Electrical puzzle

Started by Doug Sprinthall, March 26, 2006, 08:50:45 PM

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Doug Sprinthall

Okay gang, here goes:
I tried to start my 68 DVC today and the following happened.
After charging  the batt,  It turned over fairly slowly.  Not enough Omphhh to get her going.  The Pos batt cable was very hot and the insulation was starting to melt.  The Same Batt has been in the car for 6 years so I figure I might be due for a new one anyway.  The cable is old so I figure it may have deteriorated and resistance has increased.

I figure Ill remove the batt and have it  load tested.  I pull the pos cable 1st and as it touchs the radiator cap.....sparks fly.  To recap, the neg cable was still attached but the pos cable was completly off.  So here is the question:  Where is this voltage coming from?  Is it stored in the starter? alt?

I still plan on replacing the bat and cable and I think everything will be fine.  Ive just never experienced this before.

Geoff Newcombe #4719

Be interesting to hear what others have to say but my guess would be that your 6 year old (WOW) battery is shorted internally.  I wouldnt even bother load testing that "antique", loosen up that coin purse and replace it.

Ivan Zanatta

The only way youll get a spark from the positive lead of the battery is if there is another battery (unlikely ) or a large electrolytic capacitor (possibly) still across the circuit.
If someome has installed a high-powered audio system in the car, it could be the capacitor across the power line (pos. 12v)
they sometimes put in to smooth out line fluctuations. The alternator or starter wont" hold" a charge.

Doug Sprinthall

Very clever Ivan.  It does have a relatively high powered audio system (sub, x over and 2 power amps).  Now that you mention it a cap discharge seems likely as is dissapated fairly quickly.  After two attempts to duplicate the situation, the charge seemed to be gone.  Thanks for the insight.

denise 20352

   Getting the battery tested is a good idea.  The parts stores will actually come out with a box and diagnose your electrical system, these days.

    It could be the cable itself, of course, or a bad connection of the cable to the terminal end, at the battery.

   If the problem turns out to be an excessive drain from the starter, it is possible that the brushes are worn down.  There is a screw that attaches the wires to the brushes, and when there is no more brush left, it contacts the adjacent commutator bar and causes a short.  This condition will eventually cause your solenoid to fail, because it pulls a big load through the holding coil.  If this is the problem, whether you choose to repair the starter or replace it is just a matter of which you value more, time or money.


Rhino 21150

You may have burned the positive cable trying to start the car. They are not expensive, take the dud with you and match it. The cable probably got hot because the starter motor actually draws MORE current when it cant reach full speed. Its counter-intuitive, but its true. Motors are funny that way. Have you ever read the instructions for a motor driven tool and the use of extension cords? Long cords drop the voltage, motor wont rev up, pulls too much current, burns up motor and cord. Current causes heating, voltage just helps the current get where its going.
I am oversimplifying. The whole story involves MATH! Skeered ya, dint I?

Doug Sprinthall

Yeah, Ive already got a new cable.  I just have to find the time to crawl under and replace the old one.  BTW the old Batt load tested just fine so its either a cable or starter issue.
Start cheap, get spendy is my repair motto.