That's battery cable you have there , it is WAYYYYY overkill for an alternator .

10 gauge is all you needed between the alternator and battery .

Take your measured & cut cables & ends to a Welding Shop and have them solder the ends on , it'll pass 100 % of the current , unlike crimping .

Resists corrosion too .

Myself , I like to make up my own 0 gauge battery cables using welding cable as it carries even more current than what you have there .

You should also add a second ground strap from the nagative battery post , to the engine ~ I solder it right into the battery clamp when I'm making the cables ~ this simple upgrade will improve starter cranking speed and raise the charging voltage & amperage too , mosre than you can possiby imagine until you've tried it .

Mercedes uses ONLY copper wires *but* they cheaped out and used 4 gauge battery cables and this is a pinch point in your charging and starting systms .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Looks like 0 gauge to me (also referred to as 1/0). However the stuff you have appears to be the really stiff kind, due to the smaller number of strands. If so, I would not use it to connect to the alternator, because the engine moves around and the wire may not be flexible enough to deal with the movement. I used "car stereo" wire which has many more strands and is as flexible as a wet noodle. Welding cable is the same way, highly stranded, very soft & flexible.

The really stiff "battery cable" wire is ok for fixed items (i.e., battery to distribution block) but not between a fixed item (body/frame) and a movable item (engine/alternator/starter). It tends to be a lot cheaper than either car stereo wire or welding wire but I would not use battery cable for the alternator.

10 gauge cable is fine for a tiny stock alternator around 55A, if you use two 10 ga cables.

Remember the discussion here is for a 115A alternator (or larger) and 10ga is completely inadequate for those applications. maurinquina is installing a 150A alternator for his W126. This needs 4ga minimum.

Ypu're way wrong there as 4 gauge is considered fine to handle 500 amps to the starter .

I too run high output alternators in some of my vehicles but 0 gauge to the alternator is silly and means you don't understand the basic concepts here .

-Nate

Apples and oranges, my friend. And your data is slightly off. Per the W124 ETM, the wire size to the starter is 25mm˛, which is approximately 3 gauge AWG. And the starter doesn't pull 500 amps. I've measured the current with a Fluke inductive DC ammeter, it's generally around 300 or so. The starter load is not continuous, it usually only lasts a few seconds. Wire size is determined by multiple factors, including (but not limited to) intermittent load, continous load, thermal rating of the insulation, conductor material (Cu vs Al), ambient temperature, length of conductor, and desired voltage drop.



Zero gauge to the alternator is overkill (even for 150A), however it does almost entirely eliminate voltage drop, particularly in high temperatures. Mercedes used a pair of 10ga wires for their early 124's with 70A alternators, and a single 8ga for later 90A alternators. For a 150A alternator, a single 4ga would be the correct minimum size. Plus, 4ga wire is very commonly available from car stereo shops. While a 6ga wire might be barely adequate, it's also an oddball size, difficult to find connectors for, etc. 4ga simply makes sense. A smaller cable will run hotter given the same load, and will have more voltage drop. But hey, maybe I don't understand the concepts here.



Some assorted reference material that others may find interesting:

Metric (mm˛) to AWG conversion chart:
http://www.technick.net/public/code/cp_dpage.php?aiocp_dp=guide_awg_to_metric

Battery/inverter cable sizing chart (in Russian, use Chrome to auto-translate)
http://www.solarhome.ru/en/basics/batteries/sizing_cables.htm

Wire gauge current limits - note the huge difference between chassis wiring & power transmission:
https://www.eol.ucar.edu/rtf/facilities/isff/LOCAL_access_only/Wire_Size.htm

Copper conductor current capacities, note the variation based on insulaton rated temperature:
http://www.multicable.com/Content/Current_Carrying_Capacity_of_Copper_Conductors.asp

__________________
Dave
Boise, ID
Check out my website photos, documents, and movies!

While we are on gauge of wires used. Anyone know what gauge the battery cables are (ground and the one between battery + and starter)?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

From where I read ;

You're agreeing with me that 0 gauge is overkill....

Maybe we're both on the same page but say it differently .

I never said an OM617 draws 500 amps but many big V-8's certainly do so on 4 gauge battery cables .

Of course , I usually replace all factory battery cables with custom made 0 or 1 gauges ones as they remove all resistance as you and I both mentioned .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Stock , 4 gauge , nowhere near sufficient IMO .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

[QUOTE=gsxr;3046977][QUOTE=vwnate1;3046774] Ypu're way wrong there as 4 gauge is considered fine to handle 500 amps to the starter .Thanks for all your input, guys. I decided to use 2 gauge wire and 16 gauge for the alternator and 4 gauge for the starter. My logic is that if Mercedes put in a thinner gauge wire with the 70amp alternator and it worked fine for 21 years then 150amp alternator which is almost twice as much as the 70 amp alternator should have a wire twice as big. The 2 gauge is more than twice the size of the original wire. I will try this arrangement and if I notice significant voltage drop then I will resort to 0 gauge but this time with the flexible variation. I do agree with the statement that 0 gauge would eliminate voltage drop because the supply to demand would be transferred immediately without hindrance by smaller gauge wires. I will post pictures soon. Btw I will also clean all grounding straps.

When I upgraded my "84 Euro TD to an oversize alternator, I used a 4 guage Wal-mart battery cable containing a stamped-loop sheet-metal terminal. The cable lug fit perfectly on the 8mm B+ stud of my starter solenoid.
Then I cut the loop off the new cable's battery-terminal, leaving only the one 6mm lug from the battery-terminal-bolt attached to the cable. This lug exactly fit the 6mm B+ stud on the new alternator.
Finally, I used the leftover battery-terminal loop, and a bit of rubber fuel-hose, to support & isolate the middle of the new cable at the point where the support-bracket bolts to the bottom of the intake manifold. I did need to enlarge the 6mm bolt hole in the loop to fit the 8mm bracket-bolt.
My TD is non-turbo. If yours has a turbo, you may need to route your new B+ cable differently.

Happy Motoring, Mark

__________________
DrDKW

I am answering my own question. Per the FSM wiring diag, the battery cables are 25, I assume that's in square mm of cross sectional area, which converts to a little under 0.229 " in diameter. 0.229" diameter seems small to me for the battery cable. What do you guys think? I have a spare cable I will cut and measure.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

How many strands is the cable and what is the diameter of the copper bundle? Should be 0.325" diameter if 1/0 AWG. In your first pic, it looks like it has a lot more strands than a battery cable, also much larger AWG than a battery cable, which is 3 AWG if I am translating the numbers in the FSM correctly.

Maybe you want to make a super battery cable out of it?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Per the link I posted previously, 25mm˛ is approximately a 3ga AWG wire and yes, it would be roughly 0.22" diameter (NOT including the insulation). The number of strands will vary greatly depending on the exact wire used. Typical battery cable has a relatively low number of strands and is not very flexible.

I've been debating about the second ground strap to engine idea that you mentioned. I think I'll give it a try because it does make sense. The only other ground strap that I know of is the one from the engine to the transmission. Having another ground strap can only better the charging system. I have found a flag terminal which I'm thinking about using (picture below post). Two terminals to solder the ground wire to chassis and then the other ground wire going to the block. The chassis ground for the negative is a few inches from the negative post of the battery on the W126's which I have (1991 420SEL) so that'll be a short wire.

Can you tell me where to ground the second wire to the engine block ? Thinking about running a flex cable this time because it'll bend easier than the 1/0 standard wire I wrestled with initially when I did the alternator upgrade. Thanks in advance.

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In my W-123 Diesels , I connect the engine end to the intake manifold .

On my old '74 European 350SLC , I simply added a woven engine to body strap from one alternator case nut to the body and WOW ! did the chargig and lights ever improve .

Just go to any welding supply store for the cable , it'll be finer strands so it'll carry way more current and be flexible to boot .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better