W113 Pagoda SL Group > General Discussion

COILS and BALLASTS

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mdsalemi:
Gents,

My recent problems and discussions with several people have only confused me regarding the proper ignition coil and ballast setup for our cars.

I hope the experts check in here and can provide some definitive answers...please unconfuse me!

How many coils are there for our car line(s)?  I understand that there is a Blue coil, a Red coil and a Black coil?  What is the difference between them?  What is their specific application?  Which car came with which?

How many different ballast resistors are there for our cars?  I understand a .6, a .9 and a 1.8?  Which one goes with which coil?

Are there specific voltages we need to look for in the ignition setup, i.e. at the coil primary, at the ballast, etc.?

I spoke with Dr. Benz this morning, and only got confused.  My new Bosch coil, bought last week, as yet uninstalled, is labeled for "old style, non-transistorized ignition" and the box says "requires 1.8 ohm resistor".  It is a red-label coil.  The coil in my car, is a blue coil labeled for transistorized ignition (for a 1970-1971??) and does not have any ballast requirement labeled on it.  I added a .6 ohm ballast which provides about 11 volts at the coil primary.

Can someone with intimate knowledge please check in here and lay out the coil and ballast combos and which one(s) we should have??

Note that the aftermarket ignition systems are designed to work with the OEM ignition setup specs; so it is important to start at the factory specs before adding a Crane or Pertronix.  It should be noted that my "original" blue coil with the "original" .9 ballast caused brand-new points to burn up in 30 miles which is why the restorer added the Crane 5 years ago.

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

bayleif:
This topic comes up to confuse us from time to time. Joe came to our rescue the last time:
http://www.sl113.com/forums/index.php?topic=746
If this shortcut doesn't work (I've never tried it before), I just did a search for Ballast Resistor. His entry showed up on the third page.

Chuck Bartlett
1969 Signal Red 4 Speed

bpossel:
Mike, I am using the Pertronix setup.  Here is how mine is setup.  Working great!

I did the following test, per the Pertronix website:

To determine if your systems coil is compatible with the Ignitor, some measurements should be taken prior to installation of the Ignitor. Caution… While performing this test, never leave the ignition switch on for more than 30 seconds at a time.

1. Set your voltmeter to a 15 or 20-volt scale. Attach an 18 or 20 AWG jumper wire from the negative coil terminal to an engine ground. Attach positive (red) lead of your voltmeter to the positive side of the coil, and the negative (black) lead to an engine ground. Turn the ignition switch to the run position. Now read the voltage at the positive coil terminal. Turn the ignition switch off. If the voltage measured is approximately 12 volts, no resistance wire is present. A typical resistance wire will provide 9 - 6 volts.

2.  The next step is to determine the resistance in the primary ignition. Label the wires attached to the coil terminals and note their appropriate location. Make sure that the ignition switch is off and disconnect all wires from the coil. Adjust your meter to the lowest ? ohm scale. If you are using an analog style meter make sure to zero the needle. Measure from the negative terminal to the positive terminal. Write your measurement down.

Now the maximum system amperage can be determined, divide your voltage measurement by your coil resistance measurement. This will give you the system current or amperage.
Four cylinder engines should not exceed 4 amps. Six and eight cylinder engines should not exceed 8.5 amps. If the total amperage in your system is higher than the amount recommended for your application, you should install a ballast resistor.

1. Example Voltage 12
2. Resistance 1.5
3. Total Amperage 8 (12 / 1.5)
NOTE: Total amperage 8 (this number must not exceed 8.5 !)

My reading was initially as follows (with MB Electronic Ignition):
1.  Voltage 3.48
2. Resistance 0.8
3. Total Amperage 4.35 (3.48/0.8)

I then removed the OE MB electronic ignition and the 0.4 ohm ballast.  Installed the 0.6 in place where the 0.4 ohm ballast was.

The reading was then:
1. Voltage 4.80
2. Resistance 0.8
3. Total Amperage 6.0 (4.80/0.8)

On March 25, 2006, I removed my Bosch ignition coil (silver in color with a red label) and replaced it with a new Bosch “Blue” coil, pn 0-221-119-027-740.  I also removed the 0.6 ohm ballast.  So in summary, am using blue coil and no ballast resistors at all.

My reading is now:
1. Voltage 11.92
2. Resistance 3.3
3. Total Amperage 3.61 (11.92/3.3)

Also note: I am using Bosch Spark Plugs W7DC (default gap .032).  Increased by + .006, as per Pertronix suggestion



bpossel  (Memphis, TN.)
'71 280SL  /  '97 E320

JimVillers:
My experience comes from the older cars.  The Black and Blue coils have about 4 ohms of internal resistance and they do not need an external resistor.  The red coil has about 2 ohms of internal resistance and it utilizes a 1.8 ohm external ballast resistor (total of about 4 ohms).

Ballast resistors reduce the current flow through the coil and thus reduce the heat generated within the coil.  So running the coil without the correct resistance, with or without a transistorizes ignition, will affect the longevity of the coil.

If you want a "hotter" spark, obtain a high performance coil and install it in accordance with its directions.  



Jim Villers
190SL, 230SL 5-Speed, 190E 2.3-16 Kompressor, MGB 5-Speed

mdsalemi:
Anyone have any printed Bosch documentation on coils?  I'm building a collection here and so far have three different "blue" coils; from three different countries.  One red coil.

I'd really like to see what Bosch says the specs are, maybe someone has some?

Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored

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