I’m looking to have the following solution “sanity checked” to be sure I’m not missing something.
Background: I have an RV with two totally independent 12V battery systems. System 1 is the chassis battery, alternator, engine, etc. – standard automotive system. System 2 is the coach system, with its own batteries, solar charging, shoreline charger (not plugged-in in this scenario), and second alternator/regulator.
The Problem: During the winter, the RV is rarely used. While I try to take it out periodically and run it, I don’t always do that enough and the chassis battery gets drained. In addition to not being able to start the RV, this isn’t healthy for the battery. The coach battery system is maintained due to the solar charging system (real system, not the tiny RV panel they sell that supposedly keeps your battery charged).
My solution: I want to connect the coach system to the chassis system through a bridge consisting of a 2.5 Ohm resistor, rectifier and fuse. My thought is that if parasitic load draws the chassis battery down, a small trickle charge will flow through the resistor/rectifier bridge. The maximum charge level for the coach system from solar is 14.0V. So if the chassis battery goes down below 13.4V (accounting for the rectifier voltage drop), a small charge current will start to flow. This current will increase if/when the chassis battery voltage drops. For example, if the chassis battery were to drop to 12.5V, then there would be approx. 360ma of trickle charge. When the vehicle is started, the chassis battery voltage might drop significantly. But even if it dropped down to say 6V temporarily, the flow through the resistor/rectifier bridge would be less than 3A. So I figure a resistor in the 25-30W range won’t get smoked.
In coming up with this, I’m also trying to avoid overcharging the chassis battery.
The chassis battery is buried under the driver’s side floorboards, so I have not been able to measure the parasitic load.
Does this solution make sense?
Since the nominal 12 car battery voltage is around 12.6V, should I use 2 rectifiers in series to change when the charge current starts to flow (approx 12.8V vs 13.4 with one rectifier)?
Thanks
Background: I have an RV with two totally independent 12V battery systems. System 1 is the chassis battery, alternator, engine, etc. – standard automotive system. System 2 is the coach system, with its own batteries, solar charging, shoreline charger (not plugged-in in this scenario), and second alternator/regulator.
The Problem: During the winter, the RV is rarely used. While I try to take it out periodically and run it, I don’t always do that enough and the chassis battery gets drained. In addition to not being able to start the RV, this isn’t healthy for the battery. The coach battery system is maintained due to the solar charging system (real system, not the tiny RV panel they sell that supposedly keeps your battery charged).
My solution: I want to connect the coach system to the chassis system through a bridge consisting of a 2.5 Ohm resistor, rectifier and fuse. My thought is that if parasitic load draws the chassis battery down, a small trickle charge will flow through the resistor/rectifier bridge. The maximum charge level for the coach system from solar is 14.0V. So if the chassis battery goes down below 13.4V (accounting for the rectifier voltage drop), a small charge current will start to flow. This current will increase if/when the chassis battery voltage drops. For example, if the chassis battery were to drop to 12.5V, then there would be approx. 360ma of trickle charge. When the vehicle is started, the chassis battery voltage might drop significantly. But even if it dropped down to say 6V temporarily, the flow through the resistor/rectifier bridge would be less than 3A. So I figure a resistor in the 25-30W range won’t get smoked.
In coming up with this, I’m also trying to avoid overcharging the chassis battery.
The chassis battery is buried under the driver’s side floorboards, so I have not been able to measure the parasitic load.
Does this solution make sense?
Since the nominal 12 car battery voltage is around 12.6V, should I use 2 rectifiers in series to change when the charge current starts to flow (approx 12.8V vs 13.4 with one rectifier)?
Thanks