Well done Dave, a hefty Tuesday video bringing us a complete explanation of these various UPS technologies. Great tutorial!!

Love the way the bridge is used as a rectifier. 👍🏻

Great video Dave! I enjoyed the theory and teardown coupled together, was very informative.

Great video. I've learned a lot from watching your videos. I liked the bit of theory at the beginning. It helped me understand better what was going on and being said during the teardown. Keep up the good work

I am rewatching this video and I think it is Dave's best video ever!

So good, love how you explain everything, keep it up! Cheers from Sweden!

Awesome find!

This is terrific, thank you Dave!

Thanks Dave, For excellent explanation about UPS system.

Usually that's for high voltage isolation. Helps reduce surface leakage and capacitance a bit.

Very professional and very informative. Thanks for making and sharing this video.

You were reading my mind for a future video Dave. Thanks

This video is very timely, in my case, I watched this video as a study break from studying for my Power Electronics final exam. It was entertaining AND informative. Thanks Dave! Keep up the great work!

I got one hooked up to my 3d printer. No more shall power outages waste my material! Also, a bit of a question: If I have a triac-based power supply for a high power (~400W) device, would those pulses of high current damage the UPS? P.S. The device would be a heater is for the heated build plate. It really only needs to be UPS-protected for long periods of time because of the thermal mass.

Another insightful video, can't wait to see your videos as soon as they come out!

This is an "extended run" APC UPS as designated by the "XL" suffix on the part number. 2 things make it extended run: 1) the secondary battery input and 2) additional cooling fans. The extended run models are "highly desirable" for use as straight inverters because on the standards models, the transformers will overheat within about 30 minutes of heavy continuous use. Of course, now that I told you that the transformer is the "weak link" you can add your own additional cooling including thermal compound between the bottom of the transformer and the case !

I think I learned something new today, thanks Dave!

Beautiful. Appreciate you work, sir

Thanks Dave, very well explained. I've been using these units for quite some time and finally could see how they work!

This guy is really good with explanations and illustrations.

A teardown with whiteboard fundamentals is awesome!

A very helpful explanation. Thanks!..Good work.

i loved the charging system the way it fed it back , very clever

fantastic lesson, thanks dave

Nice explanation Dave, I really like your videos on DFM. A quick comment on how the charging work: Voltage reflecting on the battery side of the transformer (primary side) will never be high enough to charge the battery through the four mosfet body diodes. (battery shouldn't be charged this way because you cannot control the charge current and stop charging appropriately) In order to charge the battery, the mosfet H-bridge works like a boost converter, boosting the voltage to high enough to charge the battery, and at the same time control the charge current and do PFC (Power factor correction). In inverter mode, the H-bridge works like a buck converter having output voltage swing at line frequency. Half-bridges or full bridges are bidirectional converters. You can easily control the power flow both ways by applying correct PWM. Usually, an algorithm called dq control (similar to field oriented control) is used to control the power flow. For example, when vector q is positive, power flow forward, and when q negative, power flow backward. This idea is not new, but applying the idea to UPS to simplify the design is really smart.

I like the hybrid lecture teardown idea with a twist!

Nice video Dave, i use the 750VA Smart UPS rack version of this series for my pc and i am very satisfied with it

absolutely brilliant explanation thank you

I must catch up on your videos Dave ! Did not know you had this video on UPS! GREAT video !

The option slot is for installing additional interfaces i.e. giving the UPS a web UI so you can manage it remotely.

Good one! I liked the way this combined theory and tear down told a story.

How do you not know what Best Power is? I mean the company has been split into pieces and sold for quite a while now but that place was such a legacy. It's building is still standing in Necedah, WI being rented out by the original owner. That place is such a damn throwback, my parents met while working there and my great grandmother was one of the first to get an award for exemplary work. I was practically raised there. On the upside, since closing down, my dad has started up his own business based around UPS.

Great show as always, thanks.

Excellent video. Learned a lot. Thanks a lot

Excellent video, DAVE!

I seen this and it took me back. I worked for a large UPS maker for 10 years. I went to school for APC Anton Piller Belkin Kw controls and a few others . The company also did motor gen sets up to 500kva I could tell you every connection and what to look for to repair it. They had on line UPS and non online UPS systems . I even set up the systems for several companies including Blue Cross . I could tell you so much about UPS systems it would make your head swim.

Very cool review, thank you. If you would have done the review of UPS online class would be just super.

Fun! I just recycled one of these. Interesting to see the inside of it.

Thank you for this video. I subscribed and I stand to learn a LOT from you.

Hey Dave, the same big transformers that step up the voltage is also used to charge the batteries. That is why they put a lot of relays and series of output wires in the secodary side of the transformer. During mains off, the side of transformer connected to the heat sink serves as primary and when mains on ,it turns to seconďary to charge the battery. If you look around the heat sink, you will see some rectifiers.

To answer your question @28:43. The MOSFETs in the inverter are also used as the rectifier. It called a "Dual Headed Synchronous Rectifier"(DHSR). In a DHSR configuration. The controller synchronized to the mains/line and then switched the MOSFETs on and off in sync of the AC wave form. It also uses PWM to control the battery current as well as perform power factor correction. Hook your oscilloscope up to it and look at it.

Love this "Fundamentals & Teardown" mix. Even if you know the Fundamentals, it is a lot of fun to actually look into the device. Will open up my UPS any time soon :D Mine might even need a bit of repair as well.

Amazing video! Thanks for explaining how each type actually works. One tiny correction, though: at 6:22, the fact that for a given power, a lower voltage implies a higher current, is not Ohm's law, it's the relation between those three quantities (what we may call the power equation): P = V * I. Ohm's law has nothing to do with that.

thank you!!!!! i want to give you a hug! you exactly solved my Problem!

Yes, I have several Online and Line interactive UPS's and you can hot swap batterys

Felicitaciones! Me parece un video muy completo y has ganado un seguidor, reunir todos estos datos, la presentación y la explicación han sido espectacular!, gracias por tu dedicación y tiempo,have a nice day!

Invensys sold off the UPS business to Eaton Corp, they already made a lot of the panel gear that the UPS uses so it was a great fit for them. They build the big systems here in Raleigh NC. Liebert is big on UPS and Data Center Cooling, they are part of Emerson. APC was bought and is now part of Group Schneider who owns Square D, a big electrical panel and circuit protection corporation. They made a lot of stuff here in Zebulon, NC but moved all of it to Mexico.

Actually I do believe that they are turning on the mosfets at the same time that the body diode would be on (as stated in the comment you commented on). It would have been a simple enough optimization to figure out, and they would have the control circuitry that would otherwise be dormant. It could also allow them to do some power factor correction to make the charge circuit seem more like a purely resistive load.

I disassembled a large online UPS, and it didn't follow that schematic. It was near identical to your "offline" schematic - the main difference was that the step-up transformer was an SMPS and went before the inverter. The battery voltage was stepped up from 400 volts to 700 V (+/- 350 volts), allowing a simple push-pull topology inverter. The difference is that in an offline UPS, the load is directly supplied by the mains. If the mains fails, then the transfer relay switches the load to the inverter. In the online UPS, the load is supplied by the inverter, unless the inverter fails, in which case it transfers back to mains. The common reason for inverter "failure" is actually the output being severely overloaded or shorted (e.g. due to a fault on a single load where a UPS supplies multiple individual loads). In this case, the inverter voltage drops under the overcurrent stress, and the load is transferred to mains with its high current supply capability. This can also happen if regenerative loads are connected to a UPS (e.g. motor drives) and the reverse power exceeds the handling capability of the inverter causing it to trip out due to DC bus overvoltage. There is usually a difference in the type of switching. Offline UPS systems are designed to be cheap, so tend to use a relay. Online UPS systems are designed to be high end, so the delay of relay switching is unacceptable, so online UPS systems usually use IGBTs to switch between inverter and bypass mode.

Using the by pass diodes as bridge retifier is nice!

I've seen almost identical transformers in 'smaller' rack mount supplies, but they had just one and had 24V battery banks. Pairing them allows for fitting the whole thing in a 3U case without having to design a custom squat transformer. Also, small ones (

Nice feature of the APC SmartUPS, if you have a power failure, you can turn them on and they will run off the internal or external batteries w/o any mains connection. Many of us use these older models that nobody wants for our older amateur radios, aka Ham Radios. These older circa 1975 radios have internal transformer they do not like any square or modified sine waves. The APC SmartUPS put out full sine wave and we can run the radio off batteries for emergency use.

Great video.. I'd love to see some some scope captures of the current flowing into the batteries during charge. Have a current probe?

Good video Dave, and please, don't worry yourself over what the over-entitled fringes of the comments demand you do. keep up the great work, you're an inspiration

Great video, helps me a lot to figure out my scrappy $20 APC Smart-UPS 2200VA. i GOT THE SAME ! Difference is that i have one without the slide out battery bay, Only 2 big capacitors placed far behind the path of cooling air through the H bridge (Seems logical). Basically you have 8 small NP7-12 Lead Acid batteries in a weird configuration. APC made 2 separate 24v sections (with 2 Anderson connectors) in series (48v 14A total) with a 100A fuse in the middle. Both sections consist of again 2 individual banks of again 2 NP7-12 batteries in parallel (= 24v 7A) again in series = 24v 14A. The leads get bigger at every level. Basically the charging current is only 1A max (Maybe even a lot lower) for these 8 tiny 12v batteries switched that way. The total charge current at 48v is about 4A (only 200 Watt). Discharging each quickly ramps up (ads up voltage and amperage in the chain) the capacity of this 48v battery without damaging them individually. I only wonder about the charging profile. Does this Interactive system stop charging at all at some point if batteries reach the full capacity and if not does this explain why all the old AGM batteries in these units seem exploded or expanded with bubbles on all sides? Does this pyramid of 2x2x2 batteries equalize automatically if you leave the power disconnected? I ask because it would be possible to replace every single NP7-12 battery with a 10 x AA (1.2v) Ni-MH battery pack, Haha. Picture link: www.dropbox.com/s/leg4t0lyqml42mh/2020-03-14%2018.40.03.jpg?dl=0

Percussive maintenance. LOL! Excellent shop term! Never heard that one.

There is another type of UPS - transformerless double conversion. Just had a 40kva 3 phase unit installed. Batteries are in series and the DC side runs at 480v. This is common for large, fixed installations. It can be bypassed externally without dropping the load e.g. for servicing. When going out of external bypass it will automatically sync the inverter with the mains supply after which you can flick the bypass off. No interruption to critical load at all.

Yes, this one uses only N channel MOSFET's according to the schematic.

Got a couple in the garage that I need to do a teardown on sometime. Two SmartUPS 2200RMXL (one 5U, one 3U), a Galatrek Microbak ferroresonant 1.5kVA UPS and a transformerless NuWave Powervalue 12kVA.

Hi Dave, the patent part is the highlight of this video. I got a similar UPS (faulty). But when I hooked the transformer with the house mains my main switch immediately tripped. Why was it so? And also, it would be cool if you can dedicate one session on this patent after you have a good read of it. Thanks.

i use my back-ups 450 with a 12v 75ah sla batterys in parallel and i have a lot of time when the main goes out ! nice vid !

That was awesomely interresting, and kept me up an hour after bed time :) I have a one of those expencive UPS's wich doesn't work, so will definately search for more UPS regarding videos, so i hopefully some day will find the problem with my free otherwise prepaid 1000euro waste UPS (because of expencive shipping cost mostly)

Thank you I really good to find service manual when I don't need them, when I need them I cannot find nothing free!

very good and simple explanation

Great Stuff!

Great video. Thanks. I torn down on EATON, presumably "line interactive" because I found an autotransformer in it. Question - is it good to use this autotransformer in a power supply (obviously it does not have isolation)? Thanks

Thought I'd make a correction on you DaveCAD @20:00.The H-bridge in the UPS is all N-channel. The N-channels are connected backwards in place of your P-channels. The reason for using N-channel over P-channel is that N-channels have a lower RDS then there P-channel counterpart.

Pretty sure it's OK to use the body diode for 50Hz rectification, most mains frequency diodes are pretty crummy in terms of switching/reverse recovery performance. Not sure about the body diode, but (some?most?) MOSFETs have a positive temperature/resistance coefficient, thus they share current pretty well. Series diodes are much more of a pain since you have to get voltage sharing. As for the large number of caps, that's not unreasonable for single phase -> 100Hz power flow and all...

That is a real piece of good engineering...and one proove why APC is one of the most reliable.

To get a sine wave output it must run PWM at a higher frequency.

IBM used to sell their mainframes with a system which produced fully synthetic AC power. It was a huge machine with six independent three-phase inverters.

My brother's UPS is a Back-UPS XS 1200...the XS series is a line-interactive UPS with a built-in power conditioner, similar to what OneAC makes.

In the main designs, what are your thoughts about a online design but without the switch ? Meaning it's always the charger that power a full sine inverter. Wouldn't that effectively give the smootest output possible without the split second blackout of the relay ?

I tend to agree Binray - it won't be switching particulatly fast. There is a fair bit of series inductance in those cores (needed for the boost/active rectifier) and 13uF of output capacitance (3x4.7uF) to filter the sine wave.

APC did have some interesting design for UPS's. And they're HQ'd right here in Rhode Island. It's funny - two companies I know of in RI are Alesis of the synthesizer fame, and APC.

good review. thanks.

Excellent...

I grabbed two HP R3000 XR UPS's a while ago, unfortunately UPS(the shipper) managed to throw it off a cliff. Arrived in pieces but I managed to fix one of the two units. I'll post some pictures on the EEVBlog forum if I can find them.

Just googled and found this on the wikipedia page: "Body diodes may be utilized as freewheeling diodes for inductive loads in configurations such as H-bridge or half bridge. While these diodes usually have rather high forward voltage drop, they can handle large currents and are sufficient in many applications, reducing part count, and thus, device cost and board space." Exactly what you said dave!

The patent does not expire because the company goes bust. Of course if there is no one left to sue you that does help a lot!

I want your 555 timer circuit shirt! Lol. I've read up on this before, but i have to say, i'd much rather watch you explain sometimes.. I'm often told i can bring some things to life which are otherwise boring but you do it so damn well.. You should present how it's made/how it works/other similar programmes because you make everyone else look shit!

22:58 I notice a good air path to the main cooling fan around those capacitors, so they should stay comfortable enough for the time it takes your server to shut itself down gracefully. I doubt a company like APC would cheap out on electrolytics in something that is ostensibly mission-critical infrastructure.

Hi Dave! Great video, iam planning to use the same ups as inverter to my solar sytem, but how to trick ups to not charging battery when it gets 220v from net?, i was thinkin to give power diode close after akku and after diode connect such small 48v dc supply, think it will work?

I have an APC Smart-UPS XL Modular 1500VA. acquired from a local server management building after upgrades. I also have a few of those small 400W personal computer ones, only one with a battery still, the rest dried out.

+EEVblog Yes, the option slot is for the APC Network Management card from which you for example can shutdown multiple servers with the APC Software over the network. I have exactly this transformer - do you have an idea, what I could do with it?

Totally agree. Google operate on such a huge scale even a small energy saving per server makes it very cost effective. The scale also allows them to make it worthwhile designing their own hardware. Years ago i had some servers with a hybrid PSU made by a company called Magnum Power Solutions in Scotland. Like a traditional PC PSU but with UPS functionality. Very neat design, it would run off the internal battery if mains failed. However it could not cold-start from DC.

Sorry for two replies - now I think about it they have some form of active rectification control since it has to be a boost device (acting as an inverter it is a buck device). Hence the short circuit "charge state". But it may not be that high frequency to bother the body diodes.

Hi Dave, I have heard that the float charge on some of these is way too high and can roast cells quickly. is there a way to lower it a bit? like a power resistor in series to the battery? Thanks

The remains of Best were ultimately gobbled up by either APCC or their parent, Schneider. I can't remember who bought MGE (one of the last intermediaries that had Best) ... I had a Best FerrUPS that used that topology, big bugger. Carving circuit big enough that when I hacked it and added several more external SLAs it didn't decrease the charging time by much.

Yes, there are many different flavors.

Quality content

I do occasionally mix different pronunciations, like via.

Very Nice thank you! for a great video :)

All very interesting as normal and I'm not that technical but my question is what's a "brick dunni" as Dave mentions. 🤣 We don't seem to many of those in the UK!

This topology likely uses an "active" rectification technique, think full bridge rectifier but substitute the diodes with mosfets. By turning the right mosfets on and off at just the right time you essentially have an extremely efficient full bridge rectifier. The mosfets drop far less voltage than diodes.

Absolutely, I was thinking about getting a UPS for my networking gear at home (modem, router, switch) and then thought "Hey, all this runs on 12V DC, why use a 120V AC inverter to waste battery" and decided that I should just build one with maybe a 24V battery and some efficient switching regulators, plus a float charger. It'd probably last longer too.

I don't know, you tell us. Is there any prior art pre-1991?

i built a 200W ups for learning with same charging technique few years back. didn't know it has Patent.

Hi Dave, I have an old APC UPS, that I'm thinking of converting to a 12V DC UPS to power my router. Bypass the inverter part, as I only need 12V DC. Any instructions or links to go about doing this?

also looking forward to a followup video with oscilloscope poking. Too bad it's a rather "uninteresting" design internally(it's just "beefy" for the power), i've seen a SURT5000 (realtime, online) and it's an absolujte joy to see inside, they don't have a single big transformer, it's all toroidal core(and several) high freq transformers inside, also it had ~ 8 BIGGER caps as well and the pack operates at 96V