How does this 3000VA Transformerless UPS work? - Page 1
Forum section: electronics / projects

author: intabits
author_rank: Frequent Contributor
timestamp: September 08, 2024, 03:47:13 am
content: I did a teardown of this HP model R/T3000I transformerless 3000VA UPS, which seems to be a re-branded unit made by Eaton. The input and output voltages are from 200 to 240V, and it uses a 120V battery.Of course, there are no schematics for it. The only documentation I've found are user manuals that only discuss the user interfaces, and electrician-oriented installation details. It also seems that the same model number, but of different vintages, may have completely different internals - some seem to be not transformerless.Here's the main power board:-And the In/Out board that connects to the input and output AC sockets, and to the power board via 3 main conductors (labelled line,neutral and load)Being completely unfamiliar with these devices, I was simply guessing how it works as I went. My understanding is that the output of the UPS always comes from the converter, thus providing a clean conditioned output (online mode). But when a fault is detected in the converter, bypass mode is entered whereby the output power comes directly from the incoming mains. And of course, when the mains input fails, the converter is powered by the battery.I want to do a follow-up based on a proper understanding of the unit, so I reverse-engineered the power circuitry of the main power board. But it's not quite what I was expecting, and I'm struggling to see how it works. I'm hoping someone can explain it to me. Here's my schematic:-It looks like Q5, Q6, Q9, and Q10 form the main H-bridge that is driven by sinusoidal PWM signals, and the high frequency PWM filtered out by L1, L3 and C5, leaving pure sinewave power going to the load. Beyond that, I'm stuck:-BUS+ looks to be powered during normal operation from LINE via K6, F2A, K5, CS2 and rectified by D22, and during power loss, from the battery via K3.But I can't see how the negative DC bus (BUS-) gets powered.In battery mode, maybe via K4, K5, CS2 and D23?And in normal online mode, ??!!Do D22, D23 and Q7, Q8 form some sort of synchronous rectifier to power the DC BUS?Or are Q7 and Q8 part of the output inverter in some sort of H5 topology?I keep looking for (and not finding) a more "solid" connection from BAT- and/or Neutral (via D23?) to BUS-. I've triple checked all this on the PCB, and I'm pretty sure my schematic is correct.More questions:-Q4 is on the large heatsink with the others, what does it do?My guess is that Q20 is involved with charging the battery, but can't see how.What is the function of the huge inductor L2?How can this produce 240V output from a 120V battery?Any insights or clues as to how this thing operates would be most appreciated. Thanks...

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2024, 04:24:19 am
content: Looks like they're using L2 in a boost converter.

author: intabits
author_rank: Frequent Contributor
timestamp: September 08, 2024, 12:24:37 pm
content: I can vaguely see how that could be going on, having an inductor, switch, diode and capacitor all in the mix there.But I'm still looking for some connection to Neutral that allows the circuit to make use of the power and potential between Line & Neutral.Can you provide any more detail on how you see that working? Even just the components involved would be a help.I'm trying to simulate it, but missing that connection to neutral. The only path seems to be via Q6, but that's busy being part of the output bridge...

author: The Soulman
author_rank: Super Contributor
timestamp: September 08, 2024, 01:11:29 pm
content: Quote from: intabits on September 08, 2024, 03:47:13 amThe ones I have seen use the by-pass relays in normal mode, they can advertise clean conditioned output because of the (mandatory for back-up mode) filters that the power travels thru.The converter is much to inefficient to run 24/7 and would result in a lot of generated heat and a short overall lifespan.I'd say q20, q6 and/or q4 are involved with charging the batteries.

author: intabits
author_rank: Frequent Contributor
timestamp: September 09, 2024, 03:29:37 am
content: That was my initial assumption also. I've been trying to find a definitive statement on this, or at least the information that changed my mind.For this exact model, there is no explicit statement that the converter provides the output in normal operation, but it does describe "operate"mode and "auto-bypass" mode. The best I can find is that "operate" mode is the normal operating mode, and it switches to auto-bypass when it detects: Output power overload, Over temperature, Fan failure, or Internal UPS failure while in operate mode (meaning??). These conditions all appear related to an operating converter.Maybe the UPS's you described are lower power, consumer grade units? These higher power units are intended for commercial systems such as servers, and for the high cost (starting at $2K-$4K), one would expect that they always do more than just input filtering.This is a rebranded Eaton UPS, but I haven't found which exact Eaton model it is. At least some of the similarly rated Eaton models mention transformer AVR" (Automatic Voltage Regulation) which appears to be an active subsystem that may supply either the inverter or the output directly (in bypass). The AVR follows the input filter.The 3000VA models produce their output from either the AVR or the inverter (but not both). However, this unit has no such AVR subsystem, just the input filtering.Other Eaton documents describe "line-interactive" and "on-line" UPS types. Line-interactive is the type that uses AVR to correct abnormal voltages, but on-line types do continuous "double-conversion" (AC->DC->AC).Although there's nothing definitive, all that I've seen leads me to believe that this unit is the "on-line" type, that runs the converter continuously.Yes, Q20 and Q4 do seem separate from the converter function, and so are likely to do with battery charging.But I'm still lost on where the current paths are in this device for any function other than the final H-bridge output...

author: BennoG
author_rank: Frequent Contributor
timestamp: September 09, 2024, 06:03:05 pm
content: We used a 750VA online converter that wat $1k. So I guess the 3kVA are a lot more expensive.I think the unit is in bypas mode in 99% of the time and when the power fails it kicks in.If you have a variac you can simly test this by setting the variac at 230V and measure in and output voltage.then lower it to 220V and measure again. If in both cases the in and output are the same as the input it is the usual bypass UPS that kicks in when power is gone.A normal server can handle a dip of 100ms (the time needed to switch the relais and start inverter)Benno

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 09, 2024, 09:49:12 pm
content: Why are there three heavy wires going to the output? (Red, Black, White? Ah: Black is AC power input.) Because it's supposed to generate a sinewave output, I should expect a symmetrical connection here. In the US, (And UK I think) it's apparently common to have a real "live" and "neutral" wire. but here in europe, plugs are not even polarized, and both are treated the same.I have not analyzed the circuit, but I suspect they switch the battery between positive and negative halves of the sine waves, and maybe boost it a bit too, to get over the peaks of the sinewaves.

author: m k
author_rank: Super Contributor
timestamp: September 10, 2024, 07:26:36 am
content: My intuition doesn't say how the booster wave goes.First Q20 and Q7 on.Then loading C13 and L2.Then Q20 and Q7 off and Q8 on.Then positive through Q9 or Q5 and return through Q6 or Q10 to negative.Leftover K3 and Q4 can be a charger.

author: ramussons
author_rank: Contributor
timestamp: September 10, 2024, 09:26:32 am
content: The basic principle of a transformerless invertor is a PWM bridge invertor where the "primary" of the transformer is the load itself, as shown in the attached schematic.The 120 Volts from the battery is boosted to 350 volts and applied to the bridge.The part of the layout connected to the battery galvanically will be floating.

author: intabits
author_rank: Frequent Contributor
timestamp: September 10, 2024, 12:53:20 pm
content: Thanks for the responses!Quote from: BennoG on September 09, 2024, 06:03:05 pmI got these things for dirt cheap, I don't even know if they're broken or operational. But they have no battery packs, so I imagine powering them on without batteries would just result in some fault condition, and not reveal very much. If I had the batteries, I would have already tried this and hopefully would have been able to answer these questions myself.But it's a good plan, I wonder if there's a way to make it think it has a battery pack, without actually locating 10x12V SLA batteries?Quote from: Doctorandus_P on September 09, 2024, 09:49:12 pmThe white is the neutral, and as far as I can tell is used as a "common" for both input and output to this power board. It connects directly to neutral on the output sockets, and to the neutral of the incoming AC, via a relay.The black is line/live/active, and is input to the board, coming from the AC input socket, again via a relay.The red is marked "load" and is presumably the output from the board to line on the output sockets (via relays).These 3 wires, plus the 2 from the battery, are the only heavy wiring to the board.QuoteThat makes sense, but how is it done?Quote from: m k on September 10, 2024, 07:26:36 amI don't think that can be right: Q20 is on a small heatsink, not on the big one with all the others. It's almost certainly part of the charging.And C13 is just a tiny 100nF cap, likely just for suppresion. But maybe C11, it's a "Bus Link" capacitor like C3. These are low ESR, ESL and high current, with heavy terminals. (The upright flat white parts in the photo). I can't find any data on them but they look like this:https://www.taobao.com/list/item/41666261949.htmQuote from: ramussons on September 10, 2024, 09:26:32 amYes, that's the part of the circuit I do understand. Unfortunately, it's the only part!QuoteAnd how the boost works is also part of what I don't understand.

author: m k
author_rank: Super Contributor
timestamp: September 10, 2024, 03:42:05 pm
content: Yes, C11, but it doesn't help if Q20 is small.L2 is only loaded through Q7 and the transistor sextet is just like a 3-phase inverter.But I just can't understand how L2 is boosting, since with battery connected it must boost downwards, and like somebody said, where is the return path.So is L2 negative compared to battery negative?So its energy is not going through D23 and positive side is not going through D22.For negative and neutral, no suck absolute things, only potential differences.Turn the wave going to Y-direction.

author: oPossum
author_rank: Super Contributor
timestamp: September 10, 2024, 06:04:18 pm
content: My best guess...

author: intabits
author_rank: Frequent Contributor
timestamp: September 11, 2024, 12:08:50 am
content: Quote from: m k on September 10, 2024, 03:42:05 pmOh, but K3 is there, allowing Bat+ to BUS+, and Bat- can get to BUS- via K4,K5,D23 (but via D23 looks wrong to me).And for on-line operation, yes, where is the return path?I keep expecting to find neutral going to cathode of D23, but I've checked that area multiple times. Neutral goes only as shown in the schematic...QuoteI don't understand what you're saying there.Quote from: oPossum on September 10, 2024, 06:04:18 pmYes, that does seem to be the consensus, but how is BUS- powered?I've checked that again for the nth time and the schematic is correct.I want to use the parts from this thing in a similar way, so it would have been helpful to understand it. And I was hoping that in my unfamiliarity with such things, I was just missing something obvious, but it seems that Eaton were practicing some non-obvious witchcraft here.Thanks to all for your help and efforts, but let's wrap this up here, it's not so important, I was just curious.

author: oPossum
author_rank: Super Contributor
timestamp: September 11, 2024, 12:46:55 am
content: Quote from: intabits on September 11, 2024, 12:08:50 amVia Q8 (synchronous rectifier) and D22Q7 charges L2Q8 discharges L2 via D22

author: m k
author_rank: Super Contributor
timestamp: September 11, 2024, 04:55:58 pm
content: Quote from: intabits on September 11, 2024, 12:08:50 amFirst C11 is charged through D23.Then Q7 goes on and L2 is charged.Then Q7 goes off and L2 is floating.Then Q8 goes on and L2 becomes a power source.So charged C11 and L2 are connected again, but now battery voltage is in between.Only non solid point is between C11 and L2.L2 can't crank battery negative up, so it itself must go down, it still has the initial potential difference and stored energy.Charge arrow over L2 is from left to right.When Q8 goes on arrow over L2 is still left to right.Right of L2 is battery negative, it doesn't change.Left side of D22 is battery positive, it doesn't change either.So L2 start pulling BUS- down and C11 start charging more.Finally over C11 is full voltage and battery negative is somewhere in the middle.Then C11 is discharged to the load, I think.

author: intabits
author_rank: Frequent Contributor
timestamp: September 12, 2024, 09:49:57 am
content: Cool!Crude simulation:-Thanks!

author: m k
author_rank: Super Contributor
timestamp: September 12, 2024, 01:51:01 pm
content: One more thing, after a first charge C11 and L2 wont go under battery voltage.C11 clearly can't and L2 is disconnected before that start happening.So L2 can recharge while C11 is discharged, though it's probably bit of a necessity also.

author: Hr_Satch
author_rank: Contributor
timestamp: January 16, 2025, 07:03:56 pm
content: Hello folks, I'd like to elaborate onto this former September_2024 Topic,Hi intabits, nice work in reverse engineering a partial schematic, thanx, great job,I to am busy on such thrown-away still good operational R3000h Transformerless UPS.Just thrown away wuth the dead batteries, just for the sake of operational guarantee, . . .Good for us, electronics enthousiasts.However, no original schematic to be found yet, bummer ;-?I am into the idea of converting this excellent pure-sine inverter for more-or-lesssustained use, so specifically the cooling needs upgrading, etc . . .I enjoyed reading the actual forums Q&A,however it seems nobody really understands AC ? ? ?To try understand, one needs to get out of this simple DC-thinking,each half~cycle, the upper and lower rails change in polarity,but the Batteries string, still needs to receive only DC ;-?Now some thoughts of mine: ofcourse you need thick gauge wires in the power lines,whether they are receiving or delivering power, that should be obvious.Hence also something I never read on any forums:There is NO power gain, only conversions of Voltages & Currents.So there is no such thing as Free energy !If it states 3000Watts, that means max. current of 12,5Amps (for 240Vac)<without taking into count for all the losses and inefficiencies>Moreover, this also implies that the same 3000Watts desired output power needs to come from its input source !The Batteries. Hence the higher the voltage of the Batt-string, the 'Lower' the currents in those Batteries leads.Lets again count plain simple, for a 240Vac out, with a 120Vdc in, Currents will already double !Over 24 Amps at Max. power output.And three wires, because one remains common, the other two serve the in & output going of the AC~.To my limited knowledge: inline coils L1 & L3 serve the sine shaping towards the Load.Two coils in each line one, because of the Alternating Current ;-?One half cycle L1 is positive seen from L3-side,than the other alternation it goes opposite, . . .L2 imho serves [together with Q7 & Q8] for the alternated Buck/Boosting the Batts 120Vdc upwards in amplitude,alternating in polarity with both transistors.The coils inductance serves the swinging effect of an AC~voltage.But L2 is never the same polarity continious.To get for lets say EU 240Vac, out of a 120Vdc batt.string, it needs to get doubled.Hence L2, together with Q7 & Q8 , doubling the Amplitude of each AC~cycle ;-?Both beefy counter polarised 3x Diodes couples D22 & D23 are just to avoid damaging the H-bridged Tors Q5---Q10against the Fly-back Voltage spikes from alternating L2 voltage swings ;-?But to go really into deep theory, I have to admit, we need explications from an electronics developper of thisTransfromerless UPS-inverter design.These principles yet exists for more than 10 years, so patents & such are obsolete I'd guess.They could yet provide us enthousiast from a decent circuit schematic drawing, I'd pressume ;-?Hope to get this Topic back on track, a Happy NewYear, Harry - Belgium.

author: Hr_Satch
author_rank: Contributor
timestamp: January 23, 2025, 07:27:28 pm
content: Hi folks, dear Intabits,I'd like to revive this 3000VA transformerless UPS inverter design back engineering ?Are U still busy with this ?Somebody still of interest ? ? ?Because there appears nomore replies ?Anyhow, I am busy with one(got 2 different models, one more recent rack model and an older desktop model.Rack is a PowerWare-R3000h , desktop model is a PW-9120 with 3000i inverter.I found some schematics, but it are not straigth clear chronological drawings, but I'll manage.Components references coorespond, they are just often not on the same spot as drawn, . . .As I have read somewhere in a (service/user) manual: these can be activated as a standaloneinverter/converter, without the need for first a Mains input.But straight from the batteries power. Thu somekind of software command.However I am an analogue HardWare guy.Don't like the all to over computerisation of things.I am looking for which controlling µPC -pin- to activate for this by a Logic Hi or Low level input ? ? ?+++++++++++++++++++++++++++++++++++++++++++++++++++PLEASE everybody: know what U're doing: in such transformerless inverter design,there is NO galvanic isolation ! Not from Input, NOR from its output !And it is not only the positive line that can and will zap U !+++++++++++++++++++++++++++++++++++++++++++++++++++In some users manuals, there is stated these can run for hours, with an extra external batteries input.So I think just adding some additional cooling fans will do ;-?And an external batteries power input, with real thick gauge wires to minimise losses.Depending on the respons on this, will report back if it works, but that will be for in March or so.I just like the given fact of a pure-sine, and not those rectangular CRP cheap models.

author: intabits
author_rank: Frequent Contributor
timestamp: February 08, 2025, 11:13:51 am
content: @Hr_SatchI haven't checked in for a while, and only just saw your posts.The discussion in this thread answered most of what I wanted to know, not that it was very important, I was simply curious.I've now pulled this unit apart for the components, which I'll use for experimenting with similar types of circuits.But I do have a second unit still complete, and your post gave me the idea of using a 120VDC power supply as a simulated battery that could be used to run the unit as an inverter, and then investigate its operation while running. Maybe one day if I get curious enough...

author: Hr_Satch
author_rank: Contributor
timestamp: February 18, 2025, 07:31:31 pm
content: Hi, Intabits, finally,I had gave it already up, no response, . . .Jep, me too, need once a great amount of time to further develop things ;-?Way too busy, with way too much things, . . .Need over 500 years in my Lifea gentle reminder, such 120Vdc Batt simul. supplies, is easily made for just an Amp for testing purposes.For huge power Amps draw from it, it gets a whole different ball game, . . .So I was in the vein of making something around a LM317 HV-supply, limited to not much more than an Amp,BUT such inverters for startup take many Amps in surge, . . .So I am rather thinking making me a SG3525 PWM-regulator based pushpull up-transformerLike a 12Vdc battery to 220Vac mains pushpull converter, and than back redressing that Hi created voltage.In such that perhapse with playing with the PWM Duty-cycle, I could regulate the outputAND benefit of a regulated up transformed supply, that can give some additional Amps, . . .In addition with here: a schematic design I found online (will do only the upper left corner of the design)It doesn't matter whether it sorts a misformed sine, as I am redressing it back to DC anyways.I know, not so efficient, and huge Amps in 12Vdc line, but it's just intended for short testing purposes, . . .In the end, I am in the development of mi own Pure-Sine transformer based 10Kw MOSFET inverter,so my existing récup. UPS deveices will also serve for the power parts: MOSFETs, CAPs, COILs, etc . . .Fast-switching Diodes, . . . It will be a Low frequency desing, with a huge bulky power transformer,on a rolling trolley ;-?Anyhow, will be very labor intensive to make, but in the end will safe me a lot of $$$$ for batteries, LoLSheers mate, later, please if interested do contact me on my email, I don't consult this not often anymore.For all clarity, the inserted schematic drawing is not mine, I just upload it for illustration purpose, by-by

author: intabits
author_rank: Frequent Contributor
timestamp: February 20, 2025, 03:29:54 pm
content: Hi Hr_Satch,Yes, I realize that simulating a UPS battery would require lots of amps. But I have what's needed to provide at least 25A at 120VDC.Though it's unlikely that I would ever bother trying...Thanks for the schematics.It's always interesting to see ways that these things are implemented.