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Discussion Forum
Show Parts for Model:

Will 12 volt coil on a 12 volt conversion burn up points

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Deere63

04-18-2012 23:23:39
76.232.185.64



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I have a question for anyone who might know the answer! Ok here goes....I keep reading for a 12 volt converted 8n to get rid of the ballast resistor and 6 volt coil and go with the true 12 volt coil...however, won't a 12 volt coil burn up the points?? Obviously I haven't switched to EI yet..




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Dr. Rowbotham

04-19-2012 18:21:51
208.124.125.137



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Deere63, 04-18-2012 23:23:39  
Hello, I'm new here and wondered if you have done this 12 volt conversion and how difficult it may be? My instincts tell me to stick with the tried and true, but I still wonder about the advantages. Thank You

Dr. Rowbotham



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Dell (WA)

04-20-2012 08:32:53
71.217.25.188



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Dr. Rowbotham, 04-19-2012 18:21:51  
Doc.......you do know that there are 2-different kinds of ignition systems used on the 8N-Engine, don't you? The weird 4-nipple frontmount with squarecan coil and the more familiar 5-nipple sidemount with roundcan coil. BOTH take different solutions to the 12V conversion conundrum.

But FIRST consider WHY convert to 12V, 2-reasons; brighter headlites and sprayer accessorys ...or... worn engine that needs faster turning starter motor to start. 12V on 6V starter motor really turns FAST. Because it just takes a couple of rumpas to start on 12V, yer starter motor nebber gitts chance to gitt hot.

Now to the ignition coil. First coils don't work on direct current (DC) as in BATTERY. So you interrupt the DC with points (mechanical switches) which makes the coil transform the low volts DC to HIGH VOLTS (17,000v) sparkies. Them lazy sparkies JUMP across the gap of yer sparkplug and guess what??? The gas mixture EXPLODES and drives the piston down to turn the crank.

Remember, in 1939 batterys were NOT die-hards, they died eazy. So enter the "infamous ballast resistor". It is a temperature sensitive resistor that changes resistance due to its own internal temperature. According to Ohms Law, the more resistance, (as in internally HOT) the less the current in the coil. So when you were starting a COLD engine, the COLD battery could only supply a little bitt of sparkie power. That is when the "brilliance" of Ford's infamous ballast resistor came into play. When COLD, less resistance and more POWER fer the sparkies trying to ignited a cold wet gas mixture on a slow turning engine. As the engine warmed up, so did the ballast resistor and reduced the amps to the weaksister squarecan coil. Unfortunately, the squarecan coil insulation tar MELTS when over heated and causes weak sparkies. (even when cold again)

BOTH the original 6V and the modern 12V squarecan frontmount coil require the MANDATORY "infamous ballast resistor"...NO ARGUE!!!

Now lets talk about the 5-nipple roundcan coil. It is OIL COOLED. (and yes it gitts HOT to touch) The el-cheapo Bubba conversion uses a ceramic 12-to-6V conversion resistor and the original 6V roundcan coil. We recommend the NAPA IC-14 roundcan coil that NEVER needs a resistor to operate on 12V. Understand?

Do you know what happens when you use either the 12V squarecan coil or the IC-14 on the original 6-volt battery??? WEAK SPARKIES!!! Ittz the LAW, Ohms Law. ........HTH, Dell, yer self-appointed sparkie-meister

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TheOldHokie

04-19-2012 16:15:12
71.176.140.201



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Royse, 04-18-2012 23:23:39  
Quoting Removed, click Modern View to see

Oh I know you didn't quantify it - that was what I was trying to get at. Now we are back to my starting point - runs hotter but has an "acceptable" MTBF. But it seems there is also an improvement on ignition energy with the ballasted arrangement which is a "small" performance improvement or am I misunderstanding you?

TOH

PS> Did you have that that Milspec number and associated insulation value on the tip of your tongue or did you have to look it up :P
PPS> Yeah - I'm bored and stirring the pot to get edumicated along with a little amusement. Never know when insight into the subtleties of breaker point ignitions may win me points (no pun intended) with the NASCAR babes at my local bar :roll:

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Deere63

04-19-2012 16:07:21
50.73.52.221



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Deere63, 04-18-2012 23:23:39  
Wow...well this topic sure expolded!..haha. Well thank you everyone for all your help!. Well what I have done is eliminated the resistor from the dash, ran the wire straight to a new 12 volt coil, replaced the points and condensor and she fired right up and runs better than it ever has since I've owned it! So, apparently my points were bad all along in addition to the resistor and I kept overlooking them.
A little history I failed to mention earlier...The 8N became extremely difficult to start and kept stalling under a load. I ended up rebuilding the carburetor first since it was due anyway. Tryed that and nothing. Next I checked spark and had spark only on some plugs but not the others. I checked voltage at the resistor and had 5.86 volts as well as at the coil which is what was expected. Next I checked spark from the coil wire and had nothing. I suspected the coil was fried. I checked the voltage at the resistor one more time for whatever reason and all of a sudden had 12.86 volts which indicated the resistor was actually bad and intermittently fluctuating, in turn probably what burned out the 6 volt coil. So thats when I came on here and asked whether or not to replace the resistor and 6 volt coil, or to bypass the resistor all together and go with a 12 volt coil. So I ended up doing that and replacing the points while I was at it and she fired up so fast I couldnt believe it. I know it was a combination of everything including the readjusting of the rebuilt carb because she purrs like a kitten now and idles with the throttle lever all the way back! She never did that before. She only idled at half throttle and rough at that! So my question now is..after all those comments up there, shall I still insert a resistor with my new 12 volt coil before I burn it up or will it make so little difference in life length I wont notice??

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JMOR

04-19-2012 14:35:24
72.190.9.193



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to flembo, 04-18-2012 23:23:39  
Quoting Removed, click Modern View to seeAgain, I don't KNOW, but I would believe that it is a simpler, lower parts count, overall cheaper installation AND they have evidence that the coils will tolerate the heat. Please note that from the start, I only used the word advantage, I didn't quantify it. :wink: I still like the stabilizing influence of the ballast resistor to help keep the energy up high. In modern automotive ignition systems, they actually monitor the current & regulate coil current over time, temperature, etc., but the simple Pertronix EI for these tractors don't do any thing except switch....not current regulation, limiting, or anything!

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TheOldHokie

04-19-2012 14:21:11
71.176.140.201



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to JerryS, 04-18-2012 23:23:39  
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OK - you are starting to convince me. So why in the world are engineers putting unballasted 12V coils in things?

TOH



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JMOR

04-19-2012 13:32:37
72.190.9.193



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Britcheflee, 04-18-2012 23:23:39  
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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).

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TheOldHokie

04-19-2012 12:14:41
71.176.140.201



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to GB in MT., 04-18-2012 23:23:39  
Quoting Removed, click Modern View to see

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

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JMOR

04-19-2012 11:38:11
72.190.9.193



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Ron-MO, 04-18-2012 23:23:39  
Quoting Removed, click Modern View to seeFact 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.)

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TheOldHokie

04-19-2012 10:23:15
71.176.140.201



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to ctrycpr, 04-18-2012 23:23:39  
Quoting Removed, click Modern View to see

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 :cry:
TOH

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JMOR

04-19-2012 08:59:26
72.190.9.193



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to elmersooner, 04-18-2012 23:23:39  
Quoting Removed, click Modern View to seeSix of one, half dozen of the other. If use 6v coil plus resistor, coil current is being limited to about 4 amperes, and if use 12v coil, current is still limited to about 4 amperes. Get it? 4 amperes either way. Ignition energy delivered is proportional to current squared, so end result is the same. 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!

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Deere63

04-19-2012 08:47:29
76.232.185.64



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Deere63, 04-18-2012 23:23:39  
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.



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Deere63

04-19-2012 08:42:38
76.232.185.64



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Deere63, 04-18-2012 23:23:39  
Ok..well thank you for that Rick. It is a '51 side mount btw. Also, where exactly should I be lubricating the points/lobes?



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oldtanker

04-19-2012 04:43:53
66.228.255.239



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 Re: Will 12 volt coil on a 12 volt conversion burn up points in reply to Deere63, 04-18-2012 23:23:39  
If using the square can 12 volt you still need the resistor on the terminal block mounted to the dash. You do not need a ballist resistor in line for the coil. No, if the points are set right they should be fine and in fact points are not really voltage sensitive.

Rick



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