APC Smart-Ups 700, SU700i thinks its battery voltage is 10v - Page 1
Forum section: electronics / repair

author: erkko
author_rank: Contributor
timestamp: October 02, 2025, 02:56:34 pm
content: Anyone experienced with that old ups? UPS floats batteries with 27.7 and shows only one battery-led lit. Pushing test it tries to run from battery, but immediately switches back to AC and starts blinking that one battery-led.Meanwhile at serial console:SMB - 10.59f - 000.0g - 024So it thinks its battery is at 10.59 while it needs to be at 24. I am measuring 27.7 on battery terminals and on pcb where these cables are soldered.Is that some commonly seen issue with these models?

author: Swake
author_rank: Frequent Contributor
timestamp: October 02, 2025, 04:15:51 pm
content: 27.7V must be the charging voltage.Disconnectthe batteries, wait for half an hour and then measure them one at a time. What voltage do these have?

author: erkko
author_rank: Contributor
timestamp: October 02, 2025, 05:03:30 pm
content: I have these batteries freshly charged with external charger, they have nothing wrong with them. I have 4 batteries from same set, from larger ups, all fine in that bigger ups. Measuring 25.1 volts at the batteries without ups powered, 12.54 and 12.59 separately.

author: Swake
author_rank: Frequent Contributor
timestamp: October 03, 2025, 12:52:25 pm
content: Attached twice the schematic.One document is in Russian with some comments. I don't speak Russian, but it does not look something is written about the voltage detect or percentage charged of the battery.

author: Swake
author_rank: Frequent Contributor
timestamp: October 03, 2025, 12:58:51 pm
content: There are 2 fuses in the battery path.Since the UPS measures 10 V I think these will be ok, but better to check them out. Maybe bad contact or corrosion.

author: Swake
author_rank: Frequent Contributor
timestamp: October 03, 2025, 02:00:27 pm
content: There is a 3rd fuse F3 following those first 2 fuses. The battery 'signal' then goes over FET Q5 and is named 24VFET.This 24VFET signal is converted with IC10 ADC0838 to digital.

author: erkko
author_rank: Contributor
timestamp: October 04, 2025, 05:58:41 am
content: Lots of reading for a weekend, thanks

author: erkko
author_rank: Contributor
timestamp: October 04, 2025, 08:25:09 am
content: measured so far:IC4/1 - 26.81vIC4/3 - 11.89vIC5/1 - 11.89vIC5/3 - 5.00vIC17/1 - -7.8v...-8.0vQ5/1,2 - 27.65vQ5/3 - 13.72vQ5/4 - 27.65vIC10/1 - 3.85vF1, F2, F2I, F3, F4, F5 - OK

author: Swake
author_rank: Frequent Contributor
timestamp: October 04, 2025, 09:20:33 am
content: 27.65 V input in the voltage divider made of R99 and R100. Theoretical out is 3.93 V and you measure 3.85 V. That sounds fine to me as all those parts have some tolerance. I don't know how to check if that channel of the ADC0838 is working or not and if the µC interprets the serial data correctly.Let's assume the ADC works, then why is the console reporting 10 V? Would the voltage drop dramatically when under load? Let's test that: please measure the voltage on pin 1 of IC10 while the UPS is forced on battery. If the voltage drops we have at least a point of reference to search further, if it does not drop we'll have to search somewhere else.

author: JimboJack
author_rank: Regular Contributor
timestamp: October 04, 2025, 09:32:26 am
content: try this hint sheeta simple APCFIX if it reports back the correct param EEPROM config settings which areregisters 4,5,6 and 0 have been lost before start desoldering anything ?SU700 28, F2,FA,96 07,RM=47 Firmwarea 52.11.1orSU700RMI2U 07,B1,0D,92, 8A 152.4.1

author: erkko
author_rank: Contributor
timestamp: October 04, 2025, 09:35:13 am
content: Very minimal drop at IC10/1, looking with VOM at 10v range, needle just barely moved slightly to left of its original position. That is while the test-button was pressed and I guess ups then tries to run from batteries.PS. I mean this test only clicks the relays few times, if anything it runs on batteries very shortly. Not sure if that would even show any drop at IC10.

author: erkko
author_rank: Contributor
timestamp: October 04, 2025, 09:51:22 am
content: Thanks, hints_oldie.pdf looks interesting. I was wondering what is written on other pages before this section... Found full service manual fromhttps://pdfcoffee.com/qdownload/service-manual-for-the-apc-smart-ups-450-700-1000-1400-ups-pdf-pdf-free.htmlAttaching here also, for the next guy.

author: erkko
author_rank: Contributor
timestamp: October 04, 2025, 09:54:15 am
content: Serial session, with local echo:YSM0564285F26FANot sure how to check for rest (07,RM=47 Firmwarea 52.11.1)It is SU700I, I think - Label on its back saysSMART-UPS 700IGS9648588782

author: JimboJack
author_rank: Regular Contributor
timestamp: October 05, 2025, 01:25:36 am
content: I cann't remember if that unit you change the battery constant via changing ctrl+B via PROG be 07 or 47, if it swings the battery constant. or the voltage bridge check the values of R118, R119, R310, C86, R179, C70 C69 (page3). IC14 Bridge charger

author: erkko
author_rank: Contributor
timestamp: October 05, 2025, 02:54:23 pm
content: apcupstest from apcupsd package seems to get some information out of that one./etc/apcupsd/apcupsd.conf modifications for my usecase - serial cable with usb-serial converter:#UPSCABLE usbUPSCABLE smart#UPSTYPE usbUPSTYPE apcsmart#DEVICE /dev/ttyS0DEVICE /dev/ttyUSB0$ /usr/sbin/apctest2025-10-05 17:46:00 apctest 3.14.14 (31 May 2016) debianChecking configuration ...sharenet.type = Network & ShareUPS Disabledcable.type = Custom Cable Smartmode.type = APC Smart UPS (any)Setting up the port ...Doing prep_device() ...You are using a SMART cable type, so I'm entering SMART test modeHello, this is the apcupsd Cable Test program.This part of apctest is for testing Smart UPSes.Please select the function you want to perform.1) Query the UPS for all known values2) Perform a Battery Runtime Calibration3) Abort Battery Calibration4) Monitor Battery Calibration progress5) Program EEPROM6) Enter TTY mode communicating with UPSQ) QuitSelect function number: 1I am going to run through the series of queries of the UPSthat are used in initializing apcupsd.Simulating UPSlinkCheck ...Wrote: Y Got: SMAttempting to use smart_poll() ...Sent: Y Got: SM Good -- smart_poll() works!.Going to ask for valid commands...Wrote: a Got: 3.?=.-789>@ABCDEFGKLMNOPQRSUVWXYZ'abcefgjklmnopqrsuxyz~Protocol version is: 3Alert characters are: ?=Command characters are: ^A^N^Z-789>@ABCDEFGKLMNOPQRSUVWXYZ'abcefgjklmnopqrsuxyz~Now running through apcupsd get_UPS capabilities().NA indicates that the feature is Not AvailableUPS Status: 00Line quality: FFReason for last transfer to batteries: LSelf-Test Status: NOLine Voltage: 234.0Line Voltage Max: 237.9Line Voltage Min: 232.7Output Voltage: 000.0Batt level percent: 000.0Batt voltage: 10.59UPS Load: 000.0Line freq: 50.00Runtime left: 0000UPS Internal temp: 025.2Dip switch settings: 00Register 1: 40Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024Percent humidity: NAAmbient temperature: NAFirmware revision: 50.9.INumber of external batteries installed: 000Number of bad batteries installed: NAUPS model as defined by UPS: SMART-UPS 700UPS EPROM capabilities string: uD43132135138129uM43229234239224uA43110112114108uI43253264271280lD43103100097106lM43177172168182lA43090092081085lI43196188208204e44200155090oI43230240220225oD13115oJ13100oM13208s441HMLLq44202050710p443020180300600k4410TLNr443000060180300E443336168ON OFFThe EPROM string is 253 characters long!Hours since last self test: NA

author: erkko
author_rank: Contributor
timestamp: October 06, 2025, 10:51:04 am
content: OK can someone with more apc creds explain following?Watched some random video about guy changing his apc smartups charging voltage on his batteries... He went to PROG mode and pressed B and started + -ing to change it. And it changed. On his battery terminals! Wtf? I had an impression it is readonly value, how on earth is that user-modifiable? What am I misunderstanding here?Anyhow, went to see what happens:11PROGB10.59+5DB10.73+5E+5F+60+61+62+63+64+65+66B11.67+67+68+69+6A+6B+6C+6D+6E+6F+70+71+72+73+74+75+76+77+78+79B13.83+7A+7B+7C+7D+7E+7F+80+81+82+83+84+85+86+87+88+89+8A+8B+8CB15.99+8D+8E+8F+90+91+92+93+94+95+96+97+98+99+9A+9B+9C+9D+9EB18.02+9F+A0+A1+A2+A3+A4+A5+A6+A7+A8+A9+AA+AB+AC+AD+AE+AF+B0B19.91+B1+B2+B3+B4+B5+B6+B7+B8+B9+BA+BB+BC+BD+BE+BF+C0B21.93+C1+C2+C3+C4+C5+C6+C7+C8+C9+CA+CB+CC+CD+CE+CF+D0B23.69+D1+D2+D3B23.96RBYE* apctest query all values:UPS Status: 00Line quality: FFReason for last transfer to batteries: LSelf-Test Status: NOLine Voltage: 234.0Line Voltage Max: 236.6Line Voltage Min: 231.4Output Voltage: 000.0Batt level percent: 000.0Batt voltage: 23.96 <--- wtf is that? Battery voltage did not "really" change from 10v to 24 but this says it did.UPS Load: 000.0Line freq: 50.00Runtime left: 0000UPS Internal temp: 028.3Dip switch settings: 00Register 1: 40Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024Percent humidity: NAAmbient temperature: NAFirmware revision: 50.9.INumber of external batteries installed: 000Number of bad batteries installed: NAUPS model as defined by UPS: SMART-UPS 700UPS EPROM capabilities string: uD43132135138129uM43229234239224uA43110112114108uI43253264271280lD43103100097106lM43177172168182lA43090092081085lI43196188208204e44200155090oI43230240220225oD13115oJ13100oM13208s441HMLLq44202050710p443020180300600k4410TLNr443000060180300E443336168ON OFFThe EPROM string is 253 characters long!Hours since last self test: NAStarting an ups, it starts its test and beeps all this time. BUT does not switch it back to AC right away, keeps running a test. Returns from test to online mode, and quits beeping. Blinks single battery led.Do I need to + this B some more, from 24 to actual battery voltage?11PROGB23.96+D4+D5+D6+D7+D8+D9+DAB24.77+DB+DC+DD+DE+DF+E0+E1+E2+E3+E4+E5+E6+E7+E8B26.39+E9+EA+EBB26.66+EC+ED+EEB27.06+EF+F0B27.33+F1B27.33+F2B27.47+F3B27.60+F4B27.74-F3B27.60RBYE* apctest query:UPS Status: 48Line quality: FFReason for last transfer to batteries: SSelf-Test Status: OKLine Voltage: 236.6Line Voltage Max: 237.9Line Voltage Min: 234.0Output Voltage: 236.6Batt level percent: 002.0 <----- how the heck is that voltage equal to 2 percent of charge!?Batt voltage: 27.60 <----- voltage is about right thoughUPS Load: 000.0Line freq: 50.00Runtime left: 0003UPS Internal temp: 029.2Dip switch settings: 00Register 1: 00Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024...Pressing test again, now it runs, beeps, not dropping back to AC AND when finished, keeps 1 battery led lit and not blinking it.OK, what were someone saying about 0 -constant, it supposed to be 96?11PROG056+57+58+59+5A+5B+5C+5D+5E+5F+60+61+62+63+64064RBYE* apctest query:UPS Status: 08Line quality: FFReason for last transfer to batteries: SSelf-Test Status: NOLine Voltage: 234.0Line Voltage Max: 237.9Line Voltage Min: 228.8Output Voltage: 234.0Batt level percent: 034.0 <--- this has risen!Batt voltage: 27.60UPS Load: 000.0Line freq: 50.00Runtime left: 0077 <--- and that alsoUPS Internal temp: 029.2Dip switch settings: 00Register 1: 00Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024...Well, if that changed something, lets scroll 0 constant to said 96 then:11PROG064+65+66+67+68+69+6A+6B+6C+6D+6E+6F+70+71+72+73+74+75+76+77+78+79+7A+7B+7C+7D+7E+7F+80+81+82+83+84+85+86+87+88+89+8A+8B+8C+8D+8E+8F+90+91+92+93+94+95+96RBYE* apctest query:UPS Status: 08Line quality: FFReason for last transfer to batteries: SSelf-Test Status: NOLine Voltage: 232.7Line Voltage Max: 236.6Line Voltage Min: 231.4Output Voltage: 232.7Batt level percent: 035.0 <--- even higher nowBatt voltage: 27.60UPS Load: 000.0Line freq: 50.00Runtime left: 0119 <--- also higherUPS Internal temp: 029.2Dip switch settings: 00Register 1: 00Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024...And test button again. It runs test, does not beep, finishes test, returns online, shows one battery led and does not blink it.Some progress, it seems. But clearly I am missing something here.PS while writing it ups started showing 2 battery leds.* apctest query:UPS Status: 08Line quality: FFReason for last transfer to batteries: SSelf-Test Status: NOLine Voltage: 234.0Line Voltage Max: 237.9Line Voltage Min: 230.1Output Voltage: 234.0Batt level percent: 051.0Batt voltage: 27.60UPS Load: 000.0Line freq: 50.00Runtime left: 0173UPS Internal temp: 029.2Dip switch settings: 00Register 1: 00Register 2: 00Register 3: 00Sensitivity: HWakeup delay: 000Sleep delay: 020Low transfer voltage: 196High transfer voltage: 253Batt charge for return: 00Alarm status: 0Low battery shutdown level: 02UPS Name: UPS_IDENUPS Self test interval: 336UPS manufacture date: 11/26/96UPS serial number: GS9648588782Date battery replaced: 11/26/96Output voltage when on batteries: 230Nominal battery voltage: 024...Batteries have 27.71 now on their terminals.Still not sure at all am I even doing something right with that stumbling-around. Ideas?

author: JimboJack
author_rank: Regular Contributor
timestamp: October 07, 2025, 12:05:54 am
content: when the batteries are fully charged adjust the battery coffient so that it is measuring ~27.30,at the terminals, adjust and leave for abit, then do a load test with at least 30% load which the ups will then work out the runtime.good quality SLA's have a float charge of 2.275 V/Cell or 13.65 V/Batt

author: BradC
author_rank: Super Contributor
timestamp: October 07, 2025, 03:20:25 am
content: Quote from: erkko on October 06, 2025, 10:51:04 amHe was using a 4th generation or later (SUA->) UPS. On yours the charging voltage is fixed by a pair of resistors (usually R118/119 which are set up to provide 5V to the charger ASIC at the desired float voltage). There is no way to change it in software. On the SUA there is a PWM output the micro can use to tweak the charge voltage for temperature compensation. On yours the "B" constant only changes what the UPS thinks the battery voltage is.The micro has some pretty rudimentary algorithms to do with how it manages what state it thinks the batteries are in. If your micro thought the batteries were dead (~10V) it's going to take quite a while for its internal state to catch up with them being charged. Give it a day or so and it'll come around.You've either had an eeprom error where the B constant has been lost, or you've had an issue with the voltage divider that measures the battery voltage (usually R99/R100) from the battery into channel 0 of the ADC.Most 3rd generation SmartUPS (white face) are almost the same schematic. The earlier 1st and 2nd generation units didn't have the UPSlink protocol, and the black face 4th gen (SUA) units are different again. There is also a Gen 3.5 which is more like a 4th gen architecture with 3rd gen features. No variable battery voltage on the G3.5 either.Edit : The "0" constant defines what the UPS thinks the battery capacity is. So new factory batteries it is whatever is listed on the apcupsd list. Over time as the batteries age, the UPS will drop that constant in response to either routine tests or calibration runs. As the constant falls, the UPS will drop its calculated runtime until it reaches a point where there's only a few minutes left and it'll light up the "replace battery" light.There's a bit more to it, but fundamentally that's how it works. Constants 4, 5 & 6 define how the UPS manages its configuration (things like battery ESR, internal wiring resistance and so on). I've never really figured them out in detail. Things like input and output voltage define when the UPS goes into boost/buck mode and manage the transfer to and from battery. The rest are mostly display metrics.When I add external batteries to a SmartUPS, I calculate roughly what I believe the runtime should be under a static load (usually 1KW of incandescent lights), then I adjust the external battery count (all SmartUPS have this whether or not they actually have external battery connectors) to get the runtime in the ballpark. I then tweak the "0" constant to get the runtime to read bang on. Follow that with a runtime calibration and the "0" constant usually ends up within a couple of counts of where I put it.

author: zmetzing
author_rank: Contributor
timestamp: October 10, 2025, 03:21:48 pm
content: Quote from: Swake on October 03, 2025, 12:52:25 pmHappen to have the schematic for a SUA750 (Smart-UPS 750)?I have a similar problem: my unit thinks the battery voltage is very low (1 LED) after a brief test, but the batteries are fully charged when measuring them with a meter under 25% load (during the brief time the load test will run). I suspect a dried-out capacitor or perhaps a bad resistor.(edit: Based on the Russian article, I suspect that C63, bypassing R100, is probably the culprit on CH0 of IC10. If that cap has started to short, it will lower the voltage of CH0 and make it appear that the +24V-FET line voltage is low. I'll see if I can find the equivalent part on my unit. Getting it apart is a real pain -- look for Smart-UPS 750 tear-down on the tubes.)

author: erkko
author_rank: Contributor
timestamp: October 10, 2025, 03:59:27 pm
content: https://www.elektroda.pl/rtvforum/viewtopic.php?p=16800406#16800406https://www.elektroda.pl/rtvforum/viewtopic.php?p=12936444#12936444https://www.elektroda.pl/rtvforum/viewtopic.php?p=12935059#12935059https://www.elektroda.pl/rtvforum/viewtopic.php?p=16522891#16522891These seem to be about SUA1000, SUA1500, SUA2200 and SUA3000 but maybe family-wise similarities can be found.

author: zmetzing
author_rank: Contributor
timestamp: October 10, 2025, 07:16:07 pm
content: > These seem to be about SUA1000, SUA1500, SUA2200 and SUA3000 but maybe family-wise similarities can be found.Appreciate the links, but that crazy site is in Polish and requires a login to download. :-(

author: erkko
author_rank: Contributor
timestamp: October 10, 2025, 07:50:48 pm
content: Yeah. Only polish (I think) word I know is kurwa.PS. checking them after upload - some refer to grey wolf, which i think is older smartups, one is for SURT series... But thats what polish guys gave me. Excuse my french.

author: BradC
author_rank: Super Contributor
timestamp: October 11, 2025, 07:39:09 am
content: As far as I’ve been able to tell, Grey Wolf was the early start of the SUA series. I’ve used the Grey Wolf schematic to help with some of the newer parts of the G3.5 unit I have here where it doesn’t really match the old SU series.

author: erkko
author_rank: Contributor
timestamp: October 11, 2025, 07:56:55 am
content: And its date looks like 9/3/99 so clearly newer than my 3rd gen SU700.

author: BradC
author_rank: Super Contributor
timestamp: October 12, 2025, 09:00:48 am
content: Some of those linked schematics that are labeled SUA aren't. They're plain old G3 SU series units. The Red Wolf schematic is a new one for me. I have the rest, but I've never seen that one before. It's not far off the Grey Wolf architecture. The only real material change I can see is Red Wolf has a different watchdog on the CPU and the sine reference pwm filtering is different. There's some other analogue tweaks,but with no dates I can't really figure which came first.The "3.6" label on Red Wolf is interesting. I have a G3.5 board here which is a very late SU series (2003). It has most of the later architecture and hardware but no temperature sensor or ability to tweak the battery voltage.That's a big indicator on the architecture change. The earlier G3 SU series used a DAC to produce the sine reference, but the very late SU and all SUA series moved to a PWM.Nice. I'll add that to the collection.Edit : Scratch that bit. The Red Wolf is a full blooded SUA as it has the USB interface. There is also a date of 02 which I missed the first couple of times through. The Grey Wolf is then a very early revision and closer to the late SU I have here. Cool, that's the first proper SUA schematic I've seen.

author: erkko
author_rank: Contributor
timestamp: October 12, 2025, 09:47:07 am
content: We need some APC/ShinierElectric insider/mole to get this mess sorted out.

author: BradC
author_rank: Super Contributor
timestamp: October 12, 2025, 09:56:12 am
content: Quote from: erkko on October 12, 2025, 09:47:07 amGood luck with that. I've been trying since 2009.

author: JimboJack
author_rank: Regular Contributor
timestamp: October 12, 2025, 09:25:22 pm
content: what is the PCB number on the SU700 board you have ? 640-??did you measure all the VCC and VREF on all the IC's inputs?, did you use the trouble shooting doc ?J.

author: zmetzing
author_rank: Contributor
timestamp: October 16, 2025, 03:32:12 pm
content: I think I had both a bad solder joint on the resistive divider on CH0 of the ADC and one weak battery. After re-soldering one through-hole capacitor and re-flowing several of the divider resistors _and_ doing a manual battery calibration (34% load -- lightbulbs, fully charged batteries, unplug it and let it run down until shutdown) on a new set of batteries, the unit seems to be happy once again.Here are some internal photos of the unit, along with the modification that I made to the black battery ground wire. Now it features an Anderson power-pole connector for ease of PCB removal!

author: BradC
author_rank: Super Contributor
timestamp: October 18, 2025 12:34:41 am
content: Quote from: zmetzing on October 16, 2025, 03:32:12 pmJust be aware part of the calibration constants is to account for the total loop resistance between the board and the batteries. You've just increased that. The likely impact is the instantaneous measurement when the unit transfers to batteries. It measures the battery voltage across the transition and uses that to form an opinion as to the battery condition. Increasing the resistance makes the UPS thing the battery resistance has increased (ie they are aging) so you may see some long term knock on from that.I discovered this when I first added external batteries to a 3rd Gen SU unit and spent some time playing with the constants to try and figure out what was happening. I ended up putting new internal batteries in the unit on the original wiring in addition to the externals to get it working properly.