Jaycar PSU (rd-125B) power problem - help? - Page 1
Forum section: electronics / repair

author: Jaysun
author_rank: Newbie
timestamp: April 15, 2020, 11:04:08 am
content: Hello all!I have a small diy CNC machine, no problems with machine outside of today’s attempt as updating psu.My old (functioning) psu is a 24v 125w, nothing exciting, I need 5v for some extra features so I picked up a psu from jaycar, Which is a seemingly generic Mean Well rd-125b, Same form factor, same bus, mounting holes with the addition of dual voltage.Problem I have, the psu I bought won’t power up. It just power cycles on/off. Digital multi meter doesn’t show full 24 or 5v before next cycle. Light comes on,of,on,off etc.I thought maybe faulty psu as I’ve never had and problems prior or other psu’s of different voltages. However the other 2 (total 3) do the same.I have Tested on the bench,With load.Without load..No problem with 240v or RCD. Using the same test cable and rcd im able to power up several others (60v 48v) that I have handy.What are the chances of 3 psu’s being faulty? Or Is there something different with these Mean Well power supplies being from the Australian market vs the eBay variety?Any help would be greatly appreciated.

author: madires
author_rank: Super Contributor
timestamp: April 15, 2020, 11:23:32 am
content: Please try to load the 5V rail with 2A and the 24V rail with 0.5A (numbers are taken from the datasheet).

author: wilfred
author_rank: Super Contributor
timestamp: April 15, 2020, 12:59:06 pm
content: Just to be clear I am testing with a Jaycar MP3300 which I think is the same.I connected mine by powering two 12 incandescent lamps (brake lights) in parallel to the 5V output only. One alone just flickered on-off at about 1Hz in sync with the green LED. Two lamps in parallel glowed steadily albeit feintly. The output measured 5.026V The 24V output (unloaded) also measured 24.19V.I saw what you were reporting with no load at all. So I don't think any of your supplies are faulty. Just need some form of load.Thanks for your post which prompted me to test it. I just bought it during a recent sale because it was cheap and might be handy.https://docs.rs-online.com/6a5c/0900766b81621ff5.pdf

author: Jaysun
author_rank: Newbie
timestamp: April 15, 2020, 01:10:05 pm
content: Thanks for the help, I’ll test again.I had found this which suggests no minimum. 5v = 0-10a 24v = 0-5a.https://www.power-supplies-australia.com.au/MEAN-WELL-RD-125BDid you have a link to the other data sheet? I couldn’t find one on jaycar and the website on the PSU has more installation info for airflow and screw size etc.I wonder if the low draw will be a problem with stepper motors at idle.

author: madires
author_rank: Super Contributor
timestamp: April 15, 2020, 01:35:05 pm
content: Right, there are two different datasheets, The one on Mean-Well's site (https://www.meanwell.com/productPdf.aspx?i=173) states a current rating of "0-10A" for the 5V rail, while the one from Conrad (https://asset.conrad.com/media10/add/160267/c1/-/en/001292936DS01/datasheet-1292936-mean-well-rd-125b-acdc-psu-module-enclosure-133-w.pdf) states "2-10A". Maybe an older PSU model? Let's see. The datasheet from Conrad is dated 2011-08-19 and the one from Mean Well 2019-07-11. So the new model has no minimum load, and you got the old model with the minimum load.