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Finishing our all-new 800 W plus . . . Part 3: by Duraid Madina and Tim Blythman Uninterruptible U ninterruptible Power Supply S upply In this third article, we describe how to finish building the rechargeable lithium battery-based UPS. We’ll also cover testing, set-up and calibration. Finally, we'll discuss how to connect it to a PC so that you can monitor its status and so that it will shut down automatically before the battery goes flat. T his UPS is cheaper, smaller and lighter than pretty much any equivalent commercial UPS – at least, none that we could find. But it has another big advantage over commercial units: it can be tailored to suit your particular needs. That includes: • the possibility of increasing the runtime by using more or larger batteries • reducing the cost by using cheaper batteries • or increasing the output power through higher battery current capacity and/or a more powerful inverter. Also, since it is based on a pure sinewave inverter, its output waveform is very clean (cleaner than mains when running from the inverter!) while many commercial UPSes produce an ugly, “modified” sinewave (really just 72 Silicon Chip a two-step square wave). Since this unit is controlled by an Arduino microcontroller, you can tweak the code to suit your particular needs or you can just use the software as is, since the default settings will suit most users. Our first article in this series (May 2018 issue), described how the UPS works and detailed the design process. The second article (June) gave the majority of the construction details, including most of the wiring. Now we need to program the Arduino board with the control software, test all of its functions and calibrate it for accurate operation. Before that, however, we'll add a surface-mount USB socket to the front panel and later, we'll explain how to connect it to a computer’s USB port and establish communications using freely available computer software. This will allow the UPS to be moniAustralia’s electronics magazine tored either locally or remotely via the internet, and allows the computer to be cleanly shut down in the event of an extended power failure. Finally, we'll go into more details over the expansion possibilities mentioned above. Finishing construction If you followed the instructions last month, you now have a UPS which is mechanically and electrically complete but has no software to control it. So now let’s get it up and running. The front panel label First things first: you will note in the photo above that the UPS front panel is labelled (we like to make our projects look professional!). However, the UPS doesn't really need a front panel, except perhaps to show what the three LEDs indicate and the purpose of the push button. siliconchip.com.au Some constructors may leave the front panel blank and simply print a reminder on the rear panel with a fine marker pen, ie: Green LED: Mains On Yellow LED: Output On Red LED: Battery Low Push Button: Manual Start. But if you do want to make a front panel label, you will need to download the panel artwork from the SILICON CHIP website and print it onto clear adhesive film. However, it is almost impossible to produce a label to cover the whole panel, which is standard rack-mount size (19 inches or ~485mm) wide. Not even an A3 label (420mm wide) would cover this expanse . . . if you could even get the material to make one. Therefore the front panel artwork we have prepared is designed to cover only a 297 x 130mm area of the left side of the panel – easily accommodated on an A4 sheet. You can get clear, self-adhesive A4 sheets from a variety of sources (including ebay) suitable for use with inkjet printers. You would print the artwork onto these labels and then attach them to the front panel. If you can’t easily get adhesive clear D Fig.6: installing the TimerOne library can be done via the Library Manager. Click on the option highlighted above (ignore the greyed section) and click "install" when it appears. labels, you could mirror the images and print them onto clear film, then stick the printed side of that film to the front panel of the unit using a thin smear of clear neutral-cure silicone sealant. Incidentally, if you do use the SILICON CHIP panel artwork, the positioning of the LEDs and switch is much more crucial, simply to get the labelling to line up. Use the front panel artwork below as a template (remember the panel below is printed at 50% – if you're photocopying to use as a template, you need to enlarge it by 200%.) This artwork can also be downloaded from siliconchip.com.au Loading the software You will need the Arduino UPS firmware package, which can be downloaded from the SILICON CHIP website (free for subscribers). To compile and upload the test and control software, you need to have the Arduino IDE (Integrated Development Environment) installed. This can be downloaded from www.arduino.cc/ en/main/software, with versions available for Windows, macOS and Linux. Download and install a version to suit your operating system and start it up. If you already have the IDE installed, the minimum version required for the following steps is v1.6.4 so upgrade it first if you have an earlier version. The software needs one library installed, to allow it to perform regular sampling of the mains waveform. Open the Library Manager by going to 130mm 297mm Fig.7: front panel artwork, reproduced 50% (ie, needs to be enlarged 200% if you wish to use this to make a front panel and/or to use as a template for the LEDs and Manual Start switch). This is designed to fit on a standard A4 sheet of clear, self-adhesive film. It covers less than half the width of the rack-mount panel. siliconchip.com.au Australia’s electronics magazine July 2018  73 The three relay sockets are oriented so the vertical pins (the coil connections) are towards the rear panel and the horizontal pins (the relay contacts) towards the front. the Sketch → Include Library → Manage Libraries... menu, type "timerone" in the search box and click on the "install" button that appears. Alternatively, we supply the library in a ZIP package when you download the sketch. You can install this using the Sketch → Include Library → Add .ZIP Library menu option. Because this project involves high voltages and you will want to make sure that everything is working properly before “letting it loose”, we have created a separate test program that can be uploaded to the Arduino. There’s also another separate “sketch” which is used for calibration and setup. The download package includes three separate sketches, called “Silicon_Chip_UPS_Control_V3” (the control software), “Silicon_Chip_UPS_ Testing” (for testing only) and “Silicon_Chip_UPS_Calibration” (for setup and calibration). The differences are explained below. Initial checks Plug relays RLY1-RLY3 into the bases now. It’s very important that the relays are the right way around since if you manage to accidentally install the bases backwards, all the wiring will be wrong. So make sure that the pins for the relay coils go towards the rear of the case. Note that the connection pins for the coil are orientated differently to the other six contacts – they're 90° rotated compared to the switching contacts. 74 Silicon Chip Compare your bases to the photo at left. Once the relays are plugged in, you should be able to see the armature and contacts inside the relay and these should be on the side towards the front of the unit. Now we check that there are no short circuits between the mains and low voltage wiring or between the mains conductors. Set your DMM to its highest ohms range (usually megohms) and connect the probes between the earthed chassis and the 0V terminal on the control shield. The reading should be well over 1MΩ. If it's below 1MΩ then you will need to check your wiring carefully for mistakes. Next, check the resistance between the Active pin of the incoming mains plug and chassis earth, and repeat the test for the Neutral pin. Both readings should also be above 1M. Perform the same test with one of the GPOs, making sure that its associated switch is on. Similarly, measure the resistance between the earthed chassis and the positive battery terminal. This should also be high. Finally, the resistance between any of the earthed chassis pieces and the mains plug earth pin should be low – 1 or less. Shield testing The testing sketch displays information on the voltages being monitored and the operation of the inverter. Remove RLY1-RLY3 from their sockets; they are not needed at this stage. Make sure that the mains input cable is unplugged and ensure that the inverter control cable is connected. For the initial setup, leave the RST DIS. jumper (JP1) off the control shield. Plug the Arduino into your computer's USB socket and make sure the correct COM port is selected under the Tools → Port menu. Then open the Silicon_Chip_UPS_ Testing sketch, upload it to the Arduino (Sketch → Upload) and check the messages at the bottom of the window to ensure it was successful. Then open the serial monitor (Tools → Serial Monitor) and set the baud rate to 115,200. Every five seconds, the test sketch reads the analog inputs and displays their raw values, as well as toggling the inverter on and off. You should see something similar to the following on the serial monitor: Australia’s electronics magazine Inverter turn off:OK Battery Sense:484 Mains Sense:479 VIN Sense:79 Mains RMS: 3 Mains P-P: 7 Inverter turn on:OK Battery Sense:484 Mains Sense:479 VIN Sense:79 Mains RMS: 2 Mains P-P: 6 ... If the inverter is connected, it will produce a brief chirp every five seconds as the Arduino turns it on and off, with corresponding feedback on the serial monitor showing that it is reading the inverter state successfully. The "sense" values are in ADC units, so will be in the range of 0-1023. The battery and mains values should be close to 500 and VIN around 80. The battery value will reflect the state of battery charge, with a full battery being around 540 (29V) and a flat battery being about 409 (22V). Now measure the actual battery voltage and write down this voltage reading along with the current Battery Sense value. These numbers will be required later, for calibration. The Mains Sense value is around 500 because, in the absence of mains, the biasing resistors bring the AC waveform near the centre of the Arduino's ADC range. Plugging in the mains should cause this reading to vary between about 300 and 700 and the RMS and P-P should increase to around 85 and 240 respectively. The VIN Sense reading should also rise to around 200 as the Arduino is now being powered by the mains transformer. Measure the voltage between VIN and GND on the Arduino shield and note this down, along with the VIN Sense reading displayed, again for use later during calibration. Now (carefully!) measure the mains RMS voltage using a DMM set on a high AC volts range and write this value down, along with the RMS and P-P values displayed simultaneously in the serial console. Unplug the unit from the mains now. If your unit is not behaving as described above, go back and check the wiring and shield construction. In particular, high or low values for siliconchip.com.au any of the analog voltages are signs that the wrong resistors were used in the voltage dividers. Values close to zero or 1023 might indicate an open or short circuit on the shield. Calibrating the unit The control program relies on a number of EEPROM calibration values for correct operation. The calibration sketch allows you to set these via the USB/serial port, using a menu system. If you don't set these, the first time you run the control program, it will load a default set of values (as determined using our prototype). But component variation means that these are unlikely to be exactly right for your UPS, so it's better to use the calibration sketch first. These are separate sketches because the USB/serial interface is used to feed status information to the computer when running the control program. So open and upload the "Silicon_ Chip_UPS_Calibration" sketch to the Arduino, using the same procedure as described above and again, open the Serial Monitor and check that the baud rate is 115,200. Press "d" and Enter, followed by "p" and Enter. This will load the defaults and then display them. You can also press "?" and then enter to get the following help text: UPS SETUP ? This Help ~ Toggle voltage status output on/off A-O Enter parameter, followed by number and enter s Save current to EEPROM l Load from EEPROM d Load from defaults p Print current parameters The default values should be shown as follows after pressing "P": Current Values: A:VIN_SCALE :0.0538560 B:BATTERY_SCALE :0.0538560 C:MAINS_SCALE :2.7090001 D:BATTERY_CRITICAL :23.0000000 E:BATTERY_MIN :25.0000000 F:BATTERY_OK :27.0000000 G:VIN_MIN :11.0000000 H:VIN_OK :11.5000000 I:MAINS_MIN :200.0000000 J:MAINS_DB :20.0000000 K:MAINS_MAX :260.0000000 L:MAINS_DELAY :10000.0000000 M:VIN_DELAY :5000.0000000 N:BATTERY_CRITICAL_DELAY: 5000.0000000 O:VIN_CRITICAL :10.5000000 Now calculate the correct VIN_ SCALE value for your unit by dividing the VIN that you noted earlier by the VIN Sense reading. You should get a value similar to that shown above. Type "A" into the serial console (it must be a capital), followed by Enter, then type in the new VIN_ SCALE value and press enter. Different batteries and other options . . . While the UPS is very capable as presented, some readers might want to change the design to reduce the cost, provide a higher battery capacity, a higher maximum output power or faster battery recharging. The IFM12-230E2 LiFePO4 batteries used in this project are rated at 23Ah each. You could use IFR12-400-Y batteries instead, which have a rating of 40Ah. These are larger and heavier and would not fit in the specified case but they would almost double the runtime. Note that you would need to ensure that the cable between the batteries and those from the batteries to inverter are sufficiently thick. Also, recharging would take twice as long unless you also upgraded to a charger with a higher current rating. Depending on your planned use of the UPS, a longer charge time might be acceptable, if you just want to cover occasional outages. On the other hand, if you plan to use the unit mainly for off-line power or are in a location with frequent and long outages, a more powerful charger would be a preferable. Keep in mind that you may also need heavier cables between the charger and the batteries. If you end up with a battery bank powerful enough to deliver more than 50A, you could then consider using an inverter with a higher power output than 1200W (up to a maximum of around 2400W/10A). The good news is that if you decide to make these changes, the relays, Arduino, control shield and other interface modules do not need to be changed. If you use a different battery chemistry, you will need to adjust the Arduino configuration to suit the different voltage thresholds but that’s it. Reducing cost or increasing run time As we said right at the start of the first article, this UPS is not cheap to build and that’s mainly due to the lithium-based rechargeable batteries. As explained in that article, LiFePO4 batteries have significant advantages over lead-acid batteries but they are still considerably siliconchip.com.au more expensive. If you’re willing to accept the disadvantages of lead-acid chemistry, such as larger size, greater and weight and reduced lifespan with multiple deep discharges, you can certainly save some money. For example, you could substitute two Jaycar Cat SB1699 38Ah deep cycle SLA batteries, which would give you a slightly higher capacity (albeit more sensitive to discharge rate) and would make the total cost for the UPS project to around $800-900. That’s a lot cheaper than a commercial UPS with equivalent performance would cost. The weight penalty would be around 10kg and you would need a larger case. Or you could go all out and use two 150Ah Deep Cycle AGM batteries (Jaycar Cat SB1684). This would give you a massive 3600Wh total capacity, allowing you to draw 1200W for three hours or around 720W for about five hours. The total cost would be similar to our original design, although it would weigh nearly 100kg and would be about the size of a small fridge! Such a system would make a great power plant for a caravan, mobile home or even a shed where you don’t have access to mains power. In this case, you would probably want to use a 24V MPPT solar charger or even a generator to keep the batteries topped up. Mind you, its weight of 100kg must be considered if you have a mobile home or need to tow a caravan. Many solar regulators can simply be connected directly to the batteries and they will quite happily work with other charging sources connected at the same time but you should check the specifications of the charger before hooking it up. And if you’re using lithium-based batteries, you absolutely must ensure that the charger is designed to handle that particular chemistry. The Arduino control board in our project doesn't care how the battery is charged, as long as it occurs somehow. Charging the batteries by wind power is possible too but again this will depend on the capabilities of the wind turbine regulator. Australia’s electronics magazine July 2018  75 Repeat the procedure for the battery voltage divided by the Battery Sense reading (option "B"). This should also be around 0.05-0.06, and the mains voltage divided by the Mains RMS reading (option "C"), which is normally around 2.7 but may vary depending on the exact turns ratio of your transformer. The other values should not need to be changed but you may wish to alter them later to tweak the unit's behaviour, once it's up and running. Press "s" and Enter to save the new settings to EEPROM. You can check that the values were properly saved to EEPROM by resetting the Arduino and then using the "p" command to display the stored values. Loading the control software Do a final check over the unit's wiring to make sure that everything is as it should be, then open and upload the sketch named "Silicon_Chip_UPS_ Control_V3" (if there's a newer version, it may be V4, V5 etc). As soon as it's loaded, the piezo should sound for two seconds as the UPS attempts to start up but it cannot because the relays are not yet in place. You can now access the APC-compatible status interface by opening the Serial Monitor and setting the baud rate to 2400. Press "a" and you should get the "capability string", which looks like: 3.!$%+*.#BGKLMNQSUVYZaf You might also get an asterisk ("*") on a line by itself. This means that the Arduino has detected a loss of power and is shutting down. This indicates that the software is working as designed, given that the hardware is not yet complete. Disconnect the USB cable for the next few tests. up for some time to charge the batteries. If the incoming mains is switched off, the yellow inverter light should come on briefly before it all shuts down (as the inverter relay is still missing). You may also see the UPS spontaneously shut down if it detects any mains glitches. Testing the software Testing the inverter Ensuring that the mains lead is disconnected, plug RLY1 and RLY2 into their sockets (the two left-most relays, looking from the front). Set S1 to the off position, plug in mains and switch it on. The Arduino should power up, detect there is no 12V supply from the PSU and then shut down. If the yellow light comes on at all (except very briefly before the green light), the UPS is probably not sensing mains voltage correctly, as it is trying to switch over to the inverter. You should be able to measure 12.6VAC across the mains transformer input to the shield (CON1). If the UPS appears to be doing something unexpected, turn everything off and check the wiring thoroughly. If all these tests went well, switch off the mains, switch S1 on and then turn mains back on. The UPS should perform a normal startup, with a single beep from the inverter and the green light on the front panel will turn on. You should have mains power available at the four-way GPO. The red light on the front may be flashing if the battery is not fully charged. If all is well, you can leave it powered Unplug the mains and remove RLY1 (at left), then plug RLY3 (right-most) into its socket. Check that the internal mains plug is in one of the inverter’s output sockets and then switch S1 back off. The following procedure tests the inverter so you do not need to connect the unit to mains. Now press and hold down the button on the front of the UPS (S2). After about a second, the yellow light will come on and the green light should be flashing, indicating mains is not present. The red light will probably be flashing too unless the batteries are fully charged. When the button is released, the inverter should beep (indicating a successful shut-down), and all lights should go out. Now switch S1 back on and hold in pushbutton S2 for about five seconds before releasing it. The UPS should now stay on, running in inverter mode as above, until S1 is switched off, which should cause a total shut-down If all these tests were successful, RLY1 can be plugged back into its socket. Plug the mains plug into a socket and switch S1 back on. Calculating the voltage scaling factors In this article, we describe how to calculate the required scaling factors by measuring the voltages that are being sensed by the Arduino and then dividing them by the integral number being simultaneously produced by its analog-to-digital converter (ADC). But you could calculate these values from the component values used in the circuit. For the battery sense voltage applied to analog input A2 and the VIN sense applied to analog input A3, this is quite easy. In both cases, the divider resistor values are 100kΩ and 10kΩ and we can compute the division ratio as 11 (100kΩ ÷ 10kΩ + 1). Since the ADC has a 10-bit resolution, the values will range from zero to 1023 (210 - 1) for signals from 0V to 5V. Therefore, each ADC step represents 4.888mV (5V ÷ 1023) and by multiplying this by our ratio of 11, to compensate for the voltage reduction due to the resistors, we get a figure of 0.05376V per ADC step, very close to the default scaling factor used. The calculations for the mains sense voltage are more difficult because this involves three resistors – a 75kΩ resistor between the transformer and analog input A1, plus two 10kΩ resistors which go from A1 to ground and the +5V rail. The easiest way to understand the effect of this configuration is 76 Silicon Chip to analyse its DC and AC conditions separately. The transformer has a low DC resistance to ground, so the 75kΩ resistor is effectively connected to ground at one end and therefore is in parallel with one of the 10kΩ resistors, giving an equivalent resistance of 8.8kΩ. In combination with the 10kΩ resistor to +5V, this gives a DC level of 2.35V. For the AC analysis, since both 10kΩ resistors connect to DC rails, we can treat them as if they are in parallel, ie, equivalent to a single 5kΩ resistor. In combination with the 75kΩ resistor, this gives us a division ratio of 16 (75kΩ ÷ 5kΩ + 1). Thus, we expect a quiescent ADC reading at A1 close to 480 (1023 x 2.35V ÷ 5V). Assuming there is 6.3VAC across the transformer winding for a 230VAC input, that gives a step-down ratio of 36.5 times (230 ÷ 6.3). Multiplying this by the resistor divider ratio of 16 gives a total reduction of 584 times. So we can calculate the scaling factor as 2.85 (584 x 5V / 1023). In practice, the output voltage of a lightly loaded transformer is higher than nominal, hence the step-down ratio is lower and so our real scaling factor is 2.7. Australia’s electronics magazine siliconchip.com.au The UPS should now be operating normally, so once you switch the mains supply on, it should start up. A glitch in the mains can be simulated by turning the incoming mains off and on quickly. You should see the UPS transition to the inverter, wait for about ten seconds, then switch back over to mains power after detecting that it has been stable for a while. At any time, you can use S1 to turn off the UPS. The Arduino should recognise that it is not getting any 12V supply, and will shut itself and the inverter down. To switch it back on, toggle S1 again and switch the incoming power off and on (or press the reset button on the Arduino). S1 will also work to shut down the UPS if it is running from its battery. In this case, it can be restarted by toggling S1 back on and holding pushbutton S2 in for about five seconds. This takes a while as the inverter takes several seconds to reach a normal output voltage and then the 12V DC switchmode supply output will come up. Load testing Once the batteries have been fully charged, you may wish to do a load and runtime test, to ensure the battery capacity is as expected and that you get enough warning before it shuts down entirely. A simple plug-in type power meter like Jaycar’s MS6115 or Altronics P8137 should be used to confirm and monitor the power usage of your test load. We used an incandescent lamp and a heat gun to provide a constant load totalling close to 800W. It’s also a good idea to connect a DMM across the battery terminals with clip leads so you can monitor their voltage during the load test. Note that you can’t easily clip onto the battery 0V terminal since it is insulated. The tab of REG1 on the control shield is a convenient 0V reference point. Switch on your load(s), check that the power consumption is about what you expected, then switch off the mains input to the UPS and note the time. If the power meter has a cumulative power option, now is a good time to reset it to zero. You might notice that the load indicated on the power meter changes slightly when mains is switched off, since the specified inverter produces 240VAC, while mains can vary from siliconchip.com.au below 230VAC to above 250VAC. The red LED should start flashing after a few minutes as the battery starts to discharge. The flashing frequency will increase over time and eventually, the red LED will be on continuously. This means that shut-down is imminent. Once the unit switches off, you will probably notice the battery voltage rebounds since the load has been removed. When the shut-down occurs, check that the inverter shuts down as expected and note the time elapsed and cumulative energy consumed. If you have used the specified parts, the time elapsed should be close to that specified in the first article in this series, taking into account any differences between your load power and the nearest specification. Having completed the load test, plug the UPS back in to allow the batteries to fully recharge. This will take a few hours. Ideally, you should leave it to charge overnight. If you notice any problems with the final battery voltage or inverter shutdown, it may help to adjust the calibration values, as described later in this article. If you run into any problems, you may also find it helps to enable debug mode in the control sketch. Note that this disables the PC interface (APC protocol) but you can re-enable it later. To do this, change line 20 of the sketch from: //#define DEBUG to read: #define DEBUG and upload the modified sketch. After uploading this, you will probably also want to put a jumper shunt on JP1 on the control shield (“RST DIS.”) so that plugging the Arduino into your PC will not reboot it and reset the UPS. You'll need to have either mains or inverter power available so that the Arduino doesn't try to shut down immediately. Type “?” and press Enter in the serial monitor to see the list of available debugging commands. Type “~” and press Enter to toggle voltage information display on and off. Note that this mode uses a baud rate of 115,200. The UPS is now complete and working as designed. You can put the lid on and use it as-is, or you can follow the instructions below to add a USB port so that its status can be monitored from your computer. Adding a USB interface Computer software can be set up to communicate with the UPS and this can run “scripts” on certain events so you can, for example, shut the computer down gracefully before the UPS shuts down due to a low battery voltage (during an extended blackout). The software has other options like email notifications but we won’t cover the steps required to set that up in this article. For these features to work, you need a Type B USB socket on the outside of the UPS case to connect it to your computer. Unfortunately, most chassis-mount USB sockets are Type A, or they require an accurate rectangular cut-out. So we came up with the idea of mounting a Type A to Type B chassis adaptor backwards so that the Type B socket is on the outside. Then you just need two standard Type A to Type B cables; one goes on the inside of the case and connects The USB socket, mounted on the right side of the front panel. Precise position is not important. Inset above is the same socket seen from inside the UPS. Australia’s electronics magazine July 2018  77 from the socket to the Arduino board, while the other plugs into the Type B socket on the outside of the case and goes into the Type A socket on your computer. The part we decided to use is Altronics Cat P0835. The drilling template is shown in Fig.8. Drill a pilot hole in all three locations, then use larger or stepped drill bits, or in the case of the largest hole a tapered reamer, to expand them to the required sizes. The Altronics part is reversible, so if it looks like it would be facing the wrong way around when installed, undo the small screws and reverse the insert in the housing, then reattach the screws. Mount it in place from the outside using M3 x 10mm machine screws, M3 nuts and M3 shakeproof washers, then run a USB A-B cable from the socket inside the case to the Arduino. We chose to mount it at the front to keep the cable run short, although a longer cable will be fine as long as the total run does not exceed the USB standard of three metres. Secure the cable with cable ties, and bundle up any excess to keep everything tidy, adding extra cable clamps if necessary. If you enabled the debugging feature of the Arduino control sketch, you will need to disable it and re-upload the sketch before proceeding. Regardless, insert a jumper shunt on JP1 on the control board (“RST DIS.”). Installing the software The open-source “apcupsd” software is available for Windows (XP onwards), macOS, Linux and more. We tested it on Windows 10 but setting it up and running it on the other operating systems should be similar. The APC UPS protocol operates over a serial port at 2400 baud with 8 bits and no parity. In our case, the serial port is emulated by the USB device using the CDC protocol. Generally, the UPS host software issues single byte commands, to which the UPS replies with a brief multi-byte response. The UPS may also spontaneously generate a status signal (such as "power fail" or "battery low") for conditions that the host computer should know about immediately. The APC protocol has been chosen because it is the most widely supported and is straightforward to emulate. 78 Silicon Chip Fig.8: the front panel cutout for the USB socket is a standard "D" series pattern. This diagram is at 1:1 scale. We recommend running the computer from a separate power source (ie, not through the UPS) during the initial testing stages. The software can be downloaded from www.apcupsd.org Download and install a version to suit your operating system. We tested using version 3.14.14. Select all the possible options during installation and select the option to edit the configuration file as suggested. If you need to find the file manually, it was installed on our system at C:\ apcupsd\etc\apcupsd\apcupsd.conf It can be opened with a text editor such as notepad. You will need to set the following parameters: UPSCABLE smart UPSTYPE apcsmart DEVICE COM5 Note that the DEVICE parameter needs to match the COM port which is assigned to the UPS on your computer and it will be in a different format on other operating systems. This port number will be the same as the one you selected for uploading the sketch in the Arduino IDE. Save those changes to the configuration file. If you want more details on the contents of this file, the software manual is very detailed and can be downloaded from www.apcupsd.org/ manual/manual.pdf By default, if the apcupsd service is running, the software will shut down the computer if there is a fault detected, such as a critically low battery. Instructions for disabling this can be found in the manual. The manual also explains how to use the apctest utility, which tests both the connectivity and settings. The installer will automatically set up the service to run at boot time and it puts an icon in the notification area of the Windows taskbar. You can start it manually via the Start menu. You may also need to run the Apctray program to get the icon to appear in the taskbar. Right-click on the icon on the taskbar to view the UPS status. You can also use this menu to set the icon to start automatically with Windows, view the event log and change other settings. If you have no connection indicated from this icon, check that its configuration settings are correct, especially the port value. The port should be set to 3551, to match the port setting in the apcupsd.conf file. The IP address should be 127.0.0.1 (which refers to the local computer). You can also use this settings window to disable status pop-ups from the icon. If you need to change the apcupsd configuration, first stop the apcupsd service by selecting “Stop Apcupsd” from the start menu. The icon will stay in your taskbar but it will complain about a network error. After making changes to the apcupsd. conf file, start the service as before. Fig.9: the services window allows you to start and stop the Apcupsd service. The red arrows highlight the selections required. Australia’s electronics magazine siliconchip.com.au Fig.10: part of the status window showing the vital UPS operating parameters. Here you can see line voltage and battery voltage as reported by the Arduino, along with other statistics derived by the software such as time since last power failure, battery staus, etc. during normal operation. The software currently does not rely on this value but it may be used in a future version. • VIN_OK (option “H”). Defaults to 11.5V. If VIN is above this voltage, the unit is assumed to be running off the 12V DC switchmode power supply. Below this threshold (but above VIN_MIN), it is assumed that the mains sense relay is powering the unit via RLY4. • MAINS_MIN (option “I”). Defaults to 200V. When the mains RMS voltage drops below this level, the output will switch over to the inverter. Depending on your version of Windows, you may find that you can only start and stop apcupsd from the Services dialog. This can be accessed through the Windows Run utility (accessible through the Start menu or by holding down the Windows key and pressing R), typing “services.msc” and pressing Enter. Here, the service can be started, stopped and restarted, and more options can be found by right-clicking and opening the properties window, including whether the service starts automatically (see Fig.9). At this stage, the UPS should be up and running and interacting with the computer. If you want to test the automatic computer shut-down feature without draining the battery, shut down the apcupsd service, edit the configuration file and find the BATTERYLEVEL parameter and change it to 95. The value is a percentage and is calculated by the UPS based on the battery voltage level, with the “battery_ok” EEPROM setting representing 100% and the “battery_critical” parameter being 0%. Save the file and restart the service. The UPS can then be tested by unplugging its mains lead and waiting a few minutes for the battery level to drop to 95%. Your computer should then shut down. Remember to set the BATTERYLEVEL parameter back to 5% when you are finished testing to avoid premature siliconchip.com.au shut-downs. Once you are satisfied with the operation, check that the service is set to start automatically and remember to plug the computer’s power cord into the UPS outlet. Advanced calibration and tweaking We showed the fifteen different EEPROM calibration values earlier but only explained the purpose of the first three. The remaining settings are: • BATTERY_CRITICAL (option “D”). Defaults to 23V. This is the battery voltage at which the UPS will report 0% remaining capacity and initiate its own shut-down This is a fairly conservative value. We don’t recommend setting it any lower than 21V. This should not damage the specified batteries. • BATTERY_MIN (option “E”). Defaults to 25V. This was intended to be the threshold below which the unit will start warning the user, however, the current version of the software does not use it. It may be used in a future revision. • BATTERY_OK (option “F”). Defaults to 27V. When the battery voltage is this value or higher, the remaining capacity is reported as 100% and the red LED remains off even if the inverter is running. • VIN_MIN (option “G”). Defaults to 11V. This indicates the voltage above which the VIN rail will sit Australia’s electronics magazine • MAINS_DB (option “J”). Defaults to 20V. This is the hysteresis value for MAINS_MIN (“DB” stands for dead band). The mains RMS voltage must rise at least this high above MAINS_MIN before the unit will switch back on. • MAINS_MAX (option “K”). Defaults to 260V. If the mains RMS voltage rises above this threshold, the output will switch over to the inverter. It must fall below this by the hysteresis amount (by default, below 240VAC) before the output will switch back to mains. • MAINS_DELAY (option “L”). Defaults to 10 seconds (10000ms). This is how long the mains RMS voltage must be within the normal range when the output is running off the inverter before it will switch back to mains. • VIN_DELAY (option “M”). Defaults to 5 seconds (5000ms). Not used by the current version of the software as the unit shuts down immediately if VIN is below the critical threshold. • BATTERY_CRITICAL_DELAY (option “N”). Defaults to five seconds. If the battery voltage remains below BATTERY_CRITICAL for this long, the piezo will sound continuously for one minute, after which the unit will shut down entirely. • VIN_CRITICAL (option “O”). Defaults to 10.5V. If the VIN rail falls below this value, the unit will automatically de-energise RLY1-3 and then shut the Arduino control circuitry down. This normally will only happen when power switch S1 is turned off. July 2018  79 Some early UPS feedback from our readers . . . Why 24V and not 12V? I must ask the obvious question –why did you choose a 24V solution, rather than 12V, with the 2 x 12V batteries in parallel? The 1200W inverters are virtually the same price, 12V or 24V. The current draw on each individual battery is the same, 2 x 12V parallel, or 2 x 12V serial. Using 12V would delete the cost of a battery balancer, and I would think the cost of the small 12.6V transformer (a simple mains-sense relay could isolate the small Arduino from the now pair of batteries – imbalanced load not a problem). The cost of 10A 12V, and 5A 24V LiFePO4 chargers appears about the same? Just wondering…? Ian Thompson Perth, WA That seems like a perfectly logical alternative approach, Ian. But . . . In fact, as part of our initial deliberations, we briefly considered it but quickly rejected it. We cannot recommend it. The problem is that no two batteries are identical, with the same internal impedance and open circuit voltage. That means that they can never share the load current equally and ultimately one battery takes more of the load. Ultimately, it will lead to a reduction in life, compared to using the same two batteries in a series arrangement. If you want another opinion, see www.enerdrive.com.au/connecting-epower-b-tec-lithium-batteryseries-parallel To quote from that site: "When lithium ion battery packs are connected in parallel and cycled, matching of internal resistance is important in ensuring long cycle life of the battery pack. Specifically, a 20% difference in cell internal resistance between two battery packs cycled in parallel can lead to approximately 40% reduction in cycle life when compared to two batteries parallel-connected with the same internal resistance. Series-connected lithium batteries would have the same reduction 80 Silicon Chip life if a battery balancer was not used." Off-peak hot water tones I have some interest in your latest UPS design. My concern is our off-peak hot water signals sent down the mains interferes with lots of devices we have around the house. For those not aware of these signals, it's a higher frequency (500Hz - 1kHz) signal superimposed over the regular 230VAC, that is used to switch off peak hot water systems on and off. Switchmode power supplies mostly deal with it nicely, but not all. One brand of LED lamps we have pulsate while the signals are sent, the only way around it is to experiment with alternate brands, and replace all those with more "tolerant" lamps. My current Eaton UPS isn't immune either, it commonly false triggers during the signals too. I have an amplifier that buzzes, and I used to have a pre-amplifier that had an over-sensitive mute that conveniently muted audio at the least convenient time twice a day. My point is, this is a big deal for us, as much of the side-effects of these signals are completely unacceptable. The Arduino mains sense runs at 1000Hz, so it may "see" over voltage and under voltage conditions hundreds of times a second. While a passive band-pass filter at the transformer output might work, it may interfere with the bad-mains sense, and this is probably fixable via firmware anyway. I'm not being paranoid, I just don't want to commit to a significant cost outlay to find out it won't work, and can't be made to work after all. John Tserkezis via email You raise an interesting point, John. It is possible that the lightly loaded transformer we are using to sense the mains voltage may have an enhanced response to mains tones signals. However, while the Arduino senses the mains voltage at 1000Hz, the signal from the transformer is filtered by the attenuation network consisting of the 75kΩ and two 50kΩ resistors, shunted by a 100nF capacitor. This will have a -3dB point of about Australia’s electronics magazine 50Hz and the AC signal will be attenuated by 6dB/octave above that. Hence, a 1050Hz tone signal could be attenuated by about 50dB before sensing by the Arduino control shield. If that proves to be insufficient attenuation, it could be increased by using a larger filter capacitor, eg, 220nF or 330nF. UPS Inverters are SOLD OUT! I have been a subscriber to your excellent magazine for many years, and have built many projects from its pages. When I saw the UPS project in the May issue, I just had to build it, and now have all the required components except for the inverter, which I ordered from Giandel on 6th March. On 8th March, I received confirmation from them that my order had been filled and despatched together with a tracking number. About a week later, I received a further email explaining that unfortunately, this inverter was out of stock, would not become available for several months, and that my payment had been refunded. Since then, I have been searching for an equivalent inverter, but have only found one on eBay with an asking price of AUD800+. My question is: Can you suggest where I may find a suitable alternative inverter? Ian Hawke via email It appears that the UPS Project has either been very popular or someone is looking to make a killing in the hope that it will be! A number of readers have pointed out that the Giandel online store has sold out of the specific model of inverter that we have used in the UPS Project. The Giandel online store provides a link to eBay, where the same inverter can be purchased for $899 (about six times the price we paid). Curiously, an otherwise comparable 2200W 24V pure sinewave inverter (almost double the power of the inverter we used) can be purchased for around $270. The question we are being asked is where can these (or an alternative) inverter be purchased. We have done some research and we siliconchip.com.au would look at the following if we were building a UPS from scratch now: www.ebay.com.au/itm/332254283761 This is the 2200W inverter we noted above. It will be substantially larger than the original inverter, but being Giandel branded and sporting a wired remote control, would probably be the most electrically compatible. There are MANY other cheaper 24V 1200/1500W pure sinewave inverters on ebay – however most do not have remote control (see below) and you will have to wait for many of them to come from China! www.elinz.com.au/Pure-Sine-Wave-Inverters One of our staff members has suggested this online supplier, who appear to be based in Melbourne. They have a 24V, 1500W inverter (SKU: INTPW24V1500) which is rated slightly higher but not dissimilar in size – so it should fit. It does not have a remote control function. At press time it was on sale at $209.99 www.jaycar.com.au/p/MI5712 The best match from Jaycar appears to be the MI5712, which is currently listed online at near half its 2017 catalog price. It has a remote controlbut with a different socket so some changes to the control wiring and/or circuitry will be required/ www.altronics.com.au/p/m8018a/ The Altronics M8018A does not have a remote control facility, but otherwise appears to be suitable. It's important to note that we have not tested any of these alternative inverters, and readers should check the dimensions, power rating, input voltage and the presence of a wired remote control (which may or may not have the same wiring as our prototype) before buying such an inverter. Cheaper inverter lacks remote control I am looking to build the SILICON CHIP UPS, and online I have found an inverter that looks suitable, (ie, 24V <at> 1200W) but it does not have a wired remote control like the one used in your design. Could I still use it? Bill Blenkinsole via email Yes, but . . . the UPS itself will work siliconchip.com.au fine, however the Arduino will not be able to shut down the inverter in the event the batteries run down. If the inverter has an internal lowvoltage cutout, this case may provide some protection for your batteries. If there is no low-voltage cutout, then you run the risk of over-discharging the batteries. The inverter will continue to run even when the UPS is shut down, meaning the batteries may be slowly discharged if you wish to store or transport the UPS. The simplest solution may be a (large!) relay or switch on the 24VDC supply brought out onto one of the panels to allow the inverter to be manually shut down. A relay fed from the Arduino’s VIN and GND connections would control the relay in an appropriate manner, but we suspect a relay large enough to switch 24V (into a large capacitor on the inverter) at up to 40A might place an excessive load on the 12V supply circuits. LiFePO4 batteries are expensive I saw your article in the May 2018 issue about building your own UPS and I thought it was a great idea. So I started ringing suppliers to put together the items I would need to build it. I was shocked when I found out that the batteries alone would cost over $1000! How can it be competitive with commercial devices when they're so expensive? I can buy an Eaton UPS with a high power output for well under $1000. DT via email Well, we did say up-front (in the very first sentence!) that it would not be cheap to build. However, if you hunt around you should be able to get the specified LiFePO4 batteries in Australia for well under $500 each (hint: phone Master Instruments!). The fact remains, though, that lithium-based rechargeable batteries are still considerably more expensive than leadacid types. But they do have considerable performance advantages; primarily, a much longer lifespan if regularly deeply discharged. We asked Duraid about how the cost of building our design compared to similar commercial units and he found the following: Australia’s electronics magazine • The closest commercial equivalent to our design that Eaton has is the 5P1550GR-L which is a rackmount UPS with 1100W output and it uses lithium-ion rechargeable batteries. Its list price is US$2590 ($AU3450) – you could definitely build ours for significantly less. • They offer no information on its battery capacity or runtime, however, given that the volume of its case is around one-quarter of ours, and indeed not much larger overall than the total volume of the batteries we used, we don't think it would operate for as long as our unit. • The Eaton 5P3000RT is a larger unit (similar in size to our design) that uses lead-acid batteries. It has a very high power output (up to 2700W) but considerably lower battery capacity. It appears to have around 270Wh of batteries, ie, just a little over half that of our design and so its runtime is substantially lower by comparison, for a given load power. The cost is US$2106 ($AU2800); more than ours would cost to build. • The Eaton 5P1500R is a one-rack unit lead-acid based UPS. It costs US$1308 ($AU1750); similar to what it would cost to build our design (perhaps slightly less). It also has a similar power rating at 1100W. But its runtime is very poor, as it only has around 160Wh of batteries. At 788W, it would last only eight minutes; our UPS will last around four times as long! • The story is similar if you look at products from other manufacturers. So while our UPS design may be somewhat expensive to build, it's still cheaper than its direct commercial equivalents, at least at list prices and uses better battery technology than about 99% of commercial UPS designs. • If the cost of the batteries we specified still puts you off, there is nothing stopping you from building it with cheaper lead-acid batteries. The total cost would almost certainly be under $1000 then, for a unit which would still outperform all the above (more expensive) commercial devices. You would need to use a different battery charger and it would be heavier but it would still be a worthwhile exercise. SC July 2018  81