Condenser Capacitiance.

[Phil Gillespie]

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

[BUBBAS IGNITION]

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...

[Phil Gillespie]

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

[koates]

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.

[flatheadmurre]

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.

[Phil Gillespie]

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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.

[Lawrie]

Kevin, who is the supplier in Melb.
Lawrie

[Phil Gillespie]

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

[JSeery]

Originally Posted by Phil Gillespie

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.

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.

[rotorwrench]

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.

[Crankster]

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.

[Crankster]

Originally Posted by rotorwrench

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 the make them correctly or not.

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.

[oldford2]

What meter is needed to test for MFD?
Thanks

[flatheadmurre]

Originally Posted by oldford2

What meter is needed to test for MFD?
Thanks

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.

[JSeery]

Originally Posted by Crankster

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.

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."

[flatheadmurre]

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.

[flatheadmurre]

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.

[Frank Miller]

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.

[Phil Gillespie]

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

[JSeery]

Originally Posted by flatheadmurre

Ignition coils isn´t some kind of black art...it´s a pulse transformer.
it´s a LC circuit but the capacitor is not some magic turbo injection gizmo...

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