I finally read through all of this. It seems you are trying to build a DC power supply without a transformer by simply rectifying the AC mains. Technically that can work but these have been outlawed by regulatory agencies for half a century.
As for calculating the size of an inductor and the gauge of wire required, You are looking at a very large iron core and maybe $1,000 worth of wire. for a time constant in the range of a few seconds. This is why people usually use resistors (or actually “thermistors".) But really, the DC output MUST be isolated and for that, you need a transformer. In the past people built linear power supplies, they work well and are very easy to design but the problem is the size and cost of the transformer and the large filter capacitors Today we use switching power supplies because the parts coat is about 1/10th as much and they waste less power but switching supplies require an EE degree to design. And even them it is a specialist design. Today when we design power electronics we look at the possible failure modes and say “It must be safe, with no lethal voltage exposed even if a critical part fails or a wire comes loose. Back in 1950, they built hot-chassis TV seats and cars with no seatbelts because it was cheaper to do so and it was acceptable if it caused “only a few” deaths per year. Your best bet in 2024 is to buy a DC power supply if you need DC. > On Aug 7, 2024, at 1:45 AM, Jean-François Simon <jfsimon1...@gmail.com> wrote: > > Got it then you need a proper DC bus with charge circuit if it gets > some good power, and safety discharge, you never want charged > caps in some place around, at this high Voltage. > > Question do you build the rectifier, do you get it from something > existing ? > > Basically yes, you need slow charge to not blow something provided > the load behind is great enough to need it, otherwise you'll get > as you do, blown fuse or damage something else, that depends > on inrush current. > > I and others can perhaps provide a couple hints, depends on what > you are really going to design, ie from bulks or custom. > > Regards > > Jean-François > > On 8/7/24 09:45, Viesturs Lācis wrote: >> Hello Jean-François! >> >> I am using Mesa 8i20 servo drives that do not have built-in power >> supply, it takes DC as power input so I am trying to figure out how to >> do that properly. It seems to me that only a pair of rectifier bridge >> and capacitor is not enough to keep fuses happy. >> I do not worry about discharging the capacitor - what I observed from >> initial testing with one 8i20, it seems to me that drive does slowly >> discharge it - voltage dropped to few volts within a minute or so. >> Peter, is that intended or was it just some kind of happy moment and I >> actually should worry about discharge circuit as well? >> >> Viesturs >> >> trešd., 2024. g. 7. aug., plkst. 10:19 — lietotājs Jean-François Simon >> (<jfsimon1...@gmail.com>) rakstīja: >>> Hi good morning, >>> >>> I never eared of a power rectifier directly connected to the line, >>> usually there will be like slow charge circuit through resistors, >>> often also a filter at input stage, like LCL with inductors. >>> >>> Based on the explanations, i can't figure the details, is it so you >>> design and built a custom circuit, or implemented existed >>> modified circuits ? >>> >>> Essentially, yes it depends on the power rating, and passed a >>> point, drives have both charge and discharge circuits, as you >>> can't feed up instantly, it would exceed some ratings. >>> >>> The parts damaged at fast charge i guess would be also the >>> diode bridge, some wire and connections, for capacitors i'm >>> not sure they would be at issue, though they can overheat >>> from the internal resistance. >>> >>> If i got it right, you are trying assemble modules (like a >>> rectifier bridge with other things, DC bus and inverters), >>> then we need to look at the module datasheet and ratings >>> to fogure out these things. >>> >>> It's quite wrong Caps remain charge, that should never happen, >>> all drives discharge the internal caps at standstill, something's >>> failed or missing. >>> >>> Regards >>> >>> Jean-François >>> >>> On 8/6/24 22:44, Viesturs Lācis wrote: >>>> Hello! >>>> >>>> Recently I have posted some questions about the retrofit that I am >>>> working on and now I have encountered an issue that I cannot figure >>>> out. >>>> The thing is that I am swapping original Yaskawa servo drives with >>>> Mesa 8i20. One of the things for that was 3phase rectifier bridge (it >>>> takes 230 VAC input and provides 340V output) and 4700 uF capacitor >>>> for smoothing the ripple. >>>> It took me some time and some patience from PCW to fix the config and >>>> in the end I got one 8i20 to move one joint in the machine. So my next >>>> step was adding 2 more 8i20 drives for remaining 2 joints. It ended up >>>> with a blast in one 8i20. So I replaced it as well as I had to replace >>>> rectifier bridge. But now my issue is that protection fuse is tripped >>>> as soon as I enable machine power. >>>> 1) only rectifier bridge connected - all good >>>> 2) rectifier bridge + capacitor - fuse tripped immediately >>>> Note that I have not yet connected DC bus to 8i20 drives. >>>> I checked capacitor with multimeter, it was showing 180V DC (and it >>>> did not decrease in that time that I was holding multemeters pins >>>> there). I am not sure if that is some residual charge from previous >>>> (which I doubt) or if that was some charge that was acquired before >>>> fuse was tripped, but this seems to me like a good capacitor. Is that >>>> correct? >>>> >>>> I do not understand why was everything fine in initial testing - I did >>>> turn machine on and off lots of times and capacitor was discharged >>>> (and recharged!!!) numerous times. I have swapped that fuse for >>>> identical unit from a machine that has yet to go through the retrofit >>>> process. And it is the same. >>>> >>>> So my question to electronics gurus - could capacitor be damaged or >>>> was it just a beginners luck that everything worked and do I need to >>>> introduce some inductor between rectifier bridge and capacitor to >>>> limit the startup current that charges capacitor? >>>> >>>> Viesturs >>>> >>>> >>>> _______________________________________________ >>>> Emc-users mailing list >>>> Emc-users@lists.sourceforge.net >>>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
