I was an Electronics Technician in the Navy.
First of all, the capacitor you're using is a 200 volt capacitor,
and is designed to be charged by a higher voltage, hence the label
Secondly, the "capacity" of that capacitor is very small, meaning
it won't store that voltage for very long, and will discharge very
quickly, so even if it was charged to full capacity (200V), it
would likely discharge so quickly that it would barely cause the
light to flicker. Another way to look at this is that, although
a capacitor this size could be charged to 200V, the amount of
current it can provide will be very tiny.
A larger capacitor, one capable of providing adequate current
for enough time to see the light lit for awhile, will resemble
the battery it is acting like, and be larger in size. It will
be about the size of a C cell battery, or larger.
So you need to find a larger capacitor that is rated at 6V,
with a larger capacitance, more along the lines of 1F.
47uf (microfarads) is a mere 47 millionths of 1 Farad (F).
Another improvement to the experiment would be to use a 6V
LED bulb instead of a regular flashlight bulb. These draw
less current and will stay lit longer.
A 1F 6V capacitor should light an LED bulb for at least 15
by using an LED bulb, you may be able to use capacitors with
a lower capacitance, say as small as 15000uf (6V, still).
These won't be as large, and won't keep the bulb lit as long
(maybe 15 seconds).
You can't charge a capacitor with AC voltage.
As you guessed, just hook the negative (-) terminal of the
battery to the negative terminal of the capacitor, and the
same with the + terminals. The larger the capacitor, the
longer it will take to reach a full charge (think of how
long the whine takes when a camera's flash is recharging).
A 1F capacitor might take a few minutes, while a 15000uf
should take only a few seconds. You don't have to worry
about overcharging the capacitor - once it is charged,
it will act as a second battery and hold the charge that
is left in the battery.
If anything's unclear, or you need further explanation,
just let me know.
Please do not rate this answer until you are satisfied that
the answer cannot be improved upon by way of a dialog
established through the "Request for Clarification" process.
A user's guide on this topic is on skermit-ga's site, here:
Clarification of Answer by
23 Sep 2005 12:41 PDT
I implied the answer in what I told you - to charge a capacitor
with the 6V lantern battery you have, you need a capacitor rated
Likewise, to charge a 200V capacitor, you need a source for 200VDC.
In the simplest terms, there is no solution to charge the capacitor
with what you've described as having on hand.
You could build a power supply, using a schematic such as the one
on this page in the HeadWize Projects Library:
If you wanted to use lantern batteries, you would need to build,
or buy, a step-up converter designed to take 6V and convert it to
200V, and you would probably drain the lantern battery before the
capacitor was charged, so a car battery would be a better input
device. Such a circuit would be hard to find, due to the unusual
output voltage of 200VDC. A more common one would be 12VDC to 120VAC
to convert car battery voltage for use with AC appliances. It would
be much simpler to build a 200V power supply. If you want to give
it a try, Dallas Semiconductor has a Power Supply Cookbook page
which provides free schematics for power supplies for various
"Choose the specifications that most closely meet your needs.
Then view a circuit design, complete with schematic diagram
and bill of materials."
There's a 15V to -180V rated at 0.005A, which probably isn't
enough current for your purposes, in the CB76 PDF:
And there's a 5V to -24V and -100V at 0.12A and 0.075A,
repectively, in the CB79 PDF:
That wouldn't give you the full voltage you need, but
you might be able to modify the circuit in a way that
Another device you could build, which is sometimes used to charge
capacitors in teaching environments is the Wimshurst Electrostatic
Machine, as described on this page by Dr. Antonio Carlos M. de
All in all, the simplest and least expensive solution is to obtain
a larger capacity capacitor, such as a 1 farad capacitor, rated at
6V, and use your lantern battery to charge it, which is why I tried
to steer you in that direction.
If anything's unclear, or you need further explanation, let me know.