Resistor on 12V conversion

[Dennis Conner]

I recently installed a 12V conversion on a 1947 2N. When the supplied resistor was included in the circuit the coil did not get enough current to provide sufficient spark. The tractor would flood trying to start. When the resistor was jumpered, it started and ran fine. To test it I put the resitor back in the circuit while runnig and it started running poorly. My conclusion is that the additional resistor shoudl not be used when using a 12V coil. Does anyone feel different?

 

[Dell (WA)]

Dennis......hadda big discussion about frontmount coils and resistors 'cupple of days ago.

I say it don't matter whether yer using the original 6-volt squarecan coil with 12-to-6v converting resistor or the modern 12-volt squarecan coil, BOTH NEED the "infamous ballast resistor" under yer amp-meter. And OBVIOUSLY, from yer experience, you don't need the 1/2-ohm "safety resistor with the modern 12-volt squarecan coil. ......Dell, a 12-volt advocate for the right reasons, that said; I haven't found the right reason for my eazy starting 6-volt 1952 8-N and I know how to do it right....the first time. Infact, I know 8-ways to convert to 12-volts and they ALL work. And about a quadzillion ways that don't work

 

[Bruce (VA)]

"My conclusion is that the additional resistor shoudl not be used when using a 12V coil."

Wrong conclusion.

Resistors have values measured in watts and ohms. Coils also have resistance. If you get too much resistance in the circuit, as you did, you get a weak spark. If you get too little resistance in the circuit, you melt the coil and/or points.

So, leave the resistor out & see what happens. If you're lucky, nothing melts. If not, $35 for the new coil, $18 for the points.

Or, as an alternative, why not determine the coil resistance and add a resistor of the correct value (if one is needed)?

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 1.0 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; close & probably ok. 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 $35 coil around.

50 Tips

 

[Dennis Conner]

Very interesting, yet simple, way to look at this. In essence, my current (no pun intended) configuration works NOW. Not to say it will work for long though.

I will pull the distributor and check the resistance. I'll then make sure to get the correct additional resistance to achieve my desired 3.5A.

I appreciate the time you took to explain this and hope it helps others too. When I get my situation correct, I will post the results.

Thanks again.

 

[68_f100]

(quoted from post at 19:37:40 08/26/09) Very interesting, yet simple, way to look at this. In essence, my current (no pun intended) configuration works NOW. Not to say it will work for long though.

I will pull the distributor and check the resistance. I'll then make sure to get the correct additional resistance to achieve my desired 3.5A.

I appreciate the time you took to explain this and hope it helps others too. When I get my situation correct, I will post the results.

Thanks again.

Just get the factory resistor. Like these guys tol me it's like .4 ohms cold and 1.6 or so when hot. I was in the exact same place you were with a 12v coil. It wouldn't start so I took the resistor out and it ran like a top. I got the stock style and I am verry happy with it.

I had to make my own mout so I used this special plastic we had. I countersunk the holes so the screws wouldn't short out.

 

[Dave in Utah]

Dennis,

That coil in Bruce's photo below .... here's what it looks like if you continue to run it without the "infamous ballast resistor."

Now that I have one, the 9N starts easily and runs without threat of melting down.

 

[Dave in Utah]

Dennis,
That coil in Bruce's photo below .... here's what it looks like if you continue to run it without the "infamous ballast resistor. And this one has 1.5 ohms too."

Now that I have one, the 9N starts easily and runs without threat of melting down.

Dave

 

[Dennis Conner]

Outch! First thing tomorrow I plan to check my coil resistance and the ballast resistor value. I will make sure I have the required 3.5A.

Just for the record....I was using the OEM ballast AND the ceramic resistor that came with the conversion kit. With both in the circuit it just didn't have enough spark to start. I removed the ceramic resistor and it started right up. So, I wasn't totally in the wrong, but I know I can stand to tweak it a little it a little more.

I really love these old Ns and want to keep it in tip top shape. Thanks to all.

 

[Bruce (VA)]

Your OEM ballast resistor is needed & not the problem. It should read about .3 or .4 ohms cold & 1 ohm or better hot.

The problem is the big honkin' ceramic resistor. When you measure that, please post back w/ the results. I'm betting more than 1 ohm!
50 Tips

 

[68_f100]

(quoted from post at 05:38:28 08/27/09) Your OEM ballast resistor is needed & not the problem. It should read about .3 or .4 ohms cold & 1 ohm or better hot.

The problem is the big honkin' ceramic resistor. When you measure that, please post back w/ the results. I'm betting more than 1 ohm!
50 Tips

I did measure mine and it was like 2.7 ohms cold. So it made for a grand total of 5.2 ohms. Not I am running the factory style resistor and thats it.

 

[JMOR]

(quoted from post at 12:42:26 08/27/09)

(quoted from post at 05:38:28 08/27/09) Your OEM ballast resistor is needed & not the problem. It should read about .3 or .4 ohms cold & 1 ohm or better hot.

The problem is the big honkin' ceramic resistor. When you measure that, please post back w/ the results. I'm betting more than 1 ohm!
50 Tips

I did measure mine and it was like 2.7 ohms cold. So it made for a grand total of 5.2 ohms. Not I am running the factory style resistor and thats it.

OK, just for the record, who did you buy the kit from? Which supplier made up the kit (usually TISCO or Atlantic)? and third, was there any part number associated with their included 2.7 ohm resistor?

 

[68_f100]

(quoted from post at 09:51:35 08/27/09)

(quoted from post at 12:42:26 08/27/09)

(quoted from post at 05:38:28 08/27/09) Your OEM ballast resistor is needed & not the problem. It should read about .3 or .4 ohms cold & 1 ohm or better hot.

The problem is the big honkin' ceramic resistor. When you measure that, please post back w/ the results. I'm betting more than 1 ohm!
50 Tips

I did measure mine and it was like 2.7 ohms cold. So it made for a grand total of 5.2 ohms. Not I am running the factory style resistor and thats it.

OK, just for the record, who did you buy the kit from? Which supplier made up the kit (usually TISCO or Atlantic)? and third, was there any part number associated with their included 2.7 ohm resistor?

I don't know where it came from. I got the tractor cheap because the guy couldn't get it to run. I like to tinker so it was a good deal to me. The 12v conversion was already done. I don't know what the resistor part number is.

 

[Dennis Conner]

The coil measured 2.8 ohms. The ceramic resistir measured 3.2 ohms. If the OEM balast resistor is 1 ohm when running, then there was 7 ohms. 14.5V / 7 ohms = ~2.1A.

Using only the OEM balast resistor I would have 3.8 ohms. 14.5V / 3.8 ohms = 3.8A. Is this too much?

 

[Bruce (VA)]

OMG! Where did you get that kit? No wonder it wouldn't run.

3.8a is ok. I wouldn't mess w/ it. But, if you leave the key on, you will toast the coil quicker than if it was 3A.
50 Tips

 

[68_f100]

(quoted from post at 17:21:42 08/27/09) OMG! Where did you get that kit? No wonder it wouldn't run.

3.8a is ok. I wouldn't mess w/ it. But, if you leave the key on, you will toast the coil quicker than if it was 3A.
50 Tips

Just so I have this straight. Leaving the key on with the points closed will fry the coil and points no matter the amprage? It will just take longer with lower amprage. Is that correct?

 

[Dennis Conner]

I ordered the kit off Ebay. It was exactly the same as others I have purchased. On my 1944 2N I didn't get the ceramic resistor and never put it in. It's ran great for the last few years configured like that. Now you have me thinking I need to go check the coil resistance on that one.

Just a note...I stopped by my local Ford New Holland dealer today to pick up a brand new FD220 resistor. They didn't have one. They carried the ceramic one though. I thought this was strange considering you can order them online still. Do you know of a car parts chain that carries the FD220 resistor?

 

[GA Dave]

(quoted from post at 19:26:47 08/27/09) I ordered the kit off Ebay. It was exactly the same as others I have purchased. On my 1944 2N I didn't get the ceramic resistor and never put it in. It's ran great for the last few years configured like that. Now you have me thinking I need to go check the coil resistance on that one.

Just a note...I stopped by my local Ford New Holland dealer today to pick up a brand new FD220 resistor. They didn't have one. They carried the ceramic one though. I thought this was strange considering you can order them online still. Do you know of a car parts chain that carries the FD220 resistor?

oogle is your friend. David.............

http://www.google.com/search?source...rlz=1T4GWYA_enUS330US330&q=fd220+resistor