dr bob

Thanks for the tips, Wayne. I'll be using a multistrand marine battery cable, tinned copper. I could make it myself, but my favorite marine supply place will do it for me to spec, with fine-strand tinned copper cable that will be a lot more corrosion resistant. Most welding cable jacket isn't intended for oil/fuel/solvent exposure, by the way, or I'd use some that I have already.

DC current capacity is much less a function of surface area vs cross section than AC, by the way.

The voltage regulator is designed to lower charging voltage as it gets hotter, both to protect the alternator and protect the battery; the basic assumption is that they are close together and will be the same temperature. Bad assumption for a 928 but it's what we have.

Grounds are clean. As I mentioned above, the battery ground strap is going to be replaced too, probably with a larger (1-gauge rating) instead of the somewhere between four and six guage rated cable that's there from the factory. I looked at and measured the engine-to-chassis ground cable too, and it's still fine. It almost looks like the chassis side is cadwelded. Anyway the copper is still copper-colored, no chloride green or other discoloration to hint at looming problems. Voltage drop test on that is fine too.

The erratic symptoms have pointed to high resistance in the battery-to-alternator path. Until recently, the meter wasn't able to confirm the problem I'm sure I'll be able to find the mechanical weaknessbreak when I pull the old one out for replacement.

danglerb

DC like our electrical systems use, skin effect does not apply at all, its just about flexibility.

For copper at 70C:

S= 2837/sqrt(f)

Where f is frequency in Hertz, and S is the Skin depth in mils.

dr bob

I was trying to be gentle.

Alan

Dr Bob - I'd be interested in the exact detail of the WL2 loom structure on your '89 car.

How exactly is the loom built-up particularly where the 14 pin connections: Solenoid feed and Exciter wire get added in with the larger Alt-Starter, Alt-Jump Post and Starter-ABS pump connections. Also what is the general routing used in '89.

Alan

waynestrutt

I see you have Google.
Generally, you can think of the electrons flowing throughout the conductor as DC and low frequencies. As the frequency increases, the flow restricts itself more and more to the surface.
A simple test you can do is to replace a multistrand conductor with a single equal od strand conductor and apply sufficient current to each and measure the temperature of each .The single strand effectively becomes a heating element.

dr bob

I'll take this opportunity to short-circuit the skin-effect discussion. The formula that Mike shared works great except where we get a divide-by-zero error when frequency is DC. At DC, the "skin" depth is infinite I guess, so I don't really need any cable at all. Right? Please check my math.

The cable I found locally is an Ancor brand marine battery cable in 1-gauge. OD is exactly the same as the original cable at 0.530", so all the guides and P straps will work fine. I was sorely tempted to replace all the strap clamps with new stainless but resisted. The cable itself is like welding cable, hundreds of tiny strands, but has a hard oil-proof 105ºC rated smooth jacket.

The marine supply store had lugs but no crimp-on battery terminal clamps. Their prescription is lugs at both ends of the cables, and a positive terminal clamp with a 3/8" stud and a wing nut to secure the lugged cable. That stud looked like it would push the height of the positive terminal too high to maintain the plastic shield and still leave room for the lid to close. So I'll probably go shopping on line for the correct copper or alloy positive crimp terminal and proceed from there on the installation.

Anybody else in the LA area need a new positive battery cable? Once I get set up to crimp and sleeve, it's about as easy to do a few as it is to assemble just this one. Looks like a 50' length of cable would do 4 cars perfectly. I wouldn't recommend buying the cut length at the marine store, BTW, at about $7/ft.

-----

Alan- I wasn't planning on pulling the front harness out again. There's a single lug in that harness where two cables are joined to go forward. Eyeball is somewhere around 6 gauge plus somewhere around 8-gauge ganged there. The 50 cable was white in a past life, and is in the same sleeve coming back from the alternator. My memory is that there's a similar pair of cables at the alternator, bigger one from the starter end, smaller going to the jump post. I think but can't be sure that the smaller conductor at the starter-end lug is the ABS jumper. I'm not sure I can get the exact sequence of connections without pulling the alternator cover.

danglerb

I've been spending way too much time lately in an audiophile forum discussing the lack of merit to $1000 AC cords and the actual resistance of Ohno copper vs garden variety electrical cords. My gentle is running low.

The good news is that in practice nothing is DC, and the frequency is never exactly zero.

The other good news is that in practice we don't need to worry about it, and can treat it "like" DC, so infinite just means the full diameter regardless of size is used for electron flow, and sizing can be based on DC resistance.

Boat guys I think have to have a wingnut disconnect, but no advantage I can think of for our use. Personally I am not quite decided on how I want to terminate at the battery and tie into the CE panel wires etc.

Do you think 105C jacket will be good enough?

Rob Edwards

Bob, I'd definitely be in for a spare + cable. Dumb question- are the battery terminal clamps all a generic size? I'd guess you want to be sure that the bolt hole through the clamp is the same diameter as the OEM one, so that the bolt/distributing piece can be re-used.

dr bob

Rob--

The positive and negative are different post sizes. After that you spec material and of course the cable size for a crimp or solder connection. I'll get half dozen of each positive cable connector and we can be ready.

We need three more victims to justify buying cable and building. Anybody else in the L.A area?



Mike--

I hear you on the DC discussion. The major duty is fairly smooth DC for the starter motor, fairly smooth for the charging part just to the battery, smooth for alternator to the fans and fuel pump, and pulsed to the injectors. The battery is a fairly good-sized capacitor in its own right, and smooths the injector load pulses that the rest of the electrical system really wants to ignore. Theory goes that the changes in load are similar in effect to an AC component on top of the DC, but how much that affects the cable function is irrelevant in this case. I found the correct multi-strand cable, largest diameter that will fit in the existing guides and holders, and I likely won't get down there with the Gauss meter to see how the magnetic field swells at the bends with engine at full load. As tempting as that might be.

BTW, your audio guys have way too much time on their hands. Power quality at the outlet would be a much bigger factor than the micro difference one might see from "better" quality copper in the last few feet to the equipment. House wiring is a nightmare; generally good enough for light bulbs and the electric range, hopefully without catching the building on fire.


The nominal 105º C jacket rating is fine. There's an additional pair of sleeves over the cable where it turns across the rear of the front crossmember. Looks like it's for mechanical protection as well as for possible heat migrating up from the left-side pipe. Aft of that it's all very well shielded. Toughest test will likely be a summer drive across the desert on the way to OCIC next summer.

Jim Devine

This might be a better source for the marine cable.
Comparing their price to West Marine it's almost
$3.00/ ft less. If you buy a 50' spool, have them
cut it to rough length & send it in a couple of
Post Office "if it fits, it ships" boxes - probably
cheaper than other methods due to weight.

http://gregsmarinewiresupply.com/Zen...0fd67c17688f28

Also see post # 20 in this thread for cable ends
& video- they look well made.

Alan

OK thanks - I understand - its a lot of effort to get to and expose this stuff and you only want to do it if you have to... I have never needed to so its an area I've not experienced much first hand.

I do think I'd like to replace quite a bit of the primary wiring - old, heat & chemical soaked and could be upgraded, so far I've only really needed a new ground strap - I used a nice bare flat breaided one from waytekwire.com (needed a jacket made up) - BTW: they also have nice looking crimp on battery lugs).

Alan

dr bob

Alan-

I'm negligent in that I didn't take any notes or pictures when I swapped in the new alternator last year.

The existing engine harness on my car is amazingly young. I guess if I had the harness out for anything, I'd start diagramming it for when it needs replacement. For sure the primary cable would be a candidate since it's easy to buy and uses generic terminals. The sad part so far is that the wires from the jump post to the CE panel look pitifully small, considering how robust the rest of the system is. If I were adding any load at all to that section, it would be my first upgrade candidate.

Alan

Agreed - plus the fact that there are two small feeders is rather bad practice too.. a poor connection on just one puts all the load on the other.

Of course like so many things its all unfused...

My planned upgrades include direct Alt-Fan final stage wiring, and local relays (and supply) for the headlights/fog/aux lamps. The lighting change at least removes some CE panel loading.

All my extra battery direct feeders are already fused at the battery end - I was honestly horrified when I saw how the power was supplied...

Alan

CPR

Marine cable is not exactly the best choice....unless budgets are a concern.

Locomotive Wire is type 'DLO' with a EPDM or EPR insulated jacket (same as welding cable) BUT also has a harder more abrasion resistant CPE jacket as well. DLO wire is very similiar to standard welding cable, with the exception of the conductors being tinned to further prevent corrosion and an increased strand count for greater/unmatched flexibility.

It is loosely classified under type 'W' cable groups, although it outclasses almost all of them...with the exception perhaps oxygen free, compact strand mining cable. But that one, much like DLO, is very expensive. However, I do not think you would ever replace it in this lifetime, making it a 'permanent' part and well-worth the cost.


FYI...Strand count is:
#2=147
#1=224
1/0=273
2/0=323
3/0=456

danglerb

This place lists 1 awg as $2.73/ ft 25 ft min, but its 90C and outside dia is 0.65"

http://www.wireandcabletogo.com/Indu...Cable-2KV.html