engunir
Junior Member
- Joined
- Nov 29, 2024
- Posts
- 4
- Reaction score
- 7
- Location
- Southern California
- Ram Year
- 1998.5
- Engine
- Cummins Diesel 24-valve
Has anyone else gotten tired of replacing unbalanced 12-v batteries and decided to split them?
As an (Electrical) Engineer, I was surprised how Dodge chose to wire the (two, type 27) batteries it uses to start and support its Cummins engines (e.g., in Ram trucks,...). [NOTE: By the way, Dodge is not the only manufacturer to make this mistake; I've seen the same issue in other vehicles, especially RVs and other vehicles using large diesel engines, and having multiple batteries directly-tied in parallel.]
From an engineer's perspective, it is problematic to parallel (2 or more) batteries (or other power sources) without some sort of active-balancing or (other) protection; since the higher-charged battery will naturally try to pass some of its power directly-to the lesser-charged battery, and will do-so up to the current-carrying capacity of the interconnecting cables. For reference (e.g., in the RAM truck), this will primarily occur when the alternator is NOT actively-charging BOTH batteries; since, (when the engine is running) the alternator puts out a larger voltage to BOTH batteries, thereby dominating the flow of power in the system. This problem can be made worse when other batteries are also tied in parallel with the vehicle's batteries, as in the case when a camper and/or trailer is connected without some sort of isolation or protection.
In its simplest form, an imbalance of this type will cause a weaker battery to pull-down a stronger battery; and will initially show up as a "reduced lifetime" on both batteries. But in the limiting case (e.g., when one or more cells of the weaker battery FAIL), it can create an internal short (in the failing battery), which will try to absorb ALL the power of the stronger battery. Without fuses (or other protections) in the cross-ties, this can overheat the wiring and failing battery, even to a point where it could start an electrical fire under the hood. After experiencing this exact scenario (i.e., seeing how the uncontrolled battery-pair will (essentially begin to) self-destruct once one of the batteries looses some of its power storage), I decided to do something about it in my (1998 W3500 Ram, w/24-valve Cummins)...
- In my case, what I did was to install a high-current, continuous-duty, relay between the two batteries in my truck. More specifically, I wired a (500A) relay in series with the (large-diameter) cross-over cable which is used to tie the positive poles of the batteries together. I ONLY activate this relay when the ignition is ON (controlled from a carefully selected circuit which had spare current capacity). This provides a power-boost to start the motor, but disconnects them when the truck's ignition is OFF.
- I also added a similar relay in the (12V) power lead to my camper's battery, and in the wiring of the (12V) power lead of the 7-way connector (e.g., to a towed trailer). [NOTE: In later years of RAM trucks, Dodge did provide isolation between the truck's batteries and the (12V) power lead of the 7-way connector (e.g., to a towed trailer); but did NOT appear to provide any isolation for the power provided to electric brakes (i.e., also via the 7-way connector to a towed trailer), or between the vehicle's primary batteries.]
QUESTION: I'm wondering what other owners have done to address this situation???
As an (Electrical) Engineer, I was surprised how Dodge chose to wire the (two, type 27) batteries it uses to start and support its Cummins engines (e.g., in Ram trucks,...). [NOTE: By the way, Dodge is not the only manufacturer to make this mistake; I've seen the same issue in other vehicles, especially RVs and other vehicles using large diesel engines, and having multiple batteries directly-tied in parallel.]
From an engineer's perspective, it is problematic to parallel (2 or more) batteries (or other power sources) without some sort of active-balancing or (other) protection; since the higher-charged battery will naturally try to pass some of its power directly-to the lesser-charged battery, and will do-so up to the current-carrying capacity of the interconnecting cables. For reference (e.g., in the RAM truck), this will primarily occur when the alternator is NOT actively-charging BOTH batteries; since, (when the engine is running) the alternator puts out a larger voltage to BOTH batteries, thereby dominating the flow of power in the system. This problem can be made worse when other batteries are also tied in parallel with the vehicle's batteries, as in the case when a camper and/or trailer is connected without some sort of isolation or protection.
In its simplest form, an imbalance of this type will cause a weaker battery to pull-down a stronger battery; and will initially show up as a "reduced lifetime" on both batteries. But in the limiting case (e.g., when one or more cells of the weaker battery FAIL), it can create an internal short (in the failing battery), which will try to absorb ALL the power of the stronger battery. Without fuses (or other protections) in the cross-ties, this can overheat the wiring and failing battery, even to a point where it could start an electrical fire under the hood. After experiencing this exact scenario (i.e., seeing how the uncontrolled battery-pair will (essentially begin to) self-destruct once one of the batteries looses some of its power storage), I decided to do something about it in my (1998 W3500 Ram, w/24-valve Cummins)...
- In my case, what I did was to install a high-current, continuous-duty, relay between the two batteries in my truck. More specifically, I wired a (500A) relay in series with the (large-diameter) cross-over cable which is used to tie the positive poles of the batteries together. I ONLY activate this relay when the ignition is ON (controlled from a carefully selected circuit which had spare current capacity). This provides a power-boost to start the motor, but disconnects them when the truck's ignition is OFF.
- I also added a similar relay in the (12V) power lead to my camper's battery, and in the wiring of the (12V) power lead of the 7-way connector (e.g., to a towed trailer). [NOTE: In later years of RAM trucks, Dodge did provide isolation between the truck's batteries and the (12V) power lead of the 7-way connector (e.g., to a towed trailer); but did NOT appear to provide any isolation for the power provided to electric brakes (i.e., also via the 7-way connector to a towed trailer), or between the vehicle's primary batteries.]
QUESTION: I'm wondering what other owners have done to address this situation???
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