General recommendations for selection of charge controllers

  1. It is essential to use a charge controller that protects the battery from both overcharging and deep discharging (by disconnecting the load).
  2. It is preferable to use a charge controller with adjustable set points. The choice of the settings of the charge controller is important for all battery types and must be chosen in accordance with the specifications of the battery manufacturer for RE systems. The charge controller should allow the battery to reach an equalization voltage from time to time. Some charge controllers lower the charge voltage after reaching full charge (float charging). If no recommendations for the battery are given then following settings should be used.
    Default battery voltage set points.
    Battery type => Vented / Flooded
    V per cell at 25°C    		 Sealed / VRLA
    V per cell at 25°C
    Bulk/boost charge
    2 hours / day    		 2.4 2.4
    Equalization
    6 hours / month    		 2.45 to 2.55 2.45
    Low voltage Disconnect,
    for discharge current I10    		 1.80 to 1.85 1.80 to 1.85
    Low voltage Disconnect,
    for discharge current 10% of I10    		 1.95 to 2.0 1.95 to 2.0
    Float charge 2.35 2.30
  3. If the battery will be operated outside the temperature range of 20-30 degrees it is preferable to use a charge controller that compensates for the effect of the battery temperature. It will adjust the controller settings to ensure that charge and discharge cycles are modified based on temperature. The sensor should be attached to or placed in the electrolyte of a battery in the middle of the array to ensure that the actual battery temperature is measured instead of the ambient temperature. The control algorithm of the charge controller can be based on a SoC calculation or on voltage settings. It is preferable to use a charge controller that protects the battery from a low state of charge by calculating the SoC of the battery. The settings of the controller must be chosen in accordance with the specifications of the battery manufacturer. If no specification is given, typically a minimum SoC value of 70% for the common car battery and 20% for batteries designed for deep discharge operation should be used.
  4. It is preferable to use a charge controller with separate voltage sense-terminals. Otherwise the resistance of the cable between the battery and the charge controller, in combination with the charge or discharge current, can result in an incorrect voltage measurement.
  5. It is essential to ensure that the charge controller has a means for selecting the applied type of battery (i.e. vented or sealed) to ensure that the correct charge regime is applied for battery type. This is especially important for VRLA batteries since overcharging will dry out the battery electrolyte.
© ECN-DEGO. Last update: 27-dec-04. For information: dego@ecn.nl
Energy research Centre of the Netherlands (ECN) P.O. Box 1, 1755 ZG Petten, tel. +31 224 56 49 49