DIY a Linear Bench Power Supply on a Budget: Transformer Scavenging and Component Reconstructions

Introduction to DIY Power Supplies

Building a linear bench power supply on a budget is both a practical and creative endeavor. This guide will walk you through the process of transformer scavenging and component reconstructions to create a powerful and reliable bench power supply that can be used for electronics projects and testing.

Scavenging for Affordable Transformers

The transformer is the heart of any bench power supply, and it is often the most expensive component. However, online purchases can be costly. An alternative is to find a battery charger at a garage sale or thrift store. While you might need to replace the selenium rectifier with a silicon bridge rectifier, and add a voltage regulator, this can be a relatively inexpensive and easy task.

Step 1: Finding a Suitable Transformer

Look for a battery charger with a 120 to 24 volt 80 VA or bigger transformer. You can also find suitable transformers in old electronic equipment, such as:

Step 2: Reconstructing Components

Once you have found a transformer, the next step is to reconstruct other necessary components. For the bridge rectifier, LM338K variable voltage regulator, and a linear-taper pot, you can find these items online or at electronic component stores for around a few dollars.

Thrift Store Stereo Receivers: A Solid Starting Point

Thrift stores often have old stereo receiver models that are heavy and powerful. These receivers typically have a large power transformer, big diodes, large capacitors, and large power transistors. You can use these as a good starting point for a regulated power supply.

After removing the tuner and all other controls, except for one linear-taper pot, you can strip the circuit boards and rewire the PC board pads to the linear-taper pot. This will give you an adjustable and regulated DC power supply.

Transformers from Photocopiers

Old photocopier machines often have transformers rated at 240/110/24 volts and 500 VA or bigger. You can find these transformers by asking in office buildings that may be awaiting collection by scrap dealers.

Vintage Audio Hi-Fi Stereo Receivers

Another option is to find a 1970s or 1980s vintage audio hi-fi stereo receiver that has a broken output, but whose transformer and components are still functional.

The main bus voltage can range from 20 to 60 volts and often includes big capacitors and a bridge rectifier. To ensure the power supply can handle high currents, you will need a large heatsink and fans, as well as beefy pass transistors.

Microwave Ovens: Hardcore Transformers

Microwave ovens contain powerful transformers that can be rewound using an angle grinder. These transformers can be found at thrift stores or second-hand shops like Goodwill. However, be cautious about the baby fist-sized capacitors, as they can be dangerous when discharged with a screwdriver.

In conclusion, building a linear bench power supply on a budget involves a mix of resourcefulness and creativity. By scavenging for components and reconstructing them, you can create a reliable and powerful bench power supply without breaking the bank.