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Using Electronic Modules with Jim Rowe Mini Uninterruptible Power Supply (UPS) If there’s a blackout when using your computer, it might keep running (eg, off its internal battery or a UPS) but what about your WiFi router? It will likely drop out and not come back until power is restored. This low-cost UPS module can keep it going as well. M ost consumer-grade uninterruptible power supplies (UPSs) have similar configurations, with a storage battery that’s charged when mains power is available and switched to running an inverter to replace mains power when it fails. Many use a sealed lead-acid (SLA) battery to store the energy. In most cases, the switchover takes only 10-25ms, which usually doesn’t cause problems with loads like PCs or LCD monitors. When delivering power from the battery via the inverter, most UPSs can do so for at least 20 minutes, even when the load requires its full rated output power. That is generally enough to allow you to save your work and shut down the computer safely. The mini UPS module we’re looking at here is a bit different from that. It is intended to provide continuous 9V or 12V DC power to small electronic devices like WiFi routers while being powered from 5-12V DC. It can supply up to 12W of output power continuously, making it suitable for powering most WiFi routers and many other small devices. Instead of a sealed lead-acid (SLA) battery, it uses a small lithium-ion battery like a single 18650 cell, which is much smaller than just about any leadacid battery. All of the mini UPS module’s circuitry is on a PCB measuring 50 × 20mm. It doesn’t have an onboard battery holder; the Li-ion battery (which is not supplied) is intended to be connected alongside it. We obtained the module pictured from an AliExpress supplier called ACELEX, which had it available for only $2.01 plus shipping. Another supplier on AliExpress called MOKCUM seemed to have an identical module for $4.02 plus shipping – twice the price, but still surprisingly low. From the supplier’s photos, the MOKCUM module is set to produce a Fig.1: the block diagram for the mini uninterruptible power supply (UPS) module. It is a straightforward design with only two main sections. 24 Silicon Chip Australia's electronics magazine 9V DC output, whereas the ACELEX module produced an output of 12V DC as received. However, as we’ll explain shortly, the modules can be easily changed to produce either output voltage. How it works After examining the module’s PCB, I was able to glean enough information to produce the basic block diagram shown in Fig.1. There are two main circuit sections; on the left is the lithium-ion charging circuit, while on the right, there is a DC/DC step-up (‘boost’) converter. The offboard Li-ion cell connects to the lines between the two sections. The charging circuit accepts the incoming 5-12V DC input power and produces a regulated 4.2V DC output to charge the Li-ion cell while also driving the step-up converter to provide either 12V or 9V to the load on the right. Link JP1 lets you switch the step-up converter’s output between 12V and 9V. When a solder bridge links its pads, the module delivers 12V to the load; when they are not linked, it delivers 9V instead. Link JP2 changes the maximum charging current for the Li-Ion battery. If the pads are not joined by a solder bridge, the maximum charging current is limited to 500mA (0.5A); if they are linked, the maximum charging current is 1A. Most 18650 cells can happily charge at 1A (well under 1C for their typical capacity), but if you are unsure, you can leave it at the safer 500mA setting. For small LiPo cells like those used siliconchip.com.au Fig.2: the wiring diagram for the mini UPS module. Multiple cells can be wired in parallel if required. in mobile phones, it’s best to leave the JP2 pads open. If you want to use a large cell or several cells in parallel, you will probably want to go for the higher charging current. The LEDs shown at upper left in Fig.1 are not supplied with the module, but are regarded as an ‘optional extra’. The sketchy data provided with the modules suggests that you should fit a common-anode dual red/blue LED (even though the legends on the PCB show R−, + and G−), but of course, you can use a red/green LED or even two separate 3mm LEDs. The blue (or green) LED indicates whether a load is connected to the output of the module, while the red LED indicates the charging state of the Li-ion battery. If the red LED is flashing, no battery is connected; if it is on continuously, the battery is being charged; if it is off, it is fully charged. Fig.1 shows no circuitry to perform the switchover to battery power when the mains-derived input power fails. That’s because there is no switchover as such. The Li-ion battery is already connected to the input of the step-up converter, so it will provide current and power when needed. No switch­ over time at all! battery and a low-voltage load like a WiFi router is quite straightforward, as shown in Fig.2. The incoming DC supply connects to the IN+ and IN− pads on the left, the output load to the OUT+ and OUT- pads on the right, and the Li-ion battery to the B+ and B− pads at bottom middle and bottom right. If you want to add a couple of LEDs (or a dual LED), these can be added at centre left, as shown. Just make sure you use high-efficiency LEDs because the driving currents are low. Link JP1 is just to the left of the output pads, as indicated by the red circle. It’s shown linked by a solder bridge, so the boost converter provides a 12V DC output. If you want 9V instead, simply remove the solder bridge with a soldering iron and some solder-­wicking braid. However, note that diode D1 connects the input to the output, so if you set the unit up for a 9V output, you can’t use a 12V supply. Link JP2 at lower left is indicated by the second red circle. As shown in Fig.2, it usually comes without a solder bridge, limiting the battery charging current to 500mA. It’s best to leave it this way unless you know your battery can handle charging at 1A. By the way, the B−, OUT− & IN− terminals are not all connected together, so make sure your supply, load and battery have independent grounds or else the circuit will not work. Trying it out To check out the module, I powered it from a standard 5V DC, 1A plugpack and connected its output to a programmable DC load. I then fired up my bench DMMs and connected one to measure the module’s output and the other to measure the Li-ion battery voltage. Silicon Chip kcaBBack Issues $10.00 + post $11.50 + post $12.50 + post $13.00 + post January 1997 to October 2021 November 2021 to September 2023 October 2023 to September 2024 October 2024 onwards Hooking up the module to a low-­ voltage power source, a lithium-ion All back issues after February 2015 are in stock, while most from January 1997 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com.au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 siliconchip.com.au Australia's electronics magazine Setting it up February 2025  25 The mini UPS module is compact, measuring 50 × 20mm; the photos above are enlarged for clarity. The module is typically supplied as shown with JP1 bridged, JP2 unbridged and no LED(s). After making sure the sole Li-ion 18650 cell was fully charged, I switched off the input voltage and tested its performance at both output voltages, with load currents of 100mA, 200mA and 300mA. These tests took a few hours, and the results are summarised in Fig.3. The red/mauve and cyan/blue lines show the module’s output voltage at either voltage setting and for the tested load current levels for up to three hours from the removal of input power. For the lightest loads, 100mA in both cases, the output voltage at either setting remained essentially constant for more than two hours after input power removal. That corresponds to a load power of 1.2W at the 12V voltage setting and 0.9W at the 9V setting. There was no significant voltage droop over this time. In fact, the voltage on both settings remained within ±2mV for the duration of the tests. However, it did not last quite as long with a load drawing more current. On the 9V setting, with the load drawing 200mA, the cell voltage fell to 3.2V and I terminated the test after around 2.5 hours. I repeated the test at 300mA, which naturally gave a shorter runtime, and also with the output set to 12V, which also reduced the runtime. With the UPS module fed with 12V from a big bench supply (rated at 5A), and two charged 18650 cells in parallel, the module delivered 600mA to the load at 12V for about 10 minutes before the battery voltage dropped to 3.095V. With a third 18650 cell in parallel and the load current increased to 800mA, even with fully charged cells, the unit could only supply 12V to the load for about 5 minutes before the cell voltage dropped to 2.97V and I turned it off. The small inductor in the output boost converter became very hot in that short time. So the Mini UPS module is really only really suitable for loads up to 600mA, even with three 18650 cells in parallel. It may be rated to supply 1A, but it wouldn’t be able to do so for a useful time. That’s probably enough to power the average WiFi router; many are supplied with a 1A plugpack, although I doubt they draw anywhere near that upper limit unless they are going ‘flat out’. This UPS should be able to power your WiFi router in a blackout for long enough to make it worthwhile with sufficient battery capacity, although that is the kind of thing you should test if you are going to rely on it. Conclusion This module is nicely made, low in cost, has no switchover time and performs reasonably well, with the ability to power low power (<12W) DC loads like WiFi routers for about 10-60 minutes, depending on how much current SC they draw. Fig.3: test runs to see how long it would take the module to discharge at 100mA, 200mA & 300mA loads. The unit can deliver up to about 600mA (a little short of the 1A advertised) with reduced runtime unless larger/more cells are used. 26 Silicon Chip Australia's electronics magazine siliconchip.com.au