COILS and BALLASTS Redux

[mdsalemi]

Hello All,

I recently installed a new Bosch RED coil.  Following the instructions er warning about using a 1.6 ohm resistor, I did that.  That dropped the primary voltage at the coil to about 5.2 volts.

If you use the Bosch Blue coil, I think you'd have the .9 ohm resistor by spec, and about 8.9 volts at the primary.

Now--if the RED coil is a 26,000 volt coil, and the BLUE coil is a 19,000 volt coil (I may be off on these numbers, but we know RED is higher then BLUE) BUT you lower the input voltage to the RED by using a higher-resistance ballast, aren't you somewhat negating any effect of a hotter coil by lowering the input voltage?  Though I have not seen all their measurements yet, I'd be willing to bet that the "hotter" red coil with the specified 1.6 ohm ballast put out lower high voltage then the BLUE with a .9.  I'll be bringing my spare ballasts and coils with me next week when I pick up the car.

This question has come up because my mechanic who has the car now has it running well (yeah, for once!) but isn't happy with the voltage to the spark plugs--he wants it higher.

I'm tempted to put the .9 ohm resistor in to bump up the primary voltage.

Any thoughts on this?

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

[n/a]

Dear Mike,
Be careful about this...I recently helped a friend with a 280SL by writing a report as an expert witness (I helped win the largest Lemon Case in the US against Rolls Royce for over $400K!) in a court case against a mechanic who put in a blue coil with the lower impedance ballast...the car kept dying about a few days use. The primary resistance of the coil used for transistorized ignitions was 0.6 ohms, and the one for points about 3-4 ohms. Current is limited in an elecronic ignition by proper bias of the switching pass transistor and in some cases a series emitter resistance. In any case, the use of the wrong coil can send over 20 amps through your points, pitting and melting them, melting the rubbing block and throwing off timing/dwell, and cooking your wiring harness and leaving you stranded or causing a fire. If you wish to bump up the output on the secondary, you may wish to do what I did. I retained the points but put in an electronic capacitive discharge switch made by MSD, model 6A, PN 6200. This sucker, with its coil, will knock you on your rear end flat and cook your pacemaker, putting out well over 30-40kV, AND you keep the points...in fact, my point gap/dwell angle hasn't changed appreciably in over a year with this setup and if the unit fails, I can divert full current through the points and go back to a conventional ignition. The std. points pass milliamps to trigger the MSD. I think I spent $150 at a local speed shop for everything and installed it in 30 minutes. Also yields a decaying series of multiple sparks...more power, better economy, smoother running. Go to
http://www.msdignition.com/ignition_4_6200.htm
Trust me, you will be very, very happy. Good luck.
Best Regards,
Joe  
P.S. MSD also has 6 to 12VDC inverters as well
 

[n/a]

Hey Mike,
Here's pdf manuel for you and your mechanic to look at if you are thinking about an MSD...
http://www.msdignition.com/pdf/6%20series/6series.pdf
Again, good luck.
Regards,
Joe
 

[hands_aus]

Hey Michael,
What switching/points system do you have now?
points with MB electronic box under battery?
points without MB electronic box?
Pertronix with MB box disconnected?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[bpossel]

I am very interested in this post and how others have their system setup.

I am using the Pertronix with no ballast resistors (MB electronic ignition box removed and stored).  Earlier this spring, I swapped 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 remaining 0.6 ohm ballast.  So in summary, using blue coil and no ballast resistors at all.

My readings are as follows:
1. Voltage 11.92 (at positive coil terminal)
2. Resistance 3.3 (at primary ignition)
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

Will this setup cause any problems in the long run?  Car has preformed well with this setup, so far.  I have felt the coil after a long run and feels "warm" to the touch, not hot.

How do others have their systems setup?  I find the MSD article from Joe Bango very interesting...



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

[n/a]

Dear Bob,
I don't think you will have a problem. The Pertronix trigger is a "Hall Effect" device, which occurs when a magnetic field is normal or perpendicular to a conductive sheet of metal, so named after Edwin Hall who observed the phenomenon in 1879.

Download Attachment: Hall-effect.jpg
21.03 KB

Anyway, since the voltage induced by the magnetic field from the magnet ring placed on the distributor shaft is amplified and used to bias and trigger a high current pass transistor in the main Pertronix "box", current to the coil will be limited as this would have been taken into consideration. Your numbers look good. While I'm unsure what the Pertronix circuitry looks like, it may be possible that the circuit could tweak itself to a given coil by looking at the load and inductive "kick" of the secondary field when it falls and it's mutual inductance change on the primary...a lot of mumbo jumbo to say yes it possible to use different coils with these aftermarket ignition conversions and have things work OK.

Here's a picture of a pertronix on a MB Ponton distributor;

Download Attachment: pertdist.jpg
25.3 KB

BTW, For more info on this Ponton install, go to
http://www.mbzponton.org/valueadded/maintenance/ignitionpert/ignitionpert.htm

Anyway Bob, I would not worry about your setup an not having a ballast. The only time I believe one has to be real careful is if you keep your points and mix parts intended for an electronic ignition. Hope this helps.
R/
Joe

[n/a]

Oops!...Hall Effect diagram didn't upload right...try this
R/
Joe

Download Attachment: Hall-effect.jpg
17.1 KB

[bpossel]

Thanks Joe!  I can rest easier now...
Bob


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

[mdsalemi]

Sorry guys--was away for a few days.

My car does NOT have the factory electronic ignition.  It WAS equipped with the Crane, but that has since been replaced; the distributor rebuilt, and the Pertronix put in its place.  W/O the factory electronic, I don't think I have any "bypass" of the ballast.

The "original" setup was a Blue coil with a .9 ballast.  5 years ago this worked great--for 30 miles.  Points fried, and restorer installed the Crane.  That worked great for 5 years until this past January when I started having problems.  I THINK the ignition loss was the wires internal to the distributor collided with the optical trigger wheel; this made the wheel stop and ignition loss.  I saw some "cutting" of the insulation on the wires and could not tuck them out of the way; remember the breaker plate moves with advance.  Not absolutely certain, but one by one I began to change EVERYTHING in the ignition system.

The Pertronix is a neater install, and worked well, but the "low voltage" is one mechanic's opinion based on his connecting a scope to the whole thing.  He says the car is running beautifully now (he said he found something miswired and richened the mixture a bit) but wants to see higher voltage at the plugs.

With the old Blue coil, I had over about 7.8v (.9 ballast); 8.9v (.6 ballast)and with the 1.6 ballast feeding the new red coil, the primary voltage is down to 5.2.

The lower the primary voltage, means the lower the high-tension on the spark plug side.  I don't know if I should go higher or not.

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

[n/a]

Dear Mike,
What does the mechanic feel is a low secondary? 20-30kV should be OK. Did he measure the secondary on a scope? Is his setup accurate? I would say you are safe going to a low impedance ballast so that your secondary output is higher. Check the Pertronix installation manuel...it may recommend not even using a ballast. (I wouldn't remove it, just jumper it). A ballast is principally used to reduce the coil voltage when running as opposed to starting. When starting, the voltage drop due to the cranking starter motor drops the available potential to the coil, in addition to the fact that a hotter spark can help ignite a rich mixture in a choked engine. In any event, most electronic ignition have a voltage regulator which will yield a constant voltage to the coil regardless of the input power to the amplifier unit, within reason of course! You're not going to get 8 volts to the coil with a battery at 6...although, and that's a different story, you could with an inverter!

Anyway, go with the lowest ballast resistance and/or check the pertronix installation guide...better yet, email the company. You really may be able to bypass the ballast. I am confused about one thing. I only see listed two ballasts for this car, 0.4 ohms P/N 0.227.90.012 and one for 0.6 ohms, P/N 0.227.901.013. Which do you have? I get roughly the same figures you do if I assume a blue coil primary at 0.6 ohms, and a ballast at 0.4 ohms, and input voltage or EMF of 12. Using voltage divider, Eout=Ein (R2/R1+R2), with R2 being the coil, R1 the ballast...equals 7.2 volts. This can vary a bit depending on battery voltage, which is not really 12 volts exactly, really 2.15 volts/cell. But were splitting hairs here. Just curious on exactly what you have...oh, with the pertronix, I don't see a problem going back to a "blue" coil. I just would never advise that if one was keeping thier points, unless you use the MSD like I did...

R/
Joe
 

[J. Huber]

Hi Michael. Nothing to add really -- but throughout this discussion I see reference to 1.6 ohm resistor. Do you mean 1.8? Just because that's the one I had always heard goes best with the red coil. I don't think our parts guys sell a 1.6 just .9, .6 and 1.8. So I bet that's the one you are using. Just checking.

Ok while I am here I'll tell you my experience with all this. I had the original coil (black I believe) for many years. The ballast was .9 ohm. The car had its good moments during these years but to be honest, it seemed to need tune-ups often... Then, about 8 years ago we moved from civilization to the country -- and fearfully I took my car to a local shop. The guy knew 113s and used to have one (yeah)... Among the many things he did immediately was replace the coil with a red one and he added a .6 to my .9 making 1.5. The car was transformed! I still had a few cold start issues later (resolved with a new TTS) but overall the car has run great. Hard to say how much of this was red coil-related but I think it was a factor.

Oh, and I recently replaced the 2 ballasts (9&6) with one 1.8. No noticeable difference except the engine bay looks tidier.

James
63 230SL

[hands_aus]

Michael
If the new coil is one for transistorised ignitions it will have a higher internal resistance and combined with the 1.6 ohm resistor may be lowering the input voltage too much.
There could be a resistor symbol on the coil (and or coil box) with a number near it indicating the internal resistance value.

You need a coil for normal ignitions.

You should be able to expect full voltage out of the new hotter coil.
The Pertronix unit is designed to operate with their own high energy coils.

I would try the 0.9 ohm resistor and test what the voltage is and then take the car for a drive.
If it isn't doing what you want, then try the 0.6 ohm resistor and repeat the process.



Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[mdsalemi]

Some updates to this and earlier posts on similar:

1)  My DYING issue.  This may have been solved.  The Crane ignition system which had been in for 5 years and working well for most of that time might have been the culprit.  What there was evidence of is the plastic shutter wheel which fits over the distributor shaft may have been making contact with the insulation jacket around the wires that go to the optical assembly.  Since this wheel doesn't fit very firmly--held on by spring clips--if contacting a fixed object it might very well simply spin around on the shaft.  If that was the case, it would have prevented spark.  Try as I might I could not seem to tuck these wires out of the way--they kept spring back too darn close to the plastic shutter wheel.  The cut marks indicate something hit the wire.

2)  COIL/BALLAST  Mechanic simply bypassed the ballast, providing full voltage to the coil.  With the RED coil and the 1.8 ohm resistor, I was only getting 5.2 V at the coil primary.  Mechanic wanted to see more.  With the ballast bypassed we have 12V+ of course, and a 23kV spark as seen on the scope.  I ran home on the highway yesterday about 40 miles, at 90 degree ambient temperature, and at about 70 MPH.  I checked the temps inside the engine bay via infrared thermometer: inner fender wall (ambient) temperature, 115.  Coil case, 126.  Valve cover, 165.  I don't think this is excessive heat for the coil, so maybe the no ballast will be OK.

3)  RUNNABILITY.  I had mentioned in earler posts that at steady state 45mph, non-accelerating, I was having minor misfiring and backfiring.  Pete Lesler (National MBCA guy and long-time 113 expert)indicated it might be too lean in the mid-range.  Mechanic independently came to the same conclusion, richened up the mid range a bit, and this problem went away.

4)  CRANE vs. PERTRONIX.  Well, after item #1 above, I removed the Crane, only to find that it violates the integrity of the 051 distributor: the shutter wheel contacts the points pivot pin, thus this has to be removed to install the Crane on the 051.  Once you remove the pivot pin you can't go back to points OR the Pertronix so my advice is DON'T DO IT!!!  It may not have to be done on all distributors, but certainly on the 051.  I luckily had the distributor rebuilt with the right pin replaced, went to Pertronix and so far so good.

Mechanic also adjusted the shift rod and now there's a smoother shifting of the automatic.  Sadly, they discovered leaking at the transmission modulator and rear main seal, so back it goes after some events in the next week.  I hate leaks.

Will be going back and forth to Dr. Benz' place this weekend for Meeting of the Clans, so the car will get a good work out.

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

[Naj ✝︎]

Hello, Michael,
Glad to know your car's now sorted.
 

quote:1) My DYING issue. This may have been solved. The Crane ignition system which had been in for 5 years and working well for most of that time might have been the culprit. What there was evidence of is the plastic shutter wheel which fits over the distributor shaft may have been making contact with the insulation jacket around the wires that go to the optical assembly. Since this wheel doesn't fit very firmly--held on by spring clips--if contacting a fixed object it might very well simply spin around on the shaft. If that was the case, it would have prevented spark. Try as I might I could not seem to tuck these wires out of the way--they kept spring back too darn close to the plastic shutter wheel. The cut marks indicate something hit the wire.

Here's a picture of a Crane system installed in an '051' distributor.
Using the smaller of the two 6 slotted wheels means you can retain the post for the points and have enough room for the wiring.Hopefully it will save others from the problems you've had.

http://www.sl113.org/forums/uploaded/naj/200551573055_Tim209.JPG

naj

68 280SL