Beware - mains voltages and high current from batteries can present a shock/fire hazard. Do not copy what I am doing here unless you are confident with electronics and handling big batteries. Also don't assume the PCB is safe to handle once the mains and batteries are removed. Capacitors in the unit can give you a hefty belt long after all power sources have been removed. edit: well this turned out to be even simpler than I thought - batteries not needed to calibrate!! just use the cap! Tools needed: A multimeter that can measure DC voltage, and AC voltage A suitable breaker for the battery end of the cable (if connecting to external batteries) Suitable cable long enough to reach your battery bank, with decent current capacity A pair of crocodile clips for the meter (to monitor the capacitor below). A friend will do as well, so long as he/she is happy to hold the probes on the relatively safe capacitor terminals (its a low enough voltage and multimeter probes are insulated). A large electrolytic capacitor (5000uf or better, 75 volts or more) A large flat blade screwdriver (to lever the tight front panel off A hanky (to put over the flat blade so you don't mar the front panel) A medium sized phillips head screwdriver A usb to TTL converter (ebay) A set of batteries suitable for the ups (mine needed 2 in series - it got 8 in series parallel!) A Towel (to lay the smaller models belly up on to prevent scratches) A dremel I recently came into posession of an APC Smart-UPS1500I. This is one of the newer models that doesn't use smart protocol for reprogramming.... or does it Rear (of an american unit) showing the triangular battery isolation plug. I pinched this photo off a website while doing research on the thing LOL. Mine is the same, but instead of yankee sockets, it has iec sockets. And it puts out 230V, not 110V. Note the lack of a DB9 serial port? and that silly RJ50 does not do smart protocol. Bad APC! After doing some research I found a video on you tube by ffcossag that shows how to access the smart protocol on these things to enable access to the programming mode. As smart ups's tend to have the charger set to a slightly high float voltage, they tend to kill batteries quicker than they should. Even that geek group fella Chris Boden had trouble getting the packs out of a big rackmount one when he did a teardown. It was quite funny - I was waiting for him to swear If your willing to sacrifice 5-10% runtime and reduce the float voltage by reprogramming the ups, you can increase your SLA battery pack lifetime from 2-4 years to pretty much their documented lifespan, provided you don't deep discharge them too many times. You'll want to aim for 13.5-13.55 volts per battery. So in this ones case, I'll be reprogramming it to 27 volts exactly. If your batteries are brand new, let the ups charge them to full without making any adjustments to the float voltage. This is a conditioning or "boost charge". It helps the batteries reach full potential with this one off charge at the usually too high a float voltage. You can skip this step if they are used and have been properly commissioned, as mine were. So I got to work on this thing. I started by removing the front panel. Mine was on quite tight, and I had to lever it off gently with the big flat blade screwdriver. To do this, I placed a clean hanky over the blade of the screwdriver, put it in one of the finger release points and gave it a gentle twist. Then I repeated the process on the other side. Then gently tilted it down, and lifted it up and onto the top of the ups, screen facing up. Don't be rough here - theres a ribbon cable behind the front panel that if you yank it off, you'll cry as you'll need a new cable from somewhere. On opening the battery door I discovered that my friend who sent me up the unit had been smart and kept all the doings for the battery compartment, and dumped the dead batteries to save on shipping costs and our backs. Since it was destined for the tip, he asked me if I wanted it. I said sure I love playing with these things. So he boxed it up and sent it up with startrak express. Didn't ask for any money except the $27 it cost to ship. Bonus! I then took two of my 55Ah batteries and placed them in series (this ups has a 24V bus), and checked each battery on my multimeter. I used the fuse from the UPS to join them. I used these for testing purposes. Using the Andersons connector from the ups that was connected to the original battery pack, I connected this to a 6800uf 160V DC capacitor. The capacitor serves as a battery surrogate, and although the ups may complain the batteries are dead, its still possible to reprogram the ups using the capacitor. The capacitor reacts far more quickly to adjustments than a battery pack when reprogramming the ups, so you don't have to wait minutes for the voltage to adjust down as you change the setting. Before reprogramming, remove anything from the SmartSlot on the ups. You can put it back once your finished. Connect the rear battery isolation plug, and plug the anderson connector with the capacitor on it, into the ups's battery connector. Then plug the UPS into a wall outlet. At this point I shoudn't need to remind you that high voltages are now present inside the ups. Next I turned the ups on. I waited until it did its self test and failed and was sitting idle with the power LED on and battery failure led blinking, I then measured the voltage across the big cap. 28.7 volts - way too high - just as I suspected. Note in this picture I've done it a second time, so the multimeter reads a much more healthy 27.57 volts but still a touch high. Turn off the ups, disconnect the capacitor and unplug it from the mains. Next pop the top off the ups (theres several screws around the ups which hold the black top cover on). You only need to do this for the larger units like the SMT2200. If you have a smaller model, flip it upside down and rest it on a towel. I didn't and now mine has some very slight battle scars (they are quite heavy, even without batteries; even the little ones thanks to the big transformer). Locate J606. In the larger models with the side mounted board, its toward the back near the front panel and smart slot connectors. In the smaller models with the top mounted board, its located near the "Stickered" CPU inside the battery compartment. In this picture you can see j606 in the bottom right hand corner. I have added a red tag next to it to make it easy to spot. First lets identify the ground pin. Connect a multimeter to case ground (with the ups OFF and unplugged from all sources of power!) and then set it to continuity beep. Try each of the middle pins. One should beep. Thats pin 5! Try to imagine the ups rotated with pin 5 closest to you. Then the one above it in the middle is pin 2, and to the left of pin 2 is pin 1 which we also need to connect to. 1 2 3 . . . . . . 4 5 6 In mine, pin 5 was the rear middle pin, and the right two were TX and RX. While still imagining the pin 5 (ground) closest to you, connect pin one (top left pin to the TX line of your usb to TTL, the RX line to pin 2 (the one next to it) and the ground line to the bottom middle pin (lets call it pin 5). Its below pin 2. Now connect the capacitor, with its anderson. Attach a multimeter set to the DC volts range across the cap. Note here now that we are interrupting the signals between the main cpu and the communications cpu, which drives the front panel, so anything shown on the front panel is rubbish and to be ignored. This is temporary and once we disconnect the ttl converter the front panel operation will return to normal. Your setup should now look like this: Now download the PDF for your batteries and look for the "Standby Use" float voltage. Write it down. plug the ups back into the wall, and turn the ups back on. At this point I shouldn't need to remind you, especially in the case of the bigger units, that some of the exposed parts of the unit are at mains potential, so don't go poking around at things while its plugged in. If you have a helper holding the multimeter leads on the capacitor for you, they will be safe so long as the leads are in good condition, and they don't touch the tips. The voltage here can be as high as 55 volts for a 48 volt model, so best not to let them tempt fate. Open up putty on a windows laptop (its important that this laptop is isolated e.g. running from battery - we don't want a hazardous ground loop!) and tell it you want to communicate with the usb to TTL converters com port at 2400 baud, 8N1, xon xoff or none (try both). At this point you may see a crapload of data scrolling up the terminal window. If you see long lines of jibberish you have your TX and RX lines reversed and you're seeing the communications processor talking to the main cpu. If you get the shorter snippets of data that look like line voltage, frequency etc, you're hooked up properly. If you get nothing, try the Y command and see if you get the "SM" prompt. If you don't, double check your connections by disconnecting the usb to ttl thingy, turning off the ups and starting with the continuity check of the middle pins again. Also ensure you are connected to J606 To reprogram the unit, enter the commands that follow. Press Y (capital is important) and the ups will respond "SM" Press 1, wait 2-3 seconds and press 1 again. UPS will respond "PROG" Well well well, we have smart protocol in these things afterall! Now to bring that high battery float voltage down. Press B (capital is important). It should show the battery voltage, but ignore that reading. Give the + key a few taps until the multimeter across the big capacitor reads a satisfactory value. (mine is just north of 27 volts). If you overshoot, press - to come back up in voltage. The voltage across the cap should correspond to ever so slightly higher than the standby float voltage for your given batteries (multiplied by the number of batteries the ups model uses in series). So mine was 13.5-13.6 multiplied by 2. I erred on the lower side for longest life. For those using a much bigger than stock battery/pack now press > Mine had 2 17Ah batteries as stock. I took 220 (the size of my battery pack in Ah) and divided it by 17 (size of original pack in Ah). This gives 12 - so I need to add 12 additional battery packs by pressing + 12 times. (> tells the ups you'd like to add battery packs or EBM's as most ups manufacturers call them.). Some non extended runtime models will accept this, others wont, by responding "NO" Now press R and the ups should respond "BYE". Press Y again. It should again respond SM. You can now disconnect your TTL converter and the multimeter. Pull the mains and let the ups discharge the big capacitor and then remove it. We're finished with it now. Reassemble the ups / flip it the right way up and connect the battery bank. You should now have a SMTXXXX ups with a recalibrated charger that doesn't cost a hundred or so every few years in batteries. I noticed the source of all the noise - on the left side of my unit is a 80-92mm 24volt fan. When I'm up to taking it apart again (and can afford to take my server offline), I'll replace it with an equally powerful, but quieter model. Its a two wire fan, so the ups is controlling it via pwm or voltage, and doesn't do any sensing. Handy for us. A temperature controlled one with the thermoprobe attached to the H-Bridge heatsinks should do nicely. It may also be possible to run a more common 12V temperature controlled fan via an LM7812 regulator off the 24V line, or by using a more efficient buck converter. Either can be easily retrofitted into the ups, especially if you're planning to remove the stock batteries and run the unit of a bigger bank.