Inverter Battery Charger with Cut Off

The Blog Stat shows that most of the readers are interested in Battery Maintenance as indicated in the Tag cloud. So I wish to post a Friendly Charger circuit for the battery. This Battery charger can replenish any kind of 12 V Inverter battery or Car battery and keep it in top condition. The charger never allows the battery to Over charge or Deep discharge. It automatically charges the battery when its terminal voltage drops below 12 volts and switch off the charging process when the terminal voltage rises to 13.5 volts. So that the battery can be kept unattended.

Working of the circuit is too simple. The 15-0-15 – 1 Ampere step-down transformer with its rectifiers D1 ,D2 and smoothing capacitor C1 provides 15 Volt DC to the Three terminal variable voltage regulator IC LM317. It can handle up to 1.5 ampere current and can vary the output voltage from 1.2 volts to 37 volts. The output depends on the feed back from the out put pin (pin 3) to the adjust pin (pin1) of LM 317. By adjusting VR1 it is easy to set the output voltage from 1.2 V to 15 V DC. The charging current depends on the values of R1 and R4 and around 300 milli amperes current is available for charging at 15 volt DC.

Important : The ground connection of the transformer is seen missing  in the diagram . So connect the centre tap of 15-0-15 transformer to negative rail.

When the output is available from IC1, Green LED lights and current flows through diode D3 and resistor R4 to the battery provided the battery voltage is below 12 volts. Zener diode will not conduct in this state since the battery takes all the current for charging. When the terminal voltage of battery rises to 13.5 volts, the current flow to the battery ceases and Zener gets breakdown voltage and it conducts. The current from the Zener forward bias T1 so that all the output current from LM 317 will be drained through T1 to the ground as indicated by the Red LED. This stops the charging process. Charger remains in this state till the battery voltage drops below 12 volts (break down voltage of Zener). If this happens Zener turns off and T1 switched off allowing output current from LM317 to pass into the battery for charging again.

Battery is just like a Baby. It requires continuous attention and care. Click on the following links to read the articles related to batteries and maintenance.

Tricky charger     Battery Over charge Indicator Tubular Battery Maintenance Battery Needs Care More About Lead Acid Battery Inverter Selection Inverter Online – Off line UPS

8 responses to “Inverter Battery Charger with Cut Off

  1. we are having 30KVA ups for backup we have connected 32 nos. exide powersafe 12v 75AH batteries in series. out of 32 batteries 1 battery is showing 10.5v .so please tell me is it necessary to remove it because of this ups not giving 5 min backup ?can we add extra batteries in it or remove one from it ?,can we keep spare batteries with us ?if yes then how to charge them ?waiting for your reply,thanking you

    • Dear Yogesh
      The problem is with that faulty battery. If any one of the battery connected in series fails, it will take all the currents and will not allow other batteries to charge. Net result is all the batteries will damage. So remove the battery showing 10.5 V and check the terminal voltage of other batteries(after disconnecting the charger and load. If the charge is above 12 volts it is OK.Frequently check the terminal voltage of batteries if they are in series.Replace the batteries showing less than 12 volts( after full charging).

      • thanks a lot 4 ur reply .i have one question we are having 30 kva ups we have connected 12V 75AH 32 nos of batteries in series for backup.can we add one more battery in series or if one of the battery is faulty can we remove one battery out of 32 ? waiting for ur reply

      • Hello 12 Volt batteries are connected in series to add voltage of each. 12×2=24. 12 x 32 =? Is it in series or parallel?. What is the volt rating of the inverter. 30 KVA is its load rating. Invereters are usually 12V, 24V, 48V etc.If you add one more battery it will increase volt rating but increases backup time.

        Please specify 1. Volt rating of UPS/Inverter 2. Battery in Series or Parallel