Low Voltage Lead Acid Battery Disconnect board – Prevents Deep Discharge Of 12V Lead Acid Battery

  • Rajkumar Sharma
  • 1234
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  • easy
  • Tested

This project helps to optimize the 12V lead-acid (SLA) battery life as it prevents the battery from going into deep discharge. It is very important to disconnect the load before the battery enters into deep discharge as this may destroy or damage the battery cells.  The circuit shown here turns off the load before the battery enters deep discharge and avoids a further (deep) discharge that can shorten the SLA battery life. Once the battery is recharged or replaced you need to push a reset switch to power ON the load.  The predetermined load level is set to 12V, this voltage level is proportional to the battery voltage which is determined by resistor divider R2, and R9. Once the voltage falls below the setpoint (12V) it disconnects the load, the load-battery connection remains open until the system receives a manual reset command using tactile switch SW1.

The circuit drains 5uA + PWR LED D2 5mA, so the circuit can remain in that state for an extended period without causing a deep discharge of the battery. Users may not use LED D2 if not required.  The circuit is capable to drive continuous load up to 5A and can provide more power with forced air cool to the MOSFET Q1. Connector CN1 is optional if the user wants to use TO220 MOSFET. The project is ideal for 1Ah to 10Ah 12V lead-acid batteries. Low ohm MOSFET is used to provide continuous maximum current output.

Note: Default Trip voltage (disconnect voltage) level is set to 12V, this can be changed as per user requirement. Use this formula to calculate the V-Trip voltage V-Trip=1.15V(R9+R2)/ R9

Features

  • Input Supply (12V Lead Acid Battery)
  • Continues Load up to 5Amps
  • Deep Discharge Disconnect Voltage Level 12V
  • Large size PCB thermal area provided for MOSFET for heat dissipation
  • On-Board Tactile Switch for Reset the output
  • LED D2 Indicates Battery Power
  • LED D3 Indicated Load ON/OFF
  • Screw Terminal CN2 Battery
  • Screw Terminal CN1 Load
  • PCB Dimensions 68.10 x 60.33 mm

Schematic

Parts List

NO.QNTY.REF.DESC.MANUFACTURERSUPPLIERSUPPLIER PART NO
11CN1Q1-TO220 DNP
21CN22 PIN SCREW TERMINAL 5.08MM PITCHPHOENIXDIGIKEY277-1247-ND
31CN32 PIN SCREW TERMINAL 5.08MM PITCHPHOENIXDIGIKEY277-1247-ND
42C1,C310uF/16V SMD SIZE 1206MURATA/YAGEO
51C20.1uF/50V SMD SIZE 0805MURATA/YAGEO
61D11N4007 SMD DIODEDIGIKEYS1MBDITR-ND
71D2LED RED SIZE 0805OSRAMDIGIKEY475-1415-1-ND
81D3LED GREEN SMD SIZE 0805OSRAMDIGIKEY475-1410-2-ND
91Q1FDD4141 MOSFETON SEMIMOUSER512-FDD4141
101R11M 5% SMD SIZE 0805MURATA/YAGEO
111R2100K 1% SMD SIZE 0805MURATA/YAGEO
122R3,R71K 5% SMD SIZE 0805MURATA/YAGEO
133R4,R5,R6DNP
141R80E SMD SIZE 0805MURATA/YAGEO
151R910.5K 1% SMD SIZE 0805MURATA/YAGEO
161SW14 PIN TACTILE SWITCHC&KDIGIKEYCKN9085TR-ND
171U1MAX8212MAXIMDIGIKEYMAX8212ESA+-ND

Connections

Gerber View

Photos

Video

MAX8212 Datasheet

MAX8211-MAX8212

PCB

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