Active Load

3 Articles

Build Your Own Active Load

February 11, 2020 by 28 Comments

When it comes to testing power supplies, it’s useful to have a dummy load to put the gear through its paces. While it’s possible to just use some old heating elements or other big resistors, an active load can provide more control over the process. [Charles Ouweland] found himself in need of just such a piece of gear, and decided to build his own.

Commercial units often pack in a raft of features, operating in different modes from constant resistance, constant power, and constant current. For [Charles]’s needs, just constant current would be fine, and thus the design progressed around this constraint.

The IRFP250 MOSFET specified in the build can dissipate up to 190W, but as it heats up, this is reduced. In this design, cooled by a heatsink and PC fan, [Charles] estimates 120W continous output is a safe limit. It’s combined with an LM358 op-amp and TL431A reference voltage source to act as a current sink, controllable between 0 and 10 amps.

We’re sure that the new hardware makes testing power supplies a cinch for [Charles], and it’s always good to have a strong understanding of the workings of your own test gear. We’ve seen open-source designs in this space, too!

Improving Active Loads

May 3, 2015 by 6 Comments

[Texane]’s job requires testing a few boards under a set of loads, and although the lab at work has some professional tools for this it seemed like a great opportunity to try out the Re:load 2. It’s a nifty little active load that’s available can of course be improved with an injection of solder and silicon.

While the Re:load 2 is a nice, simple device that can turn up to 12 Watts directly into heat, it’s not programmable. The ability to create and save load profiles would be a handy feature to have, so [Texane] took a Teensy 3.1 microcontroller and installed a resistor divider in front of the Re:load’s amplifier. A simple script running on a computer allows [Texane] to set the amount of current dumped and automate ramps and timers.

There is a more fundamental problem with the Re:load; the lowest possible current that can be dumped into a heat sink is 90mA. [Texane] replace the amplifier with a zero-drift amp that brought that 90mA figure down to 7mA.

Of course the Re:load and Teensy 3.1 are sold in the Hackaday store, but if you’re looking for a ready-built solution for a computer-controlled active load you can always check out the Re:load Pro, a fancy-smanchy model that has an LCD. The Pro costs more, and [Texane] just told you how to get the same features with the less expensive model we’re selling, though…

Re:load Pro, An Open Source Active Load

April 16, 2014 by 37 Comments

Open source test equipment has to be one of the best gifts open source hardware has given back to the community. Nowhere is this more true than in the case of  [Nick’s] Re:Load Pro over on Kickstarter. Unlike resistors or similar dummy loads, an active load will always draw the set amount of current regardless of voltage. Active loads are often used to test power supplies and batteries. Is that 2500 mAh LiPo battery overstating it’s capacity? Can the power supply you just designed handle 2.5A at 12V? Both of these are jobs where active loads would come in handy.

The Re:Load Pro is actually the third version of the Re:Load. [Nick] designed the original Re:Load after becoming frustrated at the lack of a cheap active load for testing a power supply. Plenty of people showed interest in the Re:Load, but they wanted more features. That’s where the Re:Load Pro comes in. More than a straight analog design, the Pro has a Cypress PSOC 4 Arm Cortex M0 processor running the system.

[Nick] and his company, Arachnid Labs, are no strangers to us here at Hackaday. When we last covered [Nick], he was asking the USB Implementers Forum about a low cost Vendor ID option for open source hardware projects. Fittingly, the Re:Load Pro is an open source project. The schematics and source code are available on Github.

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