How to Replace the Rectifier in a Battery Charger

The Schumacher SE-4020 is a common battery charger that has been used in the field for years. Like any piece of equipment, some components can eventually wear out or fail, and the rectifier is one of the components that may need to be replaced.

When the original rectifier is no longer available as a direct replacement, a universal-style rectifier can provide another solution. In this video, Rick and Scott demonstrate how to replace the original rectifier in a Schumacher SE-4020 with PLP Battery Supply’s 696640 universal rectifier kit, including how to mount and electrically insulate the new component inside the charger.

Key Takeaways

• In this walkthrough, we cover replacing the rectifier on a Schumacher SE-4020 battery charger with the PLP Battery Supply 696640 universal rectifier replacement kit.
• Because the replacement rectifier mounts differently from the original, a new mounting location and insulated mounting hardware are required. 
• Proper electrical insulation between the rectifier plate, mounting bolt, and charger cabinet is critical. 
• All wire and cable connections should be tight to prevent high-resistance connections. 
• The replacement rectifier offers substantially greater diode capacity than the original component. 

Replacing the Original Rectifier in a Schumacher SE-4020

The original rectifier in the Schumacher SE-4020 is mounted to a plastic fixture near the rear top portion of the transformer. It uses press-fit diodes and is mounted differently from the universal replacement rectifier.

The 696640 universal rectifier replacement kit uses a compact plate design with multiple button diodes. Because it does not attach to the original plastic mounting fixture, the installation requires a different mounting method.

Rather than trying to reproduce the original mounting arrangement, the replacement rectifier is secured directly to the back of the charger cabinet using a mounting bolt. This is one of the advantages of a universal replacement: it can provide a practical solution even when the original component uses a unique mounting configuration.

1. Disconnect and Remove the Original Rectifier

Before beginning any work, make sure the charger is completely disconnected from power.

Start by disconnecting the wires from the original rectifier. The secondary wires coming from the transformer use quarter-inch push-on connectors, so carefully work those connectors loose and move the wires out of the way.

You'll also need to disconnect the charger's DC output cable from the rectifier. Set that cable aside because it will be reused with the new rectifier. 

Once all of the wiring is disconnected, the original rectifier can be removed from its plastic mounting fixture. With the old component out of the charger, you're ready to prepare the mounting location for the new one.

2. Create a New Mounting Point

The 696640 universal rectifier doesn't mount to the original plastic fixture, so you'll need to secure it directly to the back of the charger cabinet. Position the new rectifier inside the charger and determine where the mounting bolt needs to pass through the cabinet. Once you've established the proper location, drill the mounting hole.

The exact placement is important because you want the rectifier to sit securely inside the charger while leaving enough room for the wiring and other components.

3. Properly Insulate the Rectifier

This is one of the most important parts of the installation. The rectifier plate needs to remain electrically isolated from the mounting bolt and the metal charger cabinet.

The replacement kit includes the insulating hardware needed to accomplish this. Start with the nylon shoulder washer, which fits through the mounting point on the rectifier and keeps the bolt insulated from the plate. A large nylon insulating washer is also used around the mounting area to create additional separation between the rectifier and the surrounding metal.

Together, these pieces create an insulated mounting assembly. Once the hardware is stacked correctly, the rectifier can be placed over the mounting stud and secured with the included nut. Before tightening everything down, check that the insulating pieces are sitting correctly and that the rectifier plate cannot make electrical contact with the charger cabinet or mounting bolt.

Once tightened, the rectifier should be firmly mounted while remaining electrically isolated from the cabinet.

4. Reconnect the Wiring

With the new rectifier securely mounted, it's time to reconnect the wiring. The secondary wires from the transformer connect to the terminals on the new rectifier using the supplied hardware. In this particular application, the terminals are tied together on the same side of the rectifier, so there isn't a specific right-side or left-side orientation for these connections.

Next, reconnect the DC output cable that was removed from the original rectifier. The replacement kit includes the nut and bolt needed for this connection.

As you reconnect everything, pay close attention to the tightness of each connection. A loose wire or cable connection can create high electrical resistance, which can lead to heat and poor performance. Taking an extra moment to make sure each connection is secure can help prevent problems later.

The supplied hardware also includes a serrated flange washer that helps lock the connection in place without requiring a separate lock washer.

5. Testing the Finished Repair

Once all of the wiring is connected and you've confirmed that the rectifier is securely mounted and properly insulated, it's time to test the charger.

Set the charger to a low setting and turn it on. In the video walkthrough, you’ll see the charger fan starts running and voltage is present, indicating that the replacement rectifier is working correctly. A successful test confirms that the new rectifier is installed and functioning as intended.

Why Use a High-Capacity Replacement?

One of the notable differences between the original rectifier and the 696640 is the amount of diode capacity available. The original rectifier removed from the SE-4020 uses two 70-amp press-fit diodes, providing approximately 140 amps of capacity. The 696640 replacement uses six 50-amp button diodes on each side of the rectifier. That provides approximately 300 amps of capacity per side, or about 600 amps across the entire rectifier assembly.

Each diode is also fused, providing additional redundancy within the design. If one or two diodes were to fail, the remaining diodes can continue carrying the load. For an older charger like the SE-4020, that makes the 696640 a robust replacement option that can potentially outlast the charger itself.

Keep Your Older Chargers Working

Replacing the rectifier in a Schumacher SE-4020 can seem complicated at first, but this walkthrough video helps make the process straightforward. The result is a high-capacity replacement that can help extend the useful life of an older SE-4020.

Need a replacement rectifier for a Schumacher SE-4020 or another battery charger? PLP Battery Supply can help you find the right component for your application. Visit PLP Battery Supply to order the 696640 universal rectifier kit today.

Contact our team at team@plpbattery.com or 800-642-3451 with questions about your charger or replacement parts.