Staarter ground wire??

[jjrbus]

Boy all this fun!!  I DO NOT have a no start problem at the moment. I am waiting for the batteys to charge fully.  In the meantime I am going over everything for the 19th time!!! 
1979 MCI5C   6V71 automatic.   I had changed the batteries to 2 group 31's (24V system)and moved them to the engin compartment.
The positive wire has about an 18 inch run to a selector switch (heavy duty cole herse) and then a 3 foot run to the starter. This is all 2/0 welding cable with crimped on tinned ends with shrink wrap.
The negative cable has about a 2 foot run from the negative battery terminal to a stud welded to the frame, this is 4/0 cable. From the stud to the starter is about 3 foot of 2/0 cable, again all crimped on tinned ends with shrink wrap.
The 2 foot ground cable from battery to stud is old and shows cracks in the insulation. So I will replace this piece to remove all doubt on wireing!!
Now to the question, I have a long piece of new 2/0 welding cable, would you.
1. run this directly to the starter skipping the stud?
2. run it too the stud?
3. run the new piece to the starter and leave the old piece attached to the starter and stud?

As usual all advice, opinions, wise cracks and suggestions greatly apprciated.   Jim

                                                                                     

[kyle4501]

Option 4 = give it to a deserving busnut      (you did ask for wise cracks.) 


I'd consider adding it. leave the existing & add it straight from the bat to the starter.



Are you sure the $$$ cole herse switch is guiltless?

[kyle4501]

Have you put one volt meter lead on the starter end of the wire & the other meter lead on the battery end of the same wire to see what the voltage drop across all connections is while cranking?

Anything more than ~.5 volts would indicate excessive resistance.

[JackConrad]

.
1. run this directly to the starter skipping the stud?
2. run it too the stud?
3. run the new piece to the starter and leave the old piece attached to the starter and stud?

As usual all advice, opinions, wise cracks and suggestions greatly apprciated.   Jim

Jim,
  You left out one other important option  JUST RUN!!!      

I'm wondering, is 2/0 heavy enough?  All my battery/starter wiring is 4/0   If you still have a problem, try bypassing the disconnect switch (might have worn/pitted contacts in the switch).  Jack

[Sam 4106]

Hi Kyle 4501,
Would you get any reading by putting both leads of a volt meter on opposit ends of the same cable? It seems to me that one lead would have to be on negative and the other on one end of the positive of the battery and then a second reading with one lead on the negative of the battery and the other lead on the positive cable at the starter. Then subtract the lower reading from the higher reading to get the voltage drop. If your method works, please explain how.
Thanks, Sam 4106

[Green-Hornet]

 I would suggest running the ground from the battery as close to the starter as possible. That will give the starter the most energy. And use the thickest welding wire you have. Perhaps an electricion could explain why, but the distance between the positive end at the starter and the distance between the ground is more important than the length of the ground wire.

[kyle4501]

Hi Kyle 4501,
Would you get any reading by putting both leads of a volt meter on opposit ends of the same cable?

If there is sufficient resistance, yes.   I think

It seems to me that one lead would have to be on negative and the other on one end of the positive of the battery and then a second reading with one lead on the negative of the battery and the other lead on the positive cable at the starter. Then subtract the lower reading from the higher reading to get the voltage drop. If your method works, please explain how.
Thanks, Sam 4106

Where are the electrical smart guys? I don't know if I understand it well enough to explain it. 
But lack of knowledge hasn't stopped me yet,  so here is how I understand it from what 'schoolin' I remember . . . . You are measuring voltage drop across a load - the poor connection, the undersized cable, etc.

Remember those charts to help you select the proper wire size? They relate distance to voltage drop for a given current.

Anyways, what does it cost to try this out? If I'm wrong, it hasn't cost much . . . .
At least I ain't advising someone to use cheap elec fans to cool the bus radiator.       

[jjrbus]

Ok Kyle you can have the bus!!  There is just the $59K shiping and handling fees, payable upfront in cash of course.
I tested everything as best I could as per Jerry's aka Sojourner's directions. Not being a trained diagnostician I was  unsure of my findings so took the starter in for testing. They replaced the brushes, solenoid, said the rod?? was bad and that it was grounding to frame.
It seems the way to go is from negative battery post to starter and leave the existing starter to ground wire in place, That appears to eliminate one connection.  Where are all the smart electrical guys
Jack,  I rechecked my service manual and the starter calls for 2/0 cable. That was when the batterys were 25 feet away!!!

[gus]

The 2' run to stud is your ground wire for the whole bus electrical system so I would keep that in place.

Unless running directly to the starter is shorter you have nothing to gain if all the stud connections and cables are in good condition. A few inches shorter won't make much difference.

You could run 2/0 both to the stud and to the starter and from stud to starter. That has the approximate effect of having a 4/0 to the starter (I'm too lazy to figure out the areas of the two sizes!).

However, unless you also have a 4/0 pos cable to the starter a 4/0 neg won't do a lot of good since both pos and neg cables carry the same amps during starting.

However, if the starter/engine has a real good ground to the body then that will carry a lot of the starting amps. It then would be more important to increase the size of the pos starter cable.

I originally meant for this to be short, failed again!!

[Brassman]

My question is that did you tin the wires and then crimp the connections. That would be a recipe for a failed connection (ie: high resitance).

[JohnEd]

Sam,

I gotta luv ya.  What you described about subtracting voltage numbers is "exactly" the same volt number as measuring "across" the wire run.  Exactly!  We do it your way we do it twice and suffer the possibility of injecting error twice.  Kook at it this way:  everything is a resistor wether it is intended to be or not....everything has a resistive component...in DC.  The wire is supposed to NOT drop any voltage in carrying the current to the starter.  Ideally all the resistance would be zero and the starter would "see" the "full" battery voltage.  Real life doesn't work that way.  Here is the bottom line....you can run as many feet of whatever gauge you like and add as many switches and solenoids and shunts and stuff as you like.  Anything!  Just so long as the starter sees "full" battery voltage.  Now the reality is that 4 ought wire will have XXXX ohms of resistance/foot and will drop YYY volts if the current is ZZZ and the run is AAA feet long.  When we design the thing we design for a voltage drop over the entire system, except the starter, of only a volt TOTAL.  I am not sure of the exact number.  We increase the size of the wire and connector contact area and purity of the Cooper cable to achieve that low drop that is MAXIMUM ALLOWED.

The system deteriorates over time and that "total" voltage drop creeps up.  We fix that by replacing and improving the "conductivity" of the circuit/components.  Conductivity is the opposite of resistance(ohms).  A wire is only allowed to "drop" so much voltage before we replace the wire as defective.  It is almost always the quality of the connection at the ends of the wire that have corroded or become loose.  The quickest method to find the component that is dropping voltage is to measure "across" the component.  In a starter system that uses HIGH current and ohmmeter is almost useless as the resistance of the components changes dramatically when the component heats up almost instantaneously with the current draw.  The easiest is to measure the voltage drop across the starter which is to put the meter across the starter connecting the leads at the + post and frame(neg post) of the starter.  If you hit the start button and this voltage is the batter voltage less 1 volt and it isn't spinning fast Enif...buy a starter.  Discussion ended.  Too much loss?  Check the bat terminal studs...not the connector....and make sure the voltage doesn't drop more than a volt during the cranking. 

The entire circuit can be represented as a series of very small resistances.  Bat stud to bat connector tor...small resistor.  Bat connector to cable....small resistor.  Cable end to end....small resistor.  Cole Hersey bat switch....small resistor.  it only gets this complicated when you have a very old system with gremlins all over and thru or you have a very odd problem.

HTH

John

[JohnEd]

Brassman,

I agree with you.  Except that tinning the wire makes a stranded wire a solid conductor wire and we sure can crimp those and expect them to hold up.  Problem here is that the terminal and "crimper" expect a stranded wire that is easier to crush(crimp).  I have always crimped the wire and then soldered it if high current and a really spiffy connection was a really good idea.  Soldered will outlast crimp a long time but just look at how well the crimps are doing.  NOT with high current...Mary Jane.  There we solder everything that doesn't move or for sure it will be iffy in ten years.  Hummmmm!  Ten you say?

There is one fly in the ointment.  Stranded wire will "wick" moisture and the strands will deteriorate much faster than a solid.  This is where the actual wire starts to drop voltage in the middle of the run....so to speak... but not at the connectors that are soldered.  Adding the shrink is a great touch.  Putting a glob of silicone on the wire joint and then "spinning" or "winding" the shrink up the connector and then shrinking it is the al time water PROOF method.  Solid silicone inside a shrink tube is bullet proof.  In Pa. the salt roads simply destroy everything so keeping salt water out is a must.  Love near the beach?  Ever even drive through Pa in the winter?  In the rain in the spring?

HTH,

John...check my sig line for answers to your question

[Brassman]

If you want it to last, crimp then solder. If you tin the wire then crimp, under load the connection heats up, the solder melts, and the tight electrical connection is lost. This is not my knowledge, but that of the old time radio electronics's guys.

[c-coop]

replace the welding cable with battery cable. I have come across this problem many times on heavy equipment. welding cable has to many very fine strands of wire, batery cable has less but larger strands

[junkman42]

If it is possible for one to afford marine cable use it by all means!  Marine cable is tinned and when crimped with the proper lug and crimper it will last longer than any of us.  Aircraft use crimped cables and for a good reason.  Buy mil quality terminals from industrial sources and use the proper crimper.  The terminals from auto supply houses are pure junk.  If You chose to solder the lugs after crimping You should clamp a heat sink on the cable behind the lug to prevent solder from wicking up the cable.  Soldering crimped lugs actually defeats one of there good qualitys as soldering destroys their vibration resistance.  Having attended a nasa school to learn to prepare cables to their specs opened my eyes back in the early 1960's.  Also You can buy heat shrink that has an adhesive inside so when shrinking You also seal out all mositure.  My two cents, with a buck You might get a cup of coffie.  John