so im gonna replace teh condensor on the stock 24v ign. is there a difference from using a 12v or do i need to find one for 24v?
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so im gonna replace teh condensor on the stock 24v ign. is there a difference from using a 12v or do i need to find one for 24v?
I have been old by many that since they are working off of the high voltage the coil sends to the plugs, it doesnt matter on voltage for them...BUT I list a part number for the 24 volt one:
Condenser: AL869
and the 12 volt one:
Condenser: AL868
I do have the following part number:
Not true.....the points and condensor are on the primary side of the ignition system. Not the secondary where the plug wires and high voltage are.Quote:
Originally Posted by brute4c
The contact points and condensor, handle 12 volts, (or 24 in this case) switching the negative side of the coil off and on to cause a collapse of the magnetic field in the primary windings of the coil and then a high voltage surge to fire the plugs.
Thanks for the truth.
Frontline and Franks Surplus both have lots of 24V condesors if you need a place to get them.
No problem, hope it didn't sound too tough.....kinda like Jack Nicholson: "You can't handle the truth!" :DQuote:
Originally Posted by brute4c
No, no, no....I just have heard theory and hadnt thought it out myself...so many have told me so many different stories...its nice to get the truth...refreshing!
I like to think of an ignition system as two halves: The primary: all 12/24 volts, and the secondary: all high voltage of 10K-20K volts or more.
The Primary side includes the points, condensor, ignition switch, module in an electronic setup, the primary windings in the coil, and the ballast resistor.
The Secondary side includes the rotor button, the cap, the ignition wires, and the spark plugs. All the stuff that can jolt you good!
I really haven't tried using a 12 volt condensor on a 24 volt system, but I am not sure why it wouldn't work, other than it could possibly just not last as long. A condensor is just a capacitor that stores excess energy, and keeps the points from bearing the full electrical load and pitting up much sooner than normal.
Is the condensor ever discharged in normal ignition use? Would it make sense to do it once in a while...in a way that wont curl ones hair of course...
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.Quote:
Originally Posted by brute4c
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.
Wow...you guys are good with the electron world...THANKS 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.
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.Quote:
Originally Posted by amphi
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?
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.
That little ole condensor works pretty hard....I would a never thunk it.
Thanks again!!
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.
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.
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!
I wonder if the end on the condensor is different between the civvy and mil units...maybe...
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.
Sorry to dig up an old thread, but figured I'd add some more information... the condensor doesn't suddenly discharge, except in the case that engine rpms are high enough that the points re-close before the spark is completed. The combination of the condensor and the coil forms a resonant circuit, which rapidly oscillates, with the condensor going from fully charged with a positive voltage to no charge to fully charged with a negative voltage and back and forth several times slowly decaying to nothing.Quote:
Originally Posted by randyscycle
As an example, here's a 'scope display from when I showed someone what a misfire looks like:
http://www.bushytails.net/~furrywolf/spark01-small.jpg
On the first one, there's a sharp spike when the points open, a level area during the spark itself, a small peak once the spark ends, then lots of quick oscillations. (while not relevant to this discussion, the second one shows a no-spark misfire - the sharp peak happens, but rather than showing a level area as it sparks, it just decays without ever sparking)
During these oscillations (the squiggles to the right of the spark), the condensor is charged and discharged thousands of times a second with alternating polarity, slowly decaying due to resistance in the circuit.
--Bushytails
No problem brining up this old thread. Your input adds more correct information.Quote:
Originally Posted by Bushytails
I now see where the discharge of the condenser (capacitor) is not linear but is in an oscillating discharge.
The below charts are from an amplified ignition but the values would be similar to a points ignition. They show a primary voltage spike of 326.8 volts and an oscillating decay near the 40 volt mark and eventually going lower. These also show the resonance you described above.
http://www.mavericktechnology.co.uk/...cs/primary.gif
http://www.mavericktechnology.co.uk/...cillations.gif
http://www.mavericktechnology.co.uk/...t_burntime.gif
http://www.mavericktechnology.co.uk/...ages/dwell.gif
http://www.mavericktechnology.co.uk/...uced_volts.gif
This link has a very good description of the above charts that show the high voltages across the points and condenser.
http://www.mavericktechnology.co.uk/...ed_primary.htm
Thank you for your input.
Man, you guys are way over my head.
Well, how about a mechanical analogy? :)Quote:
Originally Posted by fng
Consider a mass (weight)... it has momentum. If it's not moving, you need to apply force to it to make it move. And when it's moving, it'll keep moving unless you do something to stop it.
If you apply a small amount of force over a long time, you build up stored energy. If you stop it suddenly, you get back a very large force over a very small period of time. The classic example is a hammer - you apply a small, constant force over the entire swing of the hammer, then the hammer applies a very strong force to the nail/stuck bolt/bent wheel arch/brake drum/etc for a short period of time.
Now, if you intentionally want this sudden large force, you sometimes also don't want whatever you're beating to break. To do this, you add a small spring to it (like putting a piece of rubber on the hammer, to make a rubber-faced mallet), so while the hammer is trying to smash with a very strong force, the spring absorbs some of that force, storing energy itself, preventing too much force from the hammer blow.
When the swing is over, the spring will push the hammer back slightly, then the hammer and spring will sit there jiggling up and down or vibrating, until either friction with the air slows it to a stop, or you pull back the hammer for another blow.
An ignition system works much the same way... While the points are closed, a constant voltage is applied to the ignition coil. A coil, like a mass, builds up stored energy with time, and also like a mass, doesn't like suddenly stopping. When the points open, the coil wants to keep power flowing through it, but with the circuit disconnected, it has to suddenly stop. Like the hammer hitting the nail, this sudden stop produces a very large, short burst of energy - visible as the big spike in the oscilloscope pictures, this is what triggers the spark.
However, just like the hammer, unless there's something to absorb just a little bit of the energy, things will break. A condensor (capacitor) acts like a spring - you can stick energy into it, and the more energy it's storing, the harder it is to push more in. Some of the energy released from the coil is stored in the condensor, instead of doing harmful things, which in the case of a points ignition, is burning the points.
Like the hammer+spring example, now that the condensor has stored some energy, it wants to spring back... it discharges the energy it just got back into the coil (with power flowing the opposite direction). Then the coil puts some energy back into the condensor. Etc, etc, etc. Like a weight and a spring jiggling up and down, this process resonantes until imperfections (resistance/friction) reduces it to nothing - these are the jiggles you see on the graphs.
Now, all this only describes the primary side of the circuit. The coil also has a secondary side, which for this example, can be thought of as a long lever - the big impulse when the points open is translated to an even bigger one on the other end of the lever, which is why you have a 35,000 volt spark from the 350 volt primary spike...
Did that help, or was it such a horrible analogy no one has any idea what I'm talking about? :)
--Bushytails
I remember my dad using a snap-on scope to diagnose problems back in the 70's. Always thought it was cool to look at all the wavy lines but didn't have a clue what they meant. From looking at the lines a good mechanic could quickly diagnose the source of the ignition problem.
Yep. Hence why I was showing someone what ignition problems look like on a 'scope. :)
--Bushytails