Boosting coil voltage during starting

The Super C doesn't fire until AFTER you let off the starter switch. Apparently the starter is drawing so much power that the spark is weak. I have no problems starting the tractor but it gives everyone else fits.

It's a 12V conversion, with a ballast resistor running to a 6V coil. Works fine when the battery is putting out 12+ Volts, but during starting the battery voltage drops. Different coils don't seem to make much difference.

Later tractors have a booster circuit off the solenoid that puts a full 12V to the coil during starting, but the C has a pull rod starter.

Is there a clever solution for providing 12V to the coil during starting on an old tractor like this?

What I do NOT want is a toggle switch that you have to remember to turn on and off. I'd like something that sends 12V to the coil when you pull the starter rod.

A few possibilities come to mind to raise the coils input voltage to full unballasted battery voltage (less the normal voltage drop caused by the starters high current) ONLY WHILE CRANKING which can improve cold weather starts...

1) Not sure if its an option or available on your particualr starter switch BUTTTTTTTTTT on the saddle mount mount mechanical push to start switches as used on many Deere and other starters they make what are otherwise IDENTICAL push type switches (rod activated) EXCEPT THAY HAVE AN ADDITIONAL SMALL SIDE TERMINAL WHICH IS HOT ONLYYYYYYY WHEN ENGAGED. On Deere and others you simply run a wire from that terminal up to the coils input teminal so ONLY WHILE CRANKING you are by passing the normal (12 to 6) voltage drop of the ballast resistor....

2) It would be soooooo cheap and easy to use a momentary push button switch on the dash which when depressed sends hot unballasted battery voltage direct to the coils input and simply depress it while you pull the starter rod

3) You could convert the starter and push switch arrangement to a Ford type solenoid electric start as its extra little I terminal is hot ONLY WHILE CRANKING and is used to by pass the ballast at that time by sending voltage to the coils input

NOTE you may wanna check what the coil voltage is via the ballast with ignition on and the poinst closed MAYBE THE BALLAST IS TOO HIGH OHMS AND DROPPING TOO MUCH VOLTAGE. Id expect say 6 to 8 volts butttt if its like 4 or 5 the ballast isnt the correct ohms size to match the coil. Ballast resistors may be like 1.2 ohms all the way up to near 2 ohms depending on the coil they were designed for soooooooooooooo maybe you dont have the correct coil and ballast match

NOTE are you sure of the coil you have?? You need a 6 volt coil on a 12 volt system if youre using a ballast intended to drop 6 volts WELL DUH. A coil designed for full 12 volts if ballasted results in a weak spark especially while cranking......

Hopefully other gents can add more methods if I missed any, which Im sure I did

John T

Adding to John T's ideas:
Put a water proof 10 amp rated momentary contact switch on the linkage to the starter switch. It could be either on the rod at the steering post, or the saddle switch link. This would be from bat voltage through the switch to the coil side of the ballast. A spring could keep it on first off last when pulling the rod.
A more tidy and cheap way would be to run a wire from the Starter stud at the switch through a "mouse hole" you would file into lip on the switch body, this would allow Bat volts out of the switch when starting only. Putting a 6 amp diode into the wire to prevent back feeding the starter from the ignition switch (sure to smoke Wires)feeding the coil side of the Ballast, would allow it to run. Jim

With out knowing what coil you have and whatn resistor your using and how long it takes that resistor to warm up to start dropping the voltage to the coil i am shooting in the dark here . When i do a 6 to 12 change over i use a 6 volt coild usually the stock coil and add a resistor off a older Chrysler product and it takes a bit for the voltage to drop off down to around 6-8 volts . Your feed wire to the resistor should be nothing less then a 14. ga. wire from the push pull ing. switch and you sould have at least a 10 Ga. wire supplying juice from the started pole from the battery to the dash . . JT's has a couple good ideas also .

Thanks for the ideas guys.

Unfortunately, I really don't know what the coil and resistor came off of originally. Both look pretty generic. The coil is marked "6V." It's not a standard IH coil but it's the same size. The resistor looks the same as the one they sell at Tractor Supply, with the big white ceramic block.

If you get a Ford four wire solenoid it has a wire terninal marked I that also goes to the coil and connects to the coil along with the wire from your regular ignition. While cranking over the engine a full 12 volts will travel through the I wire giving the coil a full 12 volts during start up.

<a href="http://s265.photobucket.com/albums/ii205/zebra123_1/?action=view&current=GlowPlugSolenoid_html_37ba32be.jpg" target="_blank"> </a>

Sorry, I missed you had the lever starter.
Just a push button switch to the coil with 12 volts should do it while cranking.

Yep, thats the exact Ford type solenoid I was referring to that have the extra small I terminal AND A PICTURE IS WORTH A THOUSAND WORDS ......

John T

Woooooo Hooooooooo I just thought of one more probably the easiest and cheapest way. Im pretty sure Ford and some early new generation Deeres used a short piece of thermistor wire as the voltage dropping (12 to 6) Ballast.......The way it works is when cold its very low ohms so the coil is on unballasted battery voltage for a short period as needed while cold cranking buttttttttttt once warmed up its resistance increases to like 1.5 or so ohms and it then drops say 6 volts leaving 6 on the 6 volt coil.

Now if you can just find that thermistor wire link (Fords or early new gen Deeres) all you have to do is wire it between/after the ignition switch and coil and youre off to the races. She will start at unballasted battery voltage on the coil for a hotter starting spark but then the coil only sees its intended 6 volts shortly afterwards

John T

Check the voltage through the coil while cranking the engine. You are looking for between 6 and 9 volts.

Check battery voltage (voltage drop) while cranking engine.

Check coil polarity - matches current battery ground.

John T's thought - wrong ballast resistor.

Beneficial to find out what and/or where the problem is before making changes.

I think John T and the Tractor Vet are on the right track: Issue is a mismatch between the coil and ballast resistor. A couple possibilities:

1 – You actually have an internally ballasted (so-called “12 volt” coil). Running it in series with a ballast resistor will cause weak or no spark condition during cranking. Try measuring the coil primary current with the ignition on and the engine stopped (points closed). A properly sized coil and ballast resistor package should draw 3 – 4 amps. Less than that says either your coil or resistor is wrong.

2 – If it's the resistor try one for a 60’s era Chrysler product (Autozone #AL725 or equivalent – about $7) and see what happens. It has much lower resistance for when cold. After starting it takes a minute or two for it to heat up and develop full resistance. This provides more coil current and a hotter spark during cranking.

You've got it John!

The Chrysler ballast resistor accomplishes exactly the same thing by coiling the thermal resistance wire inside a hollow ceramic block.

I've got a Chrysler resistor on my 12 volt converted Super M. It shows only a few tenths of an ohm cold. But it ramps up to ~1.5 ohms after it's run a couple minutes. (The resistor gets quite hot BTW - enough to burn off any oil etc. that finds it's way onto it.)

I almost left the words Thermistor assembly in my post above, but figgured it was over the top. Wrong O, Jim

One other possible situation is Cable resistance and mediocre battery. Voltage drop should not go below 10.5 or so durring cranking. Jim

One other possible situation is Cable resistance and mediocre battery. Voltage drop should not go below 10.5 or so durring cranking. Jim

(quoted from post at 11:00:10 02/16/10) One other possible situation is Cable resistance and mediocre battery. Voltage drop should not go below 10.5 or so durring cranking. Jim

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ery good chance that could be the problem.....
mike

two things I would consider as well. starter/cables drawing too much, and possibly a bad ground. A poor ground will do the same thing.

There is one other way to fix this:

[size=18:def938aaba][b:def938aaba]MAGNETO!!!!!!!!!!!![/b:def938aaba][/size:def938aaba]

(quoted from post at 15:00:52 02/16/10)

(quoted from post at 11:00:10 02/16/10) One other possible situation is Cable resistance and mediocre battery. Voltage drop should not go below 10.5 or so durring cranking. Jim

Click to expand...

ery good chance that could be the problem.....
mike

Click to expand...

I was going to suggest fixing whatever was wrong with it before it was converted to 12-volts. I see it has finally been suggested.

Unfortunately, I have no idea on the history of the tractor so I have no idea what was wrong with it before it was converted.

The battery, battery cables, and alternator are all new.

I discovered the coil was hooked up backwards several months ago, but changing it didn't fix the problem. Sure it fired right off when I was standing there, but the next time Dad went to start it, it wouldn't fire.

Timing, fuel mix must be pretty good. We hooked a chain on it and tow started it to take the starter out of the equation. It was running before he got the clutch completely let out, and it was COLD that day.

The thing is like Fonzie's motorcycle. I'm the only one that can start it. Maybe it's trying to tell me something? Dad's already threatened to sell it to me a couple times.

One More Item!!!
If the coil is an internally ballasted/true 12v coil, and you are also using a ballast resistor, the coil will make running voltage, but be weak on startup. Swap the coil with a known runner, and go from there! Jim

Not that there is anything wrong with most suggestions, but to get to the heart of the problem the fastest way possible, go with BOB M and, " Try measuring the coil primary current with the ignition on and the engine stopped (points closed). A properly sized coil and ballast resistor package should draw 3 – 4 amps. Less than that says either your coil or resistor is wrong. "
...and measure the battery voltage from chassis to ignition switch out during cranking........gets battery , ground connex, hot side connex and cables all in one shot.

IC 64 part # from napa. Internal resistor , no problem.