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ALTERNATIVE POWER REGULATOR Here’s a cheap, simple shunt regulator that’s ideal for use with alternative power generation systems, whether they be wind, solar, hydro . . . you name it. It will prevent your batteries from being cooked by over-charging and can even assist with hot water or other heating. Article by Ross Tester siliconchip.com.au June 2005  61 H ave you decided to generate some power yourself? It’s becoming more and more popular these days, especially as politicians keep making noises about soaring energy prices – and alternative energy generation equipment keeps getting cheaper and cheaper. For most people, the choice is solar or wind generation. Not too many people have a sufficiently reliable stream running through their back yard; even less would be allowed to dam it to get the head required. And then what happens in a drought? Solar is practical pretty much anyware the sun shines, as long as there is a large enough area with a good solar exposure. However, it is still relatively expensive and we understand government subsidies have now all but disappeared. We looked at the economics of solar power in some detail – and generated some heat ourselves – back in March 2002. Unfortunately, wind generation is not exactly suitable for the quarter-acre block in the suburbs. Uninformed (dare we say ignorant?) councils don’t like the idea of towers being erected in the back yard nor do they like those big spinning things which can upset the neighbours. But for anyone in a windy area in the sticks, especially those off the electricity grid, generating your own power from the wind is most definitely a practical solution these days. In fact, we described just how to do that yourself using a modified washing machine motor in a series of articles between December 2004 and March 2005 (back issues of these or the March 2002 issue of SILICON CHIP are available at $8.80 each inc GST and p&p). In addition, several suppliers now have efficient, effective wind generation kits available. While, say, 250500W doesn’t sound all that much, if you are in a relatively constantly windy area, that is certainly enough to keep your batteries charged and give you power when you want it. Aaah, the batteries! It’s often the last thing would-be alternative energy generators think about. After all, actual generation is the most important part of the equation, right? Yes . . . and no! Sure, you need to be able to capture nature’s energy but what do you do with it once captured? Unless you have some means of storing that energy – ie, batteries – it won’t be available when you want to use it. So it is lost – and a lot of that money you have spent is just wasted. But you can’t just chuck any old battery, such as a car battery, into the system and expect it to work properly. For a start, you need batteries designed to operate with deep discharge and charge cycles. You’re probably going to need more than one battery, especially if you run a system delivering more than the “usual” 12V (and for best efficiency, you should). Deep discharge batteries are available – in fact, most manufacturers now make batteries specifically intended for alternative energy/energy storage applications. But they are expensive – much more so than the producedin-their-millions automotive batteries. (Car batteries are designed for a short, high current discharge which does not upset them too much, as long as they are recharged immediately – which of course they are, from the car’s alternator. Start deep discharging a car battery and its life will be measured in weeks, not years, as they normally are.) The other thing that upsets batteries, of any description, is incorrect charging. Sometimes it is insufficient charging but more often than not it’s over-charging. When a battery is over-charged, it heats up. Its electrolyte evaporates (sometimes, it actually boils away) and you’re left with a large, unattractive paper weight, permanently and terminally damaged. When you have spent hundreds (perhaps even thousands) of dollars on storage batteries for an alternative energy system, that hurts. It’s enough to make you cry! Our regulator That’s where this little circuit comes in. It simply won’t let your batteries be overcharged. Once they reach the fully charged state, it switches incoming current into a dummy load (or several dummy loads if you wish). While in the prototype shown here the heat generated is simply vented to air (with fan assistance) there is nothing to stop you using that otherwise wasted energy to, say, heat water. Depending on how much energy is dumped into the dummy load, you may not get too much of a temperature rise in the tank – but any increase is good and it’s much better than wasting the energy. Here’s the shunt regulator, mounted in a junk case with dummy loads and cooling fan. It’s just one possible arrangement. 62  Silicon Chip siliconchip.com.au 120k LINK FOR 12V 22k C Q1 2N5551 C B Q2 2N5551 22k B E V+ OPTIONAL FAN TERMINALS + ZD1 15V 12nF E Q6 SDP55N03L D G S Q7 SDP55N03L D G S Q8 SDP55N03L D G S Q9 SDP55N03L D G + – – 47k 100k 1 +5V 8 100 µF A 100k 6.8k 120k VR1 2k IC1 L4949 2 LED2 1 2 1k 7 12k 22nF K 10 µF IC2a 5 6 5 A 100 µF λ K 12k 14 12k 12 3 10k B D1 1N4148 B C 1M Q5* BUZ71 IC2: 4093B 9 IC2d 10 3.5 Ω LOAD† L2 3.5 Ω LOAD† L3 3.5 Ω LOAD† L4 S E C † PART JUG ELEMENTS – SEE TEXT + E A 100 µF – ZD2 15V D G S 7 GND V– * OPTIONAL: REQUIRED ONLY IF COOLING FAN CONNECTED 2N5551 K 2005 Q3 2N5551 K 8 SC  Q4 2N5551 11 4 10k A IC2c 13 IC2b 1k LEDS λ LED1 3.5 Ω LOAD† L1 V+ (TO STORAGE BATTERIES) 1N4148 C B E SHUNT REGULATOR A ZD1, ZD2 – BUZ71 K D + G S SDP55N03L D S G D The circuit mainly consists of a 5V regulator/comparator, some NAND gates and MOSFETS which switch in dummy loads. We’ll look at the dummy load (actually made with wire jug elements) shortly. At the heart of this circuit is a 5V voltage regulator (IC1, an L4949). Its claim to fame is that it has a very low dropout voltage but also has additional functions such as power-on reset and input voltage sense. In this design the voltage-sensing comparator section and the 5V regulator are used. The system voltage is sensed via the voltage divider across the supply/ batteries with VR1 adjusting the exact voltage as required. (The top two resistors are only used for 24V systems). When the voltage at the wiper of VR1 (and therefore pin 2, the input voltage sensor of IC1) falls below 1.24V, the open-collector output (pin 7) is internally pulled to 0V. Therefore the 10mF capacitor charges to 5V via the 1kW resistor between it and pin 7. This presents a logic “0” to the input pins of both of the Schmitt NAND gates IC2a and IC2b, resulting in a logic “1” at both their outputs. IC2c, another siliconchip.com.au Schmitt NAND gate, has its inputs connected to IC2a’s output, so it has a logic “0” at its output. This turns Q3 off, which turns Q4 on, resulting in a low voltage at the gate of MOSFETs 2, 3, 4 and 5. Therefore they remain off, which means no current can flow through the dummy loads. When the batteries are fully charged, the voltage at Pin2 of IC1 will rise above 1.24V, so the opposite of what is detailed above occurs: IC2a and IC2b’s outputs go low, IC2c’s output goes high, turning on Q3 and turning off Q4. The MOSFETs now have gate voltage and are thus turned hard on, resulting in current flow through the dummy loads. The circuit remains in this state until the battery voltage falls below your pre-set trip point. There are several other components in the circuit which we haven’t considered yet. We mentioned IC2b but nothing after it. When its output goes high, the 100mF capacitor at the input to IC2d discharges via the 10kW resis- tor and the forward-biased D1. IC2d’s inputs are therefore low, resulting in its output being high. This provides gate voltage for MOSFET 1 which in turn switches on and allows a 12V or 24V fan to run, cooling the dummy loads. This is done so that the fan itself doesn’t draw power from the batteries when it is not required. While only a small drain (most fans of this type are <100mA) it would be constant and therefore would be wasteful of power. Note too that the fan is only required if you are not doing anything else with the heat from the dummy load(s). Regulator’s regulator Transistors Q1 and Q2, in conjunction with zener diode ZD1 form a simple 13.8V voltage regulator for IC1, which has a maximum supply of 28V. It is quite possible that this limit would be exceeded in a 24V system so the low-cost regulator is included. On a 12V system the voltage regulator isn’t required because this circuit keeps the battery voltage within safe levels (the supply to IC1 pin 1 would June 2005  63 Q4 Q3 2N5551 2N5551 SDP55N03L Q9 + + 100 µF Q8 L1 ZD2 SDP55N03L L1 L2 D1 1M 12k 10k 10k 4148 15V 12k 15V 1 V+ L2 L3 2N5551 SDP55N03L Q7 22k K ZD1 1 100 µF K 12nF 22nF + IC2 4093B 12k 1k 100k 1k IC1 L4949 2k Q5 BUZ71 Q1 2N5551 Q6 Q2 47k 6.8k 120k VR1 + LED2 L3 L4 100 µF 10 µF + LED1 100k 120k 22k – + 12V USE L4 – FAN LINK FOR V– SDP55N03L simply be about 1.2V less than the battery voltage). However, if the battery voltage goes above 15.2V, the regulator comes into action supplying 13.8V to the IC. Finally, the two LEDs (LED1 and LED2) operate as part of the IC2 gate circuits to indicate charging and charged states respectively. While on the prototype these LEDs were mounted on the PC board, they would normally be extended out to a panel. Hysteresis Component overlay with the same-size photograph below. The link is only required for 12V operation and can be a resistor lead offcut. As we said before, VR1 sets the exact trip point at which the regulator comes into play. While it is normal practice to set a car regulator to deliver 13.8V, it appears that it is normal to set a storage system to a float charge of about 15V. The circuit has in-built hysteresis so that it doesn’t continually “hunt” around that 15V figure. Only when the battery voltage drops to about 14V (ie, about 1V below the trip point) will the circuit turn off and the load be disconnected. Construction Parts List – Shunt Regulator 1 PC board, 98 x 47mm, coded K222 2 3-way PC board mounting terminal blocks 1 2-way PC board mounting terminal block 4 3.5W dummy load (see text) 1 12V (or 24V) fan (optional – see text) Heavy duty red & black hookup wire for connection to battery Semiconductors 4 2N5551 NPN transistors (Q1-Q4) 5 SDP55N03L power MOSFET (Q6) 2 15V 400mW Zener diode (ZD1, ZD2) 1 1N4148 small signal diode (D1) 1 L4949 monolithic 5V voltage regulator and comparator (IC1) 1 4093 quad Schmitt trigger NAND gate 1 5mm red LED (LED1) 1 5mm green LED (LED 2) Capacitors 2 100mF 33V PC mounting electrolytics 1 10mF 33V PC mounting electrolytic 1 12nF (0.012mF) polyester 1 22nF polyester Resistors (0.25W, 5%) 1 1MW 2 120kW 1 47kW 2 22kW 2 10kW 1 6.8kW 64  Silicon Chip 2 100kW 3 12kW 2 1kW There’s not much to the assembly. As usual, start with the lowest-profile components (resistors, diodes) and then move onto the capacitors, transistors and MOSFETs and finally the ICs. Check resistor values with a digital multimeter if you aren’t sure of their values. If you are using IC sockets, make sure you get the notch the right way around! Use a resistor lead offcut to form the 12V link, if needed. The final components to be soldered in are the terminal blocks, the potentiometer and the LEDs. As we mentioned before, the LEDs would normally be mounted off the PC board – use some thin hookup wire or rainbow cable to make flying leads – but watch the polarity! The dummy load(s) The Oatley Electronics kit does not contain any dummy loads – because each installation is different, these are left up to you. The SDP55N03L MOSFETs provided have an “on” resistance of around 11mW and a current rating of 50A. For a dissipation of 0.5W in the MOSFET, a current of 7A can be passed without a heatsink. If a small (eg, clip-on) heatsink is provided, the power can be more; with a decent heatsink much more. However, you would soon start to run into problems with the thickness of the PC board tracks, even if solder-coated. We have specified the dummy loads to have a resistance of 3.5W. While you can buy high power resistors of this type, a much cheaper (and in fact better) alternative is to make your own from electric jug elements. These consist of a coil of coiled resistance wire, wound on a ceramic former. In their 240V electric jug incarnation, they have a DC (cold) resistance of about 34W. Naturally, we need a lot less than that in a 12V or 24V system. The elements we used were “Phoenix” brand, cat no EJ2, as found in most hardware stores and supermarkets. Oatley siliconchip.com.au A possible arrangement for the dummy loads – note the fan blowing cold air across them. The coils here have not been straightened nor doubled (as explained in the text). Electronics will also have these available for $2.50 each (probably cheaper than you can find elsewhere!). Even though the photos show coiled coils, you don’t need them, so remove the wire and stretch it out until it is straight. Twist the two ends of the wire together and find the midpoint. Using an electric drill on a slow speed, twist the two lengths of wire together over their entire length. Simply grip the two loose ends in the drill chuck, hold the opposite end firmly (a vyce is a good idea!) and hold the length reasonably taught as you turn the drill on. A couple of short bursts will twist the strands together nicely. As you halved the original 34W wire, that means each strand is about 17W. Now twisted together, those strands are effectively two resistors in parallel, so the length of wire is now about 8.5W. You need a bit less than half that length to get to around 3.5W. Connect one multimeter lead to one end of the wire and simply drag the probe along the wire until it reads 3.5W. Add, say, 20cm to this to allow for terminations. Wind this length back on to the ceramic former and terminate it under the screw terminals. Check again that you have about 3.5W (it doesn’t need to be spot on). As we mentioned before, it’s a shame to waste the energy you’ve generated so if you can, immerse the dummy load(s) in your hot water tank to use the energy there. Otherwise connect a suitable fan to the fan terminals on the PC board so that the heat is removed from the system. Setup All you need to do is monitor your battery voltage on charge and adjust VR1 so that the regulator kicks in when the battery voltage reaches the required maximum (usually 15V). Keep monitoring the voltage while the battery discharges and ensure that when it reaches 14V the regulator switches off. Our photograph shows four dummy loads mounted in a surplus steel case which conveniently had a 12V fan already fitted. A gutted, dead, computer power supply case (but keep its 12V fan) would also be ideal. We cut most of the mounting wires off the four modified jug elements and bent those wires out 90° to allow them to be mounted in a pair of 7-way mains terminal blocks (each second terminal used). These blocks were themselves mounted in the case to siliconchip.com.au allow maximum airflow from the fan. Of course, this is all academic if you decide to use the dummy loads as water heating elements in their own right! 24V systems We’ve described operation for a 12V system but 24V systems are probably more common than 12V. The reason is simple: higher voltage equals lower current; lower current equals less line losses. In fact, 48V systems are not at all uncommon; beyond this you are starting to get into the “danger Will Robinson!” area, especially for the handyman with little technical background. Like it or not, that’s precisely the sort of person who is most likely to be building an alternative energy power system! Construction and setup are the same for 24V systems as for 12V, with the exception of the “12V” link. This time, though, you’d be looking for a kick-in at about 28V and a SC dropout 1V less. Where from, how much? This project was designed by Oatley Electronics, who retain the copyright and PC board design copyright. Complete kits (with all on-board components but no dummy loads) are available from Oatley Electronics, PO Box 89, Oatley, NSW 2223 (Tel [02] 9584 3563, Fax [02] 9584 3561, website www.oatleye.com) for $26.00 inc. GST, plus P&P. Phoenix jug elements are available at $2.50 each. June 2005  65