[urq] Electrical Experts - Question re. Capacitor installation

Wed Oct 31 08:07:15 PDT 2007

I don't think my wiring is inadequate or getting voltage drop.  I'm mainly trying to be
proactive with my current supply since the electrical loadings are greater than the
stock  wiring originally supported.  I have run extra current feeds, but still
evaluating if a cap will add value, especially since there are going to be 2 injector
drivers fully loaded, along with high RPM amplified ignition, the computers, and then
add draw from lighting, fan, stereo, etc. that are not on this circuit.

I know I have power lag in the rear to my amp, even with 10 guage wiring.  That will
definitely get a cap, but I question the methods I've see to install the capacitors.

I can always wire the cap to be hot all the time by putting directly off the jumper
post, or I can install a slow charge resistor with a diode for when the engine is off to
keep the cap charged and a switch to full current wire when ignition on.

The ignition is not something I'm doing today, but am thinking about doing it if need
presents itself or as a safeguard.  I presently have at least one 6 guage wire goine
from battery + to coil and injector feed.  That was added in addition to the factory
wiring that goes to the starter and alternator.  The #6 wire continues its rund out to
the alternator and starter where it rejoins the factory wiring - I think is a pair of #
6 wires, but was considered sufficient before, but I noticed a little too much starter
draw, and the new run of wire definitely helped that.

Ben

  _____  

From: Mike Sylvester [mailto:mike at urq20v.com] 
Sent: Wednesday, October 31, 2007 10:47 AM
To: Ben Swann
Subject: RE: [urq] Electrical Experts - Question re. Capacitor installation

I have not done this on any auto.

The did not read the link that you just sent, but from what you mentioned, I can
comment.

Caps do not like to be changed and discharged rapidly.

For that reason, I will guess that the 1F cap you have has a high ESR.

That is fine if you are using it to stabilize the power supply of an audio amp.

If you are trying to stabilize the power supply for the ignition coil, it might not
help.

It all depends on the rise time of the current draw by the coil.

It is probably fast.  If so, a cap with a high ESR can not supply current quick enough
to keep the voltage from drooping.

If you get a 1F cap with a low ESR and connect it directly to +12V, you will get a huge
instantaneous current draw when it has to charge up.  This can stress the cap to
failure.  This type of application needs what is called a soft start circuit.  This
circuit will limit the current draw at initial start-up to protect the cap and anything
supplying the current.

The other issue I see is, I doubt that the +12V on the coil is hot all the time.  It
must disconnect when you turn off the ignition.  With a cap on there, you will be
keeping 12V at the coil after you turn off the key.

Have you measured the voltage at the coil with a scope while the car is running?  Does
it sag when the coil fires?  If so, maybe a better solution is to run a larger wire from
the source to the coil.

Mike

www.urq20v.com <http://www.urq20v.com/> 

-------- Original Message --------
Subject: RE: [urq] Electrical Experts - Question re. Capacitor
installation
From: "Ben Swann" <benswann at verizon.net>
Date: Wed, October 31, 2007 9:36 am
To: "'Mike Sylvester'" <mike at urq20v.com>

Thanks Mike. Have you done this?  Any measurable results.

Ben

  _____  

From: Mike Sylvester [mailto:mike at urq20v.com] 
Sent: Wednesday, October 31, 2007 9:29 AM
To: Ben Swann
Subject: RE: [urq] Electrical Experts - Question re. Capacitor installation

Attaching the cap to the +12V lead of the coil and ground is what you need.

Putting a cap in series creates a filter.

There are 3 parameters other than capacitance that you need to look at when it comes to
caps.

Rated Voltage

Rated Temperature

ESR (Effective Series resistance)

You are putting a Cap on a +12V supply that is actually about 13.8V +/-.

Even a 16V cap might be too small.

The under hood temps can get hot.  Not over the max temp rating, but the Max Voltage
gets de-rated over temp.

The ESR can be a huge factor.  It doesn't do any good to have a huge 1F cap if the ESR
is high, because it won't be able supply the current quick enough.

Mike

 <http://www.urq20v.com/> www.urq20v.com

-------- Original Message --------
Subject: [urq] Electrical Experts - Question re. Capacitor installation
From: "Ben Swann" <benswann at verizon.net>
Date: Wed, October 31, 2007 8:24 am
To: <quattro at audifans.com>, "'URQ'" <urq at audifans.com>
Cc: 'Ben Swann' <benswann at verizon.net>

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.

Good Idea or ??? I'm doing some searches, but not finding a solid answer. 

TIA

Ben
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