Maker Sebastian Harnisch’s bench gear assortment has grown once more with the design and improvement of a programmable energy resistor, able to dealing with a 400W peak — and, as soon as once more, the result’s one thing that appears prefer it may simply have come from any one of many huge check gear makers.
“For the efficiency checks and calibration of my Agilent 6811B AC Energy Supply/Analyzer (375VA) I want a 20 Ohm resistor with a ton of energy dealing with functionality,” Harnisch explains. “The unique plan was to mount 8 wire wound 50W resistors on a warmth sink and be executed with it. Then I believed: why not reuse all of the code I’ve already written for the programmable resistor and construct a programmable excessive energy resistor that may complement my DC load for AC purposes.”
Persevering with his do-it-yourself instrument development, Sebastian Harnisch has constructed a programmable energy resistor. (📷: Sebastian Harnisch)
As Harnisch writes, again in July final yr he confirmed off one other programmable resistor design, which he self-deprecatingly described as a “glorified decade resistance field.” This offered the bottom for his newest creation, which takes the identical idea — a digital machine that may be programmed to ship the required resistance on-demand — however presents help for a excessive electrical load.
“On this utility the main focus is on energy dealing with functionality, not a lot a excessive decision (excessive variety of resistance values) or precision,” Harnisch explains. “This is the reason the topology used within the programmable precision resistor isn’t as appropriate for this utility because it has been earlier than. Additionally my ELMA circumstances are actually small (and I imply actually small, so thermals will likely be a problem by itself), so I can not merely enhance the variety of energy resistors and relays within the course of. That is why I am going to stick with the unique plan of utilizing eight energy resistors.”
The machine itself is cut up throughout two boards: a relay and interface board, which incorporates the relays required to modify the present by means of the required mixture of energy resistors to ship the chosen resistance worth; and a person interface and controller board, which an STMicroelectronics STM32G441RBT6 microcontroller — the one one within the construct. Like Harnisch’s earlier desktop thermometer, it additionally gives a Commonplace Instructions for Programmable Devices (SCPI) interface over USB, along with the programmable resistor’s front-panel controls and on-board show.
The majority of the chassis is taken up with heatsinks, to forestall the resistors overheating below excessive load. (📷: Sebastian Harnisch)
“I’ve some concepts for a second revision with some minor enhancements and variations (like integrating the PWM-to-voltage circuits), but in addition one new function: A easy voltage measurement,” Harnisch writes of a possible improve to the design. “This not solely permits for a useful show of the voltage, present and energy, but in addition extra fan management choices and safety options.”
The undertaking is detailed on Harnisch’s weblog in a sequence of posts going again to early March this yr.
