Uninterruptible Power Supply (UPS)

Enhancing Power Stability with a Manual Reset Circuit

In today's connected world, a reliable power supply is essential. While an Uninterruptible Power Supply (UPS) is the standard for protecting against power outages, it can face challenges with an unstable grid, particularly during "flickering" power—a series of rapid on-off cycles.

To address this, we've implemented a custom solution using a contactor and a manual reset button. This setup provides an additional layer of protection, preventing the UPS from being subjected to multiple, stressful power cycles and ensuring a stable and predictable restart process after an outage.

How It Works: The "Manual Reset" Advantage

This custom circuit acts as a gatekeeper for your power supply.

1. Initial Connection: When mains power is available, the system remains in a safe, disconnected state. Power does not flow to the UPS until you, the user, manually engage it.

2. Manual Activation: By pressing a "Normally Open" (NO) push button, you energize a magnetic coil inside the contactor. This closes the internal contacts, allowing the main power to flow to the UPS. Your UPS can now operate normally, charging its battery and providing conditioned power to your connected devices.

3. Power Outage: If a power cut occurs, the contactor's magnetic coil instantly de-energizes, causing the contacts to open and severing the connection from the main supply. The UPS immediately switches to its internal battery power, keeping your computer and other devices running.

4. Stable Recovery: When the mains power returns, the contactor does not automatically close. This is the critical advantage of this setup. It prevents the UPS from connecting to a potentially unstable grid that might still be experiencing flickers. The connection remains open until you are confident the power is stable.

5. Manual Reset: Once you've confirmed that the power is stable, you press the NO button again to manually re-engage the contactor, allowing the UPS to safely reconnect to the mains and resume normal operation.

Building Your Own Custom UPS: A DIY Guide

Building your own uninterruptible power supply (UPS) offers a flexible and repairable alternative to a pre-built unit. Here’s a basic guide on how to assemble a custom UPS.

1. Electrical Connections:

Main Power Supply:

• Use NO to make a direct connection in between 230v power supply and the output sockets of the assemble UPS.

 Inverter Connection:

•  Use NC to make a direct connection in between Inverter output and the output sockets of the assemble UPS.

 Battery and Charger:

(Safe-charging Current for 12v 7ah lead-acid battery = 0.7 A)

• Connect the positive terminal of the battery to the positive input of the inverter.

• Connect the negative terminal of the battery to the negative input of the inverter.

• Connect the output of the battery charger to the positive and negative terminals of the battery.

 Socket Connections:

• Connect all your output sockets in parallel. These are the outlets where you'll plug in your devices.

• Be mindful of the total power draw. A 12V 7Ah battery powering a 1.4A load at 230V will only last about 13 minutes. Avoid connecting high-power appliances to prolong the battery's runtime.

2. Control Logic

The contactor is the heart of this system, automatically switching between power sources without needing a complex transfer switch (like an ATS or SATS).

• When Main Power Is Present: The contactor's coil is energized by the main power, which closes the NO contact. This connects your devices directly to the main power supply and opens the NC contact, disconnecting the inverter.

• During a Power Outage: The coil loses power, causing the NO contact to open (disconnecting the main power) and the NC contact to close. This instantly connects your devices to the inverter, which is powered by the battery.

3. Safety and Maintenance

A. Safety First:

• Overcurrent Protection: Use fuses on both the main power line and the inverter's output to prevent damage from power surges.

• Battery Charging: Ensure your charger is correctly sized for your battery and includes overcharge protection to extend battery life.

• Grounding: Properly ground all components and the chassis to prevent electric shock.

• Enclosure: House all components in a suitable enclosure to protect them from dust, moisture, and accidental contact.

B. Regular Maintenance:

• Periodically check the battery's charge and inspect all connections for corrosion or loose wires.

• Test the system regularly to ensure it switches over correctly during a simulated power outage.

• Replace components as needed to keep the system running smoothly.

The Advantages of a Custom Build

This DIY approach offers several benefits:

• Modular Design: Using contactors creates a modular system where components can be easily repaired or upgraded.

• Flexibility: You can customize the system to match your exact power needs, whether you need a smaller battery for a few minutes of runtime or a larger one for longer protection.