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Coil Resistor?

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cjric View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cjric Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 12:34am
what coil are you using that has a built in resistor? I just noticed the other day that my 12v coil says right on it "use external resistor" but I have yet to find a resistor anywhere. Or, instead of replacing the coil, what resistor are you using? Just any ole ignition resistor? Do you have a bypass circuit for startup?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocnroll Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 2:55am
I can't put my finger on the built in resistor coil link, it was some specialty deal..
 
I'm using electronic igntion anyway so no use to compare to mine. Yes, most any ignition resistor will work I believe.
 
I did find this link for a coil and resistor together.
 
 
The internal one was made similar to this but without the bulkiness of this one...(I'll keep hunting to see if I can turn up the link)
 
You'll be able to get a resistor at any auto parts store, if that's what you are asking.
 
 
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote westforkboyd Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 4:14am
Might as well make Roc's advice something to think about.
 
So according to Sam's research there is more buildup in the coil when the points are open? Thought the opposite to be true. Dang it!
 
 My 9N Ford just has a toggle ignition switch. If inadvetantly left on (with a 6V battery) it will melt the coil. At the risk of considerable embarassment there are at least a dozen burnt out coils for that in my shop. If everything wasn't saved even I wouldn't realize how many have beeen burnt out over the past thirty years. But I counted them.
 
A few times after trying to start in the winter the switch was left on while the charger was attatched. Nother coil....... But sometimes I would find it with switch on, panic, go to start it and... no problem.  Always though it was relative to the point/distributor position and since they are closed more than open, figured the problem was in the closed position... How wrong could I be?
 
No one shouldn't save so much junk
WFB
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Post Options Post Options   Thanks (0) Thanks(0)   Quote lowenuf Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 4:23am
Originally posted by westforkboyd westforkboyd wrote:

If inadvetantly left on (with a 6V battery) it will melt the coil. At the risk of considerable embarassment there are at least a dozen burnt out coils for that in my shop.
 
and the same holds true for our 2A friend. so i dearly hope that if you ever get that keyed coil, you learned your lesson on the tractor, or you better be lining up multiple keyed coil purchases....lol  :)~~~
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Post Options Post Options   Thanks (0) Thanks(0)   Quote p3ferris Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 5:28am

WFB your coil is more likely to go bad if the points are shut.  When the points are open the coil is not shorted out.   It is shorted out when the points are shut.  That is what causes the spark when the points are  pulling away from each other.

Ed
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 2:42pm
Originally posted by samcj2a samcj2a wrote:

Isn't there a risk of burning out the coil if there is no resistor?
ABSOLUTELY!

A 6v coil operated at 12v will get 4 TIMES HOTTER, and burn out in short order.

Aside from excessive power dissipation, since the output voltage is doubled, there's a good chance that the insulation won't hold up to it, and you'll get arcing.

Sean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote cjric Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 2:50pm
So, I put in a resistor (I'm pretty sure I've got 1-2 laying around from parted out vehicles).
Do I then need to put in some sort of start only bypass? So the coil gets full 12v (in my case) during startup?

Not sure how I would rig that up since I have a linkage activated starter...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samcj2a Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 2:59pm
You won't need a bypass arangement.  Just put the resistor between the battery and the coil so the battery coil does not get the full 12 volts.  You should probably have some kind of ignition switch so that you do not run current through the coil when the engine is not rotating during starting or running.  In this case, the switch would make and break the circuit from the battery or hot side of starter switch to the coil.  The resistor would be in series between the switch and the coil.   If you don't use a switch, then be sure to quickly remove power from the coil when the engine is not running.  It's just like leaving the ignition switch on when the engine is not running and the points happen to be closed so current runs through the primary windings of the coil uninterrupted.  Ouch
Sam

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Post Options Post Options   Thanks (0) Thanks(0)   Quote westforkboyd Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 3:28pm
Ok as long as we're still discussing this.........
 
That is one reason why I've been reluctant to shell out the money for these keyed coils and convert back to 6V. First off how can you tell if the dang thing isn't burnt out already? Second what if I leave the switch on and burn it out. Considering my history the chances of that eventually happening are pretty good I'd say. Embarrassed
 
The thing I'm not getting is I've never......never burnt out a 12V coil. Why? I've left the switch on many different 12V equiptment cars, trucks, tractors, Jeeps, 4-wheelers and all its ever done is run down the battery. Why is that?
 
Burnt out Boyd 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote samcj2a Quote  Post ReplyReply Direct Link To This Post Posted: 01 Mar. 2008 at 3:34pm
Without thinking about it more, one reason is that some of those 12 volt systems where you've left the ignition on do not have points - the so-called Kettering ignition system that we've been babbling about. 
Sam

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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar. 2008 at 5:49pm
Originally posted by cjric cjric wrote:

So, I put in a resistor (I'm pretty sure I've got 1-2 laying around from parted out vehicles).
Do I then need to put in some sort of start only bypass? So the coil gets full 12v (in my case) during startup?
You shouldn't need a bypass, since a 6v coil was designed to run off a 6v battery to begin with.

Be sure your resistor is the right resistance.  It needs to be the same resistance as the coil primary in order to get the correct voltage drop.

The stock CJ-2A coil has 1.2 ohms primary resistance. I'd suspect that most 6v coils are the same, but some may be different, so if you don't know for sure what coil you have, it would be best to measure it first, and get a resistor to match.

If anything, use a resistor with slightly less resistance than the coil.  eg 1.0, or 1.1 would be fine for the stock 1.2 ohm coil.  It also needs to be rated for 30 watts or better.

re: inadvertently leaving the switch on

Allen, don't know why you have a "melting coil" problem, but that should not happen in a stock, properly maintained system.

6v or 12v is irrelevant.  Any coil should be able to handle full static current & voltage w/out failing.   It will get a bit hotter than when it is running, but not twice as hot, and that alone should not be cause for failure.

When testing a coil (real world test scenario) it needs to be brought up to temperature to begin with.  Autolite recommends this:
"warm the coil by connecting the primary to a battery of the same voltage rating as the coil.  Warm in this manner for 5 minutes ..." before performing the tests.
Sean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote westforkboyd Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar. 2008 at 6:21pm
Originally posted by sean sean wrote:

[QUOTE=cjric]

Allen, don't know why you have a "melting coil" problem, but that should not happen in a stock, properly maintained system.

Sean
 
After thinking about it the 9N is the only piece of equiptment I have had that problem with.
First and foremost reason.......IT'S A FORD!  LOLLOL
 
Sean I will not be at all suprised if you are familiar with it. The 9N and early 8N Fords have a weird coil that is actually a part of the front mounted distributor. It is clamped on top of the distributor and the cap. Still the original 6V w/6V battery as to properly maintained.... Well I did just use a toggle switch  for turning on the ignition. The kids would play on it and turn the switch on while "playing tractor". Thank goodness burning the coil was the worst that happened.
It's just sitting in my barn now (with a burned out coil) as we bought the Oliver Super 55 about five years ago and that is a much better piece of machinery both condition and feature wise. More power, live PTO and hydraulics, heavier 3-point, and not that much bigger. It's the cadillac of small utility tractors.
Someday I intend to do some work on the 9N again. It needs alot. It was my Father's and did give me good service for over 25 years.
 
Allen
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sean Quote  Post ReplyReply Direct Link To This Post Posted: 02 Mar. 2008 at 6:47pm
Allen:

I know nothing about those tractors, other than having "heard" about them before.  Without seeing the electrical schematic, it's impossible to guess what other factors may be involved.  It may simply be a case of a very marginal coil design!

In autos, there's usually enough of a margin for error built into electrical components to handle the occasional abuse that the owner might subject it to.  "Good" engineering would account for it.

Sean
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 46CJ2A Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2008 at 7:05pm
I know you thought you were through with this discussion, but . . . . . . .
 
I did as suggested and got a 6 volt battery and hooked everything up.  The fully charged battery barely turned the new (tight) engine over.  I double checked that I had a good ground on the chassis, motor and starter to insure I was getting all the power I could from the battery.  And it still just "crawls" around.
 
So now I'd like to follow the other suggestion and try a 12 volt coil (with built in resistor)with a 12 volt battery to get the motor turning over a bit faster for the first few starts - after which I'll hook up all my 6 volt components.  I want to use the 12 volt coil rather than a resitor on my 6 volt coil to avoid all the possible pitfalls mentioned.
 
Can someone give me the coil number to buy?  A NAPA equivalent number would be helpful.
 
Thanks for all the input to far.  I appreciate it.
 
Jack
 
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote westforkboyd Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2008 at 7:28pm
Jack
 
I know this isn't what you asked but......are you sure you have a 6V starter? I would have suggested checking all your ground connections but you already have. You could also use a boost type charger if you have one. It should spin better than that.
 
WFB
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 46CJ2A Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2008 at 7:38pm
Yah, it's a 6 volt starter and it spins real fast without a load on it.
 
Jack
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jus*Jack Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2008 at 7:38pm
I'm with WFB on this...it _should_ turn over more easily than what you're describing. Have you tried turning it over by hand, using a socket and ratchet on the nut on the front of the crank? I'd try that, to see that there's not something else causing it to be so tight.

Assuming that you DO use the same starter that you've now got, and use a 12V battery, just try to be careful that you don't overdo things, and burn the starter (assuming that it IS a 6V one)...Been there, done that! Keep your attempts reasonable (short), and allow it to cool down between attempts.
Seeya!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote samcj2a Quote  Post ReplyReply Direct Link To This Post Posted: 06 Mar. 2008 at 7:58pm

I, too, am wary of a good starter not being able to crank a rebuilt engine enough to start it. 

I am aware of a teenage jeeper who proudly rebuilt his 2A engine - top to bottom.   When it came time to start it, it would not crank.  The teenager thought, "Great - I did a good job with this rebuild and have a nice tight engine - no more blue smoke", and got a push-start to get that Jeep going.  A few weeks later, a rod knock developed and the teenager was much less cocky.  It turns out, that even though he knew not to mix up the rod caps and had marked them, he still managed to mix up two of the rod caps when he reassembled the bottom end.  So, that anonymous teenager learned a very expensive lesson - sort of like "measure twice and cut once" in carpenter's terms.

I would explore just how tight the engine is and make sure there is nothing too tight.

 

Sam

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