Leaky Capacitor

[cybose]

II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
regulated SMPS, on a flash unit. The thing is after awhile the main
charging capacitor in the flash unit starts heating up and leaking
fluid (obviously pretty dangerous). Is there something fundamentally
wrong in trying to replace a battery power source, with a regulated
power supply?

 

[Arfa Daily]

II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
regulated SMPS, on a flash unit. The thing is after awhile the main
charging capacitor in the flash unit starts heating up and leaking
fluid (obviously pretty dangerous). Is there something fundamentally
wrong in trying to replace a battery power source, with a regulated
power supply?

Not so long as the power supply is genuinely regulated to the correct
voltage ( a switcher should be ) and that the output is clean of switching
noise, and therein lies a different story ...

If the power supply that you are trying to use is not new, then I would
suggest checking its output with a 'scope, in case its output filter cap has
gone high ESR, as is common.

Are you saying though, that the flashgun did not exhibit this problem, and
worked completely normally on batteries ? Does it continue to work normally
up until the problem with the cap starts ?

If the cap really is leaking electrolyte, then you need to replace it
pronto. The liquid that is leaking from it is corrosive, and will damage
nearby components and print tracks. Also, if it decides to vent fully, this
action can be quite violent, and a considerable amount of electrolyte will
be sprayed around the inside of the thing.

Arfa

 

[TimPerry]

II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
regulated SMPS, on a flash unit. The thing is after awhile the main
charging capacitor in the flash unit starts heating up and leaking
fluid (obviously pretty dangerous). Is there something fundamentally
wrong in trying to replace a battery power source, with a regulated
power supply?

a buddy of mine (EE) insists that loads powered by SMPS are more
susceptible to voltage 'spikes' because the spike can occur when the switch
is in the on state and therefore just kinda passes through.

the logic seemed to make sense to me but i don't insist that it is indeed
the case.

 

[**THE-RFI-EMI-GUY**]

Are you trying to exceed the duty cycle of the unit? It was designed to
be used intermittently. If you are now cycling it on and off many
flashes a minute, perhaps the capacitor is now exceeeding its design
rating. It could indeed be dangerous. Not to mention, the electrolyte
getting on circuitry is going to cause some pretty unreliable operation.

II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
regulated SMPS, on a flash unit. The thing is after awhile the main
charging capacitor in the flash unit starts heating up and leaking
fluid (obviously pretty dangerous). Is there something fundamentally
wrong in trying to replace a battery power source, with a regulated
power supply?

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"©

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P

 

[Asimov]

"cybose" bravely wrote to "All" (16 Jan 06 17:07:57)
--- on the heady topic of "Leaky Capacitor"

cy> From: "cybose" <[email protected]>
cy> Xref: core-easynews sci.electronics.repair:355457

cy> II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
cy> regulated SMPS, on a flash unit. The thing is after awhile the main
cy> charging capacitor in the flash unit starts heating up and leaking
cy> fluid (obviously pretty dangerous). Is there something fundamentally
cy> wrong in trying to replace a battery power source, with a regulated
cy> power supply?

Depends... for example if the polarity is wrong then the electro will
definitely get hot and leak. Other than this I can't think of another
reason for the heating and liquid spillage. Someone mentioned the
switching supply noise but these are typically quite good in that
respect. There might be another factor that is being missed.

A*s*i*m*o*v

.... Real techs don't lick nine-volt batteries!

 

[Gerard Bok]

II'm trying to see if I can replace 4 AA batteries, with a 6V (2A)
regulated SMPS, on a flash unit. The thing is after awhile the main
charging capacitor in the flash unit starts heating up and leaking
fluid (obviously pretty dangerous). Is there something fundamentally
wrong in trying to replace a battery power source, with a regulated
power supply?

In this case: yes, there may well be something fundamentally
wrong. It all depends on the flash unit's design. There are loads
of (cheap) flash units that more or less rely on the poor battery
performance for their current limitation.
Those may even have a hard time if you use fresh alkaline cells.
Your's isn't particulary well designed if it allows the capacitor
to fume.

Try to imagine, what will happen if the capacitor expodes.
Look at the low price for a new flash unit. Look at your kids.
Make a decision.

 

[cybose]

Thanks

 

[jakdedert]

I was thinking along the same lines. It's also possible that there is
an initial inrush current requirement, which is not being met by the
supply he has....

 

[cybose]

I tried measuring the charge held in the capacitor (when charged by
batteries and before the leaking scenario) and it turns out to be
about 750V. But, (this probably doesnt make sense), the rating on the
capacitor is 350 SV (1050 MFD, There are no other markings on the
Cap.). If the 350 is the surge voltage rating, shouldn't it be much
more than the 750V that I measure across the Cap. terminals ?

 

[Sam Goldwasser]

I tried measuring the charge held in the capacitor (when charged by
batteries and before the leaking scenario) and it turns out to be
about 750V. But, (this probably doesnt make sense), the rating on the
capacitor is 350 SV (1050 MFD, There are no other markings on the
Cap.). If the 350 is the surge voltage rating, shouldn't it be much
more than the 750V that I measure across the Cap. terminals ?

If the inverter really tried to put 750 V on the capacitor, it would have
spilled its guts all over the room.

Are you sure you were measuring on DC?

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