Can a smart battery isolator be positioned closer to the auxiliary (leisure) battery at the other end of the system, or does it have to be placed close to the starter battery?
It’s not always necessary to place a smart battery isolator directly next to the primary (starter) battery; the location will depend on the type you’re using and how your system is set up.
Guidelines for General Placement
- Voltage-Sensitive Relay (VSR): Because they track voltage variations from the alternator, voltage-sensitive relays, or VSRs, are typically placed near the starter battery. They can react more rapidly and precisely when they are close to the source.
- DC-DC Charger Isolators: Since they control the voltage and current entering the leisure battery, DC-DC charger isolators can be placed closer to it. Long cable runs or lithium setups benefit greatly from this.
- Solid State Isolators: Although solid-state isolators are more adaptable and can be installed anywhere electrically sensible, shorter cable runs are always more efficient.
Why Placement Matters
- Voltage Accuracy: Since VSRs must directly sense the alternator’s voltage, performance may be impacted by distance.
- Length of Cable and Loss: Longer cables may result in a voltage drop and more resistance. This can be reduced by positioning the isolator closer to the battery it is charging or protecting.
- Heat & Vibration: To extend the life of isolators, keep them away from areas with high temperatures or strong vibration.
Exclusions:
- You may be able to get away with putting the voltage-sensing relay (VSR) closer to the auxiliary battery if it has heavy-duty cables and little voltage drop.
- Since DC-DC chargers more accurately control charging, they are frequently positioned close to the auxiliary battery.
The best method:
Using cables of the right size for the entire circuit, install the smart battery isolator as close to the starter battery as is practical.
If you’re using a DC-DC charger, placing it near the leisure battery ensures it delivers the correct voltage and avoids drop across long wires. But if you’re using a VSR, keep it near the starter battery for best results.
