Re: Car stereo capacitor not charging



Tony wrote:

On Fri, 26 May 2006 23:43:27 -0400, "TimPerry"
<timperry@xxxxxxxxxxxxxxxxxxx> wrote:

Pooh Bear wrote:
Tony wrote:

Connecting 1.5F (or any other cap) into a battery power circuit via a
1k resistor won't do anything. You need VERY low impedance
connections from the cap to the power amp (or whatever) to have it
work.

Some supercaps have built-in LEDs, discharge resistors, etc that
would prevent a full charge when fed via a resistor (just as you
experienced). If your 1k resistor drops 7V when feeding the supercap,
that's 7mA, and if you eliminate the resistor, whatever's in the
supercap may draw 20mA or more at 12V, so make sure the circuit is
switched so it doesn't flatten your battery if you leave it
unattended for a month or more.

100 ohms ( use a ~ 3 watt type ) would make more sense. It'll still
take several minutes to charge.

Graham

use a taillight bulb... when it stops glowing its done :)

Supercaps certainly might prefer to be charged relatively slowly, but
even 100 ohms with 1.5F is a 150 second time constant, so needs 5
minutses or so for a reasonable charge. A taillight bulb would be much
faster, and with a little more constant current (also good). But
clearly I'm missing something here; what does any of that do to
stabilize the car's battery/amplifier system, unless the load connects
directly to the supercap (which is clearly impossible if it's fed via
such an impedance)? Are these things just for show? Is this thread
really a joke that I'm not getting?

The 100 ohm/tail lamp whatever is just to charge the thing up safely. In use
it's removed.

Graham

.

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