Coil, resistance or not

rmerz3

Member
I've been looking through the forms and the service manual and can't find my answer.

My 1961 case 530, natively 12-volt gasser, should the coil have internal resistance or not? The old one is too hard to read any numbers off of it.

Thanks
 
Best I can tell there are no resistors anywhere in the circuitry now, nor do I see when on the wiring diagram.
 
I'm sure it's an internal resistor. It works best, except for the big ol V-8s that have a lot of starter motor draw, such that if you ran that thru a resistor, much lower voltage available to the coil. External resistors, factory installed, have a bypass circuit off the starter solenoid (the "other" light connector on some solenoids). Just measure the resistance of the primary circuit of your coil (the 2 small connectors, usually labeled + and -), if close to zero, no resistor, if pushing 7-800 ohms, it's resistored.
 
When 12v systems first showed up in the mid 50s, the scheme was to run the coil on 6 volts but apply 12 volts for a hot spark to start the engine. A resister was used to reduce voltage from 12 to 6. When cranking, the resister was bypassed by internal contacts in the start switch.

Today, coils are constructed to run on either 6 OR 12 volts. If you buy a coil and condenser listed for 6 volts, you should use a resistor on your 12v system. If you buy a coil and condenser listed for 12 volts, omit the resistor.
 
Since I put it in, I feel like my tractor doesn't start well, perhaps weak spark. That's why I was wondering if maybe I should have gotten a coil without the internal resistor.
 
What I said myay have been confusing, I know that my coil I just put in has internal resistance.

This was my tractor doesn't start well, and I'm wondering if it's because there's too much resistance that is causing weak spark. That's why I wanted to know if the case would have come with a 12 volt coil without internal resistance.

Thanks
 
oldproudvet has it right, measure the old one across the two little terminals. To check your spark, pull the coil wire out of the distributor cap, hold it around 1/2" away from a ground and crank the tractor with the ignition on. If the spark jumps 3/8 to 1/2", it's fine, plenty to start the machine. What do the spark plugs look like? Check 'em all, mine was giving me starting fits until I found a piece of fluffy carbon on just one plug. Dunno why it ran OK once it warmed up.
 
Another thought: If you replaced a coil that had a resistor with one that doesn't, you will get a hotter spark--but you'll also get a much hotter spark at the points, and they'll burn out in nothing flat, and may take the condenser with them.
 
Actually, condensers are rated in hundreds of Volts, and the difference between 6 and 12 Volts is MEANINGLESS to them.

Their capacitance value in mcirofarads DOES vary a bit by application,

In simple terms, there's no such thing as an ignition condenser rated for a 6 Volt system or a 12 Volt system.
 
Yes but typical voltage spike AT THE POINTS is around 65 volts, you won't see it without an oscilloscope. Take the ballast out of the circuit and that does go into the hundreds. Nothing like using the circuit as it was designed.
 
There are 2 types of 12 volt coils

One is labeled "12 volts, external resistor required". It has approximately 1 1/2 ohms resistance between + and - posts and requires a resistor of equal value to use in 12 volt system. It can be used without the resistor in 6 volt system.

Other is labeled "12 volts, no external resistor required" and works directly in 12 volt system without a resistor. It has approximately 3 ohms resistance across + and -. It will not work in 6 volt system. This coil DOES NOT have a separate resistor in the can wired in series with the primary winding. The primary windings in the 2 coils are wound with different wire and/or turns ratio to give the desired resistance.

The coil is a transformer with one side of primary and one side of secondary tied together.

Resistance from either + or - post to large center post of the could should be in the 6000 to 10000 range.

If not burned out, check the resistance across + and - of original coil and determine what it is.

A resistor added to direct 12 volt coil will likely result in hard starting and poor performance.

If negative ground system, - on coil to side of distributor, if positive ground + on coil to side of distributor
 
My coil is a "12 volts, no external resistor required". I have no other resistors in the wiring.

If I understand your explanation, I should be good to go then correct?
 
Bob is right about the condenser not being sensitive to voltage. However, the condenser is sensitive to amperage. The condenser needs to be sized to properly combat the amps produced by the coil.

Generally speaking the 1950s switch to a 12 volt system benefited the starter, the wiring, the spark plugs, etc. A hotter spark was intentionally produced. Engines started better and ran better. This required MORE AMPERAGE to run thru the coil. The condenser had to change to properly combat more amperage. The condenser and the coil have to be compatible.

Amperage has "inertia" energy that must be stopped when the points break. This energy goes into the points arcing/burning if a condenser is not used. The condenser absorbs this energy and throws it back slowly while the points are open. This is why dwell time/point gap is important and must not close during the condenser's slow throw back of electrical energy.

Just as the baseball catcher absorbs the energy of the baseball and throws it back to the pitcher slowly because the pitcher does not like a fast throw back, the coil does not like a fast throw back of the condenser's absorbed energy.

Bob may be right about a universal condenser. The modern coil's insulation may tolerate more heat and a universal condenser for either 6 or 12 volts. I think it best to replace both coil and condenser sold as a set.
 

'combat the amperage' ??? What a load of manure!

The condenser is a non fancy switch debouncer..helps prevent arcing at the points untill they have opened sufficiently.

99% of the responders here would do well to take a basic ac & dc circuits course at their local community college, or adult enrichment tech school. AFTER passing that class, then google and read up on a kettering ignition system!
 
(quoted from post at 13:43:08 08/17/17)
'combat the amperage' ??? What a load of manure!

The condenser is a non fancy switch debouncer..helps prevent arcing at the points untill they have opened sufficiently.

99% of the responders here would do well to take a basic ac & dc circuits course at their local community college, or adult enrichment tech school. AFTER passing that class, then google and read up on a kettering ignition system!

A 12V coil will have a primary ohms of 3-4 Ohms , a six volt will be about 1.5 Ohms, I have been converting tractors for many years,(retired after 52 yrs as a mechanic and it is news to me that condensers are different, and there is no number difference if you ask for a set for a 6 volt or 12v system. if a coil measures 1.5 Ohms it will require an external ballast to bring the total Ohms to the 3-4 Ohm specs that will assure normal point life. If you ask for a set of points and condenser by distributor part number they will not ask you if it is 6 or 12V.

The condenser absorbs the voltage spike created when the magnetic field collapses around the primary and secondary windings to minimize point arcing and then feeds it back into the coil to intensify the spark.

6 or 12, if the resistance is correct the current flow will be the same Ohms law covers that issue. If one takes time to learn how to use it it will make electrical issues a lot more understandable
 

If its news to you that condensers for different applications may have different specs ( capacity in yf ) for instance, you don't know nearly as much as you proclaim loudly to know.

That all said, you are preaching to the choir by replying to me.
 


Was not replying to you in particular, just used your post as a launch point , could just as easily have clicked on someone else to post.

Not going to get into peeing contest with you. I hold a federal license that required electronic theory study to receive my license. I never inferred that all condensers are of the same value, just stated fact that you can ask for a certain set of points and condenser for a distributor number , that is a fact and that certain distributor number was used in both 6 and 12 applications.

Your caustic comment says way more about you than me.
 

If you took my comment as caustic, it must have been close to home.

I also hold a federal license that required electronics knowledge, and an engineering degree.. Neither of which are relevant to this topic.
 
I wish to say something positive about Mr. souNdguy. The best I can come up with is he seems to understand the tip of the electronics iceberg. Nothing actually wrong with that amount of understanding. It probably meets his work needs.

Just for kicks,I went looking thru my storage boxes for my 2 inch thick college textbook that teaches advanced electrical engineering. I studied it 53 years ago during my 5th year of college at KU's Engineering school. My knowledge of electricity was useful during 38 years of my Engineering career.

I only made a C in the college class, like other students, but I remember a lot about the lower portion of the electronic iceberg. I'm not comfortable with writing about myself but the occasion seems right, even necessary, to remind Mr. souNdguy that he could benefit from understanding better those who he puts down.
 

I love it!

Someone complaining / claiming I've impugned their character... By impugning mine!

Sweet. ;)

While we are talking grades, I made a C in Calculus and some contemporary American history class but managed A /B in everything else.
 

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