I"m using a 12 volt battery in a farmall H tractor, eveything else is still 6 volt. My question, is it necessary to use the 6 volt resistor in the wire going to the coil. Tractor is run less than 10 hours a year. Will the 12 volt eventually fry the coil without the resistor ? Could I put in a 12 volt coil instead of the resistor ? Thank you for suggestions...Bernie
- Thread starter GentleBen
- Start date
rvirgil_KS
Well-known Member
12 volts to a 6volt coil(approximately 1 1/2 ohms resistance between + and - posts)will eventually damage the coil.
Add resistance that is close to the resistance of the coil.
yes, you could change to a direct 12 volt coil such as NAPA IC14SB or equivalent.
There is some variation in the amount of resistance in the various resistors available. The NAPA coil is not much more expensive than a resistor and would eliminate a possible mismatch between existing coil and an added resistor.
Add resistance that is close to the resistance of the coil.
yes, you could change to a direct 12 volt coil such as NAPA IC14SB or equivalent.
There is some variation in the amount of resistance in the various resistors available. The NAPA coil is not much more expensive than a resistor and would eliminate a possible mismatch between existing coil and an added resistor.
Ronald Anderson
Member
It cost me 10.00 for the wire harness that connects to the alternator with resister built in. The 12 volt coil would have cost 25.00 .
oldoliverlover
Member
I have put a 12 volt battery and coil in my Oliver. The ammeter shows a full charge when it is running. Will this hurt the battery or should I just disconnect it?
MarkB_MI
Well-known Member
- Location
- Motown USA
Your points will last longer with a resistor in the system. The simplest approach is to install a so-called "12 volt" (no external resistor required) coil.
Ronald Anderson
Member
A ballast resister drops 12 volts to 6 volts going into the coil.
The diode is in the wire coming from the alternator to the
ammeter . This prevents back feeding and draining the battery
when not being used.
The diode is in the wire coming from the alternator to the
ammeter . This prevents back feeding and draining the battery
when not being used.
LeonardWD45
Member
NAPA carries ballast resistors. Fairly cheap and easy to install with no need to replace wiring harness. Have ballast resistors on all my tractors that have been converted to 12v charging system.
Leonard
Leonard
"My question, is it necessary to use the 6 volt resistor in the wire going to the coil."
If its a 12 volt tractor but youre using a 6 volt coil YESSSSSSSS its necessary to add a series voltage dropping (12 to 6) ballast resistor or else the coil will overheat (from too much current) and the points burn up prematurely.....
"Will the 12 volt eventually fry the coil without the resistor ?"
Sure will if its a 6 volt coil it will overheat
" Could I put in a 12 volt coil instead of the resistor ?"
Sure can, that way no external ballast is required
John T
If its a 12 volt tractor but youre using a 6 volt coil YESSSSSSSS its necessary to add a series voltage dropping (12 to 6) ballast resistor or else the coil will overheat (from too much current) and the points burn up prematurely.....
"Will the 12 volt eventually fry the coil without the resistor ?"
Sure will if its a 6 volt coil it will overheat
" Could I put in a 12 volt coil instead of the resistor ?"
Sure can, that way no external ballast is required
John T
They're ~$15 here and no re-wiring required.
None at all. Not even a cut to put in a resistor.
Less connections, less points for corrosion and potential failure.
The voltage dropped by a ballast resistor varies based on current flow.
It does not automatically reduce voltage to 6 volts.
Granted, they run fine either way. Have been for years.
Texasmark1
Well-known Member
My MF service manual says that ignition points are designed for about 5 amperes of current to be reliable. 12v/5 amperes = 2.4 ohms. So, regardless of the badge on front of the cowl, that's about what you are looking for.
Get out your ohm meter, zero the leads so that you don't include lead resistance in your calculations and ohm the coil/points circuit from 12v to the distributor input wire. If it's not at least 2.4 ohms go to your NAPA dealer and buy a resistor of suitable size to get it to that value. Some have taps at different resistance values. The DC resistance of the coil is part of the 2.4 ohms total.
Mark
Get out your ohm meter, zero the leads so that you don't include lead resistance in your calculations and ohm the coil/points circuit from 12v to the distributor input wire. If it's not at least 2.4 ohms go to your NAPA dealer and buy a resistor of suitable size to get it to that value. Some have taps at different resistance values. The DC resistance of the coil is part of the 2.4 ohms total.
Mark
Geeeeeeeee whiz Bob, just think if that didoe is actually located there and wired bass ackwards your alternator may last longer, but battery never gets charged either huh lol. And all these years if I used a diode in a 3 wire alternators excitation circuit to prevent backfeed and run on, I wired them between IGN switch or coil to the alternators excitation terminal SILLY ME.......
John T
John T
Many old tractor companies actually went even further and limited the points switching current to more like 4 amps in which case at 12 volts used 3 or so ohms in the ignition primary circuit (coils LV Primary + any external ballast). Many generic ballast are like 1.5 to 1.85 ohms while some are even higher. If a person
wanted a true 50/50 static voltage divider to drop 6 volts across the ballast and 6 across the coil, the ballast resistance would be the same as the coils primary.
John T
wanted a true 50/50 static voltage divider to drop 6 volts across the ballast and 6 across the coil, the ballast resistance would be the same as the coils primary.
John T
Ronald Anderson
Member
Sorry about that I meant either the key or on and off button. From the key or switch a wire leads to the ammeter and beyond. I bow to the experts . Best advice is get a schematic and follow it.
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