Round 2 it experiment

Yesterday I had too

much time on my hands. I found a ballast resistor that may have been used on a Dodge Aspen Mopars first generation electronic

ignition. I found a 12v coil. All the used parts are in a drawer dedicated to my Jubilee's parts drawer.
So I made a series circuit, a ballast resistor on the left, a HF 10 amp meter going between the ballast and the 12v coil.

The circuit is connected to a 12v mower battery which the midtronics meter shows 12.78v. The battery was recently charged.
The HF meter on the left is showing a - 4.97v, the ballast voltage. I should have reversed the wires to meter, but who cares.
The middle HF meter is reading 3.86 amps.
The right HF meter is showing the coil voltage is 6.17v.
I ran out of HF meters or I would have measured the volts used by the wires and the ammeter.
The wire on the right is a 16g wire.
The wire on the left is the hair like wires the 4 amps is going through to the ammeter, the center meter.





Those who are sharp enough will soon ask, where is the missing voltage? Good question. I think part of the problem is meter accuracy, and some of the missing voltage is used by the ammeter and the hair like wires used by the meter.

My objective is to find a used coil and ballast resistor for my Jubilee. My son wants the tractor after I'm gone. He wouldn't have a clue what coil and ballast to buy.

When I have more time to kill. I plan to take the coil off the jubilee and use it in my experiment. If the coil off the Jubilee uses 6v and 4 amps, I would conclude the coils are the same. The coil have a 1.5 ohm primary resistance

If I have 4 amps and 6 volts going to the coil, I'm happy regardless if I have missing voltage.

For all those familiar with Ohm's law. 4 amps and 12v means 3 ohms total is the series circuit. Ballast 1.5 ohms and coil 1.5 ohms = 3 ohms. Does anyone have an ohmmeter that can accurately measure 1.5 ohms plus or minus 1% or 2%? I should ask can anyone afford an ohmmeter that can accurately measure 1.5 ohms plus or minus 1 or 2%?

So much for my round 2 it experiment.

This experiment shows the importance of having accurate and calibrated meters, which obviously I don't have.

I'll let all the EEs answer the questions. I'm sure JohnT and Mark would love to field questions.
You-alls have a good day. Is You-alls plural?

I once heard a southern congressman tell his fellows that y'all is singular, plural is all-y'all.

Yes, you did have too much time on your hands.

Guarantee you when you were leaving Tennessee the other day you didn't hear You-alls come back! The proper term is ya'll come back and yes it's plural. Lol

ZINGO!
I retired in 2004. Dang that almost 19 years ago.
I have to invent things to do.

I think that the plural is Y'all.

Voltage drop is measured ACROSS a component. People usually measure to ground, which is not always correct.

To measure the voltage drop across the resistor you need to connect the probes from your meter to the terminals on the resistor. I only see one connected, and not sure where the other ends up. I assume the - terminal on the battery. You won't get an accurate measurement that way.

I have tractor buddies in Tennessee and one of them asked me if I knew the difference between a Yankee and a Dam% Yankee--I said nope--He said a Yankee is one the visits Tennessee and goes back North----A Dam% Yankee is one that visits Tennessee and stays!!!!---Ya'll got to love it---Tee

You are correct.
You are over thinking how I wired the meters.
One meter is across the ballast the other across the coil.
The ballast has an alligator connected to the right side.
On the left side I made a splice in the wire.

Mornin neighbor, what you found confirms my experience and understanding being one who farmed with those type of tractors and was at one time a used dealer which is as follows:

1) To use a 6 volt coil on a 12 volt tractor you need to drop the coil voltage to its 6 rated volts by adding a series voltage dropping ballast IE drop 6 Volts ACROSS the ballast leaving the remaining 6 Volts be dropped ACROSS a 6 volt coil WELL DUH.

2) A 50/50 Voltage divider (1/2 across coil 1/2 across ballast) would mean the coil and ballast would have the SAME resistance WELL DUH

3) I have seen many 6 volt coils with around 1.5 ohms resistance and many ignition ballast the same around 1.5 ohms WHICH (on a 12 volt tractor) IN SERIES IS 3 OHMS AND DROPS 1/2 ACROSS BALLAST AND REMAINING 1/2 ACROSS THE 6 VOLT COIL HOWEVER I have seen some 6 volt coils in the 1.25 to 1.8 ohms and some ballasts 1+ to almost 2 ohms !!!!!!!!! Of course different vehicles used different coils and ballast so their values would be a bit different MY 12 VOLTS AND 1.5 OHMS ARE APPROXIMATIONS not intended as perfect or accurate !!!!

4) In order to limit an ignition circuits LV primary current and to reduce premature points burning many Kettering ignition points circuits limited current to around 4 max amps WHICH IN A 12 VOLT TRACTOR WOULD MEAN YOU NEED A TOTAL OF 3 OHMS LV PRIMARY RESISTANCE (12/3 = 4) which is achieved if you had a 1.5 ohm coil and a 1.5 ohm ballast. Or on a 12 volt tractor use no ballast and a full true 12 volt rated 3 ohm coil .......... On a 6 volt tractor 6 Volts/1.5 ohms coil = that 4 amps

NOTE Sure when under charge the battery voltage may rise to 13+ to near 14 and a fully charged 12 volt battery at rest and stabilized is around 12.6 volts

5) A full true 12 volt coil has typically AROUND 3 ohms resistance while a typical 6 volt coil has AROUND 1.5 ohms. HOWEVER A coil labeled 12 volts FOR USE WITH BALLAST is in reality more like a 6 volt coil and needs the ballast LIKE IT SAYS or it will overheat and has AROUND 1.5 ohms resistance IE you need the ballast to reduce current and voltage

6) What some call a coil with an internal ballast DOES NOT ACTUALLY HAVE A DISCRETE STAND ALONE RESISTOR TUCKED AWAY INSIDE THE CAN but instead achieves its resistance by the winding alone..

Nuff said, Im sure I missed something so the other fine sparky gents can add more to this

John T Live in the RV from Panama City Beach, sunny and warm in the 70's yayyyyyyyyyyyyyyyyyy

At least some of the missing voltage is voltage drop across the ampere meter's shunt.

PS before anyone has a calf lol YES they made some old car coils that indeed had stand alone resistors (some were temp compensation type or like thermistors) in the can often in the bottom and there was a separation with a noticeable ring near the bottom or the coil can.......But I never saw such on any old farm tractors

John T
https://www.yesterdaystractors.com/cvphotos/cvphoto142370.jpg

<img src=https://www.yesterdaystractors.com/cvphotos/cvphoto142373.jpg

JohnT
Did you see the coil I used said 12v and to use an external resistor? So after they converted cars to 12v what voltage did the coil use? 6v or more?
I guess I'll have to put this coil on the jubilee and see if it works. Another round 2 it experiment.
I'm 99% certain the ballast I used was one I carried in the glove box of a 12v 1978 dodge aspen wagon, first generation electronic ign.

Mark,
An afterthought. Remove the ammeter, use bigger wires and see if I get a different coil and ballast voltage.
Add the coil and ballast voltage and I should get the battery voltage.
If my coil is 12v and it says use a ballast. What voltage did the 12v use?
I remember while cranking, the coil got the full 12v.
While running it got less voltage. How much less?

Did you see the coil I used said 12v and to use an external resistor?

YES and I explained a coil so labeled is in reality more like a 6 volt coil and requires the ballast JUST LIKE IT SAYS otherwise it will overheat and the points burn soon....

We got this

John T Wont be in Eustis, Mt Dora and Leesburg until March 2023 For now its nice n sunny in the panhandle on the Emerald Coast

Stock up on those 20-30 count guf shrimp while you are there. Friend of mine whow
winters there always brings me 15 lbs of browns and reds.