Picking correct varistor and caps for in-wall power supply based HLK-PM01? - Page 1
Forum section: electronics / projects

author: Wookbert
author_rank: Newbie
timestamp: September 25, 2020, 09:29:00 pm
content: I'm an electronics NOOB, working on my very first own PCB. The attached layout and schematic shows a triple-fused in-wall power supply (supposed to fit into an enclosure for a 60 mm diameter standard EU backbox). Next to the 100-240V PSU, which is either aHi-Link HLK-PM01 (5V, 0.6 A) or a Hi-Link HLK-PM03 (3.3V, 1A)sits in this case a Wemos D1 mini ESP8266 module.My questions are as follows (sorry for asking that many):F1 - Subminiature fuseBecause of the very limited space I chose a subminiature instead of a classic glass fuse.I'm considering two options: 250V, 200 mA, time-lag but different breaking capacitya) 35A (Eska 883.010)b) 130A (Eska 883.110)See attached data sheet for details. Which one to pick?MOV - VaristorI have too little understanding on how to pick the correct varistor in terms of ratings and specifically size (S07, 10, 14 or 20??). Can you tell me which one to pick from theEpcos range of disc varistors?C1/C2 - CapsA found these output capacitors in a comparable schematic, where C1 was 0.1µF and C2 10µF. I intend to pick the following twoC1:Würth Electrolytic capacitor 0.1 µF 50 V 20 % (Ø x H) 5 mm x 11 mmC2:Würth Electrolytic capacitor 10 µF 16 V 20 % (Ø x H) 5 mm x 11 mmI'm a bit concerning here regarding the voltage. According to what I've learned caps with higher voltage rating last longer, but if the rating is significantly higher than what’s actually used, it can cause ESR problems. I can't find C1 (0.1µF) however in less than 50V.So is the combination of these two caps in terms of both µF and voltage OK?Finally: Ground-area in PCB or not?When looking at my 2-layer PCB design, do you see any need for a ground/copper area? If so, where? My worries are that, with the AC being so close, a copper area could cause leakage current, or that ground areas might block the Wifi signal from the ESP8266.Thanks in advance for your patience and not hitting me right away:)

author: Wookbert
author_rank: Newbie
timestamp: September 27, 2020, 02:58:27 am
content: No one?

author: jonpaul
author_rank: Super Contributor
timestamp: September 27, 2020, 09:22:54 am
content: Hello and BRAVO on your first effort. : Please be patient, many forum members log on every few days or even weeks.Consult HiLink on need for ANY external fuse, varistor, or thermister. They may have internal fuse, transient protection.At 5 W probably only the fuse, use the smaller breaking capacity you mention.Varistors and thermistors needed for much larger wattage. Varistors are unneeded and can catch fire on large transients.PCB: use 2 layer no ground pl neededCaps: ESR/voltage note applies ONLY to electrolytic, NOT the ceramic or plastic! 100 nF : Use 50 - 100VFor the 10 uF, not critical, for 3 ...5V out use a 10V or 16V 10 MF.Finally I would also check a low cost ready made wall PSU, which eliminates safety and PCB. Perhaps cheaper than the Hitek PSU block!Jon

author: Wookbert
author_rank: Newbie
timestamp: September 28, 2020, 01:04:07 am
content: Jon, thanks for your reply.The Hi-Link HLK-PM01 PSUs are extremely low cost (you can get the genuine onesdirectly from Hi-Link on AliExpressfor as little at less than USD 3 incl. shipping ... beware, there are knock-offs as well!), yet rather good in quality (there anin-depth dissection and detailed reviewover here).I'm picking this PSU and my own PCB over an off-the-shelf in-wall PSU, because of the size. My plan is to make a board with Wemos D1 mini or alternatively Arduino Pro Mini/Micro, which fits into a 60 mm diameter wall box.Hi-Link recommends an inductance spool and has less fuses (non for over heating, non for power surges). See here:(The recommended spool is unfortunately way too bulky for my desired size). After a long discussion (see here) and following tests the HLK-PM0x series was considered at that time (2015-2017) to be the best AC to DC low voltage module option (within reasonable price range). But tests and teardowns (includingthe one I've mentioned above) concluded that a fuse, MOV and a thermal fuse would be good for extra protection, which led to the recommended schematic I'm using.I'm having the exact same thread over atforum.allaboutcircuits.com.The guy over there recommended an even stronger breaking capacity for the F1 fuse of 1500A. However that's difficult to get. I now intend to go for the 130A breaking version, which actually is also cheaper than the 35A version. You wrote, that I should go for the 35A. Is that because you thought it might be cheaper (which it isn't), or because of electrical reasons?Regarding the caps I'm looking now at a 16V 105°C 10 µF, combined with either a 35V 0.1µF tantalum capacitor or 50V 0.1µF electrolytics capacitor. Which one do you recommend?Thank you!

author: Jester
author_rank: Frequent Contributor
timestamp: October 11, 2020, 06:53:05 pm
content: Check creepage between left MOV pad and red trace above!

author: trobbins
author_rank: Frequent Contributor
timestamp: October 11, 2020, 11:47:23 pm
content: Wookbert, many countries only allow tested and certified equipment to be connected to the AC mains, for the safety of any user of that equipment, both now and in to the future. How are you managing the regulatory safety aspect of the equipment you are preparing, as your posts indicate you have pretty much no experience or awareness in selecting parts on the AC mains side, nor likely on how parts and safety criteria should be implemented and tested?