Ford 8N Alternator upgrade

[Johnny Smack]

I have been trying to get this 1952 8n started for awhile now...6v battery/6v coil...with no luck. Tried a 12v battery and it started instantly...I decided to change the alternator & coil to do a complete 12v conversion. The directions in the kit I received had a ballast resistor shown between the battery and coil. The directions are clearly marked 12v battery and 12 coil..Why would a ballast resistor be used for a 12v battery feeding a 12v coil? Thanks for the help!!

 

[Beanmedic]

The resistor is not there to change the voltage, if I get your question. It changed amperage for starting.

If you search archives you will find a LOT of information about the ignition circuit, including the resistor.

But, if you just want to get her running on a 12 volt conversion, do yourself a favor and get a IC14 coil from NAPA. It requires no resistor and is marked such. Simply take the resistor out of the circuit by joining the two wires that went to it. One less component to go bad...fewer connections to keep "bright and tight".

Also, google wiring diagrams by JMOR and you will find some wonderful wiring aids. You can also find them by searching the archives here on this site.

Also, since you are going to buy an alternator, a three wire will insure lower RPM charging. You will also need a light or diode in the circuit to stop the voltage from feeding your points when you turn off the key. Otherwise she will keep running. Sounds confusing, but it isn't.

 

[Johnny Smack]

Thanks for the info!

 

[Johnny Smack]

Yes- I did buy a new coil at NAPA (got the coil # from this site). Its a 12v coil as i did not want an extra part as you advise. The new coil has a notation "no external resistor required". I thought the purpose of the resistor was to drop the 12volt battery voltage if someone did not want to change out their existing 6volt coil. I did check out JMOR's electric drawings and do not see a ballast resistor in any of the 12v conversion drawings- Thats why i was questioning why I would need the resistor in the circuit- Thank you for the help & picture!

 

[souNdguy]

that is sooooo incorrect..

the reason a resistor is used with a coil is to both limit current and drop voltage. In a closed circuit.. if there is resistance, serial current is dropped and there is a voltage drop across the resistor.

In the case of a 52 8n with a side mount coil, you can simply use a REAL 12v application coil like a napa ic14sb and NO resistor.

the resistor is not there to 'change the amperage for starting'.

 

[kylemorley]

Well it is actually, in a manner of speaking, since when you first turn on an ignition with a proper ballast resistor, like our Fords, it will by design deliver more amps and a hotter spark at first, before it heats up. Not the primary reason for the resistor, perhaps, but a useful one enough that many auto manufacturers stuck with the external resistance long after internal resistance coils were available.

 

[souNdguy]

sorry buddy... that still don't cut it.

BM said the resistor was not there to change voltage. only current. in a resistor.. it's partand parcel! you don't get to pick and choose what parts of ohms law apply. if you have a serial resistor and it reduces current in the series circuit.. it DROPS voltage across the resistor. PERIOD.

the fact whether it does or desnt have a temperature coeficient is immaterial to the issue. many ignition resistors sold DO not have a temp coef. change . so tossing that into the equation makes a wrong statement just muddy and wrong.
Now.. getting creative, there are things you can throw in series that will have a forward voltage drop but no serial resistance to speak of but that's another story...

 

[Beanmedic]

(quoted from post at 10:13:37 05/20/14) that is sooooo incorrect..

the reason a resistor is used with a coil is to both limit current and drop voltage. In a closed circuit.. if there is resistance, serial current is dropped and there is a voltage drop across the resistor.

In the case of a 52 8n with a side mount coil, you can simply use a REAL 12v application coil like a napa ic14sb and NO resistor.

the resistor is not there to 'change the amperage for starting'.

[b:5e9160a0cc]I stand corrected! I'm familiar with Ohm's law and of course it affects voltage![/b:5e9160a0cc]

My message should have said that the purpose of the resistor is not to "permit" a 8 volt battery in a 6 volt system...or a 12 volt battery in a 6 volt system. Thanks for clearing that up SG.