Bogus power supply specs? - Page 1
Forum section: electronics / projects

author: rea5245
author_rank: Frequent Contributor
timestamp: October 24, 2019, 12:59:12 pm
content: I bought a Dr. Meter HY3005F-3 triple output power supply. The third output is labeled "5V, 3A". But I've measured it with a 10 ohm load and the voltage drops to 4.3V. With a 5 ohm load, it drops to 3.8V.I wrote to the company and they said "please kindly be noted that the no-load voltage is 5V. If you want to get a stable 5V, please use other outputs."I had expected that the output would provide 5V at a current draw of 3A, i.e. 15W. It sounds like they're saying I can get 5V or I can get 3A, but not both at once. Was my expectation wrong? Is that how power supply outputs are spec'ed?- Bob

author: brabus
author_rank: Frequent Contributor
timestamp: October 24, 2019, 01:44:16 pm
content: The unit is faulty. The third output must provide 5V at 3A.

author: Shock
author_rank: Super Contributor
timestamp: October 24, 2019, 01:56:56 pm
content: If that was the case it would be an unregulated channel on the power supply. Normally the 3rd channel will be either fixed or variable but regulated. If it says 5V 3A you expect 3A running at 5V. It will say in the manual anyway.Did you write to the manufacturer or distributor or just the seller. The seller probably has no idea.

author: Zorc
author_rank: Contributor
timestamp: October 24, 2019, 03:20:05 pm
content: I agree with brabus.Did you contact techsupport at support@drmeter.com ?By the way, from the manual @ drmeter.com1.3Fixedoutput1.3.1Outputvoltage:5V±2.5%1.3.2Outputcurrent:3A1.3.3Lineregulation:CV≤0.01%+1mv1.3.4Loadregulation:≤0.1%1.3.5Rippleandnoise:≤0.5mVr.m.s1.3.6Protection:currentrestrictedandshort-circuitprotection

author: rea5245
author_rank: Frequent Contributor
timestamp: October 24, 2019, 03:23:56 pm
content: Quote from: Zorc on October 24, 2019, 03:20:05 pmYes. They're the ones who responded "please kindly be noted that the no-load voltage is 5V. If you want to get a stable 5V, please use other outputs."- Bob

author: TimNJ
author_rank: Super Contributor
timestamp: October 24, 2019, 03:31:36 pm
content: Multiple output power supplies (using one transformer/feedback loop) will suffer from cross-loading/cross-regulation issues.That's what their response implies.

author: rea5245
author_rank: Frequent Contributor
timestamp: October 24, 2019, 03:34:39 pm
content: Quote from: TimNJ on October 24, 2019, 03:31:36 pmBut I tested with no load on the other two outputs.- Bob

author: ArthurDent
author_rank: Super Contributor
timestamp: October 24, 2019, 05:15:35 pm
content: If you measure the voltage right at the output terminals, the voltage with a 0-3A load should remain at 5VDC within the specs of the power supply. If you measure the voltage at the load at the end of long leads then the voltage could be quite a bit less depending on lead length and wire size.That is why some higher current supplies use separate sensing leads so the supply is measuring the output voltage right at the load and can cancel out the voltage drop on the current carrying leads to the load. The fixed 5V/3A terminals on your supply are not metered, the voltage is measured right at the terminals, and should remain at 5VDC .

author: rea5245
author_rank: Frequent Contributor
timestamp: October 24, 2019, 07:22:47 pm
content: Quote from: ArthurDent on October 24, 2019, 05:15:35 pmExcellent point! I was measuring at the end of the leads. When I measure at the terminals, I see 5V.So the power supply is OK. My bad!- Bob

author: xavier60
author_rank: Super Contributor
timestamp: October 24, 2019, 08:36:41 pm
content: That's about 1.6Ω of lead resistance. What are they?

author: rea5245
author_rank: Frequent Contributor
timestamp: October 24, 2019, 08:43:14 pm
content: They're inexpensive test leads, one meter long, with hook clips that I bought on Amazon. Still, I'm surprised you can pack so much resistance into a short copper wire.- Bob

author: xavier60
author_rank: Super Contributor
timestamp: October 24, 2019, 08:58:46 pm
content: Quote from: rea5245 on October 24, 2019, 08:43:14 pmThey are likely very light gauge or use low cost copper coated aluminum wire instead of solid copper.If you want to investigate the problem some day, tables can be easily found that relate wire size to resistance per unit length.