12v internal resistor coil

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brewzalot

501 Club
Rewired my 56 Loboy last week. Installed a new 12v coil from TM that has a internal resistor. Just wondering now if that is the correct one for my situation seeing it was converted to 12 volts by PO.

I have,
12 volt negative ground battery
12v generator
6v starter
battery ignition distributor
no lights

TM states its for Loboy tractors serial#18701 and above- I'm assuming they went from 6v to 12v then? I cannot find the loboy data base to confirm that. I'm a little confused on the reason for the resistor, if anyone cares to explain the basics on that it would be much appreciated.

thanks
Tim
 
JMHO the reason for a resistor (internal or external) in the ignition circuit is to prevent the points from burning with the 12v electrical supply. Obviously it's not needed with a 6v system. Stan
 
Tim, Here's the SN change from 6v to 12v generator from the parts manual noted. Without looking it up I think it was 1964 when the red/white cubs were made. Stan1742158645468.png
 
staninlowerAL said:
Tim, Here's the SN change from 6v to 12v generator from the parts manual noted. . . .
Click to expand...
Close. Note that page lists both 6 and 12-volt generators. The serial numbers listed on that page are when the earlier (3 brush) generator was replaced by the 2 brush unit number 1100055. At serial numbers 224401 (standard Cub) and 18701 (Lo-Boy) they changed to 12-volts with generator 1100401. That change was during 1964. The serial number breaks for the change to 12-volts can be seen in the parts catalog on the pages with the wiring illustrations.
 
brewzalot said:
Rewired my 56 Loboy last week. Installed a new 12v coil from TM that has a internal resistor. Just wondering now if that is the correct one for my situation seeing it was converted to 12 volts by PO.

I have,
12 volt negative ground battery
12v generator
6v starter
battery ignition distributor
no lights

TM states its for Loboy tractors serial#18701 and above- I'm assuming they went from 6v to 12v then? I cannot find the loboy data base to confirm that. I'm a little confused on the reason for the resistor, if anyone cares to explain the basics on that it would be much appreciated.

thanks
Tim
Click to expand...
TM, or the coil manufacturer, calculated the series resistance that is needed when using a 6V coil on a 12V system.. This drops the 12V voltage to 6V at the coil primary. If you don't use the resistor, the output voltage of the secondary (voltage to the spark plugs will double). Also, the high voltage, on the secondary windings of the coil, will probably arc over the coil and destroy it.

Ford and Chevy went from 6V to 12 V systems in 1954 & 1955. My 1957 Mercury had an external resistor mounted in series with the coil primary. Car manufacturers did this in the first few years after the conversion from 6V to 12V so they they could use up their old coils and have time to get new coils manufactured with the correct primary resistance (not using an external resistor) and turns ratio between the primary/secondary coils to get the proper high voltage output from the secondary.
 
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John, the real reason they did that, was in order to use a resister by-pass circuit to increase spark voltage during start up. They continued to use this set-up until the switch to electronic ignition.
 
Thanks for the explanation. So a full 12V was on the coil during starting and then went back to a lower voltage when the start switch was released. Very interesting.
 
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