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Evolution of Dual Battery Management and Isolation
Before Electronic Dual Battery Management Systems (which are by far the best devices to isolate multi-battery systems) there were only two choices for battery charging and isolation; Manual/Solenoid or Diode.
Manual isolators
Manual isolators are a device that switches the connection of a battery on and off. They have a very simple manual switch operation.
Solenoid isolators
Solenoid isolators are like an automatic switch. When power is fed into the switching terminal of the solenoid, the solenoid is switched on, allowing the power to flow between batteries. This allows you to start from both batteries and winch from both batteries. The batteries are charged together in parallel when the solenoid is switched on. When the solenoid is switched off only the main battery will charge.
The power feed for the solenoid is usually connected to the ignition circuit, so the solenoid will switch on and off with the ignition. You can place a switch inside the cabin of the vehicle to manually switch the solenoid off and on (when the ignition is on) at your desire. If you run your auxiliary battery flat, (for example by using a fridge for a couple of days and not running the motor to charge the battery) there is a danger of flattening your main battery as soon as you turn the ignition on. This is due to the large equalising effect between the batteries. The manual switch is useful as you can stop the batteries paralleling when you turn the ignition on and flattening the main battery. You then switch the solenoid back on once you are travelling.
Problem: Can hide a faulty/flat main battery.
Note: Solenoids and manual switches create voltage spikes, therefore they are NOT recommended on EFI systems. They are also not suitable for charging dissimilar batteries.
Diode isolators
The diode isolator completely isolates each battery circuit from the other so when one battery is used (even if it is dead) the other, will remain fully charged.
Diode isolators act as a one way valve between the two batteries, preventing current flowing from one battery to another. Each battery is therefore isolated and acts as an independent power source.
Diode isolators have been around for years, and suit externally sensed alternators. They are not recommended for many modern systems, however their simplicity and long life ensure their place in the market. At Piranha we manufacture our own brand and it is excellent value for money.
Problems associated with solenoid or manual systems occur when paralleling two batteries; one fully charged and one flattened (by running accessories). We must allow both batteries to equalise, like tanks of water, before they recharge. They then charge up very slowly as one enormous battery. This creates a disadvantage in that the batteries compete for power during recharge. Diode isolators have a different problem, there is a voltage drop associated with the use of blocking diodes.
Note: Most modern vehicles, EFI or diesel, now have internally sensed and regulated alternators that do not suit diode isolators.
In the mid 1980's Piranha introduced the first Electronic Isolator (the DBE 100S now obsolete) that revolutionised the way Dual Battery systems worked. Electronic Battery Management Systems now work on the same basic principals as this revolutionary product.
Electronic isolators
Electronic isolators ensure that the main starting battery is charged before connecting the auxiliary battery. It does this by monitoring the voltage in the main battery. When the voltage in the main battery reaches a predetermined threshold, the isolator switches to charge the auxiliary battery. It will also disconnect the auxiliary battery from charging if the main battery voltage drops below that of another predetermined threshold. Thus this system ensures that the main starting battery is always given charge priority and therefore the risk of having a flat main battery is greatly reduced.
Piranha Electronic Isolators have another huge advantage; they can be fitted to any vehicle - diesel, turbo diesel, petrol carby or EFI with internally or externally sensed voltage, it doesn't matter, it will work exactly the same on all types of vehicles.
