By using diodes or Field-Effect Transistors (FETs) to only allow current to flow in one direction, a fully charged battery cannot pass current to a partially charged battery. Think of them like a gate valve, allowing the current to flow from the alternator to two or three battery banks without any of the battery banks “seeing” one another. Popular models include the Blue sea Automatic Combiner, BEP Voltage Sense Relay, and the Xantrex Digital Echo Charge.īattery Isolators also allow one charging source, such as an alternator, to charge multiple battery banks. This is why we choose to install battery combiners for battery banks that are generally similar in size and also won’t be uneven or unbalanced to avoid nuisance tripping of the fuses protecting the battery combiners. What makes this all challenging for a marine electrical system is how do you know when the fuse has been tripped or blown? Especially if you don’t know what to look for. Furthermore, the fuses installed to protect the battery combiner will trip/blow. This inrush of current from one full battery bank to an empty bank can easily exceed the maximum current rating of the battery combiner. When two battery banks are in parallel (joined together), they will instinctively want to even themselves out and the higher voltage battery will want to lift the lower battery bank’s voltage. The challenge with battery combiners is uneven battery banks, specifically when one battery bank is discharged heavily and another battery bank is full. disconnect when voltage gets to 12.8 VDC). parallel at 13.3 VDC) but isolated when discharging (i.e. Battery combiners operate based on a specific voltage so the batteries are parallel when charging (i.e. Battery combiners will put two battery banks in parallel when there is charging voltage but leave the batteries isolated during discharge. connected together) automatically when there is a charging voltage and separately when there is no charging voltage. Let’s look at what they do and how they are different?īattery combiners, also called Automatic Charging Relays (ACRs) or Voltage Sensitive Relays (VSRs) are designed to put two battery banks in parallel (i.e. Battery combiners and battery isolators serve similar purposes but achieve sharing a charge differently. In this month's Tech Talk we are going to look at some charging scenarios using battery combiners and battery isolators to automate and simplify the charging process of multiple battery banks with only one charging source. However, many boats only have one charging source, such as an alternator or inverter/charger, so marine electrical designers are forced to share one charging source to recharge more then one battery bank. In an ideal electrical world, engine and house battery banks would always be separate and have their own charging source. Thus, in most of the scenarios, Relay-based Isolator is the preferred choice for Dual Battery Applications involving battery banks of at least one Main Battery and one Auxiliary Battery.Keep Charged - Charging Scenarios Using Battery Combiners and Battery IsolatorsĪ 12VDC marine electrical system typically relies on one battery to start the engine and another battery to power the “house” loads, such as refrigeration, lights or an inverter. However, if the drain on the charging system by the auxiliary or main battery bank reduces the system voltage below a certain point, it will disconnect the battery banks from each other, protecting them from excessive drain. If the Relay-based Isolator determines that there’s not enough voltage in the primary source to perform an essential function, such as starting an engine, it will open the solenoid and allow current to flow from the auxiliary battery to make up the difference. When the engine starter is engaged, the Relay-based Isolator compares the voltage in both main and auxiliary batteries. Relay-based Isolator is best seen as switch that can direct current, enabling primary and auxiliary bank of batteries to be charged from a single source, using a solenoid. ![]() The higher the current, the bigger the voltage drop and the lower the efficiency of charging the dual battery. A Relay-based Isolator have no apparent voltage drop while for Diode-based Isolator there will be minimally 0.7V – 1.5V drop across the diode depending on the amount of current pass through.
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