Improved Performance in Heavy Duty Starting Applications
Extracting the maximum starting performance and durability of starter motors and batteries in heavy duty applications can be complex and expensive, but there are some significant improvements that can be made for little cost. The following recommendation can significantly improve cranking and battery life by overcoming a common battery wiring shortfall many trucks have from new.
When test-fitting a new Delco Remy dual-earth starter motor as a retrofit to an older Kenworth with a history of starter motor reliability problems, Craig Wilson of Baxters first step was to look at the condition of the vehicle’s batteries.
Craig found that the fleet operated Kenworth K108s running split battery banks - two batteries on the left of truck and two batteries on the right of the truck. Craig noticed in testing and this was supported by comments by the technicians that the inside battery closest to the frame rail were at a different state of charge or had a lower cranking capacity when tested compared to the outside batteries. **
This is common in this type of set up due to the way the batteries are cabled from the factory in 90% of today’s applications but a simple change can be made to circumvent this and extend the life of those batteries.
Below is a depiction of how the truck would be presently configured (top diagram). Notice the coloring of the batteries representing internal temperature. Inside batteries operate at a higher temperature than the outside batteries. Note each pair of batteries is in a parallel string. The alternator (source) responds to the internal resistance of all batteries and regulates to a target voltage. The alternator is not intelligent so it simply pumps out current to increase the system pressure. As configured as in the (top diagram) below not only will the first battery in each string have more current passed over it and thru it- when a cranking demand is required it will also off load more current than the outer most battery – current flows from negative to positive.
Now look at the bottom diagram. By simply relocating the connection point of the Negative Charge/Discharge line to the outer battery the current flow charge and discharge passes through each battery equally ensuring proper absorption and the batteries maintain the same internal operating temperature.
Ensuring that a 12 volt string has one positive and one negative connection to opposite ends of the parallel string of batteries will greatly extend battery life and ensure that the maximum potential of CCA available can be discharged.
This is a key item that is commonly overlooked by manufacturers pursuing cost savings by reducing cable lengths, but it is a very important item to practice at fleet level. If this is reviewed and changed on every truck battery life will be extended by at least 50%
**At face value one could easily assume that heat is contributing to this - well it is but not in the form of absorbed heat radiated from another source. It is due to internal heat as a consequence of the flow of current into the battery whilst charging.