Cheap and easy way to load power bricks / wall wart power supplies? - Page 1
Forum section: electronics / beginners

author: Dan123456
author_rank: Regular Contributor
timestamp: September 24, 2023, 06:37:47 am
content: Hey again all allHopefully a quick and easy on for you today!What is a cheap and easy way to simulate a load on a DC power bricks / wall wart power supply to test them?Situation is, I was testing a bunch of spare power bricks I have by just jamming my multimeter probes down the hole and was getting some voltage readings wildly higher than what was listed (like 3X on some).At first I assumed those ones had just copped the dick, but did a little research to find people saying the same thing and being advised that the power supply had to be loaded close to max output to get the correct voltage out (I’m not sure if the “max output” part is true or not but it does make sense that having a load hooked up would make a difference).Would a simple chunky potentiometer or a few nice fat resistors do the job to get a rough indication if the power supplies are good / help me determine if I do in fact need to load them close to max to get the listed voltage?Or is it a bit more complex than that?Thanks in advance!Google wasn’t being much help on this one as was just telling me how it is done with specialised tools / giving me circuit diagrams for more complex looking transistor based dummy load circuits etc

author: amyk
author_rank: Super Contributor
timestamp: September 24, 2023, 06:59:15 am
content: Power resistors with suitable wattage ratings.

author: Shonky
author_rank: Frequent Contributor
timestamp: September 24, 2023, 09:15:07 am
content: Resistors will work but for a bit more configurability my first thought was a cheap variable electronic DC load like this:https://a.aliexpress.com/_mOFFbyANo good for AC supplies of course.Pretty much anything modern should be regulated so even the smallest load if at all should be enough.

author: Peabody
author_rank: Super Contributor
timestamp: September 24, 2023, 02:40:24 pm
content: I don't think the unloaded voltage should be anywhere near 3X the rated voltage. I have 12VDC bricks that are 15+V with no load, but I don't think I've ever seen one where there was a big difference. But if you have one that was actually designed that way, where would you ever use it other than on the device it was originally paired with?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: September 24, 2023, 07:46:00 pm
content: Good Morning Dan123456, I have a selection of incandescent automotive light bulbs I use for such loads. Headlight bulbs can draw several amps. Of course their resistance changes a bit as they heat up, but for the testing you are doing it won't be a problem

author: soldar
author_rank: Super Contributor
timestamp: September 24, 2023, 11:13:10 pm
content: Quote from: Dan123456 on September 24, 2023, 06:37:47 amYou need to differentiate between the older unregulated type with a transformer, bridge and capacitor from the newer, lighter ones that are switching and regulated. They are entirely different.Yes, in the unregulated older ones it is common for the voltage to fall substantially as load is added so whatever the outside says is purely nominal. Normally the regulation was done later, inside the device being powered.I have a crate full of those of all different voltages. Sometimes I find a use for one but it is a pain because I have to match voltage, current, ripple, etc. Sometimes I just take an oversized one and add a regulator. Right now I have next to me a 9V router being fed from a 13V, 300 mA, unregulated wall wart followed by an extremely simple linear regulator I made with perfboard on the go.Nowadays switched, regulated power supplies are so cheap that the older ones are not worth much, if anything.

author: EPAIII
author_rank: Super Contributor
timestamp: September 25, 2023, 03:33:04 am
content: Yes, resistors. They convert electric energy to heat.I = E/RandP = E*I

author: Swake
author_rank: Frequent Contributor
timestamp: September 25, 2023, 06:20:01 pm
content: QuoteThis, all sizes of old spare car bulbs you'll never use anymore, or halogen bulbs, or old incandescent bulbs from Christmas lights. Solder a salvaged wire on them and you're ready to go.Lower voltage that the 12V? don't care, they'll be somewhat dim, but you're not there for the light.Higher voltage? put 2 or more in series, preferably the same wattage.Careful, they can heat up quickly, put something heat resistant under it (oven plate for example, put don't tell the others)Want to know the amps? you have an amp range on the multimeter, be cautious about the max rating and not to blow the fuse.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 25, 2023, 07:07:00 pm
content: Some piece of wire (copper, enameled copper, steel, stainless steel, Ni-Cro, whatever) some banana leads with crocodile clamps and a bucket of water. As long as the wire is submerged wit will not become hotter then boiling water, which is fine for the wire. Water can conduct a bit of electricity, but most of the current will go through the wire and just heat it. If your wire is not insulated, then make sure you do not create shorts. For example wind the wire loosely around some kind of holder before you dunk it in the water.