ignition condensor

[brute4c]

Wow...you guys are good with the electron world...THANKS Amphi!

[amphi]

You are welcome!

Rboltz is the real expert in this area. He did quit a bit of testing with both 12v and 24v ignition systems on his truck. He was able to determine an acceptable ohmic value of the ballast resistor used with 24v.

Maybe he can chime in with an answer to the original question and the results of his tests.

[randyscycle]

Yes !! It discharges immediately upon removing voltage (ignition off) because it is connected directly across the points. The first time the points close, as the engine rolls down to a stop, a short circuit is placed across the condenser discharging it.

The condenser does see a higher voltage than the 12v or 24v the points put to the primary coil windings. The same collapsing magnetic filed, Randy so correctly described above, also collapses over the primary windings inducing a fly-back voltage seen by the points. The condenser absorbs this voltage (actually current), reducing the arc across the points (longer life) this also helps the primary circuit achieve a quick discharge upon points opening because arcing is just a delayed opening or disconnect. It then has a charge, which helps the B+ build primary coil current during the next cycle.

To summarize the convoluted explanation above, the condenser provides three critical functions:

1. Reduce arcing across the points by absorbing energy.
2. Assists ignition by releasing stored energy.
3. Assists quick discharge by making a potentially long arc shorter.

This really doesn't answer the original question but since we have two different part numbers there must be a difference.

Hope this helps.

Thanks for the more in-depth explanation! I used to teach that stuff regularly, but with electronic ignition, we got away from it to a degree, only using the very basic theory, much to my dismay.

I figure if you understand the way the point systems worked, the electronic systems are a lot easier to make sense of...

I just wonder if the part number difference is possibly for a heavier guage wire on the condenser, or some minor thing like that?

[rboltz]

Basically the function of a condenser in a coil ignition circuit is to reduce the spark at the contact points as they open in the distributor and thus minimise burning and pitting of the points. Arcing is caused by the effect of self induction in the coil as the points interrupt the flow of current. The resultant collapse of the magnetic field produces a high voltage to be generated in the primary winding which then tends to flow across the points, thus causing burning or pitting. This current flows into the condenser and charges it as the points open. The rapid collapse of the magnetic field produces this high voltage in the primary windings, which can be as high as 250 volts. This further charges the condenser and the consequent collapse of the field causes a high voltage to be induced in every turn of both primary and secondary windings. As the secondary winding has about 100 times the number of turns of the primary, the voltage can reach as high as 25000 volts. Normally this voltage is not reached as it is limited by various factors such as point gap, compression, engine revs. Etc. so only sufficient voltage is produced to produce a spark at the plug. As the spark is produced at the plug gap the energy in the coil, stored in the form of magnetic flux, begins to drain from the coil through the secondary circuit thus sustaining the spark for a fraction of a second or several degrees of crankshaft revolution. During this interval the condenser discharges back through the primary winding producing an oscillation of the current flow in the primary circuit for the brief interval that is required for the primary circuit to return to a state of equilibrium. The condenser DOES NOT DISCHARGE UNTIL AFTER the spark has occurred at the spark plug.

Burning of points results from high voltage, presence of oil or other material at the points, defective condenser or too small a gap in the points. High voltage can be caused from high voltage setting of the regulator or high resistance in the charging circuit.

Contact pitting results from an out of balance condition in the system which causes the transfer of tungsten from one point to the other so that a tip builds up on one point and a pit on the other. The direction in which the tungsten is transferred gives an indication for correcting the situation. If the tungsten transfers from the negative to the positive point one or two corrections may be made. Increase the capacity of the condenser, shorten the condenser lead, separate high and low tension leads between the coil and distributor, move these leads closer to the engine block. If the transfer is from the positive to negative point, reduce condenser capacity, move low and high leads closer together and/or away from the engine block, or lengthen condenser lead.

So, in summary the condensor being 12 volt or 24 volt is not a problem. It is designed to operate at a much higher voltage then that as Amphi mentioned and most will work. Somewhere I have info on the micro farads involved. I'll keep looking.

[brute4c]

That little ole condensor works pretty hard....I would a never thunk it.

Thanks again!!

[rboltz]

Could not find anything about the common sizes so I measured a few that I have onhand. Looks like .3mfd is a good average. My old test gear may also be off calibration.

[rboltz]

My research says most ignition condensers are .27 mfd @ 600 volt so my reading of .3 mfd was OK. They were supplied from .1 to .4 in various steps.

[randyscycle]

I believe if I remember correctly, that if you look at the pattern of the Secondary Ignition on an oscilliscope, at the end of the pattern you'll see a small "bump" which we always called the "extinguishing spike." I think (not certain!) that there is where the condenser discharges......

Help me if I am wrong!

[brute4c]

I wonder if the end on the condensor is different between the civvy and mil units...maybe...

[george walker]

I understood it that all points and condensors are the same as to operating voltage. The ign. parts were built for operating at 6v, but when 12v came along instead of having to make points, cond.,coil in 6 an 12v, the ballast resistor was added to reduce the voltage back near 6v., allowing the same parts to be used in a 12v system(some coils have the resistor built in so there isnt an external resistor)as well the resistor in the coil on these trucks reduces the voltage from 24v. to a lower voltage, so the points an cond. arent 24v or 12v they are just points and cond.