Ironhead chip condenser

[ryder rick]

I figure an oil temp of 250,
+ the sun 100
+the exhaust 200 (cone motor)

Seems to me a mag might have cooler internal temps than a cone

[Chuckthebeatertruck]

Originally Posted by ryder rick

I figure an oil temp of 250,
+ the sun 100
+the exhaust 200 (cone motor)

Seems to me a mag might have cooler internal temps than a cone

Heat loads don't "add up." Thermodynamics is much more complicated than that.

To simplify; the heat seen by the timing internals on a "cone motor" is the same temperature as the timing cover, which is going to be really close if not exactly the same temperature as the cases.

You're suggesting that your timing cover and cases run at 550F (250+100+200 = 550).

Stop and pause -- do you really think your cases are running at 550F?

[ryder rick]

No, If i did I would have added the numbers.

For the point of this discussion the first element exceeds 105C

1200F exhaust is going to add some heat.

Why do you want to discredit my visual example?

You said 550

And if you want to pick something apart determine the difference in temps from a mag to a cone. Because the mylar caps in use that have been given as examples are used in a mag housing that runs at a lower temp than a cone points plate.

Don't forget about heat soak, Your part may see temps higher than oil temps on a hot shut down.

[Chuckthebeatertruck]

Commercial capacitors are rarely rated for more than 600v, 60HZ, at 125C.

Pretty much all capacitors installed in vehicles are common 70 or 105C caps with much lower voltage and frequency ratings. They are not robust and they are not heavy duty. General working life of a cap is around the same as points themselves and often longer. That's a good 20,000 miles or 20,000 hours of operation at a sustained 60mph. Not bad for a cap that is in an environment hotter than its rating.

What that working temperature value refers to is the maximum temperature at which the capacitor will reliably give the rated capacitance at the rated voltage and frequency (HZ). Beyond that limit and the cap can get "flaky" which may or may not be an issue depending on your application.

Most all commercial capacitors are designed so that they retain their value +/- 10% up to 125C to give a "standard" working range of -30 to 125C.

In other words, the temperature rating on the side of the cap is important - but it's not quite what it appears. You also have two different equations you can use to figure out all parameters; these are Ohms is related to voltage, current, and resistance; amperage, voltage, and watts are all related. Watts convert to joules of energy . . . which can be used to calculate heat.

Hence there are two different ratings:
1) Working Temp
2) Temperature Coefficient

The first is the range for stability of the rated mf at the stated max voltage and frequency. It is not the "failure" temperature because it refers to the temperature of the cap, not the temperature of the caps environment. They are related, but different.

The second helps you understand what happens as you increase the temperature of the capacitor past the working temperature. Some capacitors increase their capacitance whilst others lose capacitance.

heat absorption and radiation is directly related to the surface area of an item. A cap won't absorb as much heat as fast as it's surroundings because it has a smaller surface area and a very different temperature coefficient than the materials around it.

The tiny cap ain't absorbing as much heat as the massive amount of alloy around it.

[bill smith]

To the original poster, unless I misunderstood, you were looking for an alternative for the junk type condensors that are now available for the oem parts. I also had trouble with said junk which after several hours of research netted the results I passed on to you. The information I posted about the dry film capacitors, has been tried and proven by me on several 6&12 volt systems over a period of countless miles and under most any conditions. I have no desire to post faulty info.

[Ferrous Head]

After considering digital capacitors I began thinking holistically about my Ironhead engines.

Turns out they are fully digital.

[bustert]

one must give careful consideration to the amount of capacitance one uses as it will affect dwell time.
more is not necessarily better.
the machine will even run without the cap but will suffer rapid point destruction and loss of coil saturation.