Pro tip: don't cheap out on those 'universal' power supply testers

I grabbed a $15 one online thinking it would save me time, but it gave me a false positive on a laptop board and I ended up ordering a good DC jack for nothing, costing me about $40 total. It turns out those cheap testers don't put any real load on the circuit, so they'll light up even with a weak power rail. What's a better, budget-friendly way to actually test a power supply under load?

3 comments

3 Comments

lily3942mo agoProlific Poster

Just use a multimeter, man.

leohart2mo ago

Actually, a multimeter alone won't catch that kind of voltage drop under load. You need to put something on it that pulls real current, like that car bulb trick. I've seen power supplies show 12 volts on a meter, but then it falls to like 5 volts when you connect even a small fan. The meter itself doesn't ask for enough power to stress the circuit.

val4062mo ago

Yeah, that "no real load" thing is exactly the problem. A buddy of mine who fixes phones had the same issue. He used a cheap tester on a power supply, it lit up green, but when he hooked up the actual phone board, nothing. He ended up just using an old car light bulb as a dummy load to check for real voltage drop.