[urq] Electrical Experts - Question re. Capacitor installation

[Grant Lenahan]

Yes and no. It will increase the surge at turn-on, but will not 
increase constant load, unless the capacitor leaks.

Grant
On Oct 31, 2007, at 4:58 PM, Mark R 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 
> wired
> in parallel.  Yes, resistance is lowered, voltage is the same, but the 
> load
> in increased on the charging/supply system.  Adding a capacitor adds 
> to the
> load (albeit a small load increase).  I suspect >IF< Ben is having 
> high RPM
> 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 
> issue.
> Hopefully, this is more clear (and I feel stupid for using an 
> incorrect term
> 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 
>>> for
>> 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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