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Guide: Adding Extra Run-Time to Your UPS
Written by Gizmo   
Monday, 30 January 2006 00:00
Article Index
Guide: Adding Extra Run-Time to Your UPS
The Operation
The Operation - Removing the Face-Plate
The Operation - Removing the Battery
The Operation - Opening It Up
The Operation - Exposed Wiring
The Operation - Changing Connectors
The Operation - Splicing
First Smoke Test
Build the Battery Pack
Build the Battery Pack - The Wiring Harness
Second Smoke Test
Reassembly and Final Configuration
Reassembly and Final Configuration - Calibration
Reassembly and Final Configuration - All Done
All Pages

Extending the Run-time of your UPS

So, you've got your snazzy UPS, and it does a dandy job of keeping your equipment running during brief power outages. The problem is, it is only good for about 5 minutes or so of run-time. What this means is that pretty much as soon as the power goes out you have to start shutting down your system. You'd like to have a UPS with more run-time, but the problem with that is that there seems to be a direct correlation between the size of the UPS and the run-time. You only need a 850VA UPS, or maybe 1000VA, but the only thing that you can buy which offers a run-time of say, 30 minutes, comes in the 1500VA or 2000VA variety, and costs a whole lot more money than you want to spend.

What do you do?  If you bought a UPS that has the capability to extend the run-time, you can just buy an extra battery pack for it, and you are in business. Problem is, even those extra battery packs can be expensive. And if your UPS doesn't allow for extra battery packs, you're pretty much done as far as options are concerned, right?

Well, that all depends on whether or not you want to invalidatethe warranty on your UPS. The fact is, today's UPSes are very reliable units, rarely suffering from any failure other than bad batteries. While it is true that any modification of the UPS (including plugging in battery packs not approved by the manufacturer) will void the warranty of the UPS manufacturer, it is also true that in the vast majority of situations, you won't ever need that warranty (after all, these manufacturers wouldn't be offering $50,000 equipment replacement policies on a $100 UPS if they had a habit of failing in any fashion that would cause the manufacturer to have to honor that policy).

In this guide, I will take you through the process of extending the run-time (commonly known as adding batteries) of the APC Smart-Ups 1400NET unit from American Power Conversion Corporation. While this guide is written specifically with regard to the SU1400NET, the principles should apply to virtually any UPS currently on the market. As always though, your mileage may vary, so try to research things before undertaking any such project.

Tools Required

This project will require some modifications to be made to the UPS. You will need a #2 Phillips screw driver, a high-power (250W or so) soldering iron and solder, wire cutters/strippers, and a small to medium pliers.

Parts Required

  • 2 – 12V storage batteries rated at 18 AH each. You should be able to obtain these from a battery wholesaler.

  • Roughly 1 ft. of 6 ga. wire, red.

  • Roughly 1 ft. of 6 ga. wire, black

  • Roughly 1 ft. of double-sided foam tape.

  • Either a roll of electrical tape (also called vinyl insulating tape) or heat-shrink tubing, depending on how you choose to do the wiring.

The following items are not required, but are recommended.

  • 1 – 100A car fuse

  • 2 – Anderson-style electrical connectors, with terminals, gray, rated for 50 amps. You should be able to obtain these from your battery wholesaler.

The Operation

The first thing we have to do is disconnect power, any plugged in equipment, and remove the battery. The first two items are relatively straight-forward; just pull all the power plugs out of their sockets. However, disconnecting the battery is a bit more involved.

All Smart-Ups units, and most Back-Ups units that I am familiar with from APC ship with a battery connector on the back of the unit. According to APC, this connector is provided to allow the disconnection of the battery for shipping purposes. While this is true of units that do not support APC's extended run-time options, the actual fact is that the connector exists to allow external battery packs to be plugged in. Since many units share the same basic chassis and internal electronics, it makes things easier and more cost-effective for APC if they can use common components and simply change some internal wiring. We will be exploiting this fact for this modification.

Here you can see the battery disconnect on the back of the unit. These are called 'Anderson' connectors, and are interesting in their design because of the fact that they are universal connectors. There is no 'male' or 'female' connector as is normally the case; all you need is two connectors of the same color and you are ready to rock-n-roll. The ends of the connectors are keyed so that it is not possible to mate two connectors of different colors, thus making it possible to quickly identify connectors that can mate together.


You can also note that this chassis is used for the both the 1000VA and 1400VA models. The black bracket is a retaining bracket that is screwed down to prevent the connector from accidentally coming loose.

Now that you've got the battery disconnect loose, reach around the front of the unit and hit the 'Test' button. This should cause the unit to turn on briefly and then die with a sickening sound. We do this to ensure that any residual power stored in the input filter capacitors gets bled out of the system so that we don't accidentally fry ourselves.

Next, we remove the battery. To do this, it is necessary to remove the face-plate of the UPS:


This is a very simple operation, as the plate hinges down from the top:


Be careful as you do this; the front-panel electronics are connected to the main unit via a delicate cable. Once you have the face-plate open, you will need to remove the control panel electronics. The PC board simply snaps into place and is easily removed:


Once we have the face-plate off, we've got to remove the battery compartment access plate so that we can get at the battery. I've hi-lighted the two screws that have to be removed. Once they are taken loose, the access plate will pivot downward and out of the way the same way the face-plate did:


At this point, it's just a simple matter to reach in and pull the battery pack out far enough to access the battery connector:



After we've got the battery disconnected and removed, the next thing is to get at the internal electronics. So, we flip the UPS over on its side in order to access the screws on the bottom that hold it together:



All six screws must be removed. Once they are out, the outer case forms a clam-shell, and can be easily removed by spreading the sides apart and lifting straight up off the UPS to reveal:


The heart of the UPS. Time to do some rewiring.

It is first necessary to get the relevant wiring out where we can work with it. To do this, we need to free the cables by unfastening the connector at the rear and the wire retainer in the middle. I have hi-lighted the screws that you need to remove:


Once you remove these screws, you will be able to pull the harness for the internal battery (which we will call the 'battery' harness) and the harness for the battery disconnect plug (which we will call the 'disconnect' harness) out through the side of the unit to where you can work on them. Be careful not to pull too hard, as they are still connected to the main inverter PC board! Also, as you remove the retaining bracket that holds the battery harness in place, you will notice that the insulation has been deformed. Make note of this spot, as it will be useful later.

Looking at the wiring, you will see that the battery harness has a red wire and a black wire, while the disconnect harness has two black wires. In addition, the black wire from the battery harness is the same wire as one of the wires from the disconnect harness. The red wire from the battery harness goes directly to the inverter board. The second black wire on the disconnect harness also runs to the inverter board. When the disconnect plug on the back of the UPS is inserted, it loops the two black wires on the disconnect harness together, completing the circuit from the battery to the UPS inverter board and providing it with battery power.

What we need to do now is run power directly from the battery to the inverter without going through the disconnect plug. We will do this by taking the wire that goes from the inverter to the disconnect plug and routing it to the battery connector instead.

If you look carefully at the end of one of the connectors, you will see something like the following:


In this picture, I have removed one of the pins so that you can see things a bit better. Each pin has a 'lip' on the back side, which slides over a flat spring-steel retainer in the connector housing You can just see the retainer under the left pin, and you can see it on the right side of the housing where I removed the pin. What you need to do is find the black wire going from the inverter board to the disconnect housing and remove it from the disconnect housing. Then remove the black wire from the battery connector housing, and replace it with the black wire from the disconnect housing. When you are finished, both wires from the battery connector should be going to the inverter board. The disconnect housing will have only a single black wire. If you purchased a new pair of gray 'Anderson' connectors, go ahead and remove the black wire from the yellow disconnect housing. Hopefully by now you have observed that the battery connector is gray. Knowing that we are going to be adding an external battery pack, maybe now you are beginning to understand why we are using the gray connector; to keep things consistent so that we can swap battery packs around as we like.

Now, take the black wire and cut it into two equal lengths. Here's where we get to the tricky bit; we need to splice this wire into the wire that is routed to the battery connector. When we get done, we will have a wiring harness that looks something like this:


Be careful when doing this, as placement is crucial! If you get the splice in the wrong place, you won't be able to replace the wire harness retainer we removed earlier. The best way to do this is to place the wiring for the battery connector back in the chassis the way it was (use the deformed insulation that you observed earlier as a reference for where the wire needs to go back in place). Hint, the closer you can splice to the board, the better off you will be. Just make sure that you leave enough room to get the electrical tape on in order to fully insulate the wires (you generally want to be able to wrap a full inch to either side of the exposed wiring).

Here, you can see that I have stripped insulation off the battery harness, and prepared the ends of the wire from the disconnect harness prior to splicing:


For this operation, I am using a little wiring trick I call 'threading the needle'. Basically, when you are splicing wire, you normally take the two wires to be spliced and twist them together. The disadvantage of simply twisting the wires together is that it requires you to strip a fairly large section of both wires in order to get a good splice. What I am doing here is actually forcing the strands at the end of the first wire BETWEEN the strands in the middle of the second wire. This prevents me from having to cut the second wire, or strip away a large amount of insulation to get a good splice. All I need is enough room to force the strands together. Then I lay the spiced wires together, solder everything up, and tape well. Make sure you have at least 4 layers of tape, and tape an inch on both sides of the splice. Once you have everything soldered and taped, take the ends of the black wires that have the pins on them, and insert them into your Anderson connector. Take note that the Anderson connector has a large '+' and '-' symbol stamped into the plastic. Make sure that the wire spliced into the red battery wire goes to the '+' position on the connector, and the wire spliced into the black battery wire goes to the '-' position on the connector. THIS IS IMPORTANT! If you get this part wrong, when you plug in your external battery pack, you will get the batteries cross-connected and THEY WILL EXPLODE!

Put your wiring harness back in place and re-mount the disconnect. This will now be your external battery connector. When done, it should look something like this:\


I hi-lighted the area where the wires splice together, and where the black wires are running so that you could see them better.

First Smoke Test

Ok, now we've got the wiring done. Let's plug a battery pack in and see if everything still works. Start by plugging in your battery pack to your internal battery connector. Press the 'Test' switch and hold it down for a few seconds (the test switch will be the top one on the control board if you hold the board oriented so that the control cable exits at the bottom):


The UPS should power on and indicate that it is running on battery. So far, so good. Shut the UPS off, disconnect the battery pack from the internal battery connector, and plug it into the external battery connector that we just wired up. Once again, press the 'Test' switch and hold it down for a few seconds. If the UPS fails to come on, or gives you some kind of warning beep, or does ANYTHING differently than in the previous test, STOP! Disconnect the battery IMMEDIATELY, and double-check your wiring. Only when you have verified that everything is working properly should you proceed past this point.

Build the Battery Pack

Next, we have to build the battery pack. Smaller UPSes like this SU1400NET tend to use 24v battery packs. Larger ones, like the SU3000NET that I have at my office, use 48v battery packs. With APC, the easy way to tell what size pack you need is by simply looking in the PowerChute software; it will indicate what the nominal battery voltage is. If all else fails, simply open the thing up and look at the battery pack. If it appears to consist of two 12v batteries, then it is a 24v system. If it has two packs of two batteries each, or (more rarely) one pack of 4 batteries, then it is a 48v system. In our case, we are building a 24v battery pack, so we need two 12v batteries. Ideally, we want to use batteries of the same rating, or an even multiple of the rating that is already used in the UPS. APC always uses 18 Ampere-Hour (AH) batteries in their Smart-Ups systems that are larger than 1000VA, to the best of my knowlege. These can be purchased for about $40 each. If you want to go with a larger battery size, then the next step up that you should use will be 36 AH batteries. The reason for sticking to even multiples of the already in-use rating is because the Smart-Ups internal battery management software wigs out if the capacities are too far off what it is expecting.

To build the battery pack, we will need to take the two batteries and mate them together as a single unit. That's where the double-sided foam tape comes into play; take one of your batteries and apply three strips of tape, like so:


Carefully line up the batteries so that they are side-by-side, and the positive ('+') terminal of each battery is next to the negative ('-') terminal of the other battery, and push them together so that the foam tape adheres them together (note: hot-melt glue can also be used for this, though it is more difficult to get the batteries together before the glue cools, and hot-melt can have a rather abrupt tendency to lose its adhesion). If you have done this correctly, you will have a pair of positive and negative terminals next to each other at each end of the battery pack. At this point, take your 100A car fuse and attach it across on of the terminal pairs. Set this assembly aside for a moment.

Take your black and red wire and attach the pins for your connector to the wire, one pin to each wire. If you have connectors for attaching the wire to the battery, go ahead and attach them to the other end of the wire now, as well. Now, insert the pins into the connector housing, taking care to ensure that the black wire goes into the side of the housing marked with the '-' symbol, and the red wire goes into the side of the housing marked with the '+' symbol.

At this point, go back to your battery assembly. Attach the red wire from your wiring harness to the posive ('+') terminal of your battery pack, and attach the black wire from your wiring harness to the negative ('-') terminal of your battery pack. When you get done, the assembly should look like so:


Second Smoke Test

It's time to see if we've got it right, or if we've really messed something up. Hopefully, if things are too bad out of whack, the fuse on the battery pack will break the circuit before something Really Bad happens.

Plug your new external battery pack into your new external battery pack connector on your UPS. MAKE SURE YOUR INTERNAL PACK IS UNPLUGGED! As before, press the 'Test' button on the UPS and see if everything powers up. If it does, we're golden and can proceed to the next phase. If not, go back and double-check the wiring on the battery pack (we've already established that the connector works). Turn the UPS off, unplug the external pack and plug in the internal pack. Now, plug the external pack back in. Note: It is normal at this stage to see a fairly healthy spark as you plug the external pack in; the two packs will be at different voltages and charge levels. Once they are connected, they will begin equalizing charges. Turn the UPS on via the 'Test' button once more, and verify normal operation. As before, if the UPS behaves in ANY way that is unusual, disconnect the external battery IMMEDIATELY, shut everything down, and double-check the wiring of your external battery pack.

Once you are satisfied that everything is working properly, shut down the UPS and remove both battery packs once more.

Reassembly and Final Configuration

Now you can put your UPS back together, in reverse order from when you took it apart. Once you've got it all back together and the internal battery pack installed, reinstall your UPS into your system for normal operation, connect your external battery pack, and power it up. If you have done everything properly, you will be rewarded by seeing your systems come back up and your UPS running normally. If ANYTHING seems out of the ordinary, SHUT DOWN IMMEDIATELY and reinspect all of your work. NOTE: It is normal at this stage for your UPS to think that your batteries are either somewhat or completely discharged. If this is the case, wait for your UPS to finish recharging before you proceed to the final step. Depending on how much capacity you are adding to the system and the charge state of the batteries, recharging could take anywhere from an hour to a day, or even more. An easy rule of thumb is that if your system previously took an hour to recharge and you just doubled the battery capacity, it may take upwards of three hours to recharge now. If it takes longer than 6, there is a problem.

When your system is up and running and the batteries have fully recharged, you will need to do one of two things:

  1. Run APC's battpack utility to tell the UPS that it has additional battery capacity, or

  2. Run a terminal emulation program like HyperTerminal and manually configure the UPS directly.

As APC's utility is both documented and, err, problematic when used on 'unsupported' UPSes, I will describe the process of configuring the UPS manually.

First, according to APC you need a Smart-Signaling cable to be able to do this. I don't know if this is true or not, although I've heard that it isn't. I haven't been able to test it, because all of my units have Smart-Signaling cables. Oh, and if you've got a UPS that only has a USB port, umm.........I don't know what to tell you.

Stop the services that normally communicate with the UPS. If you are running APC PowerChute, this should be the APC PBE Agent and the APC PBE Server.

Bring up HypterTerm. Open a connection to the appropriate COM port (mine is on COM1). Configure for 2400 baud, 8 bits, No Parity, 1 Stop bit, No Handshaking.

Connect to the UPS, and type the character 'Y', without the quotes. The UPS will respond with 'SM'. Now type the character '>'. The UPS will respond with a number representing the number of external battery packs it knows about. If you have had no external packs before now, or this UPS was not originally designed for external packs, the number will be '000'. Now type the character '+' for each battery pack equivalent that you have installed. For example, if you added a battery pack consisting of two 18 AH batteries to this system, you would type the '+' one time. If you added two battery packs, each consisting of two 18 AH batteries, you would type the '+' twice, and so on. Typing '-' will remove one pack. Each time you type '+' or '-', the UPS will respond with 'OK'. When you have configured the correct number of battery packs, type the '>' again, and the UPS will respond with the number of packs it is now configured for. That's all there is to it. Disconnect from the UPS, shut down HyperTerm, restart your UPS services, and run your UPS management software.

You will now need to run a new battery calibration, and when you are done, you should find that your run-time has at least doubled, if not a bit more. As an example, here are my results:



Congratulations! You have successfully upgraded the run-time capacity of your UPS, and for a lot less than what it would have cost you if you had done it the 'conventional' way.  If you have any questions or comments about this article, drop into our discussion thread, here.


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