• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

APC brand UPS systems, any info?

Not open for further replies.


New Member
I have a few APC brand smart ups systems that have voltage sensing/load problems or do not report battery voltage or capacity correctly. the units i have are a smart 1250 va and a smart ups 1400 in both the table and rack mount flavors and find that these problems seem to be too common. I run them from a 115AH battery bank and a back up bank so i know i have lots of DC.
does any one know if there are service manuals or any other service info avalible?


I've got 2 APCs, one I've had for over 15 years. I wasn't able to find much info when it stopped charging the batteries. They don't seem to like people messing around inside, and seem to encourage people to trade in the whole unit, rather than replace the battery.

Guess you are asking, since you couldn't find anything searching. I've got a hunch that information is kept pretty tight, and only a few licensed repair people can get it. Good luck, and if you find a site, let me know. I was considiring adding a solar panel and a charge controller to keep the battery maintained, and still have a working unit, probably not for the computer though.


New Member

You need to read one of my prior APC UPS related posts under:

UPS high pitch whine noise - posted Oct 20th

Here is just 1 of the APC "highlights" that I posted there:

I kinda figured it was an APC model UPS, and a smaller single 7ah batt model as well. A somewhat newer and cheaper model as I now see online for about $100 retail. These so-so $15 units (after rebate) are after all - what you get for what you pay for them. Nothing for nothing as it were. They're all made in China today - more or less, and that's the biggest part of the problem right there!

And -

I'll let you read the rest of my post yourself - does the mind good, as you will no doubt be very interested as to the rest that's posted there - as well as for HarveyH42 as well. Your last part of your post is answered there as well.

And -

As to what you had to say about - quote -

"I have a few APC brand smart ups systems that have voltage sensing/load problems or do not report battery voltage or capacity correctly."

And - quote -

"I run them from a 115AH battery bank and a back up bank so i know i have lots of DC.

Well - you just answered part of your "voltage sensing/load problems" right there - if not your WHOLE stated problem just by that last statement quote I reposted above.

I can firmly assert that you DON'T understand anything about preprogrammed Firmware Chip parameters when it comes to the dv/dt & di/dt parameters that are custom designed (Firmware Chip wise) for each individual UPS unit - as it indeed relates to that Firmware Chip in ?.

Whether it is an APC brand UPS unit or not makes no difference - as the industry standard is pretty much the same, and doesn't vary much from one brand to another!

Myself - having worked prior for Emerson Electric Co's UPS division in the late 70's - I should know, and our units were HUGE Commercial/Industrial units that had batt banks bigger then your garage sometimes! I personally repaired and calibrated the Control Boards that set those unit's dv/dt & di/dt parameters, so again - I know! I speak from experience, and not just textbook guessing btw.

Not only are you defeating the Firmware's Algorithm that is factory preset into both of your "different model" APC UPS units there (AND HERE IS THE REAL KICKER), but you are trying to run both UPS units off the same Batt Bank, as well as whatever "backup bank" you say you have set up there!

I can only guess (imagine) what kind of batts you are using there as well, and how you have them strung together in series and/or parallel - beings both those units are 24-volt in nature, unless I missed something there as well?? That outdated APC 1250VA model calibrated for using (2) 17.2ah batts in series, and that older APC 1400VA rack mount unit looks like it uses (4) 7ah batts in series/parallel for a total 14ah capacity.

To get this 115ah capacity you are talking about my guess is that you are using "cheaper" FLA Deep Cycle car/marine batts, unless you really forked out some real cash money, and you actually bought larger AGM batts brand new? I seriously doubt the latter though - as by the 115ah rating you are talking about. Who knows what stored Ah capacity they really hold, as we were never told how old they really are either?

Which brings up another interesting factor/point I'll bet you didn't bank on? Seeings that all UPS unit Firmware Chips are set up and calibrated - Algorithm wise - using only AGM type batts - if you are indeed using the above mentioned FLA Deep Cycle car/marine batts - then you are further screwing yourself into thinking that you have all this so-called "DC" as you so put it - or call it. The "DC" part - in your own words - no doubt meaning BATT CAPACITY in Ah's in reality.

There again - you are screwing the Firmware Chips inside both UPS units, as by the over-rated batt bank sizes in Ah ratings.

A near 570% BATT CAPACITY OVER-RATING in fact! And that’s just on that 115ah batt bank you stated the Ah capacity on! What about the other "backup" batt bank you never stated in Ah?

Going from a factory preprogrammed preset of using (2) 17.2ah batts in series - for a Total batt Capacity of 17.2ah - to a 115ah batt capacity throws all the internal Firmware Algorithms off to such a degree that sometimes the units will even shutdown prematurely on their own, or else they will go into an ALL ALARM state, and not even be re-settable.

At that point the Firmware Chip may even have been damaged internally trying to overly compensate for YOUR error in adding an oversized 115ah batt bank (more external batts than what was intended to start with)! On both your "older" model units I suspect this may be the case.

Also at that point the UPS unit in ? is neither monitoring the correct batt capacity, nor is it fully recharging the batts back up when back in standby (charge) mode after Edison power is restored!

Many a times it will even blow the internal "charge circuit" pico fuse(s) that are only rated at ~ 1 amp tops, and that's only because the charge circuits on these smaller UPS units only put out less then or roughly .5 amp (500ma) tops for all those smaller UPS units brands that only have to charge a single 7 to 12ah batt back up in say 3 to 4 hours tops, or (2) each of either size if the unit is 24-volts with the same charging rate time or slightly less because of the higher batt EMF voltage.

BTW - it doesn't change preprogrammed parameters with the factory preset Firmware Chip just because you might think you have an APC Smart UPS unit there. Far from it!

Some UPS "User Manuals" (APC as well) will say that the UPS unit simply needs to be recalibrated, and though that may be part true in a sense - it only applies if you are changing the original INTERNAL batt(s) with the exact same size batt(s) - "Ah capacity rating" that is. If you try and interpret that any other way - then you are just screwing yourself - as your thinking is all back asswards!

True (as stated in various UPS user manuals including APC) - the Smart-UPS units have a microprocessor that keeps track of how long the batteries actually provided power the last time the unit ran on batteries, and this part - though a bit misleading - is true with one exception. Again remembering here that this is only the UPS unit's preprogrammed Firmware Chip, and NOT a separate CPU chip as the user manual might mislead you to believe. A little techno error there in so far as the "User Manual" goes! Of course that's all based on the INTERNAL OEM batts that were first installed - tested - and calibrated from the factory anyway!

Also - the runtime estimate provided by PowerChute and the battery light bars on the front of the unit are based on that "run time on batts" number.

Does that tell you anything right there? IT SHOULD!!

I won't even ask you if you tried to do any kind of recalibration run on both your units there - as it would be "Apples of Oranges" fruitless to start with.

Again - PowerChute is only basing its feedback off the data from the OEM original sized batts that came with the UPS unit to start with. NOT your 115ah "whatever batt banks" you jury-rigged to both unit(s) - so you could run your POWER LOADS for possibly days at a time!

Btw - are you even running the PowerChute software to start with? My guess is that you are NOT, and for very obvious reasons.


When you change out (R&R) any UPS exhausted batts for brand new ones of the same Ah rating the UPS unit is not aware that new batteries have been installed, so a recalibration is necessary. Often times, simply pressing the test button is enough to clear the bad battery light, HOWEVER, the runtime reported by PowerChute will still be inaccurate. To correct this, it is necessary to do a battery runtime calibration from PowerChute or to do one manually.

The unit can be “re-calibrated” by putting the unit through a simple process. First, allow the unit to fully charge. It should be plugged in for at least 12 hours without any interruptions to the incoming power.

Make sure that all computer equipment, and all communication cables are disconnected from the UPS unit (including network management cables), and plug in 100-watt light bulbs to the UPS until you have at least a 20% LOAD indicated on the UPS unit LED LOAD BAR. No more then 20% LOAD is needed - as you want the unit to do a gradual batt bleed down, and thus giving you a better (longer and more accurate) calibrated reference range. >>>>


NOTE - (If you should have a PCB calibrated LOAD SIMULATOR like I do, and you know how to use it internally on the PCB then go that route as from a Service Tech standpoint.) Sorry - trade secret - I promised my longtime Czech good buddy/friend, and cmptr genius to keep a zipper on it - can't give mine out!

You can - however - buy a cheap $15 (300-watt) Halogen work-light from someplace like Harbor Freight Tools like I first did, and then just buy the extra 100 - 200 - 300 or 500 watt Halogen tube bulbs for like 99 cents each, or sometimes even 2 for $1 when on sale. There are (2) 150-watt tube bulbs that come stock with that work-light (and with a little bit of modifying the work-light you can swap out the tube bulbs manually, or else even use the built-in ON/OFF selector switch to do the same - thus varying the LOAD as needed), and then you just use what you need for a cheap simulated LOAD tester. Those Halogen tube bulbs do get HOT so be EXTRA CAREFUL!!!

For example using standard 100-watt light bulbs:

Smart-UPS 700 - 1 bulb
Smart-UPS 1000 - 2 bulbs
Smart-UPS 1400 – 3 bulbs
Smart-UPS 2200 – 4 bulbs
Smart-UPS 3000 – 5 bulbs


>>>> Then - after selected the proper lamp load to achieve the 20% LOAD LED indicator - make sure that all 5 LED's are illuminated on the BATTERY CHARGE INDICATOR BAR, and unplug the UPS unit from the wall. Allow the unit to run until it clicks all the way off (totally shuts down by itself).

NOTE - If you time how long the UPS unit runs - after it is unplugged, and compare it to the User Manual - as to the time it should provide, you will have a rough percentage of the battery life remaining. Smaller difference in the 2 time periods compared (if both are close) - the better (stronger) the batts are! Larger difference in the 2 time periods compared - means the batts are getting weaker (with one exception). If your UPS unit batts give you a far longer time then the User Manual states then that is even better, as it means your batts are better then the factory batts that came with it originally!

If the unit drops the load almost immediately after you unplug it, then this means that either the batteries are bad, or there is a different internal PCB problem with the unit. If the unit does run, however, and then clicks off (totally shuts down by itself), unplug the light bulbs (LOAD), and plug the UPS unit back into the wall. Allow it to fully charge back up for another 12 hours, after which time the unit should report the correct runtime remaining, and clear the bad battery light and/or return the battery charge indicator to a solid light.

NOTE: Do not use PowerChute's “recalibrate unit” function to recalibrate the unit - as it is only a "partial recalibration", and does not provide accurate results!!

The bigger UPS units like the 2200 & 3000VA units (like those I have at home) only use a charging circuit 1 to1.5 amp pico fuse tops, and those that I've had to repair I replaced with plug in female socket type pins for easier R&R, as I didn't care for APC's crappy PCB design of them being hard soldered in place. When you've repaired and resold as many as I have - then you'd know why! APC was/is very conservative on their charge circuitry, and the charge circuit current limiting output. That in part comes from the fact that they use very cheap batts in their UPS units straight from China. Usually CSB & B&B brands, and sometimes even the PORTALAC brand.

For a 115ah batt bank like yours that is severely discharged down to 10-11 volts (depending on the UPS unit cutoff voltage preset - if it's even working right?) it would take your smaller 1250/1400VA UPS unit(s) in ? upwards of say 25+ hours just to charge the batts back up to 90% of normal rated capacity! A feat in itself for sure!

Normally it would take that long just to fully recharge those standard batt packs (or in your case as it were - your oversized batt bank), which again will severely overheat the charging circuitry as well as surrounding PCB circuitry!

Of course that's based on an APC factory chart using standard add on batt packs on the XL models (or extended models) that have the proper Firmware Chip preprogrammed to accept that added batt Ah capacity!

Again - I'm just guessing here on the XL model part - as you never stated the exact model numbers of either unit you are talking about in post.

That is why APC makes that 3000VA XL model UPS unit that uses added external batt packs daisy chained in parallel groups of (4) batts each in series at (48-volts). They can be daisy chained no problem because the Firmware Chip inside has already been preprogrammed to accept the additional batt capacity. If you think your present day batt banks there are fully charged then you are in for yet another shocker as well. Guess again!

That also goes for the longer then intended "backup state" run times when Edison power actually fails for long periods at a time, as these smaller units weren't designed to run for 24 to 48 hrs straight!!!!

It puts undue stress on the switching MOSFETS, as well as the surrounding circuitry.

If that's not enough Food for Thought then I don't know what is!

Didn't mean to sound harsh, but I hate seeing people abuse their UPS units!

Best regards,



New Member
To HarveyH42,

You too need to read what I posted before if you like good reading.

Not sure what models your 2 APC's are, but it sounds like the internal fuse is gone. Esp if they are 2200VA models. They were notorious for blown fuses! I really think those stock Pico fuses they used were a bit on the inferior side, as my Pico fuse replacements that I used never had a problem years later!

On the 2200VA units there are at least 3 or 4 PCB hard soldered (board mounted) Pico fuses. The largest is a 5 amp I believe. Why they chose to go with Pico fuses is beyond me? That's APC for you!

If you know how to a DVM it's a simple circuit check!

Your idea for a PV panel and a PV VOLTAGE CONTROLLER just to charge the APC batt (if it's indeed a 12-volt batt configuration to start with?) is not only overkill, but it will further screw up the UPS unit PCB circuitry - as you are then trying to back-feed (BUCK) the APC's charging circuit, and devices don't like that part at all. SMOKE usually appears as a result.

If either of your APC units there just has a blown fuse just repair or replace that part first, and then test out the onboard batt(s) to see if they are even any good to start with, and then go from there. If you haven't changed out the batts in 5-6 years time chances are they are partially or totally sulfated - in which case they are most likely SHOT anyway!

I try to exercise all my UPS units AGM batts at least every 4 months just to pull a short duration drain on the batts to put a bit of higher charge current through the batt(s) - thus keeping them from starting any premature sulfation, as from idleness even though the UPS units are kept plugged in and on standby 24/7.

Hope that helps you out too!

Best regards,

Not open for further replies.

Latest threads

EE World Online Articles