Cool tutorial: Converting an APC UPS into a powerful sinewave inverter - Page 1
Forum section: electronics / projects

author: cte7ds
author_rank: Contributor
timestamp: November 23, 2012, 06:57:22 pm
content: After researching my latest purchase, an APC Smart-UPS SUA1500i I ran into this cool little tutorial video that made me feel even happier with my choiceThis guy had an old SUA1500RM2U laying around, designed to deliver 120 VAC pure sinewave with 1500 VA at 980 watts for ~7.4 minutes. And with a surge capability of around 1760 watts. And efficiency of 84% with a 872W resistive load.After he was done modding the unit was able to deliver 1500 watts continuously and provide a surge power of at least 3200 watts, which is enough for a lot of household appliances. Also as a side effect the battery charging current increased from ~3A to ~7A which is a nice bonus when using bigger batteries (the unit however is known to be capable to accept an external charger in parallel with its own). Overall efficiency of the inverter stayed the same.Here's a little overview of what he did:He modified the H-bridge by soldering extra TO220 mosfets (and their gate resistors) to the unpopulated spots on the PCB. Stock configuration had 8 (IRF4104 is my best guess) mosfets populated out of 16 possible. He added 8 IRF3803's and used thermal grease (stock model didn't have any). Interesting thing about the H-bridge is that when not being used as an inverter they are actually being used on their linear region to charge the batteries.He added an unpopulated low-esr capacitor near the battery terminals (probably in parallel with the batteries)Added cooling directly over the mosfet heatsinks because they were the "high thermal mass"-kind, instead of having maximized surface area. This is because the UPS wasn't designed to run for extended periods of time.Because the transformer was bolted directly against the chassis he added thermal grease under the transformer and increased airflow over the transformer portion.He used a secret programming mode to change the calibration of the output load sensor (current transformer) to offset the overload detection. Also the buzzer could be turned off permanently using software (phew..)Overall the biggest issue was the thermal characteristics of the transformer. It's the most expensive part of the UPS so that's where the manufacturer tries to save as much as possible :-pMy use case for the UPS is gonna be like 1000VA maximum computer load (mostly SMPS with active PFC and some with passive PFC) extended run-time, so I'll probably be doing at least the thermal grease mod for the transformer and possibly adding more forced airflow. I'm getting the tower model so I'll be doing load testing of my own to see what is necessary. From what I know it should be using all the same components, just more tightly packed.I did already install a special Ground Fault Circuit Interrupter Protected 230VAC wall socket and 10 meters of triple insulated 3x1.5mm^2 copper conductor from my lab to the living room so I can have all my computers from two different rooms behind the same UPS. So I'm pretty dedicated in having a decent UPS system and might just do all the mods as what this guy on youtube did to get a bit more performanceBought my unit from the United States (someone was selling 230VAC models cheaply) so I'm never gonna be mailing it back for warranty anyways because of the cost, so I'm not that concerned about immediately voiding the warranty, and I could never keep my nose away from the internals anywaysAaanyways I just thought I'd share this tutorial with you because I thought it was really cool what he did and he clearly seemed like a talented person. And also a little heads up that I'm gonna be working on this so if someone is interested in the results or in helping out that would be cool

author: poptones
author_rank: Frequent Contributor
timestamp: November 23, 2012, 08:11:02 pm
content: Here's a bit more on that from one of my favorite youtubersCheap Backup Power

author: krish2487
author_rank: Frequent Contributor
timestamp: November 23, 2012, 08:43:28 pm
content: QuoteYou dont have to do any black magic to mod the output of the ct.Note down the burden resistor present in your UPS and note at which load level it trips.scale the resistor to follow the projected increase in power.:-)Of course the UPS will still read the and compare the old set point of the CT but will trip at a higher load level.Think of it as changing a voltage divider ratio but keeping the multimeter mode constant.

author: cte7ds
author_rank: Contributor
timestamp: November 24, 2012, 02:15:25 am
content: Quote from: krish2487 on November 23, 2012, 08:43:28 pmHmm, I'm not quite sure what you mean by the burden resistor tripping? I think a schematic would be helpful.

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: November 24, 2012, 09:54:08 am
content: I started viewing this guy's video(s) but sweet jesus its over an hour(s) long! so I went straight to part six where he changes the fets. OK I am not a hardware guy but even I know you do not tug on superman's cape, and you do not just randomly parallel unmatched fets. What is going to happen to the current sharing(balancing). Power fet cognoscente please enlighten me, shouldn't this thing turn into a smoke generator?

author: SeanB
author_rank: Super Contributor
timestamp: November 24, 2012, 10:34:22 am
content: The current transformer is loaded by a resistor in the unit. If you make the resistor lower value the current required to reach the trip point is correspondingly higher. Current transformers do not worry much about voltage ( within limits) as they provide a constant current into the load in ratio, much like the common voltage transformer. thus a lower value load resistor means the primary current has to be so much higher to reach the required voltage on the resistor.

author: ptricks
author_rank: Frequent Contributor
timestamp: November 24, 2012, 02:13:59 pm
content: Good project if you want to do it for the learning experience but not really the best way to get a powerful inverter.Look on ebay, auctions locally , military auctions.A few years ago I attended a local school surplus auction , they had a pallet of 25 APC UPS for auction, got the entire lot for $20, most people didn't know what they were and the lot was big and most people didn't want to load it on a truck.They were all rack mount, 3000 watt units , rated for full time operation complete with internal fans and jacks on the back for extra batteries. Every single one of them had the same fault, batteries were bad and wouldn't charge. Easy fix.

author: cte7ds
author_rank: Contributor
timestamp: November 24, 2012, 03:24:24 pm
content: Quote from: SeanB on November 24, 2012, 10:34:22 amLike in this slightly different model the R133 next to CT1?Full schematic:http://www.upsclub.org/schem/APC/735/E735Gschem.pdf

author: cte7ds
author_rank: Contributor
timestamp: November 24, 2012, 03:38:05 pm
content: Quote from: chickenHeadKnob on November 24, 2012, 09:54:08 amYeah I'm also amazed how easy it was, usually when repairing a device with fets the end result is like this:I've had that happen to me a few times with Chinese inverters :pQuote from: ptricks on November 24, 2012, 02:13:59 pmAs long as you stay away from the cheap Chinese no-name brands and go with something that has a known good design. Here's a great example of what eBay can get you:http://www.ludens.cl/Electron/chinverter/chinverter.html:-pProducts like this:http://www.ebay.com/itm/1500W-3000W-peak-24v-220v-Power-Inverter-Charger-UPS-Quiet-Fast-Charge-C7A-/360464406988?pt=UK_Home_Garden_PowerTools_SM&hash=item53ed5a59ccsure seem like a great deal but I doubt that they are well designed.QuoteI wish I had luck like that. You must have made quite a nice amount of extra cash with those units?

author: SeanB
author_rank: Super Contributor
timestamp: November 25, 2012, 09:20:31 am
content: Quote from: cte7ds on November 24, 2012, 03:24:24 pmYes. like R69 is the load resistor for CT2. If you make it 5R6 it will roughly double the current required to trip the UPS.

author: cte7ds
author_rank: Contributor
timestamp: November 30, 2012, 11:24:33 am
content: Just received the package from USA. I'm amazed how relatively well it survived the trip with such inadequate amount of packing material, only one dent in the product and the styrofoam in the package was completely shattered.Also the Smart Card and USB-daughterboard connectors had become lose. Nothing majorly wrong at this point. That is until I checked the battery pack voltage... a whopping 1.443 volts for two lead acid batteries in series.... great, never seen a battery that discharged ever before. Well I didn't even need the batteries in the first place but I would have assumed that a product listed as "Brand new" would have brand new batteries. Funny thing with batteries as dead as these, the UPS refuses to start up at all. So basically the unit is dead out of the box if you didn't know any better :p What do you guys think should I ask for a partial refund or something? Had the batteries been brand new I would have sold 'em and now I can't do that<dave> Don't turn it on, take it apart!</dave> I took the cover off and inspected for shipping damage and attached all the connectors that had gotten lose and then did a quick test with my bench power supply and a 40W light bulb as a load. The unit seems to be working at least, that's really all I wanted anyways hehe.So time to tear it apart and mod the sucker!

author: SeanB
author_rank: Super Contributor
timestamp: November 30, 2012, 04:24:10 pm
content: Charge up the batteries from a power supply, they possibly might still work. If you get to 15V per battery and it is still not taking more than 500ma then they are toast though.

author: cte7ds
author_rank: Contributor
timestamp: November 30, 2012, 04:34:00 pm
content: Quote from: SeanB on November 30, 2012, 04:24:10 pm0mA @ 15V :-p

author: SeanB
author_rank: Super Contributor
timestamp: November 30, 2012, 06:09:57 pm
content: Time to sell them to the scrapyard then..........

author: cte7ds
author_rank: Contributor
timestamp: December 01, 2012, 11:59:34 am
content: Here are some pictures of the SUA1500i internals and the mods I've done so far.First off I installed a connector to the 8 pin ribbon cable connecting the main board and the front panel because it was annoying having it dangling from from the main board. I don't understand why this wasn't done by the manufacturer, after all, everything else on the PCB has connectors u_uI took off the transformer and attached an aluminum plate under it with thermal grease to get much better thermal conductivity between the transformer and the chassis.Replaced the battery disconnect plug at the back with a 20mm IP68 rated strain relief socket meant for 6-12mm cables. It's just big enough that it can fit the disassembled battery cables through it. Also had to make a little aluminum square with a round hole for the socket because the existing hole was so weird.The chassis wiring for the batteries in this unit is made out of AWG10 wire, there's about 3 feet of it because the negative wire goes through the battery disconnect plug, but since I removed it I was able to reduce the wiring length to 2 feet. The connector used is a Anderson SB-50 forklift battery connector with a contact resistance of 0.2 milliohms and the 2 feet of AWG10 add about 2 milliohms to that.The mosfets used in this unit turned out to be 8 x HRF3205, a 100A 55V 0.008 Ohm N-Channel power mosfet with a power dissipation of 175W and a pulsed drain current of 390A. The total gate charge on this thing is 170nC max. with turn-on delay of 14ns and turn-off delay of 43ns. My local electronics store has IRF3205 which is basically the same part and IRF1405ZPBF which is almost twice as good. The 3205's cost 2.70EUR a pop and 1405's cost 3.50EUR, so I'm thinking ill just go with 8 x IRF3205 for 22EUR. It's really expensive compared to eBay prices, but at least they are guaranteed to be genuine and ill have them in my hands really fastFor the battery filter capacitor I was thinking of using a Panasonic FR-series (low-esr) 2200uF 35V. The one that's already in place is a Jianghai CD298 2700uF 40V.Looking at the design of this things and comparing it to the schematics of the older models it's quite clear it's still pretty much the same design. There's a good explanation of how these units work on youtube here:So all the power stuff is quite nice and simple, I don't know why they have so much control circuitry for it though, maybe because the design is almost 2 decades old :pOne thought I had is if these units could be turned in to grid-tie inverters, because from what I understand the inverter on these things is always running in sync with the AC mains input, so it might be as easy as modifying the output of the inverter in parallel with mains input and connecting your solar or wind power to the battery input. Not that I wanted to do that but just a thought

author: cte7ds
author_rank: Contributor
timestamp: December 15, 2012, 09:11:25 pm
content: I desoldered all heatsinks and installed 8 x IRF3205s in the empty mosfet spots and used 18-ohm 1206 SMD resistors for the gates. The HRF3205s had 20-ohm gate resistors, but 18-ohm was the closest value I had so I used those. I added thermal grease to the heat sinks and bolted all the fets with M3 screws, washers and nuts. Kind of a cool trick how I ended up tightening themI did have some doubts about putting the thermal grease in because I thought perhaps it could increase the resistance between mosfet tabs and the heatsinks and that way have a negative effect, but I'm not sure how plausible that is?Added the 2200uF 35V 105C 0.01ohm Panasonic FR capacitor in parallel with the 2700uF 40V 105C 0.02ohm capacitor that was already on board. I can't figure out why the stock capacitor is physically so huge. My extra capacitor looks ridiculous next to it.After I put everything back together I did some load testing. The efficiency of the unit stayed at the same 80% as it was with just 8 mosfets. Ran a 230V 1000W electric heater fan for about 30 minutes and the mosfet heatsinks stayed at around 43 degrees celcius and the transformer barely had time to warm up. I did notice my extra capacitor got quite hot, around 65C. So I'm thinking maybe I need to find some better caps? Maybe I should go overkill and do something like 2 x 4700uF 63V 105C low-esr caps? :pInterestingly the 1000W heater (measured 1005W) showed up as a 94.2% load with stock current transformer calibration value of 0xDB. The unit is rated at 980W so the calibration was quite a bit off. I changed the calibration value to 0xBC which made the 1005W load show up as 79.3%, there's still room to go higher but I'll do so if I ever need it.The battery charger is now putting out 6.4 amps, which I think is decent enough for 120Ah battery bank alone so that I don't need an external charger with my setup. The transformer makes a really nasty audible buzz during charging. The more amps it's putting out the more loud the sound is, I believe it's normal because I can hear the exact same buzzing noise in knurlgnars videos. The buzzing noise however made me wonder what kind of a horrible waveform is the charger gonna have. I figured there's probably a lot of AC ripple in the charger output and did some AC ripple voltage and current measurements. There indeed seems to be quite massive AC ripple especially when charging with a lot of current. I included some annotated scope screen captures of my measurements. I think the charger is still "good enough" but just barely. I haven't yet done testing with the big batteries, just a 100ohm load resistor and much smaller VRLA batteries. There's a good paper about this whole subject here:http://www.emersonnetworkpower.com/en-US/Brands/Liebert/Documents/White%20Papers/Effects%20of%20AC%20Ripple%20Current%20on%20VRLA%20Battery%20Life.pdfIt basically says 5 amps of AC ripple current per 100Ah of battery capacity and ripple voltage should be < 0.5% of normal float voltage. I'm guessing that even if the floating AC ripple voltage is higher (~3%) yet if it's not causing a big ripple current and there is no heating it should be ok. In any case I can always hook up the external charger that has a slightly higher voltage and that seems to really make this whole problem go away. I set the APC charger to output 27.10VDC so I can easily hook up an external charger set to 27.30VDC so it will dominate the integrated charger.My cabling currently consists of 2 meters of 10mm^2 and 0.6 meters of AWG10 joined with a 0.2 milliohm SB50 connector. This gives me a voltage drop of 0.41 volts at 50.8ADC load. That is the draw from the battery with a 964W AC load at the output. I don't have plans to draw more than that continuously, so that is why I'm not gonna upgrade the cabling any further, even though there's certainly a need to do so. Currently the system is fused with a 100A ANL-fuse which is ok for the 10mm^2 cable but probably too big for the AWG10. The rule of thumb is 10A per 1mm^2. I'm guessing I should at least replace the AWG10 with 10mm^2.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 16, 2012, 01:37:07 pm
content: I'm curious as to why the FET heatsinks have little "ears" on them, also, if it is going to be running full time, it maybe worth while to get some quiet fans to replace the ones that are in there (and add a few), so you don't go crazy and there is good airflow for continued use. Definitely swap the caps if you're going to be using it full time. Is the 10AWG connected to a different battery bank or is it an extension? 2ft at 50A is pushing your luck for 10AWG, I'd switch it, but really, it depend son how hot i gets under continuous usage.

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2012, 01:52:01 pm
content: Ears are for the drain connections to the transformer, the heatsinks are used as the one connection as there is no need to try to route a second high current plane in the board then, so you an have lower losses with more copper in the board as a common plane.

author: cte7ds
author_rank: Contributor
timestamp: December 16, 2012, 04:20:20 pm
content: Quote from: peter.mitchell on December 16, 2012, 01:37:07 pmThe fan on the unit is a 24VDC 2200RPM 29.4CFM 80x80x25mm brushless fan made by Sunon (KDE2408PTS3). It's mounted so that all the airflow passes straight between the mosfet heatsinks, so the cooling is quite good already. Also I'm only gonna be using the unit during power outages and maintenance, that for some reason requires interruption in mains input. But obviously it's nice to have a device that can do more if required. The fan only spins when the mosfets have any sort of significant load on them.With the DC input capacitors I'm not quite sure yet what I'm gonna do. I'm guessing I should go with the biggest capacitors the PCB can fit (or that I can afford). The more capacitance, voltage and lower esr, the better? right? I ordered a few capacitors in my recent tme.eu order that should be arriving in the next few days. But tme didn't really have anything that I would consider "perfect", that would be >= 4700uF, at least 50V/105C rated and low-esr. But I'm gonna experiment with the ones I got and see if they make a difference. The most suitable ones I was able to find from tme were:SAMWHA HE1J478M25040HA (4700uF 63V 105C Snap-in) which are likely not very "low-esr" and SAMWHA WL1V338M1631 (3300uF 35V 105C low-esr) which are fairly low impedance but I would have to bodge two of them in series to increase the voltage capability.The 2 feet of AWG10 is what is being used to get the battery connector outside of the chassis. One end is soldered to the main PCBs high current traces and the other terminated with an Anderson SB50 connector. From there it continues to the battery cable I made using 10mm^2 cable. I could simply solder the cable I made straight to the PCB and get rid of the stock Anderson connectors and AWG10 entirely. Then I would have 2 meters of 10mm^2 copper conductor going straight from the battery terminals soldered to the main PCB. I'll do some more load testing to see if this is necessary. During my initial testing the cables just got a bit warm to touch, nothing severe. The AWG10 wire is 105C rated and my 10mm^2 wire is 90C rated.Quote from: SeanB on December 16, 2012, 01:52:01 pmExactly, the black and white wires from the transformers low voltage primary are screwed to the ears with ring connectors and locking washers. I wonder by how much I increased the resistance between the heatsinks and drains by adding thermal paste?

author: SeanB
author_rank: Super Contributor
timestamp: December 16, 2012, 04:38:05 pm
content: You probably reduced it by excluding corrosion products that had built up, and the grease is keeping the metal contacts from further oxidation as well.

author: T4P
author_rank: Super Contributor
timestamp: December 16, 2012, 05:00:19 pm
content: Mate, samwhas are part of the badcaps

author: cte7ds
author_rank: Contributor
timestamp: December 16, 2012, 08:36:53 pm
content: Quote from: T4P on December 16, 2012, 05:00:19 pmI don't feel like paying the $30 shipping fee for a digikey order that is under $100 in value, especially when I'm not sure what kind of capacitors would be best and what effect will different esr and capacitance have. Local stores don't carry big capacitors like this and the ones on eBay although cheap are often fake and the delivery takes ages (especially now that its xmas time) at which point the unit is gonna be already hooked up and I'm not gonna be bothered to take it down to change caps :pIf someone knows what the role of these DC input capacitors is and could recommend what esr and capacitance to use, that would be great help. I'd imagine something like this would be great:http://www.digikey.com/product-detail/en/ECO-S1HA153EA/P6693-ND/131595hehe

author: cte7ds
author_rank: Contributor
timestamp: December 23, 2012, 01:27:57 pm
content: Decided to make the cabling better after all. I desoldered the stock battery wiring, and re-drilled the ~3.5mm hole with a 5mm drill bit. It was a double sided plated trough hole so by drilling it I removed the plating of course. So I had to scratch some of the solder mask off around the holes and solder my 10mm^2 cable to the PCB from both sides. Had to use two soldering irons at once and apply solder with my third hand :p So now the battery wiring is 2 meters of 10mm^2 soldered to the PCB and quick release battery terminals at the other end. I was able to reduce the voltage drop (from battery posts to PCB) at 49.5ADC to 0.20V (half what it used to be). The link between batteries consist of quick release battery terminals soldered to 16mm^2 cable and in between there is a ANL fuseholder with a 100A fuse. I decided to also solder the 16mm^2 cable to the fuseholder because the screw terminals on it were horrible, I had to use a blowtorch for all these connections :pAs a little bonus feature I added a JST RCY connector with a 1 amp in-line fuse connected to the battery input traces on the main pcb so I can get accurate voltage readings when the unit is back together. I also though about adding an external charger port by having heavy gauge wire going to the battery traces trough a beefy diode, but my cable strain relief thingy couldn't fit any more wires trough it.I decided not to do anything about the input capacitor, I left the stock one in and didn't bother to add a crappy capacitor in parallel with it, figured it might just cause problems. I'll order some quality replacement caps next time I need something from Digikey so that I have them in case I ever need to/want to replace them.I tried to do a runtime calibration but it turns out my battery bank has so much capacity that the unit simply cannot be calibrated for so much capacity. Even manually setting the runtime estimation calibration value to 0xFF in the eeprom gave me way way low estimates. The calibration also gave me an opportunity to do some stress testing of the unit. I ran my 1000W electric heater fan for over 2 hours from the inverter until my batteries were completely discharged. The fet area on the backside of the main PCB never got above 58C but at the end the Class H rated (180C) transformer was at around 100C with hot spots of 118C. It was like a frying pan and would burn fingers very quickly if touched. There was also the smell of nicely cooked transformer in the air, it wasn't smoke or anything so I didn't think it was burning. I certainly would never dare to run this unit continuously with any more load than 1000W, and even with 1000W it might not last for very long in 24/7 use... Or does anyone know what kind of abuse can a Class H rated transformer take? Is it ok as long as there is no visible smoke? :p The low voltage cutoff engaged at around 19.5VDC which was a bit surprising because I had previously specced it at <20.70VDC from my bench PSU. Anyways, when the cut off engaged, the voltage was dropping like a stone so we certainly got a 100% DOD.I hooked up my Brymen BM869 100kHz AC+DC TRMS current meter in series with the empty batteries and the UPS to get a better idea about the charger. I got readings of 4.0AAC and 6.3ADC and the UPS was pulling ~260W from the mains with a power factor of .98This concludes my modifications and testing of the unit so I was able to finally put the cover on and put the unit in use. For now it's feeding to the input of my old UPS system but I will be retiring the old system once I dare to power everything down for upgrades.Here's a list of caps this this thing eats:Electrolytic:4.7uF 25V, 1pcs22uF 25V, 5pcs47uF 63V, 1pcs100uF 35V, 1pcs330uF 25V, 2pcs2700uF 40V, 1pcs (room for 2)Filter capacitors:224k 400V red film capacitor105k 400V red film capacitor.33uF X2 plastic film capacitor1uF X2 plastic film capacitor2.2uF X2 plastic film capacitor4n7 Y2 blue ceramic capacitor, 9pcsOvervoltage protection:TVR 14681, 1pcsZNR V14471U, 1pcs (room for 3)

author: dark_hawk
author_rank: Regular Contributor
timestamp: August 15, 2014, 01:16:34 pm
content: Thank you so much for this "Really" Cool tutorial.If you had a penny for each time I viewed those pictures you'd be a very rich man.Quick question: How did your project go? Are you still using it? Have you ran into any problems that you didn't report?Thank you.

author: cte7ds
author_rank: Contributor
timestamp: December 04, 2014, 01:20:05 pm
content: Quote from: dark_hawk on August 15, 2014, 01:16:34 pmYay, I'm glad someone found it usefulSo it has now been two years since I set up the system and I just finished load testing the 2x120Ah batteries (with a normal ~100 amp resistive battery load tester). Both of the batteries showed a rating of around 1000CCA (Cold Cranking Amps). Back when I bought the batteries the reading was the same, so looks like there hasn't been any huge immediate deterioration from the float charging applied by the UPS.In the past few years while this system has been operational I've experienced many many short power drops/brownouts and a handful of longer outages and this unit has gotten me trough all of them without any sign of troubles *knock on wood*, it simply seems to be a rock solid UPS with a nicely regulated output (big-ass iron core transformers ftw?) :-)I've been loading the UPS with 500-600 watts and it even got me trough a 6 hours power outage last winter! I was really impressed at how long it was able to last. My only regret is that I didn't go with the 48V 2200W rackmount model I once saw selling for cheap, could've had even a longer lasting system :-POne other modification idea that has crossed my mind is that if I ever find another Smart-UPS 1500 for really cheap, it would be interesting to take the transformer out of it and hook it up in parallel with the existing transformer. This would essentially convert the UPS into the XL (Extended Runtime) model, I think... (I remember seeing the internals of the XL model and it was just two transformers in parallel (but maybe those transformers need to be carefully matched?)). There would actually be room inside the UPS for another transformer because I don't have the internal batteries.Anyways, I can highly recommend this UPS and the battery mod if you want something that can keep you working trough a long power outage. Also the linux support for this UPS (apcupsd) has been great to work with. You can get a small web-page that displays all the relevant details about the status of the UPS.P.S. Someone asked how to access/modify the calibration values of the UPS so here are a few links about that:http://www.jjoseph.org/notes/apc_smartups_battery_float_voltagehttp://www.crufty.net/sjg/apc.html

author: theoldwizard1
author_rank: Regular Contributor
timestamp: December 20, 2014, 03:27:40 pm
content: Great write up ! Love the pictures !I just finishedKnurlgnar24's video serieson this unit and am happy to see that someone else could successfully perform the upgrades he suggested. As an inverter there are more efficient ones on the market, but you certainly won't be buying one for that kind of price ! Besides, most of the losses due to heat are from the transformer.I have a couple of questionsHas the increase in battery wire size (to approximately 8 AWG) reduced the temperature rise in those wires ?(Getting rid of the Anderson connector was a big "win")Any good locations on the board where you could bolt a "lug" to the board and then bolt, say a 6 AWG cable ?Did you ever add a second capacitor ? What brand, model, size ?Did you do anything about improving air flow over the transformer ?The site you posted the partial schematic from appears to be dead. Can you re-post the entire schematic ?Any other sites you can recommend for information on this and other APC units ?Edit(gnif): Fixed the YouTube link.

author: cte7ds
author_rank: Contributor
timestamp: December 26, 2014, 05:11:03 pm
content: Quote from: theoldwizard1 on December 20, 2014, 03:27:40 pmI approximately halved the resistance in the cabling by taking out the original battery wires and the Anderson connector. The 1-meter 10mm^2 cables get only slightly warm at full load.QuoteYou probably could install PCB mount wire lug terminals like this:QuoteI decided not to bother with the second capacitor because I didn't have a good quality one at hand. But if I ever need to open up the UPS again I might replace the cap with something like 2 x 4,700 - 10,000 uF @ 50-63 V low-esr Panasonic caps.QuoteI couldn't think of any easy way to improve the air flow over the transformer so I didn't bother.QuoteI don't have the schematics anymore, and they were for the older 1400VA model anyways. This is the best I could find:http://master-tv.com/article/apc-back-ups/QuoteMost of the links I could find were 404, But heres a few that worked:http://www.techno-fandom.org/~hobbit/power/dumbups/http://www.techno-fandom.org/~hobbit/power/dumbups/res.htmlQuote

author: theoldwizard1
author_rank: Regular Contributor
timestamp: December 26, 2014, 06:30:51 pm
content: Quote from: cte7ds on December 04, 2014, 01:20:05 pmBased onDave's inspection video of a 2200XL, I think the main feature of the XL models us additional cooling.There is a good deal on a pair of functioning 3000XL units within a couple hour drive of my house. The down side on them is 48V battery bank. I would much prefer a 24V battery bank !Edit(gnif): Fixed the YouTube link.

author: cte7ds
author_rank: Contributor
timestamp: December 26, 2014, 08:55:59 pm
content: Quote from: theoldwizard1 on December 26, 2014, 06:30:51 pmSure, a 48V bank is more awkward to set up and handle and it doesn't look as neat, but it also means you will be getting more energy out of your batteries because they are being discharged with a smaller current (Peukert's law).I haven't been able to confirm exactly how the XL models differ from the non-XL models, but at the very least it gives more assurances that the unit will not overheat during longer periods of use, and that's definitely nice to have.Also getting a pair of them is great because then you have a spare if something goes wrong. You probably should go for it if the price is right

author: theoldwizard1
author_rank: Regular Contributor
timestamp: December 26, 2014, 10:37:56 pm
content: Quote from: cte7ds on December 26, 2014, 08:55:59 pmIf I really had a need, I would be after them in a heartbeat ! Right now they would just sit around and gather dust.Did you watchKnurlgnar24's video on converting a pair of APC UPS into 240v split phase? I would love to see some 'scope traces and testing on that setup !!Edit(gnif): Fixed the YouTube link.

author: johansen
author_rank: Super Contributor
timestamp: January 17, 2015, 02:07:14 am
content: a worthwhile mod is to place an inductor in series with the low voltage side of the transformer.these machines use the leakage inductance of the transformer to filter the pwm and its very lossy.my apc1000 when placing an inductor in series with the transformer, it not only reduced the no load loss by 10 watts, but it also reduced the switching losses because it reduced the pwm frequency.another mod is taking the 20uf capacitor off the 120vac side of the transformer and replace it with 4.7uf. this saves you about 120va's of circulating current and about 1-2 watts in power loss.I used a ferrite core of 25mm diameter and 7 turns of wire, gapped with a couple sheets of paper.don't use an iron powder core.. i was actually able to increase power loss by attempting to use two dozen t-106 yellow cores, by slipping them over the wires of the transformer.the ferrite core from a crt flyback transformer could work.. but you would need a lot of copper and a big air gap for a 1kw load. --2 of them or 4 of them would be better.the inductor will also reduce the no load loss when charging the battery.. mine did not use the linear region of the fets, but rather used the h bridge as a boost converter to charge the battery. this requires pwm, and pwm means the transformer gets warm.i don't recall what the reduction at the outlet was, but the transformer probably ran 5C cooler.

author: darkyputz
author_rank: Newbie
timestamp: June 19, 2015, 02:35:43 pm
content: Hello out there...Just found this article...and i am very impressed...I have now 2 of these devices sitting in front of me, and i would like to get one apart to complete the other...with the right parts...of course...But my question is...what is the main benefit of doing that?More Long time stable?More Watt?Better cooling?Not quiet sure...Can please someone explain?And an another question...Is there a way to tell the device that i is 230 volts from now on and 50 hertz?Or is this a total different board design than?Thx in advance...

author: johansen
author_rank: Super Contributor
timestamp: June 19, 2015, 03:27:54 pm
content: Quote from: darkyputz on June 19, 2015, 02:35:43 pmbenifit of doing what exactly.adding more mosfets to reduce the losses? the point is to reduce losses.adding an inductor works as well to significantly reduce switching losses and transformer iron and transformer copper losses.i do not believe you will be able to convert your inverters from 120v 60 hz to 230v 50hz.you could rewind the transformer to get a higher voltage.. but that is a lot of work.. you would have much better success winding a new toroidal transformer.

author: darkyputz
author_rank: Newbie
timestamp: June 19, 2015, 03:44:18 pm
content: Hello and thx for your answer...Yes...i meant putting the 8 missing pieces in and the regarding gates...and the cap...Or would you stay with two intact ones untouched instead of putting the parts from the second in the first to get it complete?And what did you do with yours in the reply prior mine?You said you added something somewhere...can you be some more detailed or have a pic?Thx in advance

author: darkyputz
author_rank: Newbie
timestamp: June 21, 2015, 08:22:14 pm
content: And onother question to this...Because i have 2 of the same ups...could i put the second trnsformer parrallel to the first and get some benefit from that?and if yes...would it be just connect the second to the same as the first?

author: johansen
author_rank: Super Contributor
timestamp: June 21, 2015, 11:38:10 pm
content: you can pull the mosfets from one board and install them on the other.. no problem there.I would also pull the electrolytic cap (its the largest one on the board) and install it on the other, as there is probably space for it.if not, solder it to the battery cables as close as possible to the h bridge.you can indeed parallel the two transformers, however this will not double the potential power output, as you will now be limited by the current capacity of the circuit board traces, the fuses.. and the 10 awg wires from the battery. however all of those things can be upgraded as well. it will also practically double the no load losses.for an inductor, i used 7 turns of wire on a 25mm diameter core. yes, that's very large, an inch in diameter. the air gap was 2 pieces of paper.you can use the ferrite core from a crt flyback transformer, but you would want 4 of those cores, not just one. although even one would help.

author: darkyputz
author_rank: Newbie
timestamp: June 22, 2015, 12:48:36 pm
content: Thx again...The extra cap amd the 8 parts were plan already...the second transformer just gave me hope to lower the load per each...so they are not getting as hot...Is that so? or just a miss leading thought?And i don't want to double the power...just have a straight 1000 watt pure sinus inverter for a long time...and that it should be able to, don't you think?

author: cte7ds
author_rank: Contributor
timestamp: March 02, 2016, 04:44:27 pm
content: Quote from: johansen on January 17, 2015, 02:07:14 amI'm pretty bummed I didn't know about this before I put my unit in to service. I still intend to experiment with this mod, if I manage to find another SmartUps for cheap (to serve as a guinea pig).Also, I'm curious, does/could this mod affect the buzzing noise that is present during battery charging and standby?Someone actually offered me a very clean looking SmartUps 1500 for 50 EUR including shipping (exceptionally cheap imo), but sadly I wasn't able to justify the expenditure at the time (you know, student life in poverty, *long sigh*)Quote from: johansen on June 21, 2015, 11:38:10 pmYeah, I remember seeing parallel transformers in some old APC XL UPS teardown pictures.And of course this guy:-APC smart UPS from 1000VA to 3000VA with two parallel transformers!Would also love to try this one out myself, if I find more than one smart ups.Quote from: johansen on June 21, 2015, 11:38:10 pmI don't have any experience with magnetics, so I have to ask; What type of core was it? Toroidal, shell, cylindrical, etc..?Would something like this work?https://www.digikey.com/product-detail/en/epcos-tdk/B64290L618X38/495-3861-ND/1830191And perhaps wrap some Kapton tape around it, to provide some gap?Aaanyways...The reason why I set out to revive this old topic was because I realized people on this thread might be interested of the tool I created for logging and graphing my smart ups statistics (via apcupsd / apcaccess)...Just a simple Bash script leveraging rrdtool to generate a HTML gallery of graphs like this:The HTML has thumbnails to select different resolutions and time periods.The code with some "instructions" can be found at:https://github.com/fld/graph-apcupsdI know it's quite a crude solution, but so far it has worked for me pretty good!Enjoy! ..or don't...or make something better!

author: johansen
author_rank: Super Contributor
timestamp: March 03, 2016, 12:46:10 am
content: QuoteIt should reduce the noise considerably if that noise is from the carrier frequency of the inverter. if you have a high line voltage your transformer may be slightly saturated and that will make both noise and heat.

author: marcone
author_rank: Contributor
timestamp: January 06, 2017, 11:56:44 am
content: I got to do some modding on a SUA1500i recently so I will share my experience.I needed a power back-up system capable of delivering 1300W at peak load to power a pellet heating furnace.Going for a 2200VA unit and 4 batteries was out of the budget so I decided to go with the 1500VA unit and 2x65Ah deep cycle batteries.In modding the unit I:*ripped out original battery wiring, Anderson connector and battery switch out back and replaced all that with 2x1m 10mm2 cables straight from the board to the battery.* got rid of the network card box which was impeding air flow in the case* added a 3rd MOSFET to each arm of the H bridge and an additional 3300uF/50Vcap*using the SMART protocol (Serial port out back + APC serial cable) I adjusted charging voltage to 27.2V and adjusted current sensing for 1300W max.Unit works just fine, no extra heat but it's not outputting the 1300W continuously, most of the time the load is around 300W.If I would go for more than 1000W continuously, I would add a second transformer where batteries normally sit, 2200VA units use 2x24 transformers in series.Great sources of information for this project werehttps://www.youtube.com/user/FFcossagandhttps://www.youtube.com/user/knurlgnar24

author: BradC
author_rank: Super Contributor
timestamp: January 06, 2017, 01:28:44 pm
content: Late to the party, but some info :- The SU(A)1400/1500 XL are 48V thus they have 2 transformers. The non XL are 24V (as you found out). The XL are basically a de-rated 2200.- The reason you couldn't calibrate the runtime correctly using the battery constant was you need to tell the unit it has extra batteries. They all use standard firmware, so even the non-XL units can be tweaked up with extra batteries. If you do a quick calculation of the estimated battery life and correct for the puekerts constant for your batteries, you crank the ext-battery count up until your estimated runtime exceeds the calculated runtime, then decrease the battery constant until it gets close. Then when you perform a runtime cal it'll be pretty close.- Be careful that your heatsink compound does not increase the resistance between the FET tab and the heatsink. It's a major current route.- The main DC filter cap is subjected to a high stress environment (seriously), which is why it is physically so big for the capacity/voltage. They are an extremely high quality cap and one part I've never seen fail yet.- Only the SUA models (generation 4 and above) can alter the battery voltage in software. The earlier models require hardware tweaking of a resistive divider. The SUA uses a PWM output from the micro to sway the 5V reference voltage on the charger. They do this to provide temperature compensated battery charging which none of the previous generations had. It actually works passably, but I still wind about 800mV off the charge voltage by default. You are changing the voltage the charger actually provides, not the voltage the UPS reads, so the UPS still thinks it's hitting its target voltage.- The MOSFETS don't operate in linear mode while charging the battery. They momentarily short the low side of the transformer H-Bridge to allow a build up of magnetic field which then discharges via the fets body diodes to charge the battery. It's a crude form of boost converter as the raw transformed low voltage is not high enough to charge the battery. This explains the noise from the transformer while charging.- 48V models can be converted from 110 to 230 and back by re configuring the transformer cabling and changing some MOV's / Caps on the board. It's a lot of work though.- You don't need to change the CT burden resistor to alter the power calibration as long as you stay within about 80% of the original power rating (in VA). There is enough headroom in the software calibration to cope. Anything more than that and you are asking for a transformer failure anyway.- The biggest difference in the XL units is the cooling. The also have a thermal cut-out on the heatsink that breaks the main logic supply rail to the MOSFETS & driver if it overheats, so it goes dead.- Battery cabling resistance is critical on these units. They have a set of constants (4,5 & 6) that are calibrated for each model and characterize the battery system. These allow for instantaneous drop when switching to load, volt drop in the cabling (to properly estimate the actual battery voltage) and battery internal resistance. Increasing the battery cable resistance does bad things to the correct runtime estimation.- A good result for external batteries is to put a new set of internals in and supplement them with externals. This keeps the internal resistance within original spec.Common failure points on pre-SUA models :- On 48V models the bootstrap caps on the FET drivers- On 48V models the 1K resistors in the FET drivers- The caps on the -8V supply- The caps on the 24V logic SMPS- The battery voltage divider driftsI've not had SUA models fail to a point they need repair yet.There are schematics out there if you look hard enough for the 2, 3 & 3.5G units (SU). I have found one schematic for an early SUA1500 which gives enough detail on the altered FET drivers & PWM reference tweak on the charger ASIC to be useful on the remainder of the SUA units. I believe the later SMT & SMX units are basically an SUA with a pretty front panel and a protocol translator to prevent accessing the internal UPS-Link interface. There are Youtube videos on how to bypass that if you look around.

author: marcone
author_rank: Contributor
timestamp: January 06, 2017, 03:58:15 pm
content: Thanks, that reminds me of another software tweak I performed, telling the UPS that it had 3 external battery packs in order to make up for the 65Ah batteries as opposed to the original 18Ah.

author: BradC
author_rank: Super Contributor
timestamp: January 06, 2017, 10:24:01 pm
content: Quote from: marcone on January 06, 2017, 03:58:15 pmIt's worth playing with. Some ups count 18ah as an external pack, and some count 36ah so you have to experiment to figure out which does what. I have standard internals + 55ah of external on my current units.

author: NJM
author_rank: Newbie
timestamp: April 04, 2017, 10:59:08 am
content: Hi , i'm new in this forum, i have a APC 3000 48v to 220 50hz 60hz , i would like use it as a power inverter. I Have a few questions; is it possible work on 110ac, can you tell me what i have to do, toimprove the runtime,i do not need more then 500w continous. But i need to use it for long period. I was thinking in easy modification,becouse i' completely uneexperint in elettronics. Thanks in advance. NJM

author: johansen
author_rank: Super Contributor
timestamp: April 04, 2017, 08:20:37 pm
content: Quote from: NJM on April 04, 2017, 10:59:08 amthe largest parasitic loss in that system may be the transformer.as such winding a custom transformer may not be such a bad idea. i would suggest a toroidal transformer but there is one problem. those inverters do not ensure zero dc volts output. they actually saturate the transformer arbitrarily by passing dc current through the low voltage side. but i have not verified this with a 48v system.so what i might suggest is you rewind the existing transformer for 110vac output. you will need to wind an additional 220v coil so that the inverter thinks its producing 220v. this coil can be of relatively low capacity.

author: NJM
author_rank: Newbie
timestamp: April 04, 2017, 08:45:09 pm
content: Hi johansen, I did the tests on the transformers using the serial lamp, from black +white i found 110v, i'm not sure but i was looking under the main board, it seens the two transformers are wired in series to, as the primary, my tought is they use just one model of transformers for many models of ups. just changing the wires. I'm not hundred % secure. Another thing, i wired its transformer on Lf main board 24v to 110v and it worked. but i would use them on APC. Thank you NJM

author: BradC
author_rank: Super Contributor
timestamp: April 05, 2017, 07:41:14 am
content: Quote from: NJM on April 04, 2017, 08:45:09 pmYou don't need to rewind the transformer as you've already found. The larger units use two identical transformers with the HV side in series for 230V and parallel for 110V. You need to re-wire those. The UPS senses mains voltage using small transformers on the PCB, so your unit will be set up for 230V. You'll need to figure out some sort of other arrangement to change the mains output sense voltage to get that to work. It wouldn't surprise me if they were a relatively "off the shelf" PCB mount transformer. If you have some more details on your unit (like generation, PCB configuration) I might be able to assist with some more info. Start with the label on the top of the main control uC. That'll have UPS generation and firmware revision.You'll also need to change the divider resistors on the output current transformer. I can't help with the values on a 110V unit, but might be able to come close by examining some of the domestic model schematics. There's a pretty wide range of tolerance on both the voltage and current sense in the software calibration.I've certainly never seen a SmartUPS deliberately put *any* DC into the transformer while on inverter. It certainly does when used as a charger as it uses the transformer as the inductor in a boost converter.What you are asking is doable, but there are a few little things you need to look out for. It'd be easier to flog that one on E-bay and pick up a 110V unit.

author: johansen
author_rank: Super Contributor
timestamp: April 05, 2017, 11:21:21 pm
content: Quote from: BradC on April 05, 2017, 07:41:14 ami can post a video of this if you want, but here's a photo of the current flowing through the low voltage side of an apc1500 24v ups.i have an inductor in the circuit, and the resistor used to measure the current is 16.7mOhms, so two divisions is one volt and that is 60 amps.rms amps should be about 53 amps, the primary is 14 vac nominal, 120vac output into 750 watt resistive load. you can see the dc offset clearly.http://johansense.com/bulk/sinewaveinvertermodwiinductor17mohm750wattload.JPGin this photo the inductor has been removed.http://johansense.com/bulk/sinewaveinvertermodwoinductor17mohm750wattload.JPGin this photo is the current through the 14vac side of the transformer, at no load, running as an inverter. there is a small inductor in series with the resistor.http://johansense.com/bulk/sinewaveinvertermodwiinductor17mohm.JPGthe transformer is fairly saturated at this point.the dc voltage offset varies with time, it is not random though. i have verified this across at least 4 smart APC ups's.the cuprit is the custom asic or whatever it is, a 16 pin dip that handles the pwm generation I believe it also has a pll in it to bring the output back in sync with the ac grid before switching back to ac mains.I have tried inserting a sufficiently large capacitor in series with the transformer to cancel out that dc offset but it doesn't work with a capacitor in series (perhaps i need a few farads rather than 100,000uf)One method to fix this might be to measure the dc offset and then add it to the output voltage sense circuitry before it gets back to the chip that generates the pwm.when the h bridge is shorted out to use the transformer as a boost converter, the volt amps are not equal on both sides of the sine wave either. but its not as bad as when its used as an inverter.

author: BradC
author_rank: Super Contributor
timestamp: April 06, 2017, 01:02:59 am
content: Quote from: johansen on April 05, 2017, 11:21:21 pmNovel. Well, if it's on the 24V models it'll be the same on the 48V models. I must say it's not behaviour I've seen, but then I've never looked at it from this perspective. If it's not random, *and* it varies with time, have you figured out what the correlation is?Quote from: johansen on April 05, 2017, 11:21:21 pmNot quite. There are two interlinked asics. The first manages the charging and mains phase comparison, the second manages the PWM. They don't have any internal power smarts and receive their sine wave reference from a DAC connected to the main CPU. The CPU generates the sine wave reference, and slews it over 4 seconds to ensure it's in sync before they switch back to mains. Aside from the funky boost charging, pretty much all the smarts in these units is in firmware. It also changes the inverter frequency depending on the incoming mains. It'd be interesting to compare that generated sine to see if there is a DC offset in there relative to what hits the H-Bridge.In *theory* (as documented in some internal APC technical docs that were found on a Russian web page), these units all default to 60Hz regardless of voltage setup. So a cold start from battery with no incoming mains should have them generating 60Hz. I've used this feature a lot, but I've never actually tested the generated mains frequency. I'll do that when I next power one up.

author: NJM
author_rank: Newbie
timestamp: April 06, 2017, 07:27:34 am
content: Hi the problem is; I d'nt have the that board to connect to my computer,to change configuration, i have the RJ jack. I tried to connect, but when i connect the cable, the ups gos off i'm not sure if can use the software without that pc card. What about to change the dc imput from 48to 24dc? I'm telling that becouse i' making some meccanichcs modification. Mounting another power inverter in the same box.thanks.NJM

author: BradC
author_rank: Super Contributor
timestamp: April 06, 2017, 07:56:56 am
content: Quote from: NJM on April 06, 2017, 07:27:34 amIf you don't have the specific APC cable, then that is normal behaviour. They mangle pinouts such that if you plug a normal serial cable in it shuts down the UPS. Yay.Quote from: NJM on April 06, 2017, 07:27:34 amForget it. There's another thread here somewhere where the originator wanted to do that, and when the magnitude of the changes required was explained he very quickly decided against it.You've got the voltage/current sensing dividers, the logic power SMPS, the H Bridge driver, the transformer configuration and then you'll halve your power handling capacity.There's a reason the 1500 is the largest 24V unit.

author: NJM
author_rank: Newbie
timestamp: April 06, 2017, 11:48:28 am
content: Thanks anyway, I am tryng to put on the smart3000 box, one power inverter 24dc to 110ac and another ups pure sine wave 24 to 230ac pure sine wave made in Italy it uses 2 toroidal transformers,i have a plan to use it on my beach house, doing some kind rondon use of the 3 componnents.i raised the original box , put heatsink for the transformers, and tryng some improvements for the intire system.Thanks.

author: johansen
author_rank: Super Contributor
timestamp: April 06, 2017, 11:17:57 pm
content: Quote from: BradC on April 06, 2017, 01:02:59 amwell, it regulates the output voltage as well, i'm not sure if that's handled by the asic or the cpu. the frequency is variable as you note. however, there are a few ways to change it. one is to insert an inductor in the transformer, which lowers parasitic loss. it also reduces the switching frequency. the other method is to change the filter capacitor on the output. usually its 10-20uF depending on the model. you can drop it as low as 3uF it will probably still work. i also tried changing the current transformer ratio by looping the capacitor through it several times, but this did not have nearly as much effect on switching frequency as i thought it should have. so why an inductor in series with the tx can case such variation, i don't know.

author: mbr89
author_rank: Newbie
timestamp: August 20, 2017, 03:53:41 pm
content: http://www.ti.com/lit/an/slaa602a/slaa602a.pdf2) Mains Mode:In the mains mode, both the high-side MOSFETs ie A side as well B side is switched off and both the low-side MOSFETs are switched with the similar PWM waveform where the duty cycle of lower side PWM signals determine the charging current.When the lower switches are turned on at the same time, there is a boosted voltage, that appear across the primary leakage inductance of transformer connected to the H–Bridge, by the Ldi/dt effect and this energy is use to charge the battery through the body diodes of the high-side MOSFETs. Also each of the high-side MOSFET’s body diode will conduct in the each half of the Sine Wave.When the mains mode is sensed, firstly all the MOSFETs are switched off and the Relay between the Ac input and the Inverter output is connected. After this, the Lower FETs are tuned on with PWM of small duty Cycle (5 to 10 percent) and the high-side MOSFETS are switched off. Now the voltage across the current sense is measured by controller and if the corresponding current is less or more than required by charging algorithm than the duty cycle is altered correspondingly ie duty cycle is increased if more charging current is required and decreased if the charging current reduction is desired.Figure 30. Waveform During the Charging Mode. The High-Side FET is Switched Off and Both Lower-Side FETs to Ground in the H Bridge are Switched at the Same Time With the Duty Cycle Proportional to the Battery Charge CurrentI think the maximum charging current is not a question of how many MOSFETs you put in....https://en.wikipedia.org/wiki/Power_MOSFET#Body_diode... they can handle large currents and ...

author: crazy_driver
author_rank: Contributor
timestamp: October 13, 2017, 09:06:30 pm
content: hi guys, i've been searching about a problem with apc ups that go in overload even with no load and that get solved by just remplacing a few caps.Do any of you know witch ones should i switch on this topic's model?

author: BaronVonChickenPants
author_rank: Newbie
timestamp: December 02, 2017, 11:05:36 am
content: I have been looking at an APC 3000VA and 7500VA 240V SmartUPS's and have notice that the inverter output has a floating neutral. When either UPS is in bypass mode running from mains they have the normal MNE readings but when the output is coming from the batteries or if the 7500VA is set the full double conversion mode the neutral measures between 90-120 volts to earth and the active is 160-120 volts to earth. With no load the neutral reads about 90 and active 150 but the balance out to 120 each way once there is a load.I believe this is due to the way the inverter circuit works where the +48v DC from the battery is connected as 0v AC and the the battery DC negative is flicked between the high and low to give 96V AC which is then fed through smoothing circuit, transformers, etc.Should the inverter output have a neutral earth bond, I fear this would likely the damage the inverter.Interested to hear other thoughts on this.Regards,Jordan

author: Bratster
author_rank: Frequent Contributor
timestamp: December 02, 2017, 07:41:30 pm
content: Quote from: BaronVonChickenPants on December 02, 2017, 11:05:36 amI have no direct experience with APC UPS' of that size.But on the couple of UPS's that I have wired up in that size range they have been terminal strip for the connections.And depending on what output voltage you want (straight 120 volts, 120v/240 split phase, 240 or 208) you can connect things to different terminals. One of the options is if you want a neutral to ground Bond.Depending on which output voltage configuration you use the neutral to ground Bond would need to be on different connections so it could be left out from the factory.Again this is all just my past experience with UPS is in that range. I have no idea what UPS you have. Take all of this with a grain of salt.I would consult the manual for your ups and see what options it lists.Sent from my Nexus 6 using Tapatalk

author: mbriaz10
author_rank: Newbie
timestamp: October 07, 2020, 06:46:22 am
content: Hi cte4dsFirst of all thanks for this wonderful tutorial. I really enjoyed the mod and feedback provided by the community. I have recently bought rundown APC3000SU and APC3000XL versions and have already mod these with additional mosfets and the watt capacity is increased. one of these units is always running on batteries 24*7 at an average load of 5-10A @ 220V without any issues. The other one is there for standby in case needed. Now i have realised that due to weather changes my power consumption is de-creased and wanted to grid tie my solar setup so can sell additional power to grid which i would like to buy back in summer. Was wondering if I can mod these UPS's to grid tie inverters with your following idea.Also if these UPS can be parallelly connected to each other in 220 AC output provided if I mod these to synch with main somehow?ThanksSolar Setup5000W Solar Array-Outback FM80 - Narada 800X 24* 2V - APC3000SU/APC3000XL2500W Solar Array-Outback FM60 - Narada 800X 24* 2V - APC3000SU/APC3000XL"One thought I had is if these units could be turned in to grid-tie inverters, because from what I understand the inverter on these things is always running in sync with the AC mains input, so it might be as easy as modifying the output of the inverter in parallel with mains input and connecting your solar or wind power to the battery input. Not that I wanted to do that but just a thought"