6v-12v OH NOOO, NOT AGAIN....

JDMorris #1 - keep in mind that when you are actually cranking, system voltage can drop to 9 volts - and some coils don't work at 9 volts. The instant you stop cranking - voltage spikes up to 12 volts and it fires. This is why it is best to have a 6 volt coil in a 12 volt system. Most do. 90% of all cars and trucks that came new with 12 volt systems use 6 volt coils. Same goes for many tractors.

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Just when I thought I had all the 6v -12v possibilities covered in my mind JDMorris throws this at me.
So what you are saying is that it's better to KEEP the 6v coil when converting to 12v battery.
Change the VR and Battery and keep the 6v coil.

Thanks,(I think)
Dell

I'm sorry, correction - JDemaris

Dell

See the answer I gave in the next post down.
A 6v coil will spark just fine and hot when operated on 10 volts (as when the engine is cranking, and the starter is taking 300 amps)
The coil will get hot if operated on 14+ volts,(tractor starts and charging system works) and the points will deteriorate faster.
So a resistor is placed between the ignition switch and the coil reducing the voltage to about 7 or so for continuous operation.
To get full voltage (10 or so) when starting the resistor is bypassed. when cranking.

If the tractor has a mechanical starter switch, a bypass can be made to work as follows.

Take off the starter switch from the starter (if it is a saddle mounted type), or disconnect the lead from switch to starter at the starter if it is the big push button style.

Solder a #12 insulated wire to the side of the starter stud (saddle mount) and make a small "mouse hole" in the side of the saddle switch to get the wire out with out pinching when the switch is installed. If it is the big button style, just use a large diameter terminal end to attach a #12 wire to the starter main terminal.
in this wire it is mandatory to place a Diode. This diode must be a 5 amp 500piv rated device.
This diode prevents back flow into the starter blocking ignition voltage from flowing through the starter when the starter is not operating, but flowing full available battery voltage to the ign when cranking.

The polarity of the diode for negative ground will have the band on the side away from the starter. and on positive ground it will be toward the starter.

The far end of the diode will be attached to the #12 wire and extended to the coil side of the Ignition Ballast resistor.

To assure you have it connected with correct polarity an easy check is to wire everything but the diode, then, with the ignition off, use a jumper wire from the non-ground battery terminal to the diode then touch the other diode lead to the wire going to the far side of the resistor. if it sparks it is correct, passing voltage to the coil on cranking. If it does nothing it is wrong, and will just smoke the Ignition resistor when the starter motor acts like a ground to the ignition voltage when running.
Best of luck, Jim

There is one advantage when you keep a 6 volt coil with the external ballast on 12 volt conversions, as follows:

With the 6 volt coil and EXTERNAL ballast, ITS POSSIBLE TO BY PASS THE BALLAST WHEN CRANKING FOR A HOTTER START SPARK WHICH CAN IMPROVE COLD WEATHER STARTING. However, if you use a 12 volt coil YOU DONT HAVE THAT OPTION as theres no external ballast you can temporarily (while cranking) by pass. The ballast by pass system applies unballasted battery voltage to the coil while cranking, which can be good beacause while cranking the battery voltage drops which can reduce spark energy WHEN ITS NEEDED THE MOST.

HOWEVER that requires use of a Ford type starter solenoid with the extra lil I terminal (See Jims excellent post below) thats used to by pass the ballast. Or else a saddle mount on starter mechanical start switch (like Deere uses) with the extra terminal used to feed the coil (by passes ballast) when the start switch is depressed.

BUTTTTTTTTTTTTTTTT if you just have a simple dash/pedestal (NOT on starter) mechanical push to start switch (NOT any electrical solenoid) THEY DONT HAVE THAT FEATURE in which case theres no advantage to the 6/12 and by pass system so you may as well just use a 12 volt coil.

SUMMARY for improved cold weather starting on 12 volt conversions, a 6 volt coil with external series ballast COUPLED WITH A BALLAST BY PASS CIRCUIT/SYSTEM is great BUT it requires EITHER a Ford type starter solenoid and associated wiring ORRRRR a mechanical saddle mount on starter start swtich (which I dont think your M has) but if its only a dash/pedestal push mechanical switch that by pass isnt available.

ONE OTHER OPTION IF THERES NO SOLENOID OR SADDLE STARTER SWITCH but you still want a 6/12 system with improved cold starting, is to use a temperature compensating (Thermistor) link to serve as the ballast and it sort of by passes the ballast, cuz when its cold its low resistance but once warm its like 3 or so ohms so you can use a 6 volt coil on a 12 volt system,,,,,,,,get better cold starts,,, no extra solenoids or by pass systems or wiring to fool with, you can still use a mechanical push to start switch ITS REALLY A GOOD SYSTEM !!!!!!!

FINALLY if you have a good engine and its well tuned and your ignition systems in top shape and you have a good heavy battery n big cables, HECK YOU PROBABLY DONT EVEN NEED ANY 6/12 OR BALLAST BY PASS ETC......Id just use a 12 volt coil n be done with it no ballast or by pass worries, MANY TRACTORS ARE LIKE THAT N WORK FINE

If I missed any options (was in a hurry) hope the other fine gents will add them, unless you need to start at sub zero temps I wouldnt worry n just use a 12 volt coil........

Thats my story n Ima stickin to it

John T

Check out the proposal in my answer. Jim

Way back when our 12 volt Ms had push button to by pass resister if needed. Normaly no need of by pass but if tractor had been left out overnight in heavy dew or cold temperature or battery was weak it sure seemed to help.

Got it. Thanks.
I have read many posts about the ballast step down resister.
I was thinking JDemaris was saying use the 6v coil without resister.
What he was saying then, is use the 6v coil AND associated resister circuitry.

Thanks,
Dell

I did, and know what, I THINK YOURS IS THE EASIEST N CHEAPEST AND BEST wooooooo hooooooo. No Thermistors to try and spec and buy,,,,,,no jury rigged electric solenoids,,,,,,,just a piece of wire and a cheap easy diode wired from the switch to the high input side of the coil and hes good to go.......NOTE Deere used the saddle mount on starter push switches that have the extra small terminal to feed the coil (6/12 systems) but those arent available on those pedestal push switches where your method shines.

John T

I don't want to complicate this discussion much further, but don't know any other way to add a few comments.

There is so such thing as a "12 volt" coil. Just coils designed for certain "12 volt systems." If a coil cannot fire at 9 volts, it's going to be useless in a 12 volt system.

One thing that is universal is . . . battery voltage normally drops to 9 volts when the starter motor is cranking in cold weather. So, if you want good spark AT that time, you need a coil that can do it on 9 volts, NOT 12 volts.

For this reason, the vast majority of cars and trucks that had breaker-point ignition and 12 volt systems used what many call "6 volt" coils.
They are often the exact same coils as had been used previously in 6 volt systems - with a resistor added.

You do NOT have to use a resistor and bypass system. If you do, you can use a stand-alone relay with a built-in bypass, or a starter-attached solenoid with a bypass (e.g. Delco), or a key switch with bypass (like Deere used on many 10 series tractors). Some tractors even used a separate "cold start bypass" switch.

Some resistors are made to be very heat and amp-draw reactive e.g. like some Ford tractors use. The resistor adjusts itself and allows full voltage when first cranking, but once the engine is running and the resistor gets hot, it cuts voltage way back.

It makes things easier to refer to coils by their primary resistance - rather then "6 volt" or "12 volt."

What about running 12 volt on an M with a magneto?

(quoted from post at 14:13:49 12/11/10) What about running 12 volt on an M with a magneto?

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A magneto creates its' own electricity. A magneto DOES NOT NEED a battery. If you want to destroy your magneto, go ahead and connect a battery to it.

IMHO


Does anyone remember the old point system, setting the dwell for proper operation? Well the dwell sets the length of time the points are closed and the coil gets electrical flow to build up the electro magnetic flux field of the coil. When the points opens the field collapses extremely fast inducing a voltage in the secondary proportional to the ratio of turns in the primary to secondary windings and coil flux density.

The amount of magnetic flux induced in the coil is based on how long and how much current is allowed to flow in the primary windings allowing the magnetic flux to saturate the metal core.

For an external resistor coil system
When starting the vehicle the battery voltage is likely down to around 9 volts. This the time the starter circuit has a direct wire bypassing the ballast resister. This gives the coil good current flow for starting. Once the the engine is running the the starter circuit wire is off and the current goes through the ballast resister. When the engine is idling the current flow to the coil is very high as the points are closed for long periods of time(electricity speaking) . This high current flow warms up the ballast resister and thus the resistance rises and lowers the available voltage to the coil. This keeps the secondary voltage to the plugs within range and the coil from frying.

when the engine rpm rises to 2000 RPM the points are closed less than 1/3 the time as at idle. The ballast resister cools off as the current flow drops and allows more voltage to the coil in decreased resistance in the resistor to keep the coil flux high and the secondary voltage to the plugs within range(12000 volts etc)

this means that the resistance in the primary circuit has to be current sensitive to increase resistance at lower rpm and lower it at high rpm to keep the output voltage in specs.

The primary winding themselves increase resistance as the coil warms up. This is a normal property of most metals as the temperature rises the resistance increases. This is what makes an incandescent tungsten filament work in a light bulb.

a coil that has no external ballast resister has the primary winding very current sensitive. At high currents as the temperature rises the resistance increases and reduces current flow in the primary circuit. When the current flow drops off at high engine rpm the primary winding resistance drops and allows the flux to stay constant in the coil making up for decreased length of time the points are closed.

so you see until the electronic ignition system came out all coils needed current sensitive resistance in them or external for the engine to run properly. The only other choice wold be to have more than one coil.

This also points out it is important to use the proper coil and resister in the ignition system for proper results. ie coil and resister must be matched for the voltage used. Using a 6 volt coil with a resister pulled off another engine on a 12 volt system would certainly give off spec performance.

George

The magneto is totally unrelated to the charging system and lights on tractors. Magentos create their own electricity using permanent magnets and thus are not connected electrically. The on off switch is a grounding switch that kills the mag output. As such the tractor with a mag has no relationship to the discussion about extra voltage.
I hope this explains your question, Jim

Good analysis George, (fun for us sparkies at least) A standard old tractor can type ignition coil, like many other electrical devices having wire (and coils have a bunch) change resistance as their temperature changes. Of course, in these low RPM few (1,2,4, maybe 6 Ollies) cyliner old tractor engines theres plenty sufficient dwell time to saturate the coil UNLIKE an 8 cylinder engine running 8000 RPM all through a single set of points AHHH the Mallory Dual Point distributors like when we were kids lol

As you note the "duty cycle" changes versus RPM and as time passes shes warmed up thereby increasing the coils resistance. Most old tractors didnt, however, use any stand alone discrete thermistor type (temp compensating) of ballast device like some Fords used and new gen Deere started using.

Still, when you walk into NAPA or Central Tractor or Tractor Supply and ask for a coil for an old tractor with points, theyre gonna ask if you want a "6 volt" or a "12 volt" and will NOT say "theyre all the same" OR they have a Universal model suitable for use with EITHER 6 or 12 volts across its terminals (NOTE thats NOT to say you cant use a 6 volt coil on a 12 volt tractor with an external series voltage dropping (12 down to 6) ballast) . They will be labeled "6 volts" or "12 volts" or "12 volts does NOT require external ballast" or "12 volts for use with ballast" (which is in reality a 6 volt coil as the ballast drops 6 volts leaving 6 on the coil) Also, if you use the wrong coil theres problems, if you apply 12 volts to a coil designed for 6 volts across its terminals, she overheats, while if you apply only 6 to one designed for 12 volts across its terminals, the spark is weak...

AS YOU WELL NOTED, YOU NEED THE CORRECT COIL AND CORRECT BALLAST AND/OR COMBINATION

In keeping with standards of use and the common terminology used in the trade, I would define (like the Industry does) what the stores call and what are clearly labeled 12 VOLT COILS as ones designed for application of a NOMINAL 12 volts across their terminals which can still produce a spark (albeit weaker) if the battery voltage is reduced (as during cranking) and also produce a spark when the battEry voltage is raised due to charging, yet still function and not overheat. Such are labled and called in the trade 12 VOLT COILS, NOT 6 OR 12 volt coils LOL.

Many (not all) 12 volt coils (per the industry definition of and labeled as a 12 volt) have a LV primary winding resistance of over 2 ohms up to near 4, with an average of around say 3 ohms. That way the points carry and switch around 4 amps as if they switch too much current they burn up prematurely. Many (not all) coils labeled 6 volts (and as defined above) have a LV primary winding resistance of over 1 up to around 2 ohms, with a typical average of 1.5 ohms WHICH AGAIN ON A 6 VOLT TRACTOR allows the points to carry and switch 4 amps so they dont burn up prematurely.

Of course you can use a 6 volt coil on EITHER a 6 or 12 volt tractor (like so many tractors did) so long as if on a 12 volt you add the external voltage dropping ballast WELL DUH otherwise the coil would overheat and the points (drawing too much current) will burn up quickly

Fun discussion George, I truly enjoyed it, thanks

Ol John T (Still a Sparky and lovin it)

With respect, I disagree with one of your statements.
I believe the percentage of time the points are open or closed is the same at all speeds (until point bounce/flutter happens at some 5000 rpm (unlikely with a Farmall for very long)
The dwell is constant.
The time the points are closed is longer at low speeds, but so is the time they are open. Thus the duty cycle is identical at starting and operating speeds, and is the ratio of open to closed.

The ignition needs to work harder (produce higher firing voltage) at idle than at high speed and load conditions. A partial vacuum 20"of HG is harder to fire a spark through than compressed air and fuel at 140psi. Looking at an ignition scope under variable throttle/load/speed conditions will illustrate this with clarity.

Cold resistors do pass more current than hot resistors do, but the load from operation is basically the same on the primary due to the slow speeds of these engines allowing the coil to have optimum saturation, and continuous "duty cycle".
On 1/3 off 2/3 only gets into overheating if the on is 10 minutes, and off is 20 minutes. Even then it would probably cool enough in 20 minutes to avoid damage. (exaggerated for emphasis) Jim

Aint this funnnnnnnnnnnnnn Jim, But Im sure the non sparkies are sick of it lol

I need some "learnin" on one of your statements, namely:

YOU STATE: "A partial vacuum 20" of HG is harder to fire a spark through than compressed air and fuel at 140 psi"

I thought as the compression increases, it takes more voltage to arc jump current across the plugs gap??????????????????? Ive always considered the voltage necessary to cause current to arc jump across a gap is a function of the gap distance and the medium (fuel and compression) in which the current must arc and that as the compression increases (higher molecule density) the voltage must rise to a higher potential to arc current across the gap

Not sure what you mean by "harder"

Are you saying it takes LESS voltage to arc current across the plugs gap outside the tractor (at atmosphere) then it does inside the combustion chamber where the pressures say 100 PSI???????????????????

As pressure is reduced theres for sure less air molecules packed in between the plugs electrode and ground strap and as its increased theres more molecules packed in between.

In racing or pulling applications where compressions are extremely high, thats where they have to use the High Voltage coils that reach say 20,000 to 40,000 volts versus stock (way less compression) where the plugs may fire at 10,000 volts SUCH AGREES WITH WHAT I THOUGHT BUT IS OPPOSITE FROM WHAT YOU SEEM TO BE SAYING???

TALK TO ME JIM ??????? Chemistry was never my best subject ya gotta realize

An ever curious John T

I was brought to the conclusion I stated through several opportunities to learn. Each from a different direction.

In Automotive trade school (Vincennes University I am a Hoosier by birth), we were taught on Sun Diagnostic scopes. On a non race passenger car, the spark lines initial peak voltage (plug gap jumping point) is highest at idle, maybe 12 to 14kv. If the throttle was flipped open, the breakdown voltage of the gap dropped to maybe 8k and as the engine revved from idle speed to the "Danger do not rev an unloaded engine higher" point the spark line proceeded to climb back to high values, near idle but not quite. As the throttle was closed some (still racing at high RPM) to avoid over speeding the engine, the vacuum readings went up as the swept volume was restricted by the reduced throttle. If the throttle was released, the spark line jumped a little over idle range, then settled back to the 13kv area. I"ve watched this happen on every car/tractor truck engine I"ve had on a scope.
We were told/informed that the reason was that at high vacuum the spark had little in the way of ionizable gasses between the electrodes, and that a vacuum was a great insulator. As the vacuum dropped (opening the throttle) the air/fuel in the cylinder went from 20" of Hg, to atmospheric, to pressure in tenths of a second. The result was more molecules of hydrocarbon, oxygen, and nitrogen between the electrodes. These molecules were far closer together and much hotter than idle rare air. (Compression Heating) and as such they were conductors (willing or not) for an arc initiation, stripping from them multitudes of electrons, and turning them into a plasma. Plasmas are very conductive, and the plug fires multiple times across this plasma bridge spraying heat and ignited atoms into the combustion chamber igniting a flame front which then travels outward to the quench boundaries of the chamber where cold metal squelches the flame.

The need for higher voltage ignition, and longer duration spark discharge lines on a race engine has to do with four factors:

Arc blow under turbulent extremes in a high compression engine at the top of its RPM range can literally make the ionization path blow out of the gap.

Probable use of wider gapped plugs to present longer arc length to the fuel.

Far more difficult fuel to burn. Alcohol and high octane fuels are much harder to ignite from anti-knock additives or chemistry.

And the shortening of the time available to get the fire started (extreme engine RPM)

A hot high voltage snap across the gap initiates ignition more reliably than a puny wisp of yellow.

That is the essence of my belief in this techno topic. Thanks for asking. Jim

well I have learned lots here today.

I will take issue with the spark at idle is harder to establish. There is compression at idle not vacuum . If you are at high RPM and then back off the throttle the engine very often does back fire proving your statement is correct about poor ionization in a vacuum. My field of working in power stations with high voltage switching equipment that has various ways for arc quenching has used that one.

The poor idle issues for most old tractors is with the magneto systems. A mag fires hotter(more voltage) as the rpm goes up. The only way to start with a mag is the impulse unit that speeds up the armature on the mag to get a spark hot enough for starting and low rpm. In the parades just about all the time one tractor starts missing with a fouled plug.

Also you are correct in your statement that dwell does not change , but I respectfully cannot agree that the difference of 600 to 2000 rpm take the same current.

(ie) dwell for chev 350 v8 is 28-32 degrees. That is with a gap of 17 thousand. If you have it at 30 degrees then open time is 15 degrees. Dwell angle for four cylinders are around to 60 degrees then the open is 30 degrees. If the points gap is smaller the dwell angle is higher as in our old tractors.

anyway I am of to pick up a 300U, good metal and tires and is supposed to run well. The wife said she would drive it in the parade of power if we get it fixed up.

George

I did (put a diode between the coil and starter stud) that on my H that was already converted to 12 volts when I got it. If I forget to put the switch on, it will fire as long as you use the starter. That is a good way to know it is working.