Automatic 12V Battery Low Voltage Cut-Off Circuit Using LM358

 A low voltage cut-off circuit is an essential protection system for 12V  batteries. Deep discharging a  battery can significantly reduce its lifespan, performance, and charging capacity. This is especially important in battery-powered systems such as solar power systems, UPS units, inverters, portable power supplies, and automotive applications.

In this project, we will discuss a simple and reliable Automatic 12V Battery Low Voltage Cut-Off Circuit using LM358. The circuit continuously monitors the battery voltage and automatically disconnects the load when the battery voltage falls below a preset level.

When the battery voltage rises again after charging, the circuit can reconnect the load automatically, depending on the circuit configuration.

This project is easy to build, inexpensive, and suitable for electronics hobbyists and DIY enthusiasts.

Circuit Diagram

The circuit uses an LM358 operational amplifier as a voltage comparator.

Batteries

The battery voltage is monitored using a resistor divider network. A reference voltage is provided to one input of the LM358, while the battery voltage is connected to the other input. Read more

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How To Build A Simple 5 V USB Solar Charger (No Battery)?

 How to build Simple 5 V USB Solar Charger (No Battery)? Charge phones/power 5 V gadgets directly in sunlight.

Chosen specs

• Panel: 15 W “12 V” nominal mono panel, Vmp ≈ 18 V, Voc ≈ 22 V, Isc ≈ 0.9 A (common size ~300×350 mm)

• Output: 5.0 V regulated, up to ~2 A peak (realistic ~1–1.5 A in good sun)

Topology

Panel → blocking diode → buck converter (to 5.00 V) → USB-A

Panel + ── Fuse(2A) ──|<|── +IN  Buck (LM2596 or MP1584)  +OUT ── +5V → USB-A pin 1

            D1: SS34   |                         

Panel − ─────────────────────── GND ───────────────── GND → USB-A pin 4

                             TVS(SMBJ24A) across +IN↔GND (optional)

BoM (example parts)

• Solar Panel: 15 W, 12 V nominal, Vmp ~18 V, Isc ~0.9 A

• D1 Blocking Diode: SS34 (3 A, 40 V Schottky) — low drop, low reverse leakage

• Buck Module: LM2596 (3 A rated) or MP1584EN-based mini buck (3 A rated)

• USB-A Female Jack: panel-mount or PCB type

• Fuse (Panel+): 2 A blade or mini inline

• TVS Diode (optional): SMBJ24A across buck input

• Cable: 20–22 AWG for short USB, 18 AWG from panel to buck if >0.5 m

• Enclosure: Small IP65 junction box, cable glands

Build notes

• Set buck to 5.00 V with a multimeter before connecting a device.

• Many LM2596-USB boards include data-pin resistors for phone charging. If using a plain USB jack, add 49.9 kΩ pull-downs or a “dumb charger” divider (D+/D− short or 2.0 V/2.7 V depending on device). Most modern phones accept D+/D− short.

• Mount SS34 in series with panel + (stripe towards buck).

Testing

1. Measure panel Voc in sun: ~20–22 V.

2. With panel connected and no load, verify buck input 16–20 V, output 5.00 V.

3. Plug a 5 V dummy load/phone—expect 0.5–1.5 A; output should hold 4.9–5.1 V.

Sourced By: Streampowers

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Simple 100W Inverter Schematic Diagram

This is the Simple 100W Inverter Schematic Diagram. An inverter will convert the DC voltage to an AC voltage. In most cases, the input DC voltage is usually lower than the output voltage of the inverter while the output AC is equal to the grid supply voltage 120 volts, or 240 Volts. Lets start it.

Simple 100W Inverter Schematic Diagram

Circuit Part List

Resistors
22K Resistor 3x
220 Ohm Resistor 2x
100 Ohm Resistor 1x

Diode
4007 Diode 1x
10V Zener 1x

IC
4047 IC + 14 Pin IC socket 1x

Capacitor
0.01uf capacitor 1x
100uf capacitor 1x

MOSFETS
IRF 3205 mosfet 2x

Varo Board

Transformer
Center Tap (CT) Transformer. Input 12-0-12, while the output refer to your standard home electricity (every county may different).

In the tutorial, it use 12-6-0-6-12 5 amp Transformer you can call it 120 VA transformer. You can use any kind of 12 -0-12 transformer.

Please take a note that this inverter can handle up to 100w of load but be careful, on the 100w of load you should use Heatsinks with those mosfets.

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Door Opener Alarm Circuit Diagram

The door opener derives its power from a 9-V battery. A momentary-contact switch, 52, is provided in the event that manual opening and closing is required. Relay Kl is a 9-V type and relay K2 is a 117`Vac latching-type, which automatically latches with the first burst of current and opens on the second burst.

Door Opener Alarm Circuit Diagram

The gate lead of the LASCR is not used; a light source triggers the LASCR unit into conduction, causing current to flow in the coil of the relay. That, in turn, causes Kl`s contacts to close, thereby energizing K2 (closing its contacts), and operating the garage door motor.

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