With Lithium batteries this is easily done as the BMS has to know current flow and voltage to operate. It may seem obvious, but the best way to measure State of Charge is inside the battery itself. For Lithium batteries such a "mixed bag" of charging devices leads to a long term problem. Imagine the difficulty when the system is a combination of various brands, or even if the same brand, different charging algoithms in each. Typically the cabling to each charge device is not even and the measured voltage will be slightly different at each charger. Victron have a "shared voltage" and "Shared current" sense values that as the name implies shares the same voltage value accross all devices by a data network. This requires all the charging devices to charge at exactly the same level with the same parameters. Victron also have a Storage mode that relaxes Lithium batteries to reduce chemical ageing. Commonly these levels are referred to as Bulk, Float levels. Based on the measured voltage at the charger, the battery charger, whether AC, Solar or DC to DC will operate at a programmed voltage level. A small voltage drop can make a difference in some systems. This introduces another problem: the voltage drop between the charger and the battery. Using a current shunt, 100A charging a battery at 14.4V and 100A discharging a battery at 12.5V will look the same, but the energy difference is 14%.įortunately, most charging systems don't use SOC but voltage levels to charge. Stored energy is measured in Watt hours which takes into account the voltage. There is another minor problem that measuring amp hours with the shunt does not take into account the voltage. At best, the calculated SOC may be 5% accurate, at worst 25%. There is a charge efficiency factor and Peukerts factor, the exact battery capacity and C5, C10 and C20 values. There are problems with this type of measurement as it is a calculation by an unrelated system based on parameters that the user enters. A 100Ah battery, for example, with a shunt measuring 100A discharge will show the "time to go" as 1 hour. Stored energy in a battery is commonly referred to as Amp Hour capacity. Then based on the enterred value for the battery capacity, the battery monitor counts down, and up, as the current flows in and out. Such a monitoring system, like Simarine, resets the SOC to 100% when the battery voltage is high and only a small amout of current is flowing. They are needed to calculate "State of Charge" in a battery by a monitoring system. They are "in the power circuit" and because they are large devices, typically are placed on the negative lead from the batteries to the loads. Traditional Shunt based Battery State of ChargeĪ "shunt" is a large piece of metal with a precision low value resistor that measures the current flow through it by voltage drop accross it. Video on compelling benefits of 48V Systems Power Packs for 400V High Energy Density Marine.Power Packs suit Caravans Outside Locker Fitment.Portable 240V Power & Lithium in a Case.Black Tie Cases with Inverter & 240V Power.Power Packs To Suit Iveco Daily and 4x4.Power Packs to Suit VW Crafter and MAN TGE.
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