9N Conversion 6V-12V

Nate Ela

New User
Howdy,

We just finished converting a 9N from 6V to 12V, following the wiring diagram that's attached (or at least that I tried to attach). Unlike some conversions we've seen online, we just ran one wire off the alternator. We also aren't using an extra resistor, since we put on a 12V coil.

The battery we're using is brand new, and the motor turns over, but it won't catch. Should we take the fact that it turns over to mean that the conversion is good, but that something else is wrong? Or might the turning but not catching be the result of miswiring? Another odd thing is that we can also turn it over even when the key's not in the ignition. Hmm.

We'd appreciate any advice you might be able to offer...
 
Nate.......would it surprize you to learn the starter switch has 'nuttin' to do with yer sparkies?? That is why you have a separate 2-wire key operated ignition switch.

And yes, the turning and not catching is probably the result of miss-wiring. I know 8-ways to convert and they all work the first time. I now know a gazillion+1 ways that don't work.

The modern 12-volt squarecan ignition coil DEMANDS the MANDATORY "infamous ballast resistor" on the backside of yer dash panel underneath yer amp-meter .....NO ARGUE!!!..... TIP: yer 2-wire ignition switch is ALSO connected to yer 3-terminal block. ......Dell, 12v advocate for the right reason
wm_A8NN12250A.jpg
 
The Fords will turn over with or without the key turned on if the trans. is in neutral,some early ones will turn over without the trans. in neutral.Check to see if you have voltage to the points when the switch is on,if not you can jumper a wire from the battery direct to the coil and see if it starts or pops,if it does you need to find out why it's not getting juice to the coil.Trace your wiring from the switch.
 
I hope your tractor would turn over w/ the key off before you converted it. That's how it was designed. It has a neutral safety switch AND an ignition switch. The circuits are separate.

And speaking of separate circuits, it is possible that you screwed something up in the ignition circuit while you were doing the conversion.

Lets start w/ the obvious problem first: a 12v coil w/o a resistor will not last very long. Technology & materials being what they were in the 30's, that square coil would melt if it ran on much more than 4 amps for any length of time. (see tip # 38 for an example). In order to get a hot spark at the same time the starter was drawing max current from the battery, a ballast resistor was added in the ignition circuit. What that did was add about .3 ohms of resistance in the circuit, added to the 1.5 ohms of the coil. That got you 3.5 amps or so at start up. As the voltage increased when the engine was running to about 7.5 volts, the resistor heated up, adding more resistance in the circuit. 1.0 ohms hot, plus 1.5 ohms of the coil got you down to 3 amps or so to keep from melting the coil. The same rule (actually, Ohm's Law) applies to a 12v circuit. I= E/R. Current equals voltage divided by resistance. Put the OEM resistor back in the circuit.

But, that has nothing to do w/ it not firing.

Turn the key on, crank the engine & look at the ammeter. What is the needle doing? Does it show a constant discharge, no movement at all, or does it move back & forth slightly? Next, get an old plug, open the gap to at least 3/16/", ground it to a rust & paint free spot on the engine, turn the key on & crank the engine. If the spark jumps the 3/16” gap, you probably don’t have a spark problem. If it won’t jump the 3/16” gap, you have a spark problem. If the ammeter needle shows a constant discharge, or doesn’t move at all, that also tells you that you have a spark problem. Jump the ignition switch w/ a jumper wire & see what happens. If it runs, you found the problem. If it doesn’t have spark after you jump the ignition switch, post back for more info on further troubleshooting. (and do not forget to turn the ignition switch off; see tip # 38)
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When I converted mine, the first thing that happened, when I tried to start it, was the ring gear spun on the flywheel. I figured the extra torque of 12 volts on the starter probably broke it loose. Maybe that's what's happening. The engine will still turn over even with the key off, if in neutral, but shouldn't start unless the key is on. Shouldn't turn over when it's in gear though.
 
Steep learning curve the 1st time around on a 12V conversion. That is probably one of the most frequently asked questions on this board. By following the advice of the great guys here about 95% of the people who asked got their tractors running again. The 5% who couldn't probably shouldn't own an old tractor. roll...
12V will give you a better electrical system over the long haul so you're on the right track.
 
bottom line.. the new 12v coil STILL needs a resistor inline.. the oem ballast resistor will work fine with a 2.5 ohm square coil.

turning over and not catching? is it coughing and kicking the bendix out? if so.. repalc ethe bendix.. though checking for good spark, compression, and fuel delivery would be a first bet.. as she won't start easy with a dirty carb and low compression and poor spark.

key ignition switch has nothing to do with the big thumb starter circuit switch.

soundguy
 
Thanks all for your ideas and pointers! We poked around a bit, thought things over, tested where we had power at different points, and realized that the problem was our ignition key. We tore that out and hotwired it, and now it fires up fine. Just need to get a new key.

One lingering question about the coil and resistor, though: Dell, you said that the ballast resistor is mandatory, and we're using one just like the one you pictured. In fact, we ordered and installed a spanking new replacement for the original, which was falling apart. But we didn't quite understand, Bruce, whether you were saying that we also need to put another resistor in the wire that runs from the original three-terminal resistor block to the coil. In the diagram that came with our conversion kit, it said that putting another resistor in that line is optional, and it seemed that it was only needed if we were keeping the original 6V coil after converting the rest to 12V. We put in a new 12V coil, but are you saying that it's still a good idea to put that "optional" resistor in the line running from the three-terminal block to the 12V coil?

Thanks again, everyone.
 
Yes, you must use the OEM ballast resistor. And, depending on the internal resistance of your coil, you may need more resistance in the circuit.

It used to be before the "Land of Almost Right" started making coils that you could count on a 12v frontmount coil as having 3 ohms of internal resistance & the 6v coils as having 1.5 ohms or less. Thus, thanks to Ohm's Law, you could calculate what additional resistance you needed in the circuit to limit coil current to 3.5 amps. So, you will need to measure the internal resistance of that alleged 12v coil & see what it is. A digital multi-meter has two probes & a switch. Set the switch on resistance. Put one probe on the top of the coil & the other on the pigtail at the bottom. It will give you a reading in ohms. Lets just say it reads 3.0 ohms. Your OEM ballast resistor (which you must use) is about 1 ohm hot. A coil a 3.0 ohms, plus the ballast resistor at 1 ohm (hot) gives you 4.0 ohms resistance in the circuit. Your 12 volt alternator puts out 14.5 volts. You need to determine current (amps). 14.5 v divided by 4.0 ohms gets you 3.6 amps; that's just fine. But, and this is the problem......what if the coil is only 2 ohms? Do the math. 14.5 volts divided by 3.0 ohms gets you 4.8 amps! Not good! And, if the coil is less than 2 ohms (and some are) it will fry quickly. So, to get it to 3.5 amps, you need another resistor in the circuit. Either that, or keep spare $30 coil around.
Coil.jpg

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Nate.......generally the "infamous ballast resistor" is all that is needed to keep from killing yer new modern 12v squarecan ignition coil. NO others resistors are needed. ...howsomevers... as Bruce explains you may need an additional low value high watt resistor (probably 'sumptin' like 0.5-ohms, 50w; those are technical terms) iff'n yer new modern 12v squarecan ignition coil is NOT 2.5-ohms. Its the LAW, Ohms Law. Unfortunately its sumptin' we can't tell from here and tractor stores don't sell them. ......Dell
 
So I tested the coil with the analog multi-meter (best that we've got) and measured it at 3 ohms. Also measured the three-terminal resistor assembly and it looked like 0 ohms or pretty close to it. Since 14.5V/3ohms will give us too many amps, I'll wire in the ballast resistor tomorrow. I just tested its resistance, and it was a solid 6 ohms. But that's cold, not hot, I figure, so once in-line and hot it should give the right resistance, no?

Thanks for all your patient help on this!
 
Nate......the 3-terminal resistor IS the BALLAST resistor!!!......And its value ranges from about 0.4-ohms when COLD to 1.7-ohms when HOT. You write......"I just tested its resistance, and it was a solid 6 ohms. But that's cold"......somehow I doubt your solid 6-ohms when cold. Its against the LAW, temperature co-efficient law. While analog ohm-meters are NOT very accurate at low values of ohms, yer 3.0-ohms is close-enuff to 2.5-ohms to semi-verify its accuracy. I would believe 0.6-ohms for yer current "cold" ballast resistance. ......Dell, retired calibration Lab Engr
 
First off, we need to get the terminology straight.

The picture Dell posted is the ballast resistor. It's about .3 ohms cold & about 1 ohm hot.

What other resistor do you have that is measuring 6 ohms? Is it ceramic? If so, it is a fixed resistor & will not change value as it gets hot. If it was a ballast resistor, it would increase in value when hot.

Go back & do the math again & see what you get.

1 ohm on the ballast resistor & 6 ohms on whatever that other resistor is. That's 7 ohms. Plus a 3 ohm coil. Now we are at 10 ohms.

14.5 volts divided by 10 ohms gets you just over 1.4 amps.

It won't run at all. That's too much resistance.

A 1 ohm ballast resistor & a 3 ohm coil gets you 3.6 amps. That's all you need.
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