Condenser Capacitiance.

[Kube]

Originally Posted by JSeery

Some folks believe anything electrical is black magic!! Good topic for Halloween.

I believe if it can't be seen, it does not exist.

[Crankster]

Originally Posted by flatheadmurre

it´s a LC circuit but the capacitor is not some magic turbo injection gizmo...if it was...why would a breakerless system work so nice...cause it charges and lets the coil disharge faster.

Nobody is claiming any magic here, quite the opposite in fact. The condenser does boost the quality of the spark as previously described. It's not so much "faster" as it is "longer". Breakerless systems precision allow for an increased dwell. Another reason is they don't need a ballast and can utilize full voltage to the coil. Contact points are more limited in the amount of current they can carry, ultimately means there is more reserve voltage available in solid state ignition. Most who have trouble with points are trying to run them in very worn distributors, running ersatz points/condenser, or all three. A properly setup point distributor is pretty much be identical in every respect to HEI, except above 5500 RPM, stuff like that. Emission controls also factored in modern engines, lighting off very lean air fuel mixtures needs wide plug gaps and hot spark.

[JM 35 Sedan]

What is the best, reasonably priced tester that would be commercially available for testing the actual microfarad range of an ignition condenser/capacitor like those used on our stock early Ford V-8 ignition systems?

[Lawrie]

Jim ,when you work out a good condensor tester ,let me know.
I want one,
Lawrie

[flatheadmurre]

For testing a condensor you need a powersource in the 400v range a constant current device keeping the current down low enough to avoid human injury and a uA meter in the 50uA range can be built just make sure the constant current device has an open failure mode or it can be very bad for your health.

[flatheadmurre]

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The colapse of the field should be as rapid as possible to get all energy out to the secondary...a bigger cap slows down this event leading to less output.
Dwell is good getting the coil satured...but if i remember right you break down saturation time in 5 periods...at third you get 78% and 4th 90% so the last bit of dwell isn´t that critical most of the time chasing increased dwell you get a sharp camgeometry and problem with points bouncing at higher speed instead.
For anyone still thinking that the capacitor provides energy in some kind that increase the spark start calculating the energy stored in it compared to what´s in the coil.
The capacitor is a snubber/damper not a power source.

[tubman]

There are any number of testers available in the $20 and up range (Google is your friend). That being said, I have been through this big time developing my "Trash Can" replacement condensers and the problem is not capacitance, but the ability to stand up to vibration and voltage and temperature fluctuations. The problem is especially pronounced on vehicles with generators and solid plug wires. The actual capacitance of the condenser is of secondary importance. Nobody minds changing points at 45,000 miles rather that 50,000, but everybody hates being stranded beside the road because a capacitor gave up unexpectedly.

At this point in time, my "Trash Can" replacements are available in .22 mfd only. This is because usable capacitors in the "point thirties" are not available in the quality needed for automotive use, at least not in a practical size. If one does come available, I will probably be making it available as an option, but it's really not needed.

[rotorwrench]

A capacitor (condenser) is more like an accumulator in a hydraulic system. It builds to a certain pressure point and stores that energy for a while till needed. The cap does the same basic thing. It can absorb electrical pressure before discharge and absorb back pressure after discharge. In that respect it's also not unlike a shock absorber (literally). If you ever got one handed to you in a charged state, you know what I mean about "literally".

[flatheadmurre]

A capacitor is like a battery and can be charged and discharged...but in the capacitor coil scenario it would be like trying to power an elevator motor with an AAA battery.
Ignition is about energy...
How much energy is stored in a coil ?
How much energy is stored in a fully charged capacitor of .22 to .36 uF ?
Will the added energy be in the 10% 1% or in the .01% range ??

[Crankster]

Testing a condenser capacitance value - MFD, or uF, or whatever it is they call it these days, is no problem for even the inexpensive standard digital units. The problem is they don't really perform a meaningful test as to whether it's "leaky". For that they need to have their rated voltage applied, in this instance several hundred volts DC.

[Crankster]

Originally Posted by flatheadmurre

How much energy is stored in a fully charged capacitor of .22 to .36 uF ?
Will the added energy be in the 10% 1% or in the .01% range ??

Maybe a better way to think of the condenser is like a shock absorber for the ignition system, it ensures that the break of the primary ignition circuit is clean, no spark at the points. It's "improving" the spark at the plugs in that sense, by directing all the energy where we want it to go.

The correct capacitance range is sort of important because they (points) will last longer. Back when points were in wide use, many mechanics would leave the condenser alone during a tuneup if it was otherwise running well. Either the + or - side of the points would tend to crater or mound if the capacitance was way off the beam.

[flatheadmurre]

I´m glad that we finally agree on that the capacitor is a snubber/damper then.
And why do we want a snubber over the points besides points life...cause if we get a spark going there the energy will burn off and the collapse of the field will be slowed down.
Why do we get metal migration to either side of the points if the capacitor is to big or small....the size of the capacitor has to be big enough to absorb the voltage until the points open wide enough so the spark can´t jump the gap....when the points close again the energy stored in the cap has to discharge somewhere unfortunately the point is the only place for it....electrons move in one direction charging...and so will metal...and the other direction discharging and that´s why you can tell if the capacitor is to big/small from looking at the points.
So what was the damper part i was talking about...that ugly voltage spike when the coil fires is way above our system voltage and will go back into the cars wiring....that spike is dampened by the capacitor and the ringing at the end of the firing cycle is also taken care of.
What happens if we don´t dampen spikes...besides the obvious high voltage hurting the cars primary we can get high frequency oscillation that transforms into the secondary of the coil.

[Frank Miller]

Here are some basics and I'm no expert so feel free to comment. When a magnetic field passes across a conductor there is a voltage induced into it. It is how a transformer works, which is much like a coil. A transformer needs AC or switched voltage/current to work. There is no connection between the two coils it is just the collapsing magnetic field in one inducing voltage into the other.
That being said when the primary is charged by closing the points there is nothing in the secondary of the coil until the collapsing magnetic field induces the voltage to the secondary. Now here is where the capacitor comes into play. When the spark plug is done there is no more current in the secondary and that magnetic field collapses and wants to power the primary. The condenser keeps that from happening. If it is too small then it will not completely do the job. If it is too big then some of the current to charge the primary may be lost to it. In the end it is hard on the switching system, meaning the points.
As a bit of an aside think for a moment how much work the ignition does. At 2000 rpms the coil fires 8000 times a minute given 4 sparks in a revolution. That meant the points have switched the coil on and off 8000 times in minute. Given 2000 rpms at 50mph it would be like 48000 times on a 50 mile ride. Sorry, this is what happens when you drive 8000 miles with no one to talk to.

[flatheadmurre]

It´s one pulsetransformer and one field...not like something is jumping back from the secondary to primary.
I´ll have a go at it again...Coil charges up and points open field collapses this produces a back EMF the "spike" in the drawing...that ends up charging the capacitor...when energy is drained by secondary firing plug primary voltage comes down to a level where the voltage in the cap is higher then in the coil and current will flow reverse from capacitor to coil.
After plug has drained the energy to a level where it doesn´t fire anymore the leftover energy in the coil will ring out in the primary due to capacitor and internal resistance being a good RC snubber.
Not like the capacitor is adding anything to performance...it´s just eating energy away with it´s losses...which is a good thing for damping and saving points...but not for getting maximum amount of energy to secondary.

[JM 35 Sedan]

Originally Posted by tubman

There are any number of testers available in the $20 and up range (Google is your friend). That being said, I have been through this big time developing my "Trash Can" replacement condensers and the problem is not capacitance, but the ability to stand up to vibration and voltage and temperature fluctuations. The problem is especially pronounced on vehicles with generators and solid plug wires. The actual capacitance of the condenser is of secondary importance. Nobody minds changing points at 45,000 miles rather that 50,000, but everybody hates being stranded beside the road because a capacitor gave up unexpectedly.

At this point in time, my "Trash Can" replacements are available in .22 mfd only. This is because usable capacitors in the "point thirties" are not available in the quality needed for automotive use, at least not in a practical size. If one does come available, I will probably be making it available as an option, but it's really not needed.

Tubman, I just connected your post here to another recent post .... https://www.fordbarn.com/forum/showthread.php?t=232019 .... but you are saying .22 mfd only and the other post is saying a perfect .36 mfd. Which post or mfd rating is correct on your "Trash Can" replacements?

[BUBBAS IGNITION]

Originally Posted by oldford2

What meter is needed to test for MFD?
Thanks

I use a older unit powered by 110 volts , its a Perry Davis , you can find them on ebay from time to time. has been the most accurate (i also have sun unit)..

[tubman]

There is something odd going on here. I am working with Jim to get to the bottom of it.

[JSeery]

Originally Posted by flatheadmurre

For anyone still thinking that the capacitor provides energy in some kind that increase the spark start calculating the energy stored in it compared to what´s in the coil.
The capacitor is a snubber/damper not a power source.

Flatheadmurre, I'm a little confused by some of your post. Not sure where you came up with this "capacitor providing energy" you keep referring to. I posted a section from some ignition systems training material on the function of capacitors, nothing about capacitors being an energy source.

• It's primary function is to provide for a rapid decay of the primary coil current.
  
• The capacitor also "third-harmonic" tunes the coil, raising the peak output voltage and increasing the secondary voltage rise time.
  
• This increases the efficiency and the amount of energy transferred to the spark plugs.

The capacitor is not a power source, it is part of a LC circuit. It is not black art or magic, it behaves like all LC circuits.

[rotorwrench]

The caps are an energy storage device but they can only store it for a short time even when in good condition. A battery stores it for long periods and a cap only stores it for a matter of minutes before it slowly leaks down after power is taken away from it. You can hear larger ones when they build a charge. A classic example is a flash lamp for photography. You can hear them whine up as they build a charge until it has reached full capacity. On larger ones like are used for strobe anti collision lights on aircraft, they whine up pretty loudly as they charge but those are some pretty large capacitors too. The instructions on these units state to wait 15 minutes after shut down before disconnecting the wiring to the lamps so you won't get zapped.

[BUBBAS IGNITION]

You guys notice i am staying out of this discussion. Too confusing for me.

However think about this for a minute.

Without a condensor the current ( 3-4 amps) continues to flow when the contacts begin to open (001-etc) (jumping the small point gap) causing a arc.

This would in some cases make the car NOT run or run very poorly based on lack of control of the circuit (that needs to see a clean on/off ).

Using the path of least resistance the condensor provides a temp storage of the voltage allowing the points to open without arcing.

By the time the condensor "loads" (capacity in mfds) the contacts close and dumps this voltage backinto the primary circuit..allowing the circuit current to again flow and does it again.....and again.....