![]() Victron also has their BMV 7xx series that has a small panel to observe data. You can see lots of valuable data with this free app. This monitor does not have a display but instead uses Bluetooth to connect to the Victron Connect app. For example, the Victron Smart Shunt is available in current ratings from 500 amps up to 2000 amps. The quality and features of each differ in various ways. Today there are a number of different shunt type battery monitors available. How do Shunt Type Battery Monitors Differ? You know this is a rough estimate and you can only guess how many miles you have left before empty. Your gauge says you have “half of a tank”. The voltage type meters are analogous to a gas gauge in a 1976 Dodge van. You can see how full your tank is, how many miles per gallon you are getting, how many miles to empty and how many miles per gallon you are getting at a given moment. Using the analogy of a fuel gauge in a car, using a shunt battery monitor is like reading the fuel gauge in a modern car. In summary, the shunt type battery monitor is more accurate than a voltage meter type. These are usually given in the specifications of the battery from the battery manufacturer. It also needs to know the resting voltage both when it is full and when it is empty. It needs to know the capacity of the battery. When you first set-up a shunt you simply need to program the battery monitor to know a few things. On the other hand, using a shunt to determine the current flow can be very accurate. As discussed previously, using voltage to determine the State of Charge (SOC) of a battery can be very inaccurate. How is the Shunt Type of Battery Monitor Different from a Voltage Meter?įirst, a voltage meter displays voltage while a shunt primarily displays current. So, by knowing the impedance of the shunt, the manufacturer is able to use even the slightest voltage drop to calculate, very precisely, the current through the shunt. This voltage drop is proportional to the current passing through the shunt. Simply put, even the slightest resistance in a shunt will cause a slight voltage drop. Ohm’s Law, V=IR can also be stated as, “at a constant resistance, any change in voltage is directly proportional to the change in current”. What is also important is that the impedance, like all resistors, is constant. It means that it will allow a high current to pass through it. The shunt in a battery monitor has an extremely low impedance. A resistor with a low impedance lets a lot of current flow through it. A resistor with a high impedance lets very little current flow through it. What does this mean? A resistor impedes electrical current from flowing through it. What is a shunt? The shunt in a battery monitor is a large resistor with a very low impedance. Why is a Shunt Battery Monitor More Accurate? ![]() As you can imagine, in an RV, the battery is rarely in this state. This means the battery has been resting for a while with no charge going in or out of the battery. In order to accurately determine the true charge of a battery, using voltage, you must read the “Resting Voltage” of the battery. Again, the voltage reading is false and causes an inaccurate reading of the amount of charge left in the battery. The more current drawn from the battery, the greater that voltage drop is. As soon as any load is put on the battery, there will be a drop in the battery's voltage. The second problem occurs when the battery is being discharged. We falsely believe the battery to have more charge than it really does. This causes the voltmeter or the 4-light gauge to show the battery voltage to be higher than it really is. The problem is that this causes a false voltage reading when that battery is being charged. The charge voltage needs to be higher because the difference in these voltages is what causes current to flow into the battery. The charger has a higher voltage than the battery’s voltage. The first occurs when a battery is being charged. There are a few reasons why these 2 types of gauges or meters are not accurate. Both of these gauges use voltage, however a voltmeter gives you a n umerical value as opposed to a series of 4 lights. Using a voltmeter is a better but still highly inferior to a good shunt style battery monitor. The stock battery gauge with the 4-lights is NOT accurate! It may tell you when the battery is fully charged and it may tell you when the battery is dead BUT, everything in between is a rough guess.
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