ballast resistors

[ja17]

quote:"Joe - would you please explain what the function of the ballast resistors is ?"

Hello Cees,
There is a lot of confusing information on these "ballast resistors". I thought a new topic may help collect the information for everyone.

I can add some photos and post more information and specs over the next few days as I search. I am sure others have good information to add also. I do have some good original Mercedes "Technical Training" literature on discription and troubleshooting (not in BBB) I can add to the string.

In general the ballast resistor cuts the voltage from 12 volts to a lower voltage going into the ignition coil. The reason for this is to lower the voltage going across the ignition points. A lower voltage creates less wear or pitting at the points. These ballast resistors are usually located on the wire going into the coil. These resistors have a resistance wire coil built inside them which lowers the voltage. They must handle a lot of heat so they are fairly large and are made of porceline. They are usually white or brown. The metal band has a ohm resistence value stamped on it. These ballasts resistors are designed to work with a specific ignition system (coil, points etc). Depending on which version is in your 113 these parts should be matched to the ignition. Often times replacement coils may be different from originals and the correct matched ballast resistor should also be changed.
Later W113 cars (69/70) 280-SL's had the factory transistorized ignitions which used two ballast resistors. A ignition by-pass circuit was added to their ignitions which simply by-passed one of the ballast resistors when the starter was engaged to aid in starting.
On standard early ignitions (non-transistorized), the minimum voltage at the outlet of the resistor is 8.5 volts. On the later factory transistorized ignitions, the minimum voltage at the positive terminal of the ignition coil (#15), *should read 2.3 to 3.5 volts (* MBNA Technical Training 496). You can see by these figures that the transistorized ignitions operate at a much lower voltage across the points so the points last much longer. These figures are correct for the original factory units. If the coils, ballast resistors or ignition systems have been changed to something other than original these values may no longer be relevant. (to be continued)


Joe Alexander
Blacklick, Ohio

[J. Huber]

Joe. Interesting topic -- thanks for the info. I look forward to hearing more. Out of curiosity, I went out to check my ballast set-up. I have an early 230SL but I know the coil and most likely resistors has been changed. I have the "red" label Bosch. I also have what appears to be the two-ballast setup. There are definitely two. I don't see any ohms or voltage info though, only the Bosch part numbers. Am I looking in the right place? Would part numbers reveal the specs of the ballasts??

Thanks.

James
63 230SL

[Cees Klumper]

With modern electronic ignition (without points) would it be ok to remove the ballast resistor from the set-up seeing there's no points to be concerned about? Would it help any in getting a more efficient / stronger spark?

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[Naj ✝︎]

JH
What are the part numbers on the ballast resistors?

Usually, on the early 113s (single resistor), you have one wire coming to the resistor from the ign. switch (on the terminal facing the firewall) and one going to the coil (terminal facing battery).
To cut out the ballast during cranking, one wire is added from the starter solenoid small terminal (which is energised during cranking) to the coil side terminal of the ballast resistor.
naj

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[n/a]

Cees, it depends on which electronic ignition set-up you get. I have used Pertronix on several occassions and prefer them to Mallory and others. I also add the hotter coil (Flame III, I think its called), along with upgraded plug wires to get the full effect, and I open up the plug gaps for a bigger spark kernel.

Anyway, Pertronix recommends removing/bypassing the resistor/resistor wire, but Mallory does not speak to it in their literature.

I've experimented and noticed a difference with/without the resistor... quicker starts, crisper throttle responce, and even better color on the spark plug electrodes. Have experienced no downsides on three different uses... a Porsche 2.0 liter, a Ford 427 FE block, and the big-ole 430 CI stove that powers my 62 Lincoln.

Just bought my 68 280sl last week, and plan the Pertronix upgrade at the end of season when I have better feel for how she performs before any mods.

Cheers!

Nervious Newbie `68 280sl

[J. Huber]

Hi Naj,

It looks something like this: on the top ballast, a wire comes in from the ignition side (off main bundle). The other side has a blue wire leading down to lower ballast. On the opposite side of lower, wire goes to coil. There is also a smallish wire on this side of coil that leads to small black nodule, #0 290 800 006  2.2** -- what would this bad boy be?

Top ballast reads: 0 227 901 013
Lower one reads:   224-509 050

Thanks

James
63 230SL

[Naj ✝︎]

JH,
The top ballast is 0.6 ohm. Cannot trace the second number (Please recheck). From what you say, the two are connected in series. For the red coil you need a 1.8 ohm ballast resistor so the second one may be 1.2 ohm to have the correct make-up.
The black box is an 'interference suppression' condenser to reduce radio crackling.
Clear as mud???
naj

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[J. Huber]

Hey Naj

Well, it really does seem to say 224 509, then in smaller numbers, 050. It appears to be original-looking to me. In reading up on the topic, I read that the early resistors were either .9 or 1 Ohm ... Could it be that the .6 was added to at least get close to 1.8??

In any case, the car has been starting quite well these days. I would attribute this to the new coil and the revamped cold-start system (thanks again Geo. D!)

Cheers

James
63 230SL

[Naj ✝︎]

JH
Yes, the early resistor with black coil is 0.9 ohm.


naj
'Kloines Scheisserle'
65 230SL
68 280SL

[J. Huber]

Ok next question then is:

If I wanted to bring my resistor in line with the red coil -- is it just a matter of ordering a 1.8 and hooking it up? one side to ignition, other to coil.  (Just use existing wire to coil?)

And what kind of  benefit would the 1.8 have over my cumulative 1.5? Longevity of points? even more oomph?

For less than 30 bucks it seems like a reasonable upgrade, if its that simple ...

James
63 230SL

[Naj ✝︎]

JH,
Higher resistance will reduce current to the coil and probably prolong point life.
All 1.8 ohm resistors I've seen have a reddish/'rose' fixing band around the ceramic.
Parts #s
Merc:   000 158 1745
Bosch: 0 227 901 014
Beru:   W2 18-2
naj

naj
'Kloines Scheisserle'
65 230SL
68 280SL

[ricoled]

After reading this thread, I went out and got a 'red label' coil which comes with a 1.8k resistor. Ironically, I got it from a VW shop and the owner told me that they (old-VW owners) don't usually make use of the 1.8k resistor.  Instead, thanks to Joe Alexander's post, I decided to avoid the confusion on resistor values and be guided by input voltage.

Using a typical voltmeter, I found that I had 8.5-9.0 volts at the 2 wire feed point normal running. Attaching the 1.8K resistor dropped the reading to 3.5 volts which ran as well, but which I considered too low to be getting a good spark from these supposedly hot coils.  I then connected the coil without a resistor, directly to the +/- wires and I am now very happy with the car's performance.  Easy starts, no misses and great plug burn color. The coil feels mildly warm, not hot, which is a good sign.  

As a finishing touch, I read a post that discussed platinum-tipped plugs.  I went ahead and got WR8DP which is a bit hotter than the usual WR7.  Now my engine sounds really healthy cruising at 3500-4000 rpm.  Yup, it really pays to read, analyze and DIY.  What a great group!  

[ja17]

Hello ricoled,
What model and year is your W113? do you have the standard ignition (non transistor ignition)? Let us know how the points hold up. Glad to see you are making progress!


Joe Alexander
Blacklick, Ohio

[rwaw]

Hello ricoled,

Do I understand you correctly when you're saying the ballast resistor can be left out the equation altogether ?
I fitted the red coil (genuinely red colour as well BTW) and 1.8 kOhm resistor a while ago.

Raoul.
280sl 1969 (Euro)

[Naj ✝︎]

I too would be interested to find out how those points hold out without the ballast resistor. I had my 230 running with a 0.9 ohm resistor and a red coil for a while and the points did not look very clever after a couple of hundred miles!
naj

'Kloines Scheisserle'
65 230SL
68 280SL

[Cees Klumper]

Any set of points I have looked at (not THAT many, but I figure at least five) all looked pitted, even though they were not worn. Do we have some pictures of what a set of worn vs. a set of "not new, but performing fine" points look like?

Cees Klumper in Amsterdam
'69 white 280 SL automatic

[bayleif]

When I first got my 280, it had a 051 distributor, a blue coil (not just the label, the whole thing) and a .4 - .6 ohm resistor in series. It also came with an intermittent miss. In the course of time, the .4 ohm burnt out. It was not the Mercedes .4 ohm and was obviously added as an after thought. When I jumpered around the resister leaving only the .6 in place, the car could not run sufficiently to get me home. It missed and sounded like the timing was really hosed.
I ordered a new resistor and a coil giving the dealer only model and year since I didn't know any better. The coil was silver; I don't know the number off hand but I assume it is the newer "hotter" coil that is used with the transistorized ignition. The logical choice since I also ordered the .4 ohm resister. But my car didn't have the transistorized ignition.
It ran the same as before. And oddly enough, it could run at all with anything less then the total 1 ohm resistance. Eventually, thanks to this list, I ordered the "red label" coil and the 1.8 ohm. Since then, all ignition problems have been solved.
I don't know why the car couldn't run with the smaller resistance. You would have thought that as long as the point weren't burnt out, it would have made the spark stronger. I suspect that maybe the higher voltage caused some arching either where the wire goes from the coil to the points through the stud in the distributor or perhaps in the condenser (which I had also changed). Anyway, the moral of the story, at least for me, is to go original and get it working. Then maybe try making changes to see if it runs better.


Chuck Bartlett
1969 Signal Red 4 Speed

[George Davis]

My 12 cents worth:

I go along with Chuck, only maybe a little more so.  Original is good; modifications are ok as long as they are tried and proven;  experimentation is fun, but things get fried once in a while.  I have a lot to learn about ignition systems, but I've always understood that the correct ballast resistor is necessary to help keep the coil alive.  The coils we typically use are designed for lower voltage rather than the 12-13.5 volts from the battery.  Higher voltage makes them run hotter and shortens their life.  They do give a hotter spark when they get 12 volts, though, so starting may be easier.  Many cars, including maybe the later 113s (?), bypass the ballast during cranking to get a hotter spark for starting, but as soon as the key is released, the ballast is no longer bypassed.  Best of both worlds there, hot spark to start, but long coil life.

There are coils that are designed to run without an external ballast resistor.  These coils either have an internal resistor, or are designed for the full 12 volts (not sure about the latter, maybe they all have internal resistors ?).

Last, and I know many will disagree with this (especially companies that market high perf ignition systems!), but there is little or no power to be gained from a hotter ignition system, IF the stock system is working well.  In 30+ year old cars, it's quite conceivable that many of these ignitions are no longer doing the best job, so replacement may make a big difference.  If you put in a hot coil and the car really perks up, there was probably something wrong with the old system.  Which is not to say a hot coil is a bad thing - I use a red coil, too; but it made no difference in how the car ran.


George Davis
'69 280 SL Euro manual

[ja17]

Hello ricoled,
George makes a good point here. Running without the designed ballast resistor could be hard on other componants of the system (points, coil). Be careful that you are not compensating for the real undetected problem like bad plug wires or plug wire ends, coil wire etc. Keep us up to date.

Joe Alexander
Blacklick, Ohio

[ricoled]

Hi Everyone  
As far as I know, Bosch has 2 types of silver casing coils.  One explicitly says "For Transistorized Ignition Systems" on the label. I initially bought this coil (didn't come with a resistor) thinking I could make it work.  The other silver casing (w/red label) coil is for non-transistorized systems which is the correct type for my car.

The transistorized coil cannot take more than 4 volts at its input.  It will heat up like a toaster and burn-up the windings inside. Happened to me[:p] I experimented by using a resistor w/ 2.3K value, dropping feed voltage to 2.7 volts.  It worked OK, but the car started with difficulty and forcing an incorrect component didn't sit well with me. The other coil is rated 12V (30kv spark) and I figured that 8.5 volts is sufficient voltage to get a decent spark out of the coil.  Had I used the resistor, I would have been feeding it much less voltage and likely getting less spark.  

There are other factors that affect spark - such as dwell or hi-tension wires.  Whether a hotter spark makes a difference?  I believe it does - I've cured the misses at idling and acceleration.  And when I turn the headlights on, the idling no longer gets rough.  I do not recommend to do away with resistors.  My car is peculiar in that it feeds the proper voltage without having need for a resistor. Until I get to the root of its peculiarity, I will leave the setup this way.

I agree that if my ignition system was at optimum, changing the coil would not have made any difference.  I suspect my previous coil wasn't up to the task anymore (Bosch blue circa 1974).

In general, driving my 113 has always been a pleasant, exhilarating experience, and we all work hard at making our rides better. If part of the improvement called for a new set of points every 5000 kms, so be it! I don't want to get bogged down with perfecting the car when I'm missing out on the best part - which is driving it!  Thanks!

Martin

[ja17]

Hello Martin,
The 8.5 to 9.0 volts falls into the correct specs for the non-transistorized ignitions, so you may be ok? Some coils have built in resitance. As you mentioned real problems occure when people incorrectly combine parts from the transistorized and standard ignitions. Keep us up to date.



Joe Alexander
Blacklick, Ohio