Condenser Capacitiance.
 

A question for the experts please.
Flathead standard 85hp 6v system. Running standard distributor,coil and condenser.
The condenser should be in the 0.33 to 0.35mf range?
What effect if any providing all other components are in good order,
would a condenser of say 0.22 to 0.30mf have any effect on smooth operation especially in higher rpm and speed range.
Thanks in advance.
Phil NZ

Re: Condenser Capacitiance.
 

Yes a .22 mfd might arc and cause a miss based on lack of storage capacity...especially in the early crabs etc. .22 would great in a later small cam indivudal point set...

Re: Condenser Capacitiance.
 

Ok Bubba thanks for that info. So maybe the minimum should be around 0.30mf for the 37 to 41 type distributor.
Phil NZ

Re: Condenser Capacitiance.
 

Phil, Early V8 condensers should be in the range of .30 mfd. to .36 mfd. The higher end would be preferred as that is the original specification. I have used a Mallory type 400 condenser which is rated at .28 mfd. guaranteed value. I have tested about a dozen of these and all are around .30 mfd. I have fitted several to early V8s including my own 34 Ford and they work very well. In the past I have purchased reproduction Ford V8 condensers for various years and most soon packed up. Some were even faulty straight out of their plastic bag. MACS and others sell them but I no longer buy them. I think they come out of CHINA. The price of the Mallory 400 varies from around $10.00 to $30.00 each, so shop around. Look for a supplier on Ebay. I buy mine here in Australia, (Melbourne). Most other new condensers are in the range of .22mfd. to about .26 mfd. and while they would seem to work OK the ignition coil output could be compromised and distributer contact life would be reduced somewhat. Regards, Kevin.

Re: Condenser Capacitiance.
 

A to small value can give you arcing.
The capacitor value should be just big enough to absorb the voltage over the point until they open enough so the voltage can´t jump between the points.
A value bigger then needed affects the coil output since the colapse of the field goes slower with a bigger value of the capacitor.
So you want a small value from performance point of view...but big enough to give you a acceptable points life.
If you look at the points after they been run there should have equal wear on both contact surfaces...more metal on one side means the capacitor value is to big or small.

Re: Condenser Capacitiance.
 

Appreciate all information given. and the reason for these values and effects if too far outside stated values. In my case for the 37 to 41 distributor as close as possible to stated values but see a recommended mallory 400 at .28mfd should also do the job.

Just checked today and my 38 PU which is fitted with an 8ba with a Chev converted distributor was still running through the underdash resistor. Output of 3.8v.
Today bypassed this and nnow have 5.8v to round type coil, KEM U11A 6v.
Is the issue of reduced input voltage to coil that significant?
Phil NZ.

Re: Condenser Capacitiance.
 

Kevin, who is the supplier in Melb.
Lawrie

Re: Condenser Capacitiance.
 

On our local "Trade Me" was able to buy at NZ $24.64. with free shipping Mallory 400 600v .28mfd.
Phil NZ

Re: Condenser Capacitiance.
 

What is important is the total resistance in the circut and will depend on the coil resistance pluse any external resistance. Most of the 6v can coils are around 1.5 ohms and do no use any external additional resistance. They would not use a ballast resistor.

Re: Condenser Capacitiance.
 

The early type helmet coils were not the most efficient set up but they worked OK. The rebuilds by Skip are an improvement but a lot of the difference is the design of the core so not much can be done to change that if a person wants an OEM type coil. The late can type coils have a bit more efficient core and are oil filled so that can take less of a capacitor charge to function normally. Henry was a good friend with Marion Mallory and thought his designs to be compact and simple so they worked together untill Henry died to utilize his designs. The can type coils didn't work well with the helmet type distributor so the design was changed to suit it. They were reliable enough and inexpensive to replace at the time. Now if the current manufacturers in the business would just make decent condensers instead of the rip off crap they produce now. With modern materials, the capacitors should be very reliable but they just don't care if they make them correctly or not.

Re: Condenser Capacitiance.
 

To use a radio analogy, I got the impression that the coil and condenser together are a "tuned circuit", the capacitance has to be in a certain range for best possible spark. The condenser not only prevents arcing of the points but boosts the resulting spark at the plugs.

Re: Condenser Capacitiance.
 

Automotive condensers have a fairly high voltage rating and capacitance, in a small package. I suspect that's the problem, and they try to meet a price point. There isn't much call for high voltage capacitors in modern electronics, but they are still made. If you look at what's offered by Sprague and others, they are physically quite large. For example a .22uF or .33uF @ 600 or 1000 volts, they are pretty chunky. A good quality capacitor should last a long time, as well.

Re: Condenser Capacitiance.
 

What meter is needed to test for MFD?
Thanks

Re: Condenser Capacitiance.
 

Capacitance meter...but it only measures the value...not if the capacitor leaks or arcs over when used.

Capacitors drying out can show a value higher then it was from start and still be just crap.

You really need a highvoltage source with a limited amount of current (to keep yourself from frying if things go wrong) and a mA meter to see what is going on in real.

Re: Condenser Capacitiance.
 

Yep, it is often referred to as "ring" in the circuit.

"The capacitor performs several functions. It prevents the points from arcing and prevents coil insulation breakdown by limiting the rate of voltage rise at the points. 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. If the coil secondary voltage rises too quickly, excessive high frequency energy is produced. This energy is then lost into the air-waves by electro-magnetic radiation from the ignition wiring instead of going to the spark plugs where we would like it to go."

Re: Condenser Capacitiance.
 

Ignition coils isn´t some kind of black art...it´s a pulse transformer.
Besides the points life...you have back EMF to deal with...nothing magic it can be calculated using Lenz´s law.
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.
The ringing in the primary circuit of an ignition coil starts first after there´s not enough energy left for the spark to jump the gap in the plug.

Re: Condenser Capacitiance.
 

1. points close voltage drops charging coil.
2. coil saturated fully charged
3. points open coil fires plug
4. coil disharges through plug
5. not enough energy left to fire plug leftover energy rungs out.

Re: Condenser Capacitiance.
 

Condensers prevent arcing between the points. If the pitting is on one side it is too small and on the other it is too big. The properties of the coil is what determines the right value. There is a lot of info on the net about this.

Re: Condenser Capacitiance.
 

Thanks for all the offered information on this subject. Hoping to finally finish up a long going problem with my 39 coupe in this area very soon.
Was almost at the point of quiting the car but pleased i got over that down phase for sure.
Phil NZ

Re: Condenser Capacitiance.
 

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

Re: Condenser Capacitiance.
 

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

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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?

Re: Condenser Capacitiance.
 

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

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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".

Re: Condenser Capacitiance.
 

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 ??

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

Re: Condenser Capacitiance.
 

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)..

Re: Condenser Capacitiance.
 

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

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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.

Re: Condenser Capacitiance.
 

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

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.....:eek: