspam]

Thanks for the offer. I really appreciate it. But I do have some
Mylar caps of appropriate capacitance and voltage and in any
case, given the vagueness of any practical application I have in
mind at the moment, it's not worth the hassle and expense of
international shipping. On top of that, they may just get seized
by overzealous/corrupt customs people at my side.

My questions have been answered clearly and positively -
1. Whether a film cap will dump its charge efficiently into a
triggered xenon tube. I rather expected that it would, and it was
nice to have it confirmed.

2. How well the cap would stand up to the shock treatment: I
didn't know what to expect about that. It's nice to know that it
's likely to take that kind of abuse in its stride.

Thanks to all who contributed to the thread.

[Phil Allison]

"tuinkabouter"

> Phil Allison wrote:
>> "David Eather"
>>>
>>>> No. It means X2 caps won't catastrophically self destruct if anything
>>>> goes wrong.
>>
>>
>> ** Complete nonsense.
>>
>> An X2 cap may develop an internal short our and smoke and burn if
>> mistreated
>> or at the end of its life.
>
>
> Ever connected an electrolytic capacitor revere on a 48 volt battery?

** Ever had your foot caught in a rat trap ?


> I can tel you that is gives a big bang ....


** Nah, that happened billions of years ago.

WTF is this raving loon on about ??



.... Phil

[Cydrome Leader]

Dontspam <dont...@invalid.invalid> wrote:
> John Fields wrote:
>> On Fri, 5 Oct 2012 01:20:44 +0530, "Dontspam"
>> <dont...@invalid.invalid> wrote:
>>
>>
>>> Thanks for your interest, but there are no thrift shops where
>>> I
>>> live, at least not the kind that sells such stuff.
>>
>> ---
>> I have a nice assortment of polyester (Mylar) caps and if you'd
>> email
>> me a physical address I can send then to, and what voltages and
>> capacitances you'd like, I'll see what I can do.
>
> Thanks for the offer. I really appreciate it. But I do have some
> Mylar caps of appropriate capacitance and voltage and in any
> case, given the vagueness of any practical application I have in
> mind at the moment, it's not worth the hassle and expense of
> international shipping. On top of that, they may just get seized
> by overzealous/corrupt customs people at my side.

want me to ship you some charged caps?

[Dontspam]

Now there's an idea.