Just like diode based battery isolators the FET variant is being used to charge one or more additional batteries off the generator/alternator or grid connected charger without combining the auxiliary batteries with the starter battery.
Important: Isolator relay, FET or any other more or less simple battery isolatation technology is only recommended, when connecting auxiliary batteries of the same type as the starter battery. Reason for this is the controller on the generator, which has a special cutoff voltage optimized for the chemistry of the starter battery. So if your car is equipped with a standard lead acid starter battery, you cannot use an isolator circuit to add a gel type battery to the system, because these gel types have different charging characteristics. If you want to mix battery types, you will need to use a so called A2B or B2B (alternator to battery or battery to battery) charger, which in turn adapts the voltage levels to the different cell type and also does the isolation for you. Additionally it is highly recommended to have the charge voltage temperature compensated, which can be done automatically by these units, when connected to a temperature sensor. See our inventory for a range of b2b charge controllers. Feel free to mail with questions.
The fundamental difference to a standard relay isolator is just this: Isolation. While standard relay will connect both batteries as soon as the engines runs, a FET isolator does not directly connect the batteries like that. A direct connection always means, that the stringer battery will feed the weaker battery. Thus, our good starter battery is being discharged by the emptied aux battery. Of course the running alternator will nor charge both batteries, but this conecpt implies, that you keep the engine running long enough to charge both batteries. That would of course result in zwo full batteries. But what if you drive just a short time? You will end up with the starter battery being lower than before. Do that 10 times, you you know what happens. Enter the FET isolator: Once the engine is running, it distributes charge current to the aux battery without ever touching the starter battery. So no matter how long you keep the engine running, the starter battery won't be emptied. This difference is important depending on your personal application, but you should keep that in mind. If you want emergency start, you will need to purchase a seperate battery switch - just like with any other isolator technology.
Compared to diode based battery isolators the voltage drop of FET isolators is marginal. Typically less than 0.02V at low currents, and around 0.1V at high currents. Nevertheless you should keep the connection wires as short as possible, because you want as much of the voltage of the alternator charge controller to reach your aux batteries. Essentially there is no practical reason for using diode based isolators anymore these days.
Max. charge current: 100A
Max. generator current: 100A
Number of batteries: 2
Connection: M8 bolts
Dimensions (HxWxD): 120 x 200 x 68mm (incl. bolts)
|Product weight:||1,30 kg|