Author Topic: Symptoms of ballast resistor failure ? (Read 29637 times)

Ben · « **on:** February 02, 2005, 08:59:09 »

Just curious really !

My 230 has a very old coil and resisitor and having largely sorted out any starting problems recently I now discovere that if I twist the ignition key it will turn over and only fire the instant I release the key !

Meaning I could sit for 5 seconds spinning the starter, let go the key and it'll start, or I can try to get the starter spinning as little as possible and it'll start !

I wondered about the ballast resistor and to be honest its so long ago since I learnt any of this stuff I cant remember it function and now I've started to doubt anything I do think I know !

Anyone care to explain ?

Regards,
Ben in Ireland.
'64 230SL 4sp.

George Davis · « **Reply #1 on:** February 02, 2005, 09:25:49 »

Ben,

I think it goes like this: most ignition coils are designed to operate at less than full battery voltage, like in the 6-8 volts range. During normal running, which is any time EXCEPT when you are cranking, the ballast resistor is in the circuit. It's job is to reduce battery voltage to 6-8 volts. However, for starting a hotter spark is desirable, so during cranking the ballast resistor is typically bypassed so the coil gets full voltage to temporarily make a hotter spark. As soon as the key is released, the ballast is back in the circuit.

So I'd say yours is good. I'd expect the symptoms of failure to be no spark except during cranking. So the engine might fire, but die as soon as you release the key. If the resistor somehow managed to short-circuit so it no longer provided resistance but still allowed current to flow, it would run well until the coil failed prematurely from overheating.

George Davis
'69 280 SL Euro manual

George Davis · « **Reply #2 on:** February 02, 2005, 09:32:40 »

Interestingly, the circuit diagram for the 280 SL doesn't show any ballast resistor by-pass during cranking, so that part apparently does't apply to these beasts.

George Davis
'69 280 SL Euro manual

A Dalton · « **Reply #3 on:** February 02, 2005, 09:46:34 »

Ballast on .042 is in the start/run circuit all the time.
Your problem is most likely a worn rotor buss bar in the ignition sw.

J. Huber · « **Reply #4 on:** February 02, 2005, 09:49:24 »

Hi Ben, nothing to add really except that I think the ballasts tend to last a long time. I have my original (a .9 ohm).

What's noteworthy is somewhere along the line my mechanic added a .6 in series with the .9. Thus, I have a 1.5. This is alongside a Red Coil. Most people recommend the 1.8 with the red but I have had no problems. Which coil & ballast are you using?

James
63 230SL

Naj ✝︎ · « **Reply #5 on:** February 02, 2005, 11:06:05 »

Ben,
I suspect you ign. switch as well.
Rig a test lamp to the ballast and see if it lights up while cranking.
Some late cars did have an arrangement to cut out the ballast resistor during cranking but even my '68 280 does not have it. Worth considering though; good for winter cold starts. I regularly use a jumper to bypass the ballast when I start the car on a cold day after its been sitting a few weeks.
I believe one of the cold start relays has power when cranking and could operate a relay to cut out the ballast. Have looked at wiring diagrams but not gone any further.
Happy fixing.
naj

65 230SL
68 280SL

Benz Dr. · « **Reply #6 on:** February 02, 2005, 11:52:29 »

The ballast resistor protects the coil from over heating if you leave the key on and the engine isn't running. The coil will get hot but would get very hot without one - running or not.

Daniel G Caron

A Dalton · « **Reply #7 on:** February 02, 2005, 12:18:20 »

quote:
Originally posted by naj

Ben,
I suspect you ign. switch as well.
Rig a test lamp to the ballast and see if it lights up while cranking.
Some late cars did have an arrangement to cut out the ballast resistor during cranking but even my '68 280 does not have it. Worth considering though; good for winter cold starts. I regularly use a jumper to bypass the ballast when I start the car on a cold day after its been sitting a few weeks.
I believe one of the cold start relays has power when cranking and could operate a relay to cut out the ballast. Have looked at wiring diagrams but not gone any further.
Happy fixing.
naj

65 230SL
68 280SL

Living in the cold NE , it was common on the old 108 injected models [ same system] to run a wire from the TTS switch terminal "G" to the coil pos +.
This jumpered the ballast only when cranking the engine over .
The main reason US cars used this system was b/c when cranking , there is a voltage drop due to the starter draw, so between that draw and ign feed going through the ballast , the coil gets too low a voltage for solid ignition when cranking, specially in the Winter.
Remember , there should be NO overlap of voltage to the coil/ballast on a 113 regardless of the ign sw being in the Start or Run positions.. if there is , you have worn contacts in the sw section of the ign switch.
As stated , a simple 12v test lamp and turning of the key to each position and back will verify this fault.

ja17 · « **Reply #8 on:** February 02, 2005, 18:00:13 »

Hello,
Only the later 280-SL has the ballast resistor bypass. I believe it is on the cars with the factory electronic ignitions? The 230-SL and 250-SL do not have a ballast resistor by-pass.

One way to check the ignition switch; run a hot wire from the + side of the battery to the + side of the coil. Try to start the car, if it contiues to run as long as the jumper wire is on,you may have a bad ignition switch.

The electrical part of the ignition switch can be replaced without disturbing the steering lock assembly or the key assembly. Three screws hold the electrical switch on the back of the assembly.

Joe Alexander
Blacklick, Ohio

ja17 · « **Reply #9 on:** February 02, 2005, 18:12:37 »

Hello,
You may be interested to know that the switch or relay which actually operates the ballast resistor by-pass on the later 280 SLs, is actually the engine starter solenoid!
These later heavy duty starters have an second small terminal on the solenoid which sends current directly to the ignition coil bypassing the ballast resistor when the starter is engaged!

These later starters are about .4 horse power stronger. They fit earlier engines also. They really spin the engine a lot faster especially during cold weather. These starters are used in most era common sedans after 1969. Every W113 owner with the early starter, should have one of these later starters on their donor car shopping list!

There is an easy way to identify these without taking them out of the car. Look for that second small wire on the starter solenoid. I can post pictures of each type if anyone is interested.

Joe Alexander
Blacklick, Ohio

George Davis · « **Reply #10 on:** February 02, 2005, 19:22:57 »

Naj, your manual ballast by-pass is a great idea, thanks! I may give it a try to see if speeds starting, and if it does, then I'll wire in a by-pass.

Joe, would the starter from '74 240D be among the ones you recommended? Thanks!

George Davis
'69 280 SL Euro manual

ja17 · « **Reply #11 on:** February 02, 2005, 21:27:27 »

Hello George,
No the starters from the diesels are completly different.
The 0.8 HP starter used in the pre 1970 Mercedes gasoline cars was replaced by a 1.4 HP in all Mercedes after 1969 sometime. 75% More horse power! The physical size is about the same, just a bit larger.

So all the W113 SLs had the 0.8 except the late 280SLs 1970, 1971 (possibly some 1969). They bolt right up. The solenoid as metioned has an additional terminal for the ignition bypass.

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starter 2.JPG
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Joe Alexander
Blacklick, Ohio

George Davis · « **Reply #12 on:** February 03, 2005, 14:42:37 »

Joe, rats, but thanks for the info!

From Joe: "Hello George,
No the starters from the diesels are completly different."

George Davis
'69 280 SL Euro manual

Ben · « **Reply #13 on:** February 04, 2005, 06:56:47 »

This is all great info guys !

I think I'll print this off and go checking tomorrow !

Regards,
Ben in Ireland.
'64 230SL 4sp.

knirk · « **Reply #14 on:** June 10, 2005, 13:37:30 »

Nice weather in Norway to day so I went for a spin. Driving up a hill on a rough gravel road the engine started to sputter and almost died. Then it ran nice for a while before starting to run very rough again. I made it home and immediately suspected a fuel problem since it happened when the car was shaking a lot. I emptied the fuel tank and cleaned the filter on the fuel drain plug. Also disconnected the fuel hoses from the fuel filter and fuel tank and blew through with air. Finally changed the fuel filter and tried to fire it up. Nothing happened. But after a while the ballast resistor started to smoke. It was really hot. After removing the resistor I connected the cables directly and the engine fired up and ran like a dream.

Could the engine sputter earlier be related to the ballast resistor starting to fail?
If I run the engine without the resistor in place will I destroy any of the other ignition parts?
I have a Crane optical ignition system, the coil is black, and the ballast resistor is marked WZ 09. I guess this means 0.9 ohm.

From SLS spare part list the available resistors are 0.6 ohm silver TSZ, 0.4 ohm, 1.8 ohm red, 1.8 ohm silver. Which one should I order?

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ballast.jpg
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Per G. Birkeland
69 280 sl aut 834
Norway

George Davis · « **Reply #15 on:** June 10, 2005, 14:12:20 »

Per,

you need the 0.9 ohm ballast resistor. I just checked SLS and they list it.

Added: running without the ballast will eventually damage the coil, but I don't know how long it will last without it. I wouldn't drive it this way, personally.

George Davis
'69 280 SL Euro manual

knirk · « **Reply #16 on:** June 10, 2005, 15:49:11 »

Thanks George,
I normally select the English version on SLS. When I checked the ballast resistors in the German version the 0.9 ohm type showed up. There are obviously some mistakes in the translation.

Per G. Birkeland
69 280 sl aut 834
Norway

knirk · « **Reply #17 on:** June 16, 2005, 02:48:57 »

Ben, did you figure out what your problem was?

Per G. Birkeland
69 280 sl aut 834
Norway

knirk · « **Reply #18 on:** June 16, 2005, 08:10:14 »

In my case it was not the ballast resistor.
The resistor started to smoke and went very hot during a start attempt – so I ordered a new one. While waiting for the new I tried to start the engine by use of some other ballast resistors I had lying around, without success. I needed to bypass the resistor to get the engine running. I got a new one today and while changing it I removed fuse number 4, fuel pump, to check the voltage to the coil without the fuel being pumped into the engine. Then I discovered that fuse number 6, relay for starter valve and relay for rich mixture, was blown. When replaced everything worked. I checked the old resistor and it was OK. I guess the smoking resistor was due to current going in to the resistor and not coming through to the coil since the fuse was blown. Lesson learned – always check the fuses first.

Per G. Birkeland
69 280 sl aut 834
Norway

Bearcat · « **Reply #19 on:** June 16, 2005, 09:38:03 »

ehh sorry to be a pain but dont we have cb's in aircraft and fuses in cars?

(tin hat on....could'nt resist it!)

knirk · « **Reply #20 on:** June 16, 2005, 11:02:34 »

Yepp you're right - it's edited. I work with aircraft that's why....

Per G. Birkeland
69 280 sl aut 834
Norway

Naj ✝︎ · « **Reply #21 on:** June 16, 2005, 12:33:02 »

Just wondered if the early 'open back' ballasts become more resistant with age/corrosion/moisture attack thus allowing less current thru and causing hard starting etc?

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This one from my 230 does not look too bad though after 40 years +

naj

65 230SL
68 280SL

hands_aus · « **Reply #22 on:** June 17, 2005, 03:25:49 »

This sure proves the worth of the start system.

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

Ben · « **Reply #23 on:** June 20, 2005, 06:44:59 »

quote:
Ben, did you figure out what your problem was?

.........I never actually checked it out !!

I did a lot of other testing with the CSV and Warm Up Device. In the end I added a shim under the WRD, changed some settings and now the car starts instantly,hot or cold. I have the car 43 years and its now better than ever before !

I'm not touching anything !!

Regards,
Ben in Ireland.
'64 230SL 4sp.

Ricardo · « **Reply #24 on:** June 20, 2005, 07:34:54 »

43 years Ben....a very early prototype then??

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Author Topic: Symptoms of ballast resistor failure ? (Read 29637 times)

Ben

George Davis

George Davis

A Dalton

A Dalton

George Davis

George Davis

Ben

knirk

George Davis

knirk

knirk

knirk

Bearcat

knirk

Ben

Ricardo