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Ballast resistor question

T

thelasthour

Member
"Does a ballast resistor "

"Does a ballast resistor "resist" voltage when it is cold or only when it gets hot? If it is resisting when cold, should a bypass wire be run from the starter to coil for startup only? If you run the bypass wire do you need to worry about a diode so the starter does not get energized from the coil after the engine is started?
Steve"
 
The purpose of the ballast res

The purpose of the ballast resistor is to drop the battery voltage down to approximately half its value for ignition coil operation and to reduce or minimize wear on ignition components.
 
"I realize that, but my intent

"I realize that, but my intention is to get a full 12volts to the coil at a cold start. What I don't understand is if the resistor only starts "resisting" once the internal spring gets hot. Does it allow 12 volts to flow at the beginning, and then as it heats up it reduces it to 6. If it allows 12 at when it is cold, then there is no need to bypass it on startup."
 
"Steve:

You've got an e

"Steve:

You've got an entirely wrong understanding of this issue.

When the ballast resistor is in the circuit (more on this in a moment) the 12 volts going to the coil is dropped down to around 9 volts--and ALWAYS. Heat and time has nothing to do with it. While starting, however, a BYPASS circuit sends a full 12 volts to the coil to improve spark. Soon as the motor starts, and you let off the key, the ballast resistor circuit takes over and the coil gets only 9 volts again. If not, a full 12 volts would soon burn up the coil. Get it?

Why this crazy arrangement? It's an old fashioned idea that--thankfully--has gone away. Modern engines use a full 12 volt coil and make enough spark to start it easily.

So where does that 12 volts to the coil come from? On mine, it's from a circuit on the starter solenoid, the "S" terminal. When you crank the motor, the solenoid not only engages the starter, it sends 12 volts directly to the coil. Naturally, when you let off the key, that circuit de-energizes, and the ballast resister circuit (9 volts) takes over.

Jeff

Note: I adapted a Mopar electronic ignition system to run an outboard. It uses a 12 volt coil--no ballast resistor--and it starts super!

Jeff"
 
"Couple of clarifications here

"Couple of clarifications here:

The ballast resistor limits the current flow thru the primary side of the ignition. This produces a voltage drop leaving around 9V DC on the + terminal of the coil.

The older crusader's provide the ignition with current, during cranking, from the starter solenoid's "I" terminal. If it comes from the "S" terminal, it has to flow thru a diode (not standard). If there is direct connection, the key will keep the starter engaged and one expensive mess could result.

The "I" terminal during cranking approach was deemed a good idea to minimize any starting issues due to marginal voltage levels at the coil. I've seen many start fine without it and I also seen a few that wouldn't once removed.

As stated above, the "I" terminal feed to the coil is not needed for most electronic systems."
 
"Great, most of my questions a

"Great, most of my questions are answered. I was very worried about the "expensive mess" that Mark described. How do I tell if my coil is 12 volts or not? The engines are 2006 "powerpacks" that included ignition systems. The wiring diagrams included the ballast resistor in the schematic. Either way, if I change the coils to 12 volt, and remove ballast resistors, I may have better cold starts right?
STeve"
 
"It will say (on the coil&

"It will say (on the coil) "external resister required" (meaning it's a 9 volt coil), or "no external resister required" (12 volt).

If yours is painted over, you'll have to check it's resistance with an ohm meter and compare it to a new coil at your (hopefully) friendly NAPA store.

Jeff"
 
"Steve:

the ballast bypass

"Steve:

the ballast bypass system should be all you need for startups, with the engine hot or cold. If your setup has a ballast resistor, it should have the bypass fromm the starter solenoid up to the coil. If it is not there, it is easy to add IF the starter solenoid has the small "I" stud.

Does the wiring diagram the "extra" lead from the coil to the solenoid?"
 
"Steve:

I just checked my o

"Steve:

I just checked my old (mid-80's) crusader wiring diagrams. The "I" terminal described above is labeled as "R" in those diagrams.

I also checked the merc diagram from ~1980. It also used the "R" descriptor.

Both were consistent in showing the "R" terminal as the small one in the 9 o'clock position when viewed from the terminal end of the solenoid. If the wire is installed from the factory, it should be purple, maybe another color with a purple stripe."
 
""R" has got to mean &

""R" has got to mean "resistor" circuit, dontcha think?

Jeff

PS: Many have tossed the resistor out and installed modern 12 volt coils ("no external resistor required"). They claim their motors run perfectly, and there's no ballast resistor to burn out or have the connector fall off (and make a fool of the "Captain" as he tries to "fix" the carb since the motor won't stay running. Ah-hem!)

Jeff"
 
"Maybe "to the Resistor ci

"Maybe "to the Resistor circuit".

How many chevy starter motor solenoids have you had apart?

Then isn't any resistor on that lead. Typically, the stud has a brass 'finger' that is energized when the plunger disk passes current from the BAT lug to the starter motor lug."
 
""(and make a fool of

""(and make a fool of the "Captain" as he tries to "fix" the carb since the motor won't stay running. Ah-hem!)"

Tell me about it!! This year spent $1600 on mechanic replacing plugs, points, adjust timing, rebuild carb, etc. Still shutting down after engine warmed up. Replaced $30 coil myself after finding this website, presto! Needed the tuning, but I sure wanted to finish one day on two engines this year...."
 
"I seem to remember the ballas

"I seem to remember the ballast resistor is a variable resistor which changes resistance with different RPM's and prevents the points from burning up if the ignition switch were left on while the points were in the closed position. When an engine is cranked, the starter drain can reduce the available voltage to as low as 10 volts. If only 10 volts is going through the resistor, the coil will not have enough power to deliver a spark and therefore the resistor is by-passed when the starter is engaged. I googled the question and found this interesting information on a mopar performance website.

"The ballast reduces the current flow thru the coil at low speeds and keeps the coil from overheating. As was said the coil can handle more amperage but not for long periods of time. So at idle and low eng speeds the points have more time to be closed and thus the current heats the ballast up and causes it to have more resistance and drop current flow at lower eng speeds when full coil output is not needed. When you go faster and speed the eng up the points have less time to be closed so the ballast cools down some and the resistance drops causes more current to flow thru the coil and letting the coil output higher when it is needed at higher eng speeds. And when cranking the ign system needs full output to help start the eng so the ign switch bypases the ballast and gives full battery volts to the coil while cranking.""
 
...""The ballast reduc

...""The ballast reduces the current flow thru the coil at low speeds and keeps the coil from overheating. As was said the coil can handle more amperage but not for long periods of time. So at idle and low eng speeds the points have more time to be closed and thus the current heats the ballast up and causes it to have more resistance and drop current flow at lower eng speeds when full coil output is not needed. When you go faster and speed the eng up the points have less time to be closed so the ballast cools down some and the resistance drops causes more current to flow thru the coil and letting the coil output higher when it is needed at higher eng speeds. And when cranking the ign system needs full output to help start the eng so the ign switch bypases the ballast and gives full battery volts to the coil while cranking.""

Where did this blurb come from? A ballast resistor is NOT variable; it reduces the voltage to the coil the same amount indefinitely. Period. Engine speed has nothing to do with it.


Jeff
 
"Bob: that's a neat analog

"Bob: that's a neat analogy but full of as much urban myth as real fact. The resistance variation with temperature is dependant upon the composition of the wire. Being as they are relatively cheap, I'd doubt it was tightly controlled. I don't think you will find a significant variation in the operating temp of the resistor, so the current variation will be small as well.

I'd bet it was crafted by the ex-master mechanic that turned service writer for the high end repair shop in some town. "...so you see how complicated this device really is? That's why it took so long to diagnose your problem, Mr. Smith, and that's why we accumulated 3 hours repairing your engine...." Or maybe it was a marine shop..."
 
"I know that resistor producti

"I know that resistor production is based on techniques that produce resistors of varied impedance. The percentage of deviation from its intended resistance value is coded by color bands on the resistor. They can vary by well over 20% and those measured within 1% tolerance are a premium. As all elecronics produce heat, it is their operating environment and typically do not change value under those conditions. As Mark says...I'd doubt it was tightly controlled."
 
"Bob:

the opinions expresse

"Bob:

the opinions expressed at that link make for some entertaining reading. I'm glad I don't have to back them, financially - I like my boat. Even without the ballast resistors.

Al: tolerance on multi-watt dissipation wirewond resistors is typically printed on one of the sides of the body. Most suppliers will deliver "20%" varieties if left unspecified. Depending upon the OEM, that "20%" could be +/-20% or +/-10% (20%, total). I've actually purchased and used parts that had a tolerance rating of +/-0.1% - true precision resistors - which also had temperature coefficient specs on them."
 
"That's why the code them.

"That's why the code them...Once tested, they know whether or not they meet spec. Those that fall out side are labeled 10 or 20 percent. The good ones get better money...You must pay a premuim for 0.1%"
 
"Are we talking about the wire

"Are we talking about the wire wound ceramic ignition resistors available at NAPA for between $10 and $20?? Here's a link to wikepedia concerning self variable ballast resistors...I had thought that automotive ignition resistors fell into that category: http://en.wikipedia.org/wiki/Electrical_ballast#Self-variable_resistors
heres another link to the second chance garage and their interpretation of how an ignition resistor operates:
http://www.secondchancegarage.com/public/122.cfm
I also seem to remember that some coils have internal resistors and do not require an external resistor."
 
"Same beasts though I can'

"Same beasts though I can't believe the going rate is that high nowadays.

Notice that the wiki discusses ignition systems' use of these devices in the "fixed" catagory (immmediately preceding), not the self-variable catagory...the author had a good reason for doing this.

Coils fall into two broad catagories, like you noted: those with internal resistors and those without. The coil also has a property called internal resistance. This resistance plus that of the resistor (internal or external) is what limits the flow thru the point set and keeps themm from burning up in the key on, engine off state. You will find that the internal resistance is due to the intrinsic resistance of the copper wire making up the primary winding. This, too, will vary will temperature. Most conductors will have a positive coefficient, copper being 3.9 * 10^-3/deg C, so their resistance increases with temp. When discussing the voltage at the coil, you need to consider this part as well as the changes the ballast resistor may undergo."
 
Man...I can't remember whe

Man...I can't remember when I used the formula for velocity factor in a LONG time ! I had to replace it with Set and Drift
 
"ballast resistor [?bal·?st ri

"ballast resistor [?bal·?st ri?sis·t?r]
(electricity)
A resistor that increases in resistance as current through it increases, and decreases in resistance as current decreases. Also known as barretter (British usage).
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


--------------------------------------------------------------------------------
Ballast resistor
A resistor that has the property of increasing in resistance as current flowing through it increases, and decreasing in resistance as current decreases. Therefore the ballast resistor tends to maintain a constant current flowing through it, despite variations in applied voltage or changes in the rest of the circuit.

The ballast action is obtained by using resistive material that increases in resistance as temperature increases. Any increase in current then causes an increase in temperature, which results in an increase in resistance and reduces the current. Ballast resistors may be wire-wound resistors. Other types, also called ballast tubes, are usually mounted in an evacuated envelope to reduce heat radiation.

Ballast resistors have been used to compensate for variations in line voltage, as in some automotive ignition systems, or to compensate for negative volt-ampere characteristics of other devices, such as fluorescent lamps and other vapor lamps.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.


<font color=""ff0000"">I had no idea that the ubiquitous 1.4 ohm coil resistor varied R as a function of current (or temp). Apparently, they do. I learned something today!</font>"
 
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