using my MSD 12 volt coil with a ballast resistor 1.82 ohms

Hi, I did buy a 12 volt starter for my 12 volt conversion for my 51 8n side mount tractor. I have more information. my coil that I have is a MSD Blaster 2 its primary resistance is .7 Ohms. will this work with my ballast resistor that I have also? ballast resistor is 1.82 ohms. I don't want to burn up my points, I want to make the tractor reliable. appreciate it thank you.
 
(quoted from post at 14:58:29 03/01/15) Hi, I did buy a 12 volt starter for my 12 volt conversion for my 51 8n side mount tractor. I have more information. my coil that I have is a MSD Blaster 2 its primary resistance is .7 Ohms. will this work with my ballast resistor that I have also? ballast resistor is 1.82 ohms. I don't want to burn up my points, I want to make the tractor reliable. appreciate it thank you.
hen running, and assuming about 14volts on charge, then you will end up with about 5.6 amperes coil/points current. Points upper end is pretty well established at about 4 amperes. I would say expect shortened point life. I would add 2.8 Ohms to that coil, not 1.82.
 
oh so I should use 0.8 ohms ballast resistor, since my coil's primary resistance is .7 ohms? would that be correct? thank you.
 
(quoted from post at 15:32:50 03/01/15) oh so I should use 0.8 ohms ballast resistor, since my coil's primary resistance is .7 ohms? would that be correct? thank you.
ou will need to explain further, as your logic escapes me.
 
That is similar to the Accel Super coil with a .7 ohm primary winding we are using on one of our parade / tractor trek toys. It also supposed to use an additional .8 ohm resistor in series with the stock 1.5 ohm primary resistor or resistance wire. You need to end up with at least 3 ohms combined resistance ( coil primary winding plus ballast resistors) to not overload the points and burn them up.
We ended up with a single resistor from the auto parts store of a little over 2 ohms + the .7 ohm coil primary.
Primary amps are still a bit over 4 amps, but not enough to drastically shorten point life.
 
No.

Do the math.

As JMOR said, anything over 4 amps will burn up the points.

14.5v divided by 3.7 ohms gets you 3.9 amps. So, add a 3 ohm resistor. If you insist on using that coil.
 
Make it simple on your self. Go to a good parts store and ask for a true 12 volt coil that will have printed right on it NO External resister needed. Then wire it up with No resister and be done with it. Easy and simple and one less part to go bad
 
On an old Ford truck I used to drive,I added a Mallory super coil[60,000 v] with a Mallory dual point distributor. I foolishly didn't use a resistor and quickly burned two sets of points.After going through the resistor,no more problems.
 
Richard,
It's really simple. Too small resister and points go toast real fast. Too large resister, points last, but you have a weak spark.

Now you have to ask, why did cars in the 60's that had 12v batteries, still use a ballast resister? I know the answer. Does anyone else? Some of my cars built in the 70s, came with electronic ignition, but they still used ballasts. I even carried spare ballasts, because they would burn out. And it was very easy to tell when ballast went poof.

Most people who convert to 12v think all they have to do is get the right ballast and all is well. No so, it has to be wired like the old school cars with points and condenser.
So, what is the trick and how do you tell when you have the right ballast and coil combo??
 
OEMS's often used a ballast resistor with a "starting bypass" because that combination compensates for lowered battery voltage during cranking.

As we all know, the "N" Ford OEM system took a different approach....and used a PTC (Positive Temperature Compensated) ballast resistor that has low resistance when the ignition is first switched "ON", for good spark while cranking, then quickly warms up and resistance increases to a level that controls primary current to ovoid overheating the coil and burning the points.

If you know what to ask for, you can buy resistors for stuff in the more modern era that either is or isn't PTC.

I've posted some numbers and info on that and will find it and re-post it later.
 
Regardless of what Bob and others may say, it was done that way because YT contracted the Big Three to do it that way, knowing that in future years, that it would generate incredible traffic for YT. Great payback! :wink:
 
thank you for your information. you explained the same procedure as the MSD tech guy said. he said use the 1.82 ohms resistor with the 0.8 ohms MSD resistor. this way it won't burn the points. so that's what I am going to do. thank you.
 
Bob,


OEMS's often used a ballast resistor with a "starting bypass" because that combination compensates for lowered battery voltage during cranking.

You are absolutely right. But how many converting to 12v know how to bypass the ballast resistor.

The person who converted my tractors uses a ballast that dropped 6 v when points are closed and the old 6v coil used 6v. But when starting the cranking voltage dropped below 12v and my spark wasn't strong enough to start tractor until I got off the starter. It would then start while engine was still turning over. My ballast wasn't bypassed.

I had no connection on solenoid to bypass ballast. I didn't have a 12 v relay. So I ran a wire with a diode from starter to + of coil. The anode of diode was facing the starter and the cathode was connected to the + of coil. Solved my problem.

If I recall my old cars used an 8v coil and a ballast that dropped 4v.
 
(quoted from post at 18:41:28 03/02/15) Bob,


OEMS's often used a ballast resistor with a "starting bypass" because that combination compensates for lowered battery voltage during cranking.

You are absolutely right. But how many converting to 12v know how to bypass the ballast resistor.

The person who converted my tractors uses a ballast that dropped 6 v when points are closed and the old 6v coil used 6v. But when starting the cranking voltage dropped below 12v and my spark wasn't strong enough to start tractor until I got off the starter. It would then start while engine was still turning over. My ballast wasn't bypassed.

I had no connection on solenoid to bypass ballast. I didn't have a 12 v relay. So I ran a wire with a diode from starter to + of coil. The anode of diode was facing the starter and the cathode was connected to the + of coil. Solved my problem.

If I recall my old cars used an 8v coil and a ballast that dropped 4v.

Plenty of ways to skin a cat. I've owned quite a few old cars (and still own one) that had a 12V coil and no ballast resistor. About to have a 12V 8N conversion that will work the same way....

TOH
 
By 65 barracuda had a ballast. So did my 67 cuda
and 71 duster. The duster had electronic
ignition. It used 2 ballast resistors. It could
be one of the resistors was a load resistor for
the power transistor.

Do you remember the simple test to determine you
had a defective ballast without using a meter?

I've never seen an old car from the 60's that
didn't use a ballast. They mounted them on the
firewall which I think they did that as a heat
sink. Mine were easy to get to and I had a spare
in glove box.

What kind of car do you have? Is it possible
someone upgraded yours to 12v coil?
 
(quoted from post at 21:19:36 03/02/15) By 65 barracuda had a ballast. So did my 67 cuda
and 71 duster. The duster had electronic
ignition. It used 2 ballast resistors. It could
be one of the resistors was a load resistor for
the power transistor.

Do you remember the simple test to determine you
had a defective ballast without using a meter?

I've never seen an old car from the 60's that
didn't use a ballast. They mounted them on the
firewall which I think they did that as a heat
sink. Mine were easy to get to and I had a spare
in glove box.

What kind of car do you have? Is it possible
someone upgraded yours to 12v coil?

I have a 1962 Triumph TR4 and it never had a ballast resistor. None of the various TR's I have owned over the years ever had a ballast resistor. AFAIK no 12V Triumph 1960-1980 used a ballast resistor. Same for MG's o fthat vintage. I would imagine there are plenty of others.

TOH
 
I wasn't thinking brittish iron. My 62 XKE, lucas
ignition, had no ballast either. What about
american cars from the 60's?
 
(quoted from post at 22:59:46 03/02/15) I wasn't thinking brittish iron. My 62 XKE, lucas
ignition, had no ballast either. What about
american cars from the 60's?

I have no idea what if any domestic vehicles might have used an unballasted ignition. I did discover that beginning with the TR6 Leyland started using a ballast in the TR's. It was resistance wire in the harness and I never realized it was there....

TOH
 
IMHO, generally, high output, low primary resistance coils are made to be used with high-dollar ignition boxes that manage dwell time to limit primary current and coil heating WITHOUT the use of a ballast resistor.

Using such a coil with points or an original-type Pertronix where you have to use a resistor 3 times the value of the primary winding is just SILLY, as you are simply dissipating energy as heat at the resistor and not "driving" the coil to it's full potential.

What DO you think you are gaining with the $$$ specialty coil for this application?
 
(quoted from post at 23:42:00 03/02/15) IMHO, generally, high output, low primary resistance coils are made to be used with high-dollar ignition boxes that manage dwell time to limit primary current and coil heating WITHOUT the use of a ballast resistor.

Using such a coil with points or an original-type Pertronix where you have to use a resistor 3 times the value of the primary winding is just SILLY, as you are simply dissipating energy as heat at the resistor and not "driving" the coil to it's full potential.

What DO you think you are gaining with the $$$ specialty coil for this application?
think" is a good word here, Bob, as it may be a loss rather than a gain.
 
This past summer I rewired neighbor's 1963
Massey, MF35. Did Harry use a 12v Lucas coil on
it?

The Massey came from factory 12v, had a 12v
generator with old school voltage regulator. No
ballast on the coil.

The answer to how you would instantly know how
you had a bad ballast on American cars? The car
will start and instantly die the second the key
goes from start to run position.

The way I wired around my ballast using 12v off
starter and a diode, my tractor will start and
die when I push down on starter button and the
key in the off position.

If my ballast dies, I think I'll replace mine
with a straight 12v coil or be cheap about it and
use an old coil I have in spare parts drawer. To
figure out what ballast to use, I'll start out
with a 6v drop on ballast sending 6v to the coil.
 
thank you for all your guy's help. I understand now how to do the math on the coil and ballast resistor. sorry for any confusion if happened.
 
(quoted from post at 23:54:08 03/05/15) thank you for all your guy's help. I understand now how to do the math on the coil and ballast resistor. sorry for any confusion if happened.

Most people here are more than willing to take the time to explain "stuff" to anyone willing to try and understand. Sometimes that understanding comes hard so congratulations on your perseverance ;-)

TOH
 

We sell tractor parts! We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today.

Back
Top