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<whitequark> azonenberg: btw did you know about C++11 raw string literals
<whitequark> R"(foo)" is the same as "foo" but escapes, newlines, etc are all legal and treated literally
<whitequark> and quotes
<whitequark> very convenient for ShowUsage() type functions
<azonenberg> Interesting
<lain> nice
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<rqou> offtopic: nice glibc footgun/bustage: https://sourceware.org/ml/libc-alpha/2016-11/msg01026.html
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<rqou> offtopic question for people who like weird power hacks (azonenberg :P ): do you know of the magic search terms necessary to find an inverter that outputs 120vac and takes as input around 190-250vdc?
<rqou> i was thinking around 2000w and _without_ MPPT
<rqou> for context: I want to see if solar inverters have dropped in price enough to make a "tap power from a hybrid car traction battery" hack (http://techno-fandom.org/~hobbit/cars/plugout/) cost less $$$
<whitequark> rqou: any inverter that has a rectifier stage?
<whitequark> i.e. literally any inverter
<rqou> most are rated only for 12v/24v/48v
<whitequark> no, I mean, an UPS or something
<rqou> not all the way up to ~250v
<whitequark> get an UPS that has 240V input and 120V output
<rqou> that's even more hacky :P
<whitequark> really?
<rqou> especially since you don't need any of the other parts of the UPS other than the inverter
<whitequark> I think that powering SMPSes with DC is a perfectly legitimate way to use them
<whitequark> oh, in that sense
<cr1901_modern> A UPS with 240V=>120V out isn't going to have a step-down transformer for AC?
<rqou> probably not
<rqou> step down transformers are heavy :P
<whitequark> expensive
<whitequark> takes place and copper
<whitequark> and a buck converter is rather easy to build, especially if you're staying under like 5kW
<rqou> the normal way to do this is to take the AC in and immediately rectify it into DC
<rqou> then use a DC-DC SMPS
<whitequark> then the ghettiest UPSes will just output a square wave
<whitequark> if everything you power from it is just another SMPSes then that will work, because they don't care
<whitequark> if you try and run a fridge from it, lol
<whitequark> your fridge is fucked
<cr1901_modern> My UPS outputs modified sine wave
<rqou> apparently some active PFC power supplies have problems too
<cr1901_modern> Which is jargon for "square wave with a dead zone"
<cr1901_modern> And sure you can go without. Just I'm used to seeing a transformer in a power supply lol.
<cr1901_modern> https://4donline.ihs.com/images/VipMasterIC/IC/SGST/SGSTS13078/SGSTS13078-1.pdf?hkey=EF798316E3902B6ED9A73243A3159BB0 Page 6/12... in this specific circuit, looks like the main use for transformers *is* step down, but only after mains has been rectified
<rqou> yes, but the transistors are switching the power into the transformer at a much higher frequency
<rqou> so the transformer can be much smaller
<azonenberg> All of my upses are pure sine, i dont know what i might need to run off it
<azonenberg> so i want something that i can use for anything
<whitequark> cr1901_modern: SMPSes still hve transformers usually
<rqou> azonenberg: yeah, i was looking for a pure sine inverter that is ~200Vdc in rather than 12Vdc in
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<azonenberg> rqou: get a 110-250VAC input one?
<azonenberg> look at the input stage
<rqou> oh a UPS?
<azonenberg> yeah
<azonenberg> or spare inverter for a ups
<azonenberg> etc
<rqou> yeah, whitequark suggested that. I think it's silly because you only need the inverter part of the UPS and not the rest of it
<azonenberg> What's in a ups besides an inverter?
<azonenberg> a couple of batteries and a float charger?
<cr1901_modern> whitequark: And furthermore, they're doing step down! I just mentally placed the transformer in the wrong place
<rqou> a bunch of giant batteries?
<whitequark> cr1901_modern: yup
<rqou> the hack i was trying to check the feasibility of was
<rqou> tap the 240Vdc from the HV battery in e.g. a prius
<whitequark> you can do SMPS topologies without transformers but not at like 240V
<rqou> and feed that into some kind of inverter
<whitequark> you can use non-isolated bucks and boosts up to maybe 48V
<whitequark> 90V if you're really feeling it
<whitequark> then you need a trafo
<cr1901_modern> what's important about the isolation?
<rqou> i thought that suitable inverters should exist for people with solar power
<rqou> but somehow a cursory search of aliexpress only finds 12/24/48Vdc input ones
<whitequark> cr1901_modern: duty cycle mostly
<rqou> not ones that take up to 240Vdc
<whitequark> not isolation per se
<whitequark> you don't want to run your buck on very low or very high duty cycles
<cr1901_modern> Oh, if they're not isolated, charge leaks faster and thus requires higher duty cycle?
<whitequark> no
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<rqou> azonenberg: one thing that might actually work is to find a junk UPS with dead batteries
<azonenberg> That would indeed work
<whitequark> cr1901_modern: so basically you have several parts in an SMPS that are sometimes kinda merged
<rqou> now i just need to know where to find a junk 2000+ W UPS
<whitequark> you have switch, energy storage, and voltage transformation
<whitequark> in a flyback converter energy storage and voltage transformation are performed by the same component
<whitequark> the gap in the transformer acts as an inductor
* cr1901_modern nods/is listening
<whitequark> so imagine you boost voltage from 10V to 1000V
<whitequark> you can't do it in one step because you don't have semiconductors that tolerate 1000V
<whitequark> for example
<azonenberg> y u no IGBT? :p
<whitequark> so what you do, is you take your entire input voltage range, say 5V to 15V
<whitequark> boost it to 20V
<whitequark> then, instead of outputting that 20V, you wind another winding on the inductor, which multiplies 20V by 50x
<whitequark> does this make sense to you?
<whitequark> there's a variety of configurations with inductors and transformers connected in different ways
<whitequark> but the idea is the same: you store energy in an inductor, and maybe match impedance to something more convenient
<cr1901_modern> Yes, it makes sense. Just digesting it since it's been a while lol
<whitequark> http://www.smps.us/topologies.html look at a forward converter here
<whitequark> you can see that it's basically a boost that got interrupted by a trafo
<rqou> how do you know so much about smps design?
<cr1901_modern> The 20V output needs to be AC. So if you boost it, you'll need an inverter
<cr1901_modern> Inductor isn't useful for DC
<whitequark> rqou: I built a few shitty SMPSes and then drilled the brain of a friend EE until I understood why they didn't work
<whitequark> I actually don't know that much about SMPSe
<whitequark> *es
<whitequark> I still have a loooot to learn
<rqou> ah, much more effective than my "stare at TI appnotes" :P
<whitequark> SMPSes aren't inherently hard to understand (but are hard to master)
<cr1901_modern> The 20V from the first boost is AC when it reaches the inductor, correct?
<whitequark> but you do need a change in point of view, so to say
<cr1901_modern> whitequark: I understand. I asked b/c I'm not very good with isolation as a concept period. I know what it means (voltage at output terminals cannot be easily referenced to input terminals), but aside from a few (life saving) applications, i don't know much else about it.
<whitequark> ok, I think I'm not explaining this very well, because there are so many topologies to talk about
<whitequark> let me try again
<whitequark> so let's say we have a naive buck converter
<cr1901_modern> That website is REALLY cool, btw
<whitequark> we take 240V from mains and output 5V
<whitequark> at low loads, this converter will have to run at *extremely* low duty cycles
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<whitequark> for various reasons that you're better off reading the appnotes for, SMPS controllers don't do them well
<cr1901_modern> Understood/makes sense. I can imagine/do my own calculations later :P
<whitequark> so, what you do instead, is you use a transformer to take high voltage to much lower voltage
<whitequark> you want to run at 90-240V, so you design for 90V, and then gradually lower your duty cycle as your input voltage rises
<whitequark> given constant load
<whitequark> and you take the turns ratio such that on the entire input range, your duty cycle stays in reasonable limits
<cr1901_modern> But *with* the transformer, the duty cycle is still better than if you were controlling directly even with 240V input
<cr1901_modern> ?*
<whitequark> um, what?
<cr1901_modern> "then gradually lower your duty cycle as your input voltage rises" <-- by the time we reach 240V input, do we still have shitty duty cycle?
<cr1901_modern> From what you're saying, as long as you use a transformer to step down the voltage, the duty cycle over your entire input voltage range should be okay
<cr1901_modern> whitequark: This site you linked to is absolutely amazing :o