Re:load Pro

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Re:load Pro


The Re:Load Pro is an active load. It acts as a current sink, always drawing the same amount of current regardless of the voltage across it.

Active loads are incredibly useful for all sorts of electronics testing requirements. You can use one to see how a power supply performs under load, check if a battery lives up to its manufacturer’s specifications for capacity or current draw, test motor drivers, or a variety of common constant-current tasks, such as testing LEDs, or even doing electroplating. With computer control of the load, you can even do your own IV-curve tracing.

The original Re:load was born out of my frustration at being unable to find a reasonably priced active load for my fairly modest testing needs. Commercial units typically cost several hundred or even thousand dollars and require substantial bench space - far from ideal for a hobbyist.

The Re:load has turned out to be an incredibly useful device for many people, but while its minimalist feature set is well suited to some applications, often you want something with a bit more oomph, better precision, or extra features. That’s where the Re:load Pro comes in.

The Re:load Pro takes the robust design of the original Re:load and rebuilds it around a microcontroller. As a result, it offers a USB interface for power and control/monitoring, a good quality backlit display, and accurate voltage and current measurement. And that’s just for starters!

Features & Specifications

  • Dissipate 25 watts continuously, or more for short periods. Even more with the fan kit (see below!)
  • Handle up to 6 amps or 60 volts. Works right down to 0 V, too!
  • Easy to use and intuitive user-interface.
  • Current adjustable with milliamp precision over the whole range.
  • Protection against overcurrent, overvoltage, overtemperature, ESD, and reverse polarity.
  • Power supplied over USB from either a computer or a USB charger.
  • Fully isolated USB interface. Your computer is isolated from any direct interaction with dangerous voltages and currents.
  • Fully controllable over USB, with monitoring functionality. You can use your computer to program in a profile!
  • Configurable display, showing voltage, current, power, resistance, and total energy dissipated.
  • Open Source, with a USB bootloader, so you don’t need expensive development tools if you want to make your own modifications. Firmware updates will be easy to install, too! Check out the source repository.

What’s Inside the Box?

The Re:load Pro’s heart is a PSoC 4 microcontroller, from Cypress. The PSoC 4 combines an ARM Cortex M0 processor with configurable digital and analog blocks, making it possible to design incredibly flexible digital and analog solutions. This is ideal for the Re:load Pro, because it both cuts down on external components, which reduces cost and improves reliability, and makes it more flexible since a greater degree of the circuit is under firmware control.

The PSoC 4 in the Re:load Pro includes an integrated opamp, which the Re:load Pro uses to implement the active load functionality. Sophisticated features like a trim register and configurable compensation make it possible to wring the absolute best performance out of the opamp.

The other vital component of the Re:load Pro is the pass transistor - a BTS141. This unique component from Infineon acts like a regular FET transistor, but incorporates built in overcurrent, overvoltage, ESD and overtemperature protection. The BTS141 is a large part of what makes the Re:load so robust.

The heatsink and the enclosure are both high quality black anodised Aluminium. The heatsink is a custom extrusion, designed specifically for the Re:load Pro.

While the Re:load Pro was designed to be absolutely silent with passive cooling, adding even a little active cooling with some small fans can substantially increase the maximum continuous load the Re:load Pro can handle. Although it comes passively cooled by default, I’ve designed the PCB and the heatsink with optional active cooling in mind.

An optional fan kit adds two fans and a mounting plate that attaches to the heatsink - you can see the thick fins on either side that it’s intended to attach to - as well as a PCB with a fan controller that plugs into an expansion slot on the Re:load Pro.

Re:load Pro Fan Kit

Increase your Re:load Pro's sustained power dissipation from 25 watts to 50 watts!

This is a fan kit for the Re:load Pro, containing everything you need to boost your Re:load Pro’s sustained power limit from 25 watts to 50 watts! It includes a fan controller PCB with dual smart fan controllers, fans, and mounting hardware to attach it to your Re:load Pro.

These are currently in production, and will be shipping in January. Preordering now ensures you’ll get yours as soon as it’s available.

Full Kit Contents:

  • Pre-populated PCB with intelligent fan controllers
  • Headers for attaching the expansion PCB to the Re:load Pro
  • Thermistor, to be attached to the Re:load Pro heatsink, so fan speed can adjust with load
  • Two high quality 5v 40mm fans
  • Fan plate and mounting hardware (screws and standoffs) for mounting the fans to the back of your Re:load Pro

Is It Open Source?

Yes! Everything from Arachnid Labs is open source. The Re:load Pro is licensed under the Apache Public License, and you can get the current source code and schematics right here.

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Arachnid Labs

Arachnid Labs is a one-man operation that makes interesting, functional, and high quality electronic stuff.

Nick Johnson

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