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Constructional Project Project by John Clarke Repurposing the Mains Power-up Sequencer Generators and inverters are not always powerful enough to run more than one high-current appliance at a time. For example, if you have more than one refrigerator or a separate freezer and fridge and want to run them off-grid, they may need to run at different times. The Mains Power-Up Sequencer from the February & March issues can be programmed to do that automatically. T he Mains Power-Up Sequencer from the February & March issues earlier this year was intended for powering up appliances in sequence with brief delays in between to avoid overloading a circuit breaker at switch-on. However, the fact that each outlet is controlled independently by a microcontroller means that the way each outlet is controlled can be changed with new software. We hadn’t considered this second application until a reader wrote to us. In part, he wrote: Say a business has several fridges/ freezers to run from a small emergency power source. It would be very useful to be able to sequence the output to several loads for varying periods, like 15 or 20 minutes, making it unnecessary to manually switch loads to avoid overloading a generator or inverter. A shortlist of features » Powers on two to four mains outlets individually in a rotating sequence » Adjustable powered-on period of eight seconds to 30 minutes » Optional daisy-chain connection for up to four more outlets (up to eight total) » ‘Phantom Appliance’ load detection option (for up to four outlets) 52 Happily, we can satisfy this request. The re-purposed version of the project mainly requires the microcontroller software to be changed, plus some minor wiring adjustments. Three options Three new versions of the Sequencer are described here, all using the same revised software. The first is called the Primary unit (see Fig.1). It operates with a rotating sequence, switching on Outlet 1 for a period, then switching it off before switching on Outlet 2 for the same period. This sequence continues for all outlets, and when Outlet 4 switches off, the sequence repeats. The power-on period is adjustable from eight seconds to 30 minutes. The eight-second period is mainly useful for testing the unit to see if it works without waiting too long. As with the original Sequencer, you can build it to have fewer than four outlets. If only two or three are required, it will return to Outlet 1 after Outlet 2 or Outlet 3 switches off. The second version operates similarly to the Primary version but includes current detection. When an outlet is first powered, it monitors the current drawn. If an appliance draws power, the outlet stays powered. The outlet switches off after the timeout period, or earlier if the appliance draws less than 35W. We call this the Phantom Appliance Detection (PAD) mode, where only the outlets that have an appliance connected (or are ready to run in the case of a fridge or freezer) will be included in the sequence. This mode can be useful for powering refrigerators and freezers because they don’t run constantly. Powering an outlet for an appliance that is not doing anything useful wastes time, since it could power the next fridge or freezer instead. Also, the fridge or freezer may finish running its compressor before the timeout expiry. In this case, the PAD unit will move on to power the next appliance early. This mode is also useful where you have the four outlets on the Sequencer, but you may sometimes only use it for two or three appliances. The Sequencer will skip over the unused outlets, and you won’t have to manually change the configuration to set the number of outlets used. It also gives you the flexibility to switch one or more loads off when you want them to be skipped. Daisy-chain mode The third configuration, Daisy Chain, can give you more than four outlets (up to eight). Daisy-chaining is impractical for PAD units; only the Primary unit can be daisy-chained. That is because the AN4 input of microcontroller IC9 used to enable daisy chaining is also Practical Electronics | July | 2025 Repurposing the Mains Sequencer Mains Power Input To power point Primary or Phantom Appliance Detect unit software but run different sections of the code. The software checks the RA3 and AN4 inputs to the microcontroller at power-up. If the RA3 input is low (near 0V), the software runs for a PAD unit, while if RA3 is high (5.1V), either the Primary or Daisy Chain code runs. To discern between these two options, it checks the AN4 input. If the voltage is low, the software determines it is a Daisy Chain unit. If the AN4 input is above the threshold voltage for mains voltage detection, it runs the code for a Primary unit. It is important to build the Sequencer according to the build details for the version you are making so the software runs correctly. SILICON CHIP Mains Power-Up Sequencer OUT1 OUT2 OUT3 OUT4 Appliance 1 switched on then off Appliance 2 switched on then off Appliance 3 switched on then off Appliance 4 switched on then off Building it Fig.1: when used as a Primary unit, it continually sequences through up to four outlets, switching them on for a fixed time in turn. The PAD unit is similar, except it will only switch on outlets with an appliance connected and drawing at least 35W. Otherwise, after a 1s delay, it skips that outlet. used for current detection on a PAD unit, and it can’t perform both jobs simultaneously. Fig.2 shows how a Daisy Chain unit is connected to the Primary unit. The Daisy Chain unit monitors the last outlet from the Primary unit via its Mains Detect Input. Its Outlet 1 is powered after the last outlet from the primary unit (shown as Outlet 4) powers on and then off. The Daisy Chain unit then powers each outlet on and off in sequence, stopping after the last outlet. When used in this mode, the Primary unit powers each outlet on and off in sequence, but after powering Outlet 4 off, there is a delay before powering Outlet 1 again. That gives the Daisy Chain unit time to run its complete sequence. We call this delay the return delay, and it is set so that the Daisy Chain unit finishes its entire cycle before the Primary unit starts the cycle again. The return delay can be selected as between one to four times the usual delay period that is set with VR1. That allows you to build the Daisy Chain unit with between one and four additional outlets, with the delay multiplier on the Primary unit set to match the number of outlets on the Daisy Chain unit. Version selection The three versions use the same OUT1 OUT2 OUT3 OUT4 Double adaptor or Piggy-back Appliance 1 Appliance 2 Appliance 3 Appliance 4 mains plug switched on switched on switched on switched on then off then off then off then off Mains Power Input Fuse 10A Mains Power Input Fuse 10A SILICON CHIP Mains Power-Up Sequencer Daisy Chain Sequencer To power point SILICON CHIP Mains Power-Up Sequencer OUT1 OUT2 OUT3 OUT4 Mains Detect Input Fuse 1A Primary Sequencer To power point This article mainly describes the changes required for the new functions, so for the full PCB assembly instructions, you will need to refer to the articles in the February & March 2025 issues. Those articles describe various build options. You can build a unit with between one and four mains outlets (see Table 1), and the optional Current Detection and Mains Voltage Detection circuitry may need to be included. With the new software, switches S1-S3 provide functions different from the original Mains Power-Up Sequencer, as shown in Table 2 and Table 3. VR1 is now only used to adjust the poweron period for each outlet. The wiring and PCB changes for all three versions are shown in Fig.3. In all cases, the two connections at CON7 are bridged using 10A mains wire. Appliance 5 Appliance 6 Appliance 7 Appliance 8 switched on switched on switched on switched on then off then off then off then off Fig.2: for more than four outlets (up to eight), you can connect a Daisy Chain unit to a Primary unit, as shown here. The Daisy Chain unit is triggered when the last Primary outlet switches off; the Primary unit waits for the Daisy Chain unit to finish before restarting the sequence. Practical Electronics | July | 2025 53 Constructional Project Photos of the completed Mains Power-Up Sequencer before of any of the modifications in this article have been made. Changes to the hardware are minimal. Current transformer T1 is only used for the PAD unit, with the mains Active wire passing through T1’s core. The snubber components for the OUT1 circuitry across TRIAC1 are a 10nF X2-rated capacitor for C1 and a 330W 1W resistor for R1. Do not use the alternative 220nF X2 rated capacitor and 470W 1W resistor values mentioned in the original articles. Microcontroller IC9 must be programmed with the revised software, coded 1010823M.hex. You can download the HEX file and assembly language source code (siliconchip.au/ Shop/6/358) and program the chip using a PIC programmer. Or you can purchase a programmed microcontroller from the Silicon Chip website. The above components and wiring changes are common to all the revised versions, but specific modifications Table 1 – setting the number of outlets (for all units) # outlets RA1 (pin 18) RA0 (pin 19) 4 (default) 0V (PCB bottom layer) 0V (PCB bottom layer) 3 0V (PCB bottom layer) 5.1V (PCB top layer) 2 5.1V (PCB top layer) 0V (PCB bottom layer) 1 5.1V (PCB top layer) 5.1V (PCB top layer) 54 are required for each version, as described below. Primary unit For the Primary unit, the current and voltage detection sections are left unpopulated. The mains Active wire shown going through the current transformer for the original Sequencer instead goes directly to CON6. Place a wire link between pins 4 and 5 of the pads for IC11 so that the Sequencer will run the Primary unit version of the code at start-up. You can select the number of active outlets by making the linking options as shown in Table 1. Set VR1 for the required on-period of each outlet. Fully clockwise sets a 30-minute timeout; a mid setting is about 15 minutes. If the Primary unit is not being used with a Daisy Chain unit, set switch S3’s Table 2 – return delay setting Return delay S3 position No Left (open) Yes Right (closed) Table 3 – return delay multiplier (for daisy-chained Primary unit) Multi. S1 position S2 position ×4 Left (open) Left (open) Right (closed) Left (open) ×2 Left (open) Right (closed) Right (closed) Right (closed) ×3 ×1 lever to the left, so there is no return delay (see Table 2). The switch positions for S1 and S2 do not matter for this version. If the Primary unit is used with a Daisy Chain unit, set switch S3’s lever right so there is a return delay (see Table 2). The return delay setting is made using switches S1 & S2, as shown in Table 3; select the ×4, ×3, ×2 or ×1 delay multiplier to match the number of outlets used on the Daisy Chain unit. Daisy Chain unit The Daisy Chain unit requires the voltage detection circuitry to be installed, with no wire link between pins 4 & 5 of IC11’s pads. You can select the number of outlets installed in the Daisy Chain unit as per Table 1. Set VR1 for the required power-on period of each outlet, but ensure it is slightly less than the period set for the Primary unit. Set switch S3 for the Daisy Chain version with the lever to the left so there is no return delay (see Table 2). The switch lever positions for S1 and S2 do not matter for this version. Phantom Appliance Detect (PAD) unit The PAD version requires the current detection circuitry to be installed, with the Active wire from CON5 looping through current transformer T1 before terminating at CON6. You will also need to connect a wire between the 0V test point and the bottom of the 10kW resistor that conPractical Electronics | July | 2025 Repurposing the Mains Sequencer NOTES Use 10A mains wire except for CON8 to CON9, where 7.5A wire can be used. Also Earth lead should be one continuous length with insulation removed at each GPO Earth connection. OUT1 OU T 3 OUT2 OUT4 Dashed active wiring is for primar y and daisy chain versions. Active wiring via T1 is for phantom appliance version. MAINS IN 470nF X2 Secure IEC connectors using Nylon screws A N C U R R EN T DETECT MA S T ER 1kW 5W CON 7 OUTPUT2 OUTPUT3 N A N A N A OUTPUT4 CON4 N A RT334730 + + COIL COIL COIL COIL RLY4 RT334730 RLY3 RT334730 RLY2 RT334730 (DAISY CHAIN OUT) CON3 CON 2 CON1 RLY1 – ~ OUTPUT1 B R1 W04 ~ 1MW 1W ZD1 5.1V 10kW IL4208 IL4108 IL4208 IL4108 IL4208 RA 1 RA 0 NON-DETECT O U T3 A OUT4 S3 100nF O U T2 NO DELAY A LED4 OUT1 10nF X2 Wire link for phantom appliance version A LED3 A IC9 PIC16F1459 LED2 POWER LED1 A TP 5.1V LED5 + 1kW 1W 10mF CURRENT/DAISY CHAIN DETECT S1 S2 SWITCH OFF SWITCH ON TP 0V 10kW 1.5kW IC11 4N25 10mF 680W IL4108 750W IL4208 750W IL4108 100nF IC8 680W IC7 750W IC6 10kW ~ 10nF X2 330W 1W IC5 100kW 4.7kW ZD2 12V CON 9 22nF X2 – ~ 330W 1W IC4 SILICON CHIP Link for primar y version (voltage detection not required) 10nF X2 330W 1W IC3 230V AC BR2 W04 330W 1W 10nF X2 330W 1W IC2 680W 10mF 10mF ALL PARTS AT 330W 1W TRIAC4 300W IC1 750W CAUTION! 1MW 1W Daisy chain version requires voltage detection section 10nF X2 330W 1W 300W Cable tie L4 680W IC10 330W 1W 300W TRIAC3 1kW 1W CON8 300W TRIAC2 10nF X2 Cable tie L3 1kW 1W 18kW TRIAC1 10nF X2 Cable tie L2 1kW 1W 15kW 10nF X2 Cable tie L1 CURRENT DETECTION COMPONENTS P4KE15A 30kW 10kW MCP6272 IEC CONNECTOR TVS1 20kW 2.2kW L4 L3 L2 1kW 1W Phantom appliance version requires current detection circuitr y L1 T1 CON5 AC1010 1000mF IEC CONNECTOR 1MW 1W CON 6 Join for all versions VR1 10kW START RATE UP DELAY IC9 programmed with revised firmware coded 1010823M.HEX Fig.3: besides reprogramming IC9 with the new software, just a few changes are required to the hardware. Add one of the wire links shown in red if building the Primary or PAD version. The mains Active wire only goes through T1 for the PAD version; otherwise, it connects directly to CON6. nects (through tracks on the PCB) to the pin 4 RA3 input of IC9, as shown above. This informs the software that the unit is the PAD version. With the revised software, the RA3 pin is set as a digital input rather than as a master clear (MCLR) reset line, as it was in the original version of the Sequencer. Put switch S3’s lever left so there is no return delay (see Table 2). The switch lever positions for S1 and S2 do not matter for this unit. Testing As per the original Mains PowerUp Sequencer articles mentioned, all wiring and adjustments must be made with the input mains power disconnected since the circuitry is live when plugged in. Also, any adjustments of the period using VR1 are only detected at power up, so there is no benefit Practical Electronics | July | 2025 to adjusting VR1 with the power on. So, each time you want to make an adjustment, ensure that the power is off before opening the lid of the enclosure. Replace the enclosure lid before reapplying power. If VR1 is set to its minimum fully anti-clockwise position, the period for each outlet will be short, at eight seconds. That makes monitoring and checking its operation easier. You can see the sequencing occur as the indicator LEDs light up for each outlet. For the PAD unit, the output LED indicator for each channel will only light when an appliance that draws power (at least 35W) is detected. That is because only the Triac for each channel is switched on initially, while the current drawn by the appliance is first detected, and the LED indicators only show the relay status. Using the Triac to apply voltage initially saves the relay from operating if there is no current drawn by the appliance, extending the relay life considerably. For the PAD sequence, you can check each outlet by connecting a load that will draw 35W or more, such as a 40W 230V AC halogen lamp. Cycling through outlets that do not have a load connected takes PE one second per outlet. Warning: Mains Voltage All circuitry within the Mains Sequencer operates at Line (mains) voltages. It would be an electrocution hazard if built incorrectly or used with the lid open. Only build this if you are fully experienced in building mains projects. 55