NCP1117 Board Load Test (Part 1)

I’ve always wanted to push my voltage regulator board to its limits. The easiest way I figure is to get some low value power resistors to draw “high” amounts of current from the regulator board. I happened to pass by a local electronics supplies store today so I picked up a couple of power resistors, as well as some test leads and a flush wire cutter.

As a side note, I was actually looking for some test leads that have that wire hook thing but they didn’t have any that I liked. I didn’t own any test cables so I’m glad I picked up these alligator-to-alligator test cables. They were an impulse buy on the way to the cash register, where the cashier commented that he personally liked them. They are actually quite nice, though I find them a bit slippery when trying to squeeze open the clips.

Anyways, lets look at how the test went.IMG_20150628_163532 (1)It was a pretty simple setup, especially with the help of my new test leads. I connected the resistor between the +5v and ground output terminals of the regulator board. I had my multimeter in series with the resistor to measure the current. I used a 9v power supply to power the board.

One of the resistors is a 5-ohm 22-watt resistor. It pulled 880mA from the board. The other resistor, which is connected in the picture above, is a 6.8-ohm 5-watt resistor. It pulled 650mA from the board. Both tests caused the thermal overload protection to kick in. In under 15 seconds with both loads, I could hear a buzzing noise coming from the board and see that the current was dropping. The current dropped rapidly to about 350mA where it slowed its pace dropping down, about a mA per second. I didn’t want to leave it for too long so I pulled the plug around this point.

Blowing on the board to attempt to cool it off brought the current back up. I always thought that the thermal overload protection would act like a switch where you’d get no current at all from it, but it looks as though it doesn’t work quite like that.

Linear voltage regulators can be trickier than they seem, at least if you plan on pulling good amounts of current from one. It’s a good idea to expect that your linear regulator will get hot (that’s how they work anyway, it’s sometimes hard to appreciate it with low current projects producing negligible heat) so consider heat sinks and ventilation.

To update those who actually follow along with new posts, I got a job earlier this month (not electronics related, unfortunately). While I don’t have as much time as I did before to work on my projects, the income does allow me to buy more things for my experiments. Coming in next week is a new bench power supply which should make this load test experiment more interesting with different input voltages and current readings from the source power supply. I’m excited.

I also updated my Atmega328p Breakout Board and am waiting for those PCBs.

I hope I can start posting more again as I adjust to things. Stay tuned and thanks for reading!


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