Rob Posted September 9, 2009 Share Posted September 9, 2009 I know you guys, (and gals) run trucks that have more than one battery for the electrical system so I'll talk a bit about interconnecting cables: Have you ever had a set of batteries that will repeatedly run down with the truck sitting, but seem to readily charge with the engine running or an external charger, only to go flat within a few hours? You again charge the batteries, have them tested and are told they are good, but the same thing happens again? There are exceptions to the general rule but most motor vehicles out there have standardized on the 12VDC operating system and the batteries are connected in a parallel electical circuit to provide the 12VDC, at high current. Whether you have two series circuits of two six volts cells each connected in parallel to provide this voltage, or a set of many 12 volt cells connected in a parallel arrangment, they all work to produce the needed voltage and current for the electrical system.I have found through many years of experience that clean, tight, and maintained electrical connections are a must to ensure an acceptable service life from your storage batteries. The environment in which they exist is very harsh with the heat, cold, vibration, cycling of charge, and discharge etc. they endure. Typically a wet cell battery that is used in motor vehicle applications has a specific gravity weight of 1.25 in a fully charged condition. This is a given and does vary slightly with temperature but is close enough.Less than optimum interconnecting points for multiple batteries have many negative detriments and contribute to shortened battery life. For instance let's say the battery cables have minor corrosion on the passenger side of the truck, yet both sides appear to be relatively clean. In this instance the truck will not start after sitting overnight, but will start multiple times when ran for a few moments. An evaluation with a temperature compensated battery hydrometer reveals the driver's side battery bank is reading about 1.21 in specific gravity, yet the passenger side batteries are 1.12 specific gravity. All batterys' cell to cell readings are equal in specific gravity readings. A quick check with a multimeter reveals a steady 14.2VDC being supplied from the alternator to both banks, and with the engine shut off, and the cables disconnected, a reading is obtained of 13.6 VDC from the driver's side, and about 8VDC from the passenger side. Now what would cause this problem on the passenger side if the batteries are connected in a parallel circuit, and are charged at the same rate as the driver's side, at the same time? Why are the passenger side batteries flat? (I'm going to tell you right off the batteries are not defective).It can be proven in the above scenario that the passenger side battery cables are high in resistance and limiting the charge current from the alternator. It would not matter what set of batteries an external charger is connected to as the bulk of the charging current will reach the driver's side bank in this example as currrent follows the path of least resistance. What is happening as the truck will not start itself the next morning is the high resistance connections on the passenger side bank is not an infinite, (open) electrical circuit and the banks try to equalize themselves. Citing the passenger side is dead, the driver's side gives up some of it's charge to equalize the system. When the high current load of the starting circuit is energized, the high resistance connections will not pass the needed current to start the truck.If one were to remove the cables from the batteries, properly clean them at all points, use electrically conducting grease on the connections during reassembly and shield them from the elements, they will go a long time without maintenance. I typically clean and protect mine annually and seldom have problems. I do not use clamp on ends of the type you purchase at a parts store with a strap across the back retained by two bolts. I like the type that use a threaded "pinch" type affair within the terminal end itself after stripping 1/2" of insulation from the cable. I then shrink wrap the cable to terminal end termination. This serves very well in the elements and provides a long service life. Also do not forget to address the other end of the cables as in where they attach. This is another neglected point and can lead to failure.Hope you find this information interesting, or entertaining. Now I must get to working on my turkey dinner as it didn't turn out too good.Rob Quote Plodding along with no job nor practical application for my existence, but still trying to fix what's broke. Link to comment Share on other sites More sharing options...
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