See full version: How to Troubleshoot a Dual Battery Isolator
Place your meter leads on the large contacts that were previously attached to the batteries. Trigger the isolator to engage. Most triggers come from a switch or from the vehicle's ignition. Set your meter to ohms. A reading of 0 ohms indicates that the isolator is working. An open load reading indicates that it is not working. here
If an open load is observed, test the triggers by disconnecting the wires going to them. Place an alligator clip on one trigger and connect the free end to ground. Connect the other alligator clip to the remaining trigger, and place its free end on a 12V source. You should feel and hear the isolator click and the meter should read 0 ohms. If there is no click, or if the meter still reads open load, replace the isolator. [links]
Understand that a standard battery isolator has four contacts, two large contacts and two smaller ones. To start, disconnect the large gauge cables from the larger contacts. These cables lead to each battery's positive terminal, so care must be taken to keep the end of the cables from grounding out on the exposed metal of the engine compartment. Use the electrical tape to cover these ends. here
A battery isolator is an important part of a multi-battery electrical system. When it is operating properly, it ensures that both vehicle batteries are charging when they should be, and that the vehicle's main battery will have enough juice to start the car in the event that the accessory battery has been drained. If the isolator is not operating properly, a number of problems can occur. Being able to troubleshoot an isolator may be the difference between your car starting or not starting at all. more
If the isolator passes the test but you are still experiencing problems, you may have more serious electrical issues.
On one of our earliest RV adventures, we learned the hard way about the importance of a battery isolator system. After our first night on the road, a chilly one where the furnace ran during the night, we found we couldn’t start the truck up. The RV had “stolen” power from the truck battery, leaving us wandering around with a set of jumper cables, looking for a hot jump.
In practical terms, one authority tells us that the typical vehicle alternator may send 15 to 20 amps of current to a deeply discharged battery. Let’s say your trailer’s house batteries are 20 feet back from the alternator. If you use two wires to charge (a “hot” wire and a return wire), this is actually a two-way trip, so in reality your batteries are effectively 40 feet away from the alternator. A quick look at a wire size chart reveals that to send 20 amps over 40 feet of wire, you’d need to use 6-gauge wire for your installation. This may sound like overkill, but in reality, if you use smaller gauge wire, the voltage drop created by the smaller wire will dramatically increase the amount of time it takes to charge your batteries.
In normal operation, the Battery Doc isolator senses the charge level of the SLI battery, charging it before sending charge current to the house batteries. Once the SLI battery is charged, full charge current is sent to the house batteries, always giving priority to making sure you can get your running system started. Further, if there is a short in either the house or SLI system, the isolator will detect this and stop current flow to the shorted circuit.
On one of our earliest RV adventures, we learned the hard way about the importance of a battery isolator system. After our first night on the road, a chilly one where the furnace ran during the night, we found we couldn’t start the truck up. The RV had “stolen” power from the truck battery, leaving us wandering around with a set of jumper cables, looking for a hot jump.
In practical terms, one authority tells us that the typical vehicle alternator may send 15 to 20 amps of current to a deeply discharged battery. Let’s say your trailer’s house batteries are 20 feet back from the alternator. If you use two wires to charge (a “hot” wire and a return wire), this is actually a two-way trip, so in reality your batteries are effectively 40 feet away from the alternator. A quick look at a wire size chart reveals that to send 20 amps over 40 feet of wire, you’d need to use 6-gauge wire for your installation. This may sound like overkill, but in reality, if you use smaller gauge wire, the voltage drop created by the smaller wire will dramatically increase the amount of time it takes to charge your batteries.
In normal operation, the Battery Doc isolator senses the charge level of the SLI battery, charging it before sending charge current to the house batteries. Once the SLI battery is charged, full charge current is sent to the house batteries, always giving priority to making sure you can get your running system started. Further, if there is a short in either the house or SLI system, the isolator will detect this and stop current flow to the shorted circuit.
Re: Battery isolator/switch problems more
Re: Battery isolator/switch problems [links]
I think my battery isolator and/or selector switch has failed - but not sure.
Here's my problem. I have two battery banks - a starting battery and a house deep cycle. They are connected to a selector switch. When I physically disconnect the #2 battery but place the battery selector switch to #2, I get a reading on my dash volt meter.