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(quoted from post at 11:47:29 04/19/12) Another question actually. Is there any advantage to switching to the 12 void coil like for starting, hotter spark, etc. Or shall I just keep the dash resistor and 6 volt coil? Again, I was under the impression that doing this burned up the points but doesn't seem to me to be using the full 12 volt potential. Thanks for the help in advanced!
Rick E.
There is actually an advantage to your 6v coil +resistor and that is that the heat in the coil is reduced (now part of that heat is in the resistor & part in coil), whereas with 12v coil & no resistor, ALL the heat is in the coil!
Allow me to stir this pot a bit - "advantage" for whom? Correct me if I'm wrong but the advantage has to do with the design and attendant cost to build a 12V coil capable of safely dissipating that additional heat rather than anything you as the end user will realize in performance? Is the MTBF of a quality 12V coil shorter than a 6V version? We already know the OEM front mount coil isn't all that robust even at 6V/4A
TOH
act is that virtually any electronic component will have a longer life & higher reliability when it runs cooler (less heat). That is well established and can be verified through many sources. Performance should not differ. "Is the MTBF of a quality 12V coil shorter than a 6V version?" I have never seen MTBF data on tractor or tractor replacement coils of any kind, so that would be be a "don't know" on my part. He did say his was a side mount, but there is a world of difference in the plastic encased (read that heat-insulating) front mount square can coil than an oil filled metal can (virtually same whether 6 or 12). Given the same heat dissipating capacity (I say same based on oil filled construction, same physical size and all other common characteristics), then I contend that the 6+res at ~11 Watts will run cooler than the 12v at 64 Watts. Now we end facts and begin opinion. Yes, I call that an advantage for the 6+resistor. Now it is a valid argument to consider the additional component (res), it's connections, wiring, etc. So, in the end, it would require a lot more data, analysis, reliability studies to provide a definitive overall answer and to which 'total system' is more reliable/run more years, etc. Still, heat is the killer of electronic devices.
P.S. The 11W comes from the 0.5 Ohm coil +ballast and the 64W from the IC-14SB, both key on/stalled engine/points closed. Ratio still approximately the same running, but Watts can be divided by ~9. 6:1 is still huge.
NAA/6v round can comparable number is ~32-45W. (Expect ~same for round can side mt 6v 8N.)
Allow me to stir a bit more. I realize heat is the enemy, cooler is always "better", and 6:1 is a substantial difference. But is it meaningful in any practical sense? How long would you expect to wait for an IC-14SB to fail on a bench test subjecting it to a constant 64W load? Hours? Days? Weeks? Months? Years? How does that compare to an NAA coil in a similar full load test? In case you haven't guessed my gut feeling is we are splitting hairs. But then you are the engineer with practical experience and I'm just a pot stirrer :shock:
TOH
I don't know how long to fail at 64W, but it takes about 2 hours at 17W to reach 200F (experiment).
My SMTA metal can coil will reach about that same 200F in 3 hours of bush hoggin. That is "probably" about stable, particularly since it is bolted to an engine which is about that same temperature. Typical magnet wire insulation is rated at 221F-enamel, 392F-teflon, 464F-Mil-Spec Polyimid. A document describing automotive electronic devices in harsh environments gives distributor, alternator field windings at 260-280F during GM Arizona desert proving grounds testing, just for comparison.
Looking at nothing more than the composite of all the info before me, and considering that normal operation (duty cycle & exponential current rise times) the running power is close to about 64/9= 7Watts, then my "edumicatied" guess is that the sucker wouldn't see days at 64W, but if you send me one I'll be happy to blow the sucker up & record the blow point. Love experiments of that kind!
Now, on a related but different area of coil vs coil + ballast: Ballast is a stabilizing element, as in ballasting a ship. An unballasted coil current will change according to the copper winding temperature, all other factors held constant. Example: start at 70F ambient and then raise windings to 200F and the resistance will increase by 33% (1.33 times base), current will decrease by 25%, yielding an energy output decrease by 43%. I.e., now operating at 57% of room temperature spark energy. Our friend the ballast (current stabilizer).......insert a resistance in series with the coil & this copper heating/reduction of current & energy as function of temperature is diluted. Diluted by how much, depends on how much resistance you insert. To make it easy to visualize, let us say we inserted a ridiculous amount such as 100 ohms ballast with a 1 ohm coil, now you can clearly see that the current is hardly affected by the coil resistance increasing from 1 ohm to 1.33 ohms (total 101 vs 101.33). You can grab a calculator and play numbers games with whatever coil res & ballast resistance values you like, but the benefit it there, especially with temperature dependent resistors such as 12250 (Ford engineers were at least somewhat on the ball).