Upgrading to a large external UPS battery - Page 1
Forum section: electronics / projects

author: shiftline
author_rank: Contributor
timestamp: December 24, 2015, 11:12:43 pm
content: Is there any issues with adding a much larger battery to my UPS? I have an older APC 1500 ( with 2x 7AH batterys) I want to hook it up to a 147AH sealed led acid battery.. its the same chemistry and should eb the same float/charge voltages.Aside from taking ages to re-charge would there be any issues doing this?

author: alank2
author_rank: Super Contributor
timestamp: December 24, 2015, 11:17:49 pm
content: I've done it with no problems. I had a large SLA battery and decided to put it to good use.

author: johansen
author_rank: Super Contributor
timestamp: December 24, 2015, 11:24:32 pm
content: if you install a ferrite inductor in series with the secondary (low voltage side) of the main transformer in your apc unit you will save about 10$ a year in electricity. last time i did this i used 7 turns on a 1 inch diameter ferrite core, with a paper thin air gap.also recommend replacing the 10 gauge battery cables with 8 gauge if you load it more than 1kw.

author: shiftline
author_rank: Contributor
timestamp: December 24, 2015, 11:59:41 pm
content: Thanks for the tips. Sounds like there shouldn't be any issues. Good tip on increasing efficiency!

author: nctnico
author_rank: Super Contributor
timestamp: December 25, 2015, 12:57:00 am
content: I'd check the charge voltage. APC UPSs are notorious for cooking the batteries due to a way too high charging voltage. AFAIK there is a mod for this.

author: wblock
author_rank: Regular Contributor
timestamp: December 25, 2015, 01:42:05 am
content: Quote from: nctnico on December 25, 2015, 12:57:00 amThe crappy "home" units are famous for that. And maybe the really old higher-end units. But my Smart-UPS 1500 from 2003 was dead on, and so are the few other Smart-UPS units I've checked. Still, knowing for sure is worthwhile.

author: BradC
author_rank: Super Contributor
timestamp: December 25, 2015, 02:30:11 am
content: Quote from: wblock on December 25, 2015, 01:42:05 amPretty much all Smart-UPS units were dead on from the factory. Unfortunately over time the voltage divider resistors drift and it does not take much drift to push the voltage up a couple of hundred mV. They all have a resistive divider which provides the battery voltage into the charger ASIC. This must be 5.00V at your desired float voltage. It's a pretty cheap fix for an older unit to replace the divider resistors with newer and more precise units. There are plenty of web pages around with instructions on how to change the float voltage in software, but they are all pretty much wrong. They'll change the way it reports voltage, but the charge voltage is set in hardware.

author: Don Hills
author_rank: Regular Contributor
timestamp: December 26, 2015, 07:45:29 am
content: Not all UPSes can use a higher capacity battery. Many small units don't have proper heatsinking - they use a block of aluminium instead of fins and a fan, and depend on the battery giving out before the heatsink gets too hot. If you increase the run time, it will overheat.

author: station240
author_rank: Unknown
timestamp: December 26, 2015, 10:43:12 am
content: Get a suitable DC rated circuit breaker to put near the batteries. That way there is a safe way to isolate them for testing or relocating everything.

author: cs.dk
author_rank: Unknown
timestamp: December 26, 2015, 10:45:32 am
content: Quote from: johansen on December 24, 2015, 11:24:32 pmI'm just courious, but what different does it make to stick a ferrite on the secondary? I don't understand it

author: SeanB
author_rank: Super Contributor
timestamp: December 26, 2015, 10:54:27 am
content: A caution is many of the cheap UPS devices also have no isolation, so the battery is connected to either one side of the mains, or is on a rectified mains supply. Treat the battery cabling as if it is mains connected, and put the external batteries in a plastic box suitable for mains use. In the space vacated by the battery put a high value electrolytic capacitor, 10 000uF 25V or so for a 12V unit, to provide local decoupling for the UPS, and use 4mm wire to connect the external battery pack. Inside there is now room to add a 12VDC 80mm fan, powered by the battery, to cool the inside of the unit. Place so the fan cools the transformer and the heatsink of the power devices, and if you have the ability add an extension to the heatsink to improve the cooling, but make sure it does not foul anything.Still not going to be a great UPS, just a better cheap one, which will run longer. Done that, and it has improved runtime to around a hour, though I am using 10 7Ah SLA packs in parallel, used ones but still reasonable.

author: wblock
author_rank: Regular Contributor
timestamp: December 26, 2015, 04:28:07 pm
content: Quote from: BradC on December 25, 2015, 02:30:11 amHm, just checked my SUA1500 and it has drifted up. Haven't disconnected it yet, that'll be a project. From photos, the original resistors were standard 1% precision types--what would be a better replacement?

author: edpalmer42
author_rank: Super Contributor
timestamp: December 26, 2015, 06:07:30 pm
content: I agree with Don Hills. When you add bigger batteries, the heatsinking may not be adequate. Also, the charging circuit probably won't be able to recharge the batteries in a reasonable time. The charger could actually burn out trying to charge a big battery!The problem with trying to set the charging voltage is that it's temperature dependent. Cool room, warm room, idling, full load, what voltage do you use? Better UPS systems use a different charging method. The typical system uses a current limited charge, then constant voltage (aka float) charge. The better systems cut off the constant voltage charge after a couple of weeks and then just monitor the battery voltage and recharge as necessary. Instead of a battery life of maybe two years, you get a battery life of more like 5 to 7 years.I think I heard that some of the newer APC units used this type of modified charger, but I haven't looked into it.Ed

author: johansen
author_rank: Super Contributor
timestamp: December 26, 2015, 10:08:58 pm
content: Quote from: cs.dk on December 26, 2015, 10:45:32 amfurther testing should be done to investigate, you can read about my experiments here:http://www.fieldlines.com/index.php?topic=148266.0oztules, reports that adding an inductor to his custom wound toroid transformer (in his 6kw inverter, but it might be 15, i cant recall) reduces no load idle watts from 200 to 20 watts.

author: BradC
author_rank: Super Contributor
timestamp: December 27, 2015, 03:15:05 am
content: Quote from: wblock on December 26, 2015, 04:28:07 pmA pair of 1% resistors that are closer to valueOddly enough one of the schematics I have for an SUA2200 has the main high value divider listed as a 0.1% resistor (I suspect its a typo but it's there). My 2200 is currently reading the load about 30% high, so grossly underestimating the runtime. It looks like the capacitor in the CT burden circuit is drying out, so when I take it down to service it I'll do the divider resistors at the same time. Mine is less than 100mV up and I have 4 years on this battery set so far.Outside of gross over or undercharge, the biggest factor on UPS battery life is the quality of the battery. Generic replacements just are not as good as either CSB or Vision batteries. I seem to get better life out of CSB.

author: DanielS
author_rank: Frequent Contributor
timestamp: December 27, 2015, 04:05:30 am
content: Quote from: BradC on December 27, 2015, 03:15:05 amWhen you compare the 15 minutes rating of CSB batteries to most other generics, it becomes quite obvious that most generics are simply not intended for applications more intensive than 1-2h discharge - they lose effective capacity two or three times as fast.

author: wblock
author_rank: Regular Contributor
timestamp: December 28, 2015, 10:58:03 pm
content: After swapping out my SUA1500 floor model for an SUA1500RM2 rack-mount, it appears that the only schematics I've found might have nothing at all to do with this model.Can anyone point me to a schematic of the SUA1500? Or at least verify exactly which resistors and values are the voltage divider in this model. Right under VR1, R118 is 22.6K (label 2262, so pretty good), R119 is an inch away next to the QFP and labeled 1002. It's only reading half that, but it's in circuit (no, I'm not going to pull it without a replacement and a reason to believe it's the right one). R124 is right next to R118, labeled 1302 but reading 12.86K. 1.1% high, maybe it... Another chance to use this smiley:Photo: (yes, the solder on R118 looks a little dented from probes being jammed through the flux on it):

author: BradC
author_rank: Super Contributor
timestamp: December 29, 2015, 12:39:58 am
content: I can't help you with a usable schematic I'm afraid. My small unit is a SU1400 which is the model before yours and the schematic I have is for the model before mine. It will be a 24V unit though, so your divider resistors are 22.1K & 100K. My schematics have them listed as R118 & R119, but that's not right on my unit either. My SU2200 is the last through hole version (schematics are correct for that) and the SU1400 is the first SMD version (I don't have an accurate schematic for that).See if you can find the charger ASIC and have a poke around pin 13. That is the voltage input after the divider. Maybe you can work backwards from there.When you find the 100K resistor, you should have ~27.x volts on one side and 5.00V on the other. The 22.1K will have 5.00V and 0V respectively.

author: moya034
author_rank: Regular Contributor
timestamp: December 29, 2015, 01:14:17 am
content: For a while now I've been using a 12v battery bank with aSamlex Battery Charger(configured to charge a battery bank with a load attached) as a "DC UPS" for my ham radio gear, LED lighting in the shack, and just about anything else that can run off 13.8vSamlex makes these units in 15, 20, 50, and 80 amp models.You can have as big of a battery bank as you can afford!I have been wanting to use another large battery bank and higher current Samlex Charger to run my FiOS gear, networking equipment, and servers as follows:Power Streammakes ATX PSU's that accept a 9-18 VDC input voltage.For mini-ITX motherboards there are theMini Box 160 watt PSU's.These however require a 12v REGULATED input as the 12v input goes right to the +12v power rail, so you would need a DC-DC converter to hook it up to your battery bank.All your other devices like switches or WAP's that have wall worts, may run off 13.8v directly or custom power supplies can be made.Anything that absolutely must have have 110v ac can run off a Power Inverter. (Only thing I can think of in my application is the monitor)

author: wblock
author_rank: Regular Contributor
timestamp: December 29, 2015, 01:16:21 am
content: Quote from: BradC on December 29, 2015, 12:39:58 amI did find a schematic by searching on the board number, 640-7732H... Aha, pin 13 of IC21, like you say, goes to R216, 100K, 1/8W, 1% to VBAT, and R184, 22.1K, 1/8W, 1% to ground. R184 is reading 20.62K. R216 is reading 69.7K, but that's in circuit. Now to decide whether to patch on some nice higher wattage stick-through resistors, or do it neatly with SMT 0805s. Thanks!

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 01:47:20 am
content: So I popped open my UPS and it had the 2 batteries wired in series for 24v (I guess I need to add a second giant battery!)The cooling seems a little lacking. I may put a 120mm of fan in the old battery area to provide some better cooling. The two exhaust fans are pretty tinyThe heat sinks are solid chunks aluminum and seems Cool to touch however I feel a lot of heat coming from the transformer.Is there anything I should be enhancing for cooling aside from a possible fan addition?If I add a fan or two into the battery compartment would it be better to push air in it suck it out?

author: BradC
author_rank: Super Contributor
timestamp: December 29, 2015, 02:34:57 am
content: Quote from: shiftline on December 29, 2015, 01:47:20 amThat does not look like any SmartUPS I've seen. Is it a BackUPS by any chance?There is a significant difference in firmware. The BackUPS is hard-coded to work with the battery capacity it is designed for. The SmartUPS is adjustable for battery capacity. The problem with the BackUPS is the thermal design is for a very limited runtime, and without significant upgrade you will literally cook it both charging a big battery bank and running an extended runtime. The transformers in the BackUPS are designed right on the thermal limits, and as you see there are tiny little heatsinks on the switching FETs. The SmartUPS transformers have a significantly bigger core with both more thermal mass and a larger surface area to dissipate the heat, and the switch gear has heatsinking designed to be efficiently air cooled rather than relying on convection and thermal mass.If you plan on putting bigger batteries in that unit, you want as much airflow over both the transformer and the heatsinks as you can muster, and both for charging and discharging. Additionally, the on-battery runtime is going to be a bit unpredictable as the firmware won't and can't adapt to a larger battery, so it relies solely on voltage. If you use the comms interface to remotely shutdown your systems, you might find the systems shutting down well before the battery is exhausted as the firmware knows that at X load you get Y runtime from the designed battery capacity.I tried extending a BackUPS 650 for a while, but ended up picking up an old SU1400 on E-bay. A much better solution for an extended runtime when you want the software to do what it is supposed to do, properly.

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 02:43:24 am
content: Yes it's a BackUPSSo it's hard coded to to turn down after a specific time rather than the the actual battery voltage?Well that may be a problem!The actual load would be low as its running fish tank pumps which I could wire directly the batteries. (2x 12v pumps and 1x 24v pump.) a controller and possibly a heater or led light would be the only thing plugged into ups for a drawI'm sure this isn't much better but I also have one of theses. BackUPS as wellOr would I be better off just using a trickle/float charger and wiring the pumps directly to the battery(s) and skipping the UPS?

author: BradC
author_rank: Super Contributor
timestamp: December 29, 2015, 02:59:06 am
content: Quote from: shiftline on December 29, 2015, 02:43:24 amNo, its just that the runtime estimation is a relatively complex calculation and the battery capacity component of that is generally hard coded in the BackUPS series, so it's not likely to get it right. As I said before, it's only important if you are using the comms interface to remotely shutdown a PC. The UPS will keep on running until the battery goes flat, and for a dumb load (like your fish tank gear) it should all keep on trucking quite nicely.With such a low projected load, the issues I raised about heat will be a lot less while in discharge mode, but you'll have heat problems while charging so you'll still need some good cooling. You might be better with a smaller unit (like my aforementioned 650) as they are 12V units and you'll only need the one battery. Cooling problems are the same though.

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 03:06:32 am
content: Is it worth going the float charger route instead? I could run the essentials off 12v the 24v stuff is more of a nice to have. The max load of nice to have on outlets would be a couple hundred watts and the rest could run off batteriesAssuming I use the UPSFor cooling I could do a fan blowing (or sucking ) across the transformer and possibly one on top of if the unitOr if you think I'm better off with a single battery unit this 550 ($25!) would prob work? I really only need the charging circuit and some plugs to run a few hundred watts of dumb load.Or spend 120 on a used smart ups..I just want to make sure I come up with something reliable and safePs thanks for all the help on figuring this out

author: wblock
author_rank: Regular Contributor
timestamp: December 29, 2015, 03:40:52 am
content: Quote from: wblock on December 29, 2015, 01:16:21 amReadings with new 1% resistors are 20.61K and 69.7K. I would test the removed ones, but true to their nature, the 100K resistor bounced off the bench and shot into some dark corner at near lightspeed, and the carefully-saved 22.1K was not in the plastic bag when I looked for it.Just because it's open and I'm looking at it, for future reference the smaller eletrolytics are Jamicon, and the large is a "Jianghai". The fan is an 80mm, 24V 0.08A "NONOIse" sleeve bearing A8025M24D. It is a standard fan held by a clipped-on plastic bracket, and blows inwards through the heatsink fins.Update: reassembled and charging two batteries at 27.73V. Perfect. Now I just have to repair the silly front panel cable, which has an intermittent because it got flexed too much flipping this ungainly thing around.

author: wblock
author_rank: Regular Contributor
timestamp: December 29, 2015, 04:31:25 am
content: Quote from: shiftline on December 29, 2015, 03:06:32 amPlease don't spend money on those home units. They are cheap in the worst sense. Battery life of under one year in some cases.Or spend 120 on a used smart ups..I just want to make sure I come up with something reliable and safeThe Smart-UPS is made for businesses. Much better build quality, power quality, battery life, and capacity. The only bad part about used ones is that the batteries usually need to be replaced.Check your local Craigslist and school/county auctions to avoid having to pay shipping.

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 05:49:06 am
content: So what is different form a UPS to a a little smart charger like a NOCO? I have thats pretty small and will charge/float/maintain ect...Would it be easier to just pop one of those on the batteries rather than using a UPS?

author: miguelvp
author_rank: Super Contributor
timestamp: December 29, 2015, 06:05:46 am
content: Quote from: shiftline on December 29, 2015, 05:49:06 amIsn't the NOCO just for 12V? how is that going to help a computer without extra hardware? also what model are you referring to? 12V @ 3.5A is just 42 W.Or do they make inside PC UPS modules that can handle more power?

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 06:08:27 am
content: Im building this for a reef tank to prevent any loss of fish or coral during an extended power outageI'm debating if it's worth ditching the UPS and just float charging my 147ah battery. And running my 12v devices directly off it. (Or alternatively have two and series and charger at 24v and tap it both 12/24v devices.Now is there a minimum amperage I would need to charge the battery (s). ? Or as long as it's within the float voltage range and a couple amps I'm good?

author: miguelvp
author_rank: Super Contributor
timestamp: December 29, 2015, 06:17:37 am
content: You'll need -12V, +12V, 5V and 3.3V rails, On older style motherboards you'll need -5V as well.Your image didn't show power consumption. I might be missing something obvious, but first glance it doesn't seem to fit the bill.

author: shiftline
author_rank: Contributor
timestamp: December 29, 2015, 06:32:19 am
content: This is not for a computer(at least not a regular one) no 3.3/5v rails required!I want to have a battery backup for my aquarium. I have read lots of horror stories of people loosing thousands of dollars in fish and corals for extended power outages so i'm trying to build something to keep the tank going for a day or two in the event of a power outtage.I do have some cheaper home PAC backup UPS laying around as well as 1-2 147AH datacenter UPS batteries at my disposal. My origional plan was to just wire the UPS to the giant battery however it appears there could be some issues with the longevity of the circuit board in the cheaper UPS for extended charge or run time.My power consumption wont be huge... a few hundred watts.. Half of which i could wire directly to the battery, or more if i went 24v route as i have converted most of my system to DC pumps.. the only bigger draws would be the heater.. 200W or the lighting 3x 75W So still using the UPS may be a simpler option as its free and sitting beside.. if there is a big overheating/melting down issue the i was debating if i should just buy a smart charger and wire it directly to the batteries.I'm just trying to figure out the best route to go.

author: shiftline
author_rank: Contributor
timestamp: December 31, 2015, 12:52:39 am
content: So is it best to use the UPS or just get a single or dual bank battery charger?

author: BradC
author_rank: Super Contributor
timestamp: December 31, 2015, 02:48:21 am
content: It's tough to say and really your call.If your devices are DC powered then obviously you'll get more runtime connecting them directly to the battery than via the inverter.

author: nctnico
author_rank: Super Contributor
timestamp: December 31, 2015, 10:37:41 am
content: For long power outages I'd get a generator. Much cheaper and less maintenance than a UPS. A UPS is to bridge short outages for 15 minutes at most so a generator has time to start.

author: station240
author_rank: Unknown
timestamp: December 31, 2015, 03:02:45 pm
content: I've got a Eaton UPS here with the same profile of heatsinks, your's are taller.They are attached to the PCB by two thick pins, if you suck all the solder off, the heatsinks can be pried off with a screw driver.Then either install proper finned heatsinks onto the PCB, or mount the power devices to a big heatsink and run wires back.Not much you can do about the transformer, it's just a cheap lossy unit. Put a cooling fan over it until you can find something bigger to replace it with.

author: DanielS
author_rank: Frequent Contributor
timestamp: December 31, 2015, 07:28:21 pm
content: Quote from: nctnico on December 31, 2015, 10:37:41 amIt depends on the type of UPS and the size of attached batteries. The UPS I currently use for my PC should be able to hold 60-70 minutes. If I got one of the APC models that can use an external 400Wh battery pack, that would bump it up to ~5h. One of the places I worked at had a "small" 20kVA UPS with enough batteries to keep the servers running for 10 hours - hopefully long enough to repair a generator that failed to start, re-wire remaining generators to get around the fault(s) or truck in a rental instead of having to pay sysadmins overtime for emergencies outside business hours.

author: shiftline
author_rank: Contributor
timestamp: December 31, 2015, 11:40:56 pm
content: Thanks for all the imput./ Well i mind as well try hacking this one by adding some cooling fans and extra batteries as I already have it and its freeI just need to pick up a second battery to run it at 24V.Since the UPS will be charging the UPS as one.. if i run each 12v backup pump to each battery then the return across the 2 it should keep the discharge evenA little wire and a fan or two and i should be set

author: BradC
author_rank: Super Contributor
timestamp: January 01, 2016, 01:52:45 am
content: Quote from: shiftline on December 31, 2015, 11:40:56 pmDo not do this. It takes very little imbalance to ruin a set of lead acid batteries. Using the batteries as a voltage divider by drawing a different load from each is a very quick way to do that, no matter how small the theoretical difference.

author: DanielS
author_rank: Frequent Contributor
timestamp: January 01, 2016, 03:46:00 am
content: Quote from: shiftline on December 31, 2015, 11:40:56 pmThe UPS' built-in charging circuitry might not be able to put out enough power for all the stuff you plan to put on its batteries and it might mess up its charge/discharge cycle. The UPS might even complain about dead batteries due to failing to reach something resembling full state of charge in a remotely timely fashion. For example, many UPS state that 8-10h are required to recharge the battery after a full discharge and for the 7.2-9Ah batteries found in most modern UPS, this means only ~1A of available charge current. If your loads use a significant chunk of that ~28W of charging power, batteries will take that much longer to charge.If the UPS decides that the batteries are dead and quits trying to charge them for safety reasons, your equipment ends up running on whatever charge is left on the batteries even when AC power is available.

author: shiftline
author_rank: Contributor
timestamp: January 01, 2016, 06:23:51 am
content: So am I better off just putting a float chargers on the battery? The controller shouldn't pull from the battery unless there is an outtageAny chance you could recommend a decent not to pricey float charger that would work on a 147ah sla battery?

author: johansen
author_rank: Super Contributor
timestamp: January 01, 2016, 10:38:59 am
content: Quote from: BradC on January 01, 2016, 01:52:45 amonly if you can't add water. lead acid batteries have endless overcharge absorption.

author: johansen
author_rank: Super Contributor
timestamp: January 01, 2016, 10:43:03 am
content: Quote from: shiftline on January 01, 2016, 06:23:51 amyou could dump 1 amp into those batteries for eternity just to match the self discharge rate. (actually, on that note, i have no idea, it is highly chemistry dependent).if they are flooded cells: charge them at 10 to 20 amps, when they reach 15 to 15.5 volts, turn off the charger, wait a couple days. if the open circuit voltage is higher than 12.6 volts add water, or ask the manufacturer why the acid content is too high.

author: DanielS
author_rank: Frequent Contributor
timestamp: January 01, 2016, 03:50:39 pm
content: Quote from: shiftline on January 01, 2016, 06:23:51 amYou would need a "float" charger powerful enough to supply all of your load power with current to spare for actually charging the battery.If you are using a flooded cell batteries, you would also need a charger powerful enough to 'gas' them (high over-charge current for a minute or two) once or twice a month to remix the electrolyte, otherwise its different liquid components may start to stratify by specific mass, causing uneven electrode wear and premature failure if the cell gets charged or discharged repeatedly while in that state.

author: shiftline
author_rank: Contributor
timestamp: January 01, 2016, 06:31:52 pm
content: They are sealed batteries and there should only be a load in the event of power loss. So a 1-4a charger should be sufficient?

author: ataelim
author_rank: Newbie
timestamp: April 11, 2017, 08:52:24 am
content: Folks, when reading this thread, it seems the right one to ask one question bugging me for some time now: i am 'extending' battery life in my APC SmartUPS 1500 (unmodified to date) by feeding some additional power to the batteries from solar charger. The 'load' output of that charger drives a 'inversed' relay so that the UPS is disconnected from mains as soon as the charger tells that the battery is fully charged. This allows to run the UPS in 'standalone-inverter' mode as long as there is sufficient solar power and some time after sunset till the batteries reach a discharge level of about 60% (i dont want to go lower, since those lead-acid batteries are no deep-cycle ones). Now, the problem is, that the UPS shows the batteries discharged almost all the time, blinking the lowest batt load indicator LED. This causes the apcupsd daemon try to shutdown computers and report wrong lifetime (although the UPS does not shut down .. yet ...) Now the question to you guys: is there a tweak (in 'PROG' mode of SmartUPS ?) howto tell the UPS to not try to be clever and calculate battery life from in and out Amps to the battery, but from the voltage level of the batt ? I have 28-29.6 Volts on the Anderson Batt connector and the 'Smart'UPS still tries to convince me that the battery is depleated ... any idea ? yr input greatly appreciated !

author: BradC
author_rank: Super Contributor
timestamp: April 11, 2017, 10:19:20 am
content: Quote from: ataelim on April 11, 2017, 08:52:24 amNo there isn't. There *is* a way in Prog mode to tell the UPS the battery is full, but you'll need to put it into Prog mode each time you want to do that. Nothing a bit of python couldn't sort out, but it's not going to be compatible with apcupsd.The charge indication on the UPS is a combination of voltage and time. You need to be at the float voltage for a few hours with the power on for it to believe it is charged. It sounds like you are doing that, so maybe there is something else going on. Have you done a runtime calibration? Are the batteries any good?

author: ataelim
author_rank: Newbie
timestamp: April 12, 2017, 07:26:17 pm
content: Hello BradC! when i run those batteries (its 2 pcs of 50Ah 12V, about 3 times more than originally built into that unit) on the UPS alone for a while, the UPS is quite happy with them, also calibration works and gives expected results. Since the Unit is running on batteries almost all day, since there is sufficient sunshine this time of year, the UPS says 'batteries near empty' at around 11:00 am , after running on batteries for 3 hours (with the batteries not even been used, since the solar charger supplies the Amps to the UPS) ... just because the UPS thinks, 3 hours is 'enough' :-) I have a raspberry near the unit, which is connected to the serial port of the UPS and also receives data from the solarcharger - so, that box could easily tell the UPS to 'shut up and dance' ... what would be the 'magic letter' to send to UPS pretending the battery is full ? thanks & happy evening !

author: BradC
author_rank: Super Contributor
timestamp: April 13, 2017, 12:47:35 am
content: According to my 2012 notes it's Ctrl-F (^F). It was something I stubmled across by accident. The UPS I found it on was a 3.5G, so black face, SMD Smart UPS *prior* to the upgrade to the SUA series. It might work on yours, but then it might not. They tended to change a lot of the undocumented calibration stuff from generation to generation.

author: Miamijerry
author_rank: Newbie
timestamp: October 26, 2017, 11:17:42 pm
content: SUA1500 schematic, board 640-7734

author: Zucca
author_rank: Unknown
timestamp: January 11, 2023, 02:47:51 pm
content: here the schematics apc_640-7732h

author: Vovk_Z
author_rank: Super Contributor
timestamp: January 11, 2023, 08:52:48 pm
content: Quote from: wblock on December 26, 2015, 04:28:07 pmWhat I've seen is that 22uF 25V electrolytes die because of a heat. And together with them everything drift and charging voltage too. This is an in-built feature of all 400-1500W Back-UPS and Smat-UPS.

author: Zucca
author_rank: Unknown
timestamp: January 12, 2023, 04:35:09 am
content: My board is the 640-7734H (SUA1500I)can anyone send/PM me the schematics?Quote from: Miamijerry on October 26, 2017, 11:17:42 pmthe linkheredoes not work anymoreI need to modify the floating voltage of the charger