Electrical Experts - Question re. Capacitor installation
LL - NY
larrycleung at gmail.com
Wed Oct 31 15:21:28 PDT 2007
Hah! We're all right!
One thing, IF the original power lead is inadequate and it's hard to thread
the lead, one other
option would be to run a parallel lead for power. I had missed the original
point of this, which was
to add the cap filter to an ignition system that was unstable. As Huw, Mark
and others stated, it's
big no-no, you're building a RCL (resistance, capacitance, inductor (coil))
circuit, and unless you
like solving diffy Q's (differential equations), not a lot of fun, I think
even Audi does a better job at
that then we do. Add a bigger ignition lead.
As for using a parallel cap for the stereo, go for it. It'll either help, or
not. No loss but time.
Thanks to Huw, Mark, et al.
LL-NY - get to exercise my RCL muscles, which doesn't occur too often. Well,
I flexed them a bit.
On 10/31/07, Mark R <speedracer.mark at gmail.com> wrote:
> As always Huw is more eloquent than myself on these things. =)
> Let me rephrase.... adding the capacitor is adding more load to the supply
> system (alternator and supply wiring). Think of a bank of 4 batteries
> in parallel. Yes, resistance is lowered, voltage is the same, but the
> in increased on the charging/supply system. Adding a capacitor adds to
> load (albeit a small load increase). I suspect >IF< Ben is having high
> voltage stability problems, it's likely the +12V line is inadequate due to
> being undersized, poor quality, corrosion, or poor connections. Or his
> engine ground(s) is(are) poor. A capacitor won't "fix" this kind of
> Hopefully, this is more clear (and I feel stupid for using an incorrect
> earlier in explaining myself.). =)
> Not many lists have such posts! Ben's questions have made us think and
> discuss. How cool is that?
> Thanks Larry and Huw!
> Mark Rosenkrantz
> On 10/31/07, Huw Powell <audi at humanspeakers.com> wrote:
> > > Something new to my realm of expertise.
> > >
> > > I would like to install an electrolytic capacitor to act as a buffer
> > an ignition
> > > system – sort of like placing a second battery up close to the
> > load.. Since the
> > > distance of the battery to the coil is about 7-8' and my understanding
> > that a circuit
> > > may lag, it seems installing a large capacitor might be a good idea.
> > If so, it makes
> > > sense that I'd install it in parallel with respect to feed wire and
> > ground, however
> > > diagrams for most stereo AMP installations show the cap to be inline,
> > with no other
> > > current path to the amp.
> > >
> > > Is it OK to install an electrolytic cap. as sort of a buffer or quick
> > discharge
> > > batteryin parallel with the circuit? That is basically to connect the
> > positive end to
> > > battery post near load and ground as normal, leaving the original
> > positive feed path
> > > intact. I have some 1 and 2 Farad caps and this is mainly to prevent
> > lag at high RPM,
> > > similar to stereo clipping at high volume.
> > Many others have commented, saying most of what I thought in response to
> > this, but I figured I'd chime in anyway.
> > 1. Any diagram showing a DC filter/stiffener cap in series with the load
> > is simply wrong.
> > 2. If the wire to your coil is too small, replace it. If the wire to
> > the coil is too small to keep battery voltage at the coil, a capacitor
> > is not going to help. The current to keep the cap charged has to come
> > through that wire.
> > 3. It might make things worse, but my head hurts when I try to look at
> > the equations in my old college electronics class notes. But basically,
> > while the coil is "recharging", the capacitor might also be trying to do
> > the same, using *more* current. Also, the capacitor will have a
> > "discharge rate" curve, that may not coincide well with the operating
> > cycle speed.
> > 4. So in conclusion, run a bigger wire, and don't do the cap unless you
> > figure out a way to get the circuit exactly right for the application.
> > --
> > Huw Powell
> > http://www.humanspeakers.com/audi
> > http://www.humanthoughts.org/
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