Coil installed on 12v conversion

[cearlp]

I recently converted from 6v to 12v on a 1951 8N (side mount distributor) and replaced the old 6 volt coil with YTC's part number 105299 (12 Volt Coil with internal resistors). Shouldn't I use a 12v coil without resistors? Does having internal resistors change the voltage being delivered to the distributor?

 

[HCooke]

Shouldn't I use a 12v coil without resistors?

No use the 12 volt coil you have. No other resistors are needed.

 

[old]

Modern 12 volt coils do not have an internal resister they are just wound for 12 volts instead of 6 volts and do not need a ballast resister in the circuit

 

[cearlp]

Why do I even need resistors if I have converted to 12 volts?

This post was edited by cearlp on 11/05/2022 at 09:52 am.

 

[old]

If you have a true 12 volt coil you don't need a ballast resister but if the coil is 6 volts or says external resister needed you need a ballast resister or the point will not last very long and the coil can also burn out

 

[cearlp]

Since I converted to 12 volts (battery, alternator and wiring), I'm thinking I should NOT have the 12 volt coil WITH internal resistors.
Is this true or is there something I am missing?

 

[old]

As I said NO modern coil has internal resisters there just made to handle 12 volt simple as that so what you have is in fact a true 12 volt coil and that is as simple as it is

 

[Bruce (VA)]

See tip # 30.

The front coil, 6v or 12v, ALWAYS needs the oem ballast resistor.

A 6v front coil on a 12v system ALWAYS needs the oem ballast resistor AND and additional resistor.

A 12v front coil on a 12v system ALWAYS needs the oem ballast resistor AND NO additional resistor.

That's because a 12v front coil will hardly ever exceed 2.25 ohms. And to keep it below 4 amps running current, it needs the oem ballast resistor to keep from
burning up the coil.

No modern automotive coil has an internal resistor. Internal coil resistance is determined by wire gauge and the number of turns. Higher resistance is
provided by smaller gauge wire with greater turns. If the coil is marked or sold with a notice requires an external resistor that simply means it has a low
internal resistance and will be damaged by excessive voltage. It does not mean the coil has an internal resistor. Yes, plenty of coils are advertised as having
an internal resistor. Thats called advertising, not electrical engineering. To be both accurate and precise, every automotive coil should simply state the
internal resistance of the coil. But that would require a basic understanding of the Kettering Ignition system. So to keep it simple, ANY side coil with an
internal resistance of 3.25 ohms will work fine on your 12 volt 8N w/o any external resistor. Like the NAPA coil, p/n IC14SB. Many folks just add a 12 volt coil
rather than dealing with trying to find an external resistor to work with their existing 6v coil. Too much resistance gets you a weak spark; not enough and the
coil melts.
75 Tips

 

[old]

He states clearly he has a side mount distributor

 

[Bruce (VA)]

Yep.

My bad.

No need for all the info on a front coil

 

[old]

Plus with a side mount there is no factory resister

 

[Bruce (VA)]

Yea, that's in my epistle
75 Tips

 

[jimtrs]

Cear, it's just really a play on words. Here is the first two lines of ytmags' description of the part number:

This is a universal 12 volt coil with internal resistance. It can be used with 12 volt conversions if you don't want to put a resistor in line

Truth be told, the second part of the first line, [b:e937f44eb2][i:e937f44eb2]"with internal resistance"[/i:e937f44eb2][/b:e937f44eb2] is meaningless.
ALL coils have resistance. The key here is " how much" resistance.

You're original coil, back on a 6 volt system would have somewhere around 1.5 ohms of primary resistance (measured between the two small terminals, with everything disconected)
As Bruce said, you want to limit the coil to around 4 Amps of current. So using ohms law ....
6 volts / 1.5 ohms = 4 amps

This coil can be used on a 12 volt system with additional resistance, again ohms law ....
12 volts / 3.0 ohms = 4 amps

If you used this coil on a 12 volt system without additional resistance ...
12 volts / 1.5 ohms = 8 amps
It would burn up.

The new coil you purchased has additional windings so that the resistance between the primary terminals is about 3.0 ohms. Remember from above .....
12 volts / 3.0 ohms = 4 amps
This coil can [b:e937f44eb2]only[/b:e937f44eb2] be used on 12 volts. Too much internal resistance for a 6 volt system

So ......
Ytmag description is actually trying to say that this coil has enough resistance to be used on a 12 volt system [b:e937f44eb2]without[/b:e937f44eb2] any additional resistance needing to be added inline. As you would have needed to do if you kept your old original coil.

Ytmag description just has a weird way if saying that.
Again, a play on words.

Note that resistance numbers just need to be approximate. Voltages change on a running system.
So .....
6 volt Coil 1.0 -- 2.0 ohms OK
12 volt Coil 2.5 -- 4 ohms OK

This post was edited by jimtrs on 11/05/2022 at 03:45 pm.

 

[cearlp]

Thank you all for your replies, especially jimtrs for your complete explanation about resistance in coils. My question/concern has been solved!

 

[t.henrie]

It's actually pretty easy, even without all the explanations. If your new coil says "12V internal resistor" on it, you don't need any other ballast resistor. If it does not say that on the coil, then you need a ballast resistor (even though it is a 12V coil). The ballast resistor that is already on the tractor works fine if you need one. If you don't have one, or if the one on the tractor is bad, then a simple ceramic ballast resistor will do. Connect it between your ignition switch and the coil, such that when the switch is turned on, the coil gets juice through the resistor.

The ballast resistor works on heat, such that when you first start your tractor, the resistance is low, so that your coil provides a hot blast to the points. As current goes through it, it heats up. As it heats up, the resistance increases, thus reducing the voltage, saving your coil, points, and condenser. If the coil is internally resisted, it takes care of all that on its own.

This post was edited by t.henrie on 11/16/2022 at 09:39 pm.