Showing posts with label Solar Power. Show all posts
Showing posts with label Solar Power. Show all posts

‘Green’ Solar Lamp

Category: LED and Light, LED Flasher, Solar Power
Energy saving is all the rage, and here is our small contribution: how much (or rather how little) current do we need to light an LED? Experiments with a super-bright 1 W green LED showed that even one microamp was enough to get some visible light from the device. Rootling in the junk box produced a 0.47 F memory back-up capacitor with a maximum working voltage of 5.5 V. How long could this power the green LED? In other words, if discharged at one microamp, how long would the voltage take to drop by 1V?

‘Green’ Solar Lamp Circuit Diagram

A quick calculation gave the answer as 470 000 seconds, or about five days. Not too bad: if we use the capacitor for energy storage in a solar-powered lamp we can probably allow a couple more microamps of current and still have the lamp on throughout the night and day. All we need to add is a suitable solar panel. The figure shows the circuit diagram of our (in every sense) green solar lamp.


By Burkhard Kainka (Germany, Elektor)
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4 Amps Photovoltaic (Solar) Charge Controller

Category: DC Power Supply, Solar Power
The use of solar photovoltaic (PV) energy sources is increasing due to global warming concerns on the one hand, and cost effectiveness on the other. Many engineers involved in power electronics find solar power tempting and then addictive due to the ‘green’ energy concept. The circuit discussed here handles up to 4 amps of current from a solar panel, which equates to about 75 watts of power. A charging algorithm called ‘pulse time modulation’ is introduced in this design. The current flow from the solar panel to the battery is controlled by an N-channel MOSFET, T1. This MOSFET does not require any heat sink to get rid of its heat, as its RD-S(on) rating is just 0.024 Ω.

Schottky diode D1 prevents the battery discharging into the solar panel at night, and also provides reverse polarity protection to the battery. In the schematic, the lines with a sort-of-red highlight indicate potentially higher current paths. The charge controller never draws current from the battery—it is fully powered by the solar panel. At night, the charge controller effectively goes to sleep. In daytime use, as soon as the solar panel produces enough current and voltage, it starts charging the battery. The battery terminal potential is divided by resistor R1 and trimpot P1.

4 Amps Photovoltaic (Solar) Charge Controller Circuit DIagram
4 Amps Photovoltaic (Solar) Charge Controller Circuit Diagram
The resulting voltage sets the charge state for the controller. The heart of the charge controller is IC1, a type TL431ACZ voltage reference device with an open-collector error amplifier. Here the battery sense voltage is constantly compared to the TL431’s internal reference voltage. As long as the level set on P1 is below the internal reference voltage, IC1 causes the MOSFET to conduct. As the battery begins to take up the charge, its terminal volt- age will increase. When the battery reaches the charge-state set point, the output of IC1 drops low to less than 2 volts and effectively turns off the MOSFET, stopping all current flow into the battery.


With T1 off, LED D2 also goes dark. There is no hysteresis path provided in the regulator IC. Consequently, as soon as the current to the battery stops, the output of IC1 remains low, preventing the MOSFET to conduct further even if the battery voltage drops. Lead-acid bat- tery chemistry demands float charging, so a very simple oscillator is implemented here to take care of this. Our oscillator exploits the negative resistance in transistors—first discovered by Leo Esaki and part of his studies into electron tunneling in solids, awarded with the Nobel Prize for Physics in 1973. In this implementation, a commonplace NPN transistor type 2SC1815 is used.

When the LED goes out, R4 charges a 22-μF capacitor (C1) until the voltage is high enough to cause the emitter-base junction of T2 to avalanche. At that point, the transistor turns on quickly and discharges the capacitor through R5. The voltage drop across R5 is sufficient to actuate T3, which in turn alters the reference voltage setting. Now the MOSFET again tries to charge the battery. As soon as the battery voltage reaches the charged level once more, the process repeats. A 2SC1815 transistor proved to work reliably in this circuit. Other transistors may be more temperamental—we suggest studying Esaki’s laureate work to find out why, but be cautioned that there are Heavy Mathematics Ahead.

As the battery becomes fully charged, the oscillator’s ‘on’ time shortens while the ‘off’ time remains long as determined by the timing components, R4 and C1. In effect, a pulse of current gets sent to the battery that will shorten over time. This charging algorithm may be dubbed Pulse Time Modulation. To adjust the circuit you’ll need a good digital voltmeter and a variable power supply. Adjust the supply to 14.9 V, that’s the 14.3 volts bat- tery setting plus approximately 0.6 volts across the Schottky diode.

Turn the trimpot until at a certain point the LED goes dark, this is the switch point, and the LED will start to flicker. You may have to try this adjustment more than once, as the closer you get the comparator to switch at exactly 14.3 V, the more accurate the charger will be. Disconnect the power supply from the charge controller and you are ready for the solar panel. The 14.3 V setting mentioned here should apply to most sealed and flooded-cell lead-acid batter- ies, but please check and verify the value with the manufacturer. Select the solar panel in such a way that its amps capability is within the safe charging limit of the battery you intend to use.

Author: T. A. Babu (India - Elektor)

Resistors:
R1 = 15kΩ
R2,R3 = 3.3kΩ 1% R4 = 2.2MΩ
R5 = 1kΩ
P1 = 5kΩ preset

Capacitors:
C1 = 22μF 25V, radial

Semiconductors:
D1 = MBR1645G (ON Semiconductor) D2 = LED, 5mm
IC1 = TL431ACLP (Texas instruments)
T1 = IRFZ44NPBF (International Rectifier)
T2 = 2SC1815 (Toshiba) (device is marked: C1815)
T3 = BC547

Miscellaneous:
K1,K2 = 2-way PCB terminal block, lead pitch 5mm
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Solar Cell Voltage Regulator

Category: DC Power Supply, Solar Power
This device is designed to be a simple, inexpensive ‘comparator’, intended for use in a solar cell power supply setup where a quick ‘too low’ or ‘just right’ voltage indicator is needed. The circuit consists only of one 5V regulator, two transistors, two LEDs, five resistors, two capacitors, and one small battery. Although a 4-V battery is indicated, 4.5 V (3 alkalines in series) or 3.6 V (3 NiCd cells in series) will also work.

The specifications of voltage regulator IC1 are mainly determined by the size and number of the solar cells and the current pull of the equipment connected to the output. Here the low-drop 4805 is suggested but other regulators may work equally well as long as you observe the output voltage of the solar cells. Transistors T1 and T2 are complementary types i.e. one each of the pnp and npn variety.

Circuit diagram:
solar cell voltage regulator circuit schematic
Solar Cell Voltage Regulator Circuit Diagram

Although the ubiquitous BC557B (pnp) and BC547B (npn) are indicated, any small-signal equivalents out of the junk box will probably do. The values of voltage dividers R1/R6 and R3/R4 may need to be adjusted according to the type of transistor and its gain, or according to the desired voltage thresholds. Using the resistor values shown in the schematic, LED D2 turns on fully when the voltage is just above 5 volts.

LED D1 turns on when the voltage drops below 4.2 volts or so. Between those two thresholds, there is a sort of no man’s land where both LEDs are on dimly. A buzzer or other warning device could be connected across the terminals of LED D1 to give a more substantial warning if the voltage drops below operating limits. The current consumption of the circuit is about 20 mA at 5 V, and it decreases with the voltage supplied by the solar cells.
Reuben Posthuma
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Solar-Powered High Efficiency Battery Charger

Category: Battery Charger, Solar Power
This is a simple NiCd battery charger powered by solar cells. A solar cell panel or an array of solar cells can charge a battery at more than 80 % efficiency provided the available voltage exceeds the ‘fully charged’ battery voltage by the drop across one diode, which is simply inserted between the solar cell array and the battery. Adding a step-down regulator enables a solar cell array to charge battery packs with various terminal voltages at optimum rates and with efficiencies approaching those of the regulator itself.

However, the IC must then operate in an unorthodox fashion (a.k.a. ‘Elektor mode’) regulating the flow of charge current in such a way that the solar array output voltage remains near the level required for peak power transfer. Here, the MAX639 regulates its input voltage instead of its output voltage as is more customary (but less interesting).

Circuit diagram:

Solar-Powered High Efficiency Charger circuit schematic
Solar-Powered High Efficiency Charger Circuit Diagram

The input voltage is supplied by twelve amorphous solar cells with a minimum surface area of 100 cm2. Returning to the circuit, potential divider R2/R3 disables the internal regulating loop by holding the V-FB (voltage feedback) terminal low, while divider R1/R2+R3 enables LBI (low battery input) to sense a decrease in the solar array output voltage. The resulting deviation from the solar cells’ peak output power causes LBO (low battery output) to pull SHDN (shutdown) low and consequently disable the chip. LBI then senses a rising input voltage, LBO goes high and the pulsating control maintains maximum power transfer to the NiCd cells.

Current limiting inside the MAX639 creates a ‘ceiling’ of 200 mA for I out. Up to five NiCd cells may be connected in series to the charger output. When ‘on’ the regulator chip passes current from pin 6 to pin 5 through an internal switch representing a resistance of less than 1 ohm. Benefiting from the regulator’s low quiescent current (10 microamps typical) and high efficiency (85 %), the circuit can deliver four times more power than the single-diode configuration usually found in simple solar chargers. Coil L1 is a 100-µH suppressor choke rated for 600mA.

Author: D. Prabakaran - Copyright: Elektor July-August 2004
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Garden Lighting Powered by Solar Cells

Category: Home and Garden, LED and Light, Solar Power
Completely ‘self-supporting’ garden lamps using solar cells as their energy source are gradually becoming more and more common. How do they actually work? We took one apart to find out. From environmental and technical considerations, buying such a solar-cell garden lamp has a lot to recommend it. It’s a great thing that the energy necessary for the lamp to burn in the evening can be drawn from the sunlight that is available for free during the day. In addition, such a lamp is enormously practical, since you can place it in any desired location in the garden without having to dig a trench through the lawn or flowerbeds.

Garden Lighting Using Solar Cells circuit diagram circuit project circuit schematic
You are also free to change your mind about the best location for the lamp - something that would have unpleasant consequences with ordinary garden lamps. What makes up a typical solar-cell garden lamp? A certain number of elements are in any case necessary for it to function. It’s clear that there must be a light bulb and some solar cells.

However, the bulb is naturally not powered directly from the solar cells, so there must be a storage battery and a suitable charging circuit to allow the battery to be charged by the solar cells. In addition, the idea is that the lamp should only burn during the evening and the night, and that needs a twilight switch with a light-sensitive cell.

Garden Lighting Using Solar Cells circuit diagram circuit project circuit schematic
It’s not necessary to do anything to switch off the lamp, since that happens automatically as soon as the battery is fully discharged. Some of the more luxurious models have a small fluorescent tube in place of a normal light bulb, and in this case a small converter is also necessary. However, the model that we examined contained a small 2.5V/75-mA halogen bulb, and thus did not need a converter. As far as the electronics are concerned, the whole thing can thus remain very simple.

Simplicity wins out:

Our garden lamp consists of a simple plastic structure. Eight solar cells are mounted at the top, and inside there are a small halogen bulb, two penlight NiCd cells and a small printed circuit board for the electronics. As can be seen from Figure 1, there isn’t all that much inside. This lamp costs around 15 pounds, and it can be found in several different shops. The electronics also turn out to be extremely simple. Figure 2 shows the complete schematic of the internal circuitry. The twilight switch is on the left, and its output controls the lamp via transistor T4. To the right are the on/off switch, a diode and the eight solar cells.

Charging:

During the day, as long as there is sufficient light, the voltage generated by the solar cells is 8 × 0.45 V under ideal conditions, with a current that depends on the size of the cells - in this case, approximately 140mA. With less light, less current is supplied. The charging circuit consists simply of a single Schottky diode (D1). The current generated by the solar cells passes through this diode, with its typical low voltage drop of 0.3 to 0.4 V, and charges the NiCd cells.

There is no overcharge protection. It is not actually necessary, since all NiCd cells can handle a continuous charging current equal to 1/10 of their capacity (60mA in this case), while modern cells are so robust that twice this amount of current does not cause any problems.

Garden Lighting Using Solar Cells circuit diagram circuit project circuit schematic
The advantages of using a somewhat higher charging current are naturally that the battery is already fully charged after several hours of sunlight, and that a certain amount of charging takes place even on rainy days and during the winter. Solar cells act as light-dependent current sources, so the more light there is, the more current they produce. The voltage is determined by the load, but it can never be higher than the previously mentioned 0.45 V per cell.

Approximately 2.8 V is necessary to charge two NiCd cells. If we add the voltage drop across D1, we arrive at a required voltage of 3.2 V. This is 0.4 V per solar cell. Charging takes place continuously, even when switch S1 is off. It is important to make sure that both NiCd cells are fully charged the first time. Otherwise, one cell may become fully discharged before the other one when they are discharged.

As a result, this cell may have a reverse-polarity voltage applied to it, which will shorten its useful life. Therefore, when first putting the lamp into service, you should place it outside with S1 switched off for at least one day in full sunlight, or two days if the weather is cloudy.

Burning:

When S1 is closed, voltage is applied to the part of the circuit containing the light bulb. An LDR is used to determine whether it is light or dark outside. During the day, the resistance of the LDR is low, and the voltage on the base of T1 is also low, so that it is cut off. T2, T3 and T4 are then also cut off, so that the bulb is not illuminated. As soon as it becomes dark, the resistance of the LDR increases, and the voltage on the base of T1 rises. T1 starts to conduct when the voltage is around 0.65 V.

This causes T2, T3 and T4 to conduct as well, and the lamp starts to burn. T1 then receives a bit of extra current via R4, so that positive switching takes place when the circuit is sitting ‘on the edge’. This is called hysteresis. It means that a threshold is set such that the light level has to drop a bit more before the lamp will switch on again once it is off, and vice versa.

This means that the circuit does not react to every passing cloud or insect that is flying around. As long as it remains dark, the lamp continues to burn until the battery is fully discharged. A fully charged battery has a capacity of 600 mAh, which is enough to supply the 75-mA bulb for approximately eight hours. This is sufficient for the evening and a large part of the night. In the winter, this is not possible, since the battery will probably not be fully charged due to a lack of sunlight.

When the battery becomes fully discharged, its voltage drops. If the voltage drops below 1.25 V, T2 and T3 are cut off, since their base-emitter junctions are in series and thus need at least this amount of voltage. The lamp is then switched off, and the battery is not further discharged.

In the long term:

NiCd batteries usually have a lifetime of around 500 to 1000 charge/discharge cycles. After two to three years of continuous use, therefore, the two penlight cells of the garden lamp will probably be ready for replacement. However, these cells are presently so inexpensive that this is not a serious disadvantage. Naturally, there is also a limit on the life-time of the light bulb, but here again, making a replacement is quick and inexpensive.
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Lead-Acid-Battery Regulator For Solar Panel Systems

Category: DC Power Supply, Solar Power
The design of solar panel systems with a (lead-acid) buffer battery is normally such that the battery is charged even when there is not much sunshine. This means, however, that when there is plenty of sunshine, a regulator is needed to prevent the battery from being overcharged. Such controls usually arrange for the superfluous energy to be dissipated in a shunt resistance or simply for the solar panels to be short-circuited.

It is, of course, an unsatisfactory situation when the energy derived from a very expensive system can, after all , not be used to the full. The circuit presented diverts the energy from the solar panel when the battery is fully charged to another user, for instance, a 12V ice box with Peltier elements, a pump for drawing water from a rain butt, or a 12V ventilator. It is, of course, also possible to arrange for a second battery to be charged by the super-fluous energy.

In this case, however, care must be taken to ensure that when the second battery is also fully charged , there is also a control to divert the superfluous energy. The shunt resistance needed to dissipate the superfluous energy must be capable of absorbing the total power of the panel, that is, in case of a 100W panel, its rating must be also 100 W. This means a current of some 6–8 A when the operating voltage is 12 V. When the voltage drops below the maximum charging voltage of 14.4V growing to reduced sunshine, the shunt resistance is disconnected by an n-channel power field effect transistor (FET), T1.

Circuit diagram:
 
Lead-Acid-Battery Regulator Circuit Diagram For Solar Panel Systems

The disconnect point is not affected by large temperature fluctuations because of a reference voltage provided by IC1. The necessary comparator is IC2, which owing to R9 has a small hysteresis voltage of 0.5V. Capacitor C5 ensures a relatively slow switching process, although the FET is already reacting slowly owing to C4. The gradual switching prevents spurious radiation caused by steep edges of the switched voltage and also limits the starting current of a motor (of a possible ventilator).

Finally, it prevents switching losses in the FET that might reach 25W, which would m a ke a heat sink unavoidable. Setting up of the circuit is fairly simple. Start by turning P1 so that its wiper is connected to R5. When the battery reaches the voltage at which it will be switched off, that is, 13.8 – 14.4V, adjust P1 slowly until the output of comparator I C2 changes from low to high, which causes the load across T1 to be switched in. Potentiometer P1 is best a 10-turn model.

When the control is switched on for the first time, it takes about 2 seconds for the electrolytic capacitors to be charged. During this time, the output of the comparator is high, so that the load across T1 is briefly switched in. In case T1 has to switch in low-resistance loads, the BUZ11 may be replaced by an IRF44, which can handle twice as much power (150 W) and has an on-resistance of only 24mR. Because of the very high currents if the battery were short-circuited, it is advisable to insert a suitable fuse in the line to the regulator. The circuit draws a current of only 2 mA in the quiescent state and not more than 10 mA when T1 is on.
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Solar Panel Voltage Regulator

Category: DC Power Supply, Solar Power
Our energy-hungry and environmentally aware society has been slow to make good use of the sun's "free" power. But now it's finally taking off. Using the sun's heat directly, for cooking and other applications, is already a common and popular technology in countries that have good weather. Hot-water panels are nowadays used in many parts of the world, in combination with a gas or electric powered water heater to help out when the weather doesn't help.

But at the same time, electric solar panels are still expensive, justifying their use only as a novelty, or in locations where little power is needed, and bringing in commercial power would be even more expensive. A solar electric power system needs panels for generation, batteries for storage, a regulator to keep the batteries within a safe operating range, and in some cases a power converter for AC output.

For those who need to set up a few panels for a summer cottage, a boat, a remote mountaintop installation, or whatever, I'm herewith providing a version of the regulator circuit that I have used in a lot of such installations. Such a solar panel regulator should perform at least two operations: The obvious one is protecting the battery from overcharge at times of strong sun and little consumption, and the other is protecting it from excessive discharge in bad weather conditions. Both overcharge and deep discharge are harmful to a battery.

Circuit Project: Solar Panel Voltage RegulatorFor regulating a solar panel's output, there are several possible ways. A linear series regulator can be used, but has the disadvantage of causing some voltage drop and having some internal power consumption at times when the sun is weak and the load is heavy. It's much better to use a shunt regulator, which is inactive at such times, and springs to life only when there is excess energy. For this reason, most solar panel regulators use the shunt scheme, the one presented here being no exception.

But such shunt regulators come in two flavors: Most commercial units are ON-OFF regulators. That means, they have a simple switch device, most often a transistor or MOSFET, sometimes even just a relay, that stays off until the battery reaches over voltage, and then switches in, shorting out the panel until the battery voltage has dropped off. Then the full panel current is switched on again. The only advantage of this method is that's cheap. The power switch operates with very low power dissipation, allowing a small, low cost construction.

But the disadvantages of this system are major: The voltage output is all the time fluctuating between about 13 and 14.5V. The battery is cycling between getting overcharge and having to deliver all the load current, which severely reduces the battery's lifetime. And in the event of battery disconnection or failure, the regulator cycles quickly, applying pulses of full panel voltage to the output, which can destroy sensitive equipment powered by the system!

The circuit presented here uses linear shunt regulation. Simply spoken, it burns off all excess energy from the panel, keeping output voltage constant. At times when the solar panel output is equal or greater than the load, and the battery is fully charged, the load gets its power from the panel, while the battery rests at full charge. Five years battery lifetime are entirely normal with this system, while the same batteries last only two to three years when used with pulsing regulators!

The second responsibility of the regulator is watching over the battery voltage, and dropping off the load when the battery gets discharged too much. Lead batteries are severely damaged by deep discharges, so it's far preferable to drop off the load, then to have the battery die in a bad weather spell. This regulator is designed for 12V systems employing panels of up to 7A total current, and loads of not over 20A. It can be easily modified for greater currents.

U1A compares an adjustable sample of the present battery voltage to a 5V reference from a highly stable source. According to the result, it controls the power transistors Q1 and Q2, which shunt off the excess power generation from the panel. A diode (D1) avoids battery voltage to go back to the panel under no-light condition. To avoid imprecise voltage control due to varying diode drop, the sample is taken from the battery side, even if this means a very small power waste.

The power resistors R1 and R2 are dimensioned in such a way that under maximum shunting, these resistors will dissipate almost all power (about 100W total), leaving the transistors running cool. The highest dissipation in the transistors happens when the regulator is dissipating half of the panel output; in this case, each transistor will dissipate about 12W.

U1B is a Schmitt trigger that compares the battery voltage to the same stable reference of the other section, but for another purpose: It controls the load switch Q3. This circuit will disconnect the load if the battery gets close to deep discharge, and reconnect it only when recharge is well underway. The negative side of the load is switched, simply because N-channel MOSFETs are much cheaper and better than P-channel ones.

Component notes:

D1 can be any diode that can safely survive the panel's current. If the panel has a very low voltage output (less than 33 cells in series), it is an advantage to employ a Schottky diode in this place. Q1 and Q2 are common power Darlington transistors. They need to be heatsinked for safe long-term operation at the 12 Watt dissipation level. That's easy enough to do, but many newcomers misjudge how much thermal resistance is introduced by a mica insulator! Plan on 1K/W thermal resistance inside each transistor, two times as much in the insulator (if you use any), and 370K safe junction temperature. For typical environmental conditions, this makes you need a heatsink having a thermal resistance of about 1.3K/W. If it is larger, you get more safety margin.

R1 and R2 will have to be made by combining a number of power resistors in parallel. Yes, you need to make two resistor arrays of 4 Ohm, 80W each! This 80W figure includes a reasonable safety margin. These resistors will produce a lot of heat, and you may cook your coffee on them! Be sure to mount them in such a way that they have lots of ventilation, and that the heat from them will not reach the other components. R3 and R4 may to have be built from parallel combinations too, because of the low value of only 0.15 Ohm.

U2 is a voltage reference IC. You cannot replace it by a standard Zener diode! Zeners are much too unstable! If you can't find this chip locally, you may use the ubiquitous 7805 regulator instead, but the power drain from the battery will be higher. In this case, of course you don't need R8, but you would need a 1uF capacitor at the 7805 output. Q3 is a power MOSFET that has a very low Rds(on). You may use a different one, provided that it has a resistance that's low enough for your application. You may use several in parallel. The one I used has low loss even at loads of 20A, and can handle much more!

Calibration:

Once the circuit is assembled, calibration is quite easy. Connect the panel, leave the battery and load disconnected. With a nice sun on the panel, adjust RV1 for the desired voltage at the battery output. I recommend 13.8V for sealed batteries, and 14 to 14.2V for open cell ones, to which water can be added if necessary.

Now you need either a variable power supply connected to the battery lines, or some kind of variable load. You may also use your panel as variable power supply, by tilting it away from the sun while a fixed load is connected to the battery lines. The idea is to adjust the voltage at the battery lines to the desired shut-off value (I recommend 11.5V), and then move RV2 until Q3 shuts off, as indicated by a voltmeter across the load output, a 12V light bulb, or whatever you can use to detect it.

After Q3 has shut off, increase the voltage across the battery lines and see at which level Q3 switches on again. This should happen above 12.6 and below 13.4 V. You may have to retouch RV2 and look for a compromise between ON and OFF voltages. If your components are not too much out of value, then both potentiometers should have ended up reasonably close to the center position.

Using more panels:

You can use this regulator for larger installations. Simply add one group like R1-Q1-R3 for each additional 3.5A panel, and use a diode for D1 that handles the total current. Remember that large diodes need heat sinks! U1A can drive at least 8 such transistors. If you intend to build a really large system, you may want to add an emitter follower between U1A and the power transistors. If you need to handle large load currents, you can place as many MOSFETs in parallel as you need. There is no practical driving limitation in this case. [via]
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Portable Solar Lamp/Lantern

Category: LED Flasher, Solar Power
This portable solar lantern circuit uses 6 volt/5 watt solar panels are now widely available. With the help of such a photo-voltaic panel we can construct an economical, simple but efficient and truly portable solar lantern unit. Next important component required is a high power (1watt) white LED module.

When solar panel is well exposed to sunlight, about 9 volt dc available from the panel can be used to recharge a 4.8 volt /600mAh rated Ni-Cd battery pack. Here red LED (D2) functions as a charging process indicator with the help of resistor R1. Resistor R2 regulates the charging current flow to near 150mA.

Solar Lantern Circuit Schematic
Circuit Project: Portable Solar Lantern

Assuming a 4-5 hour sunlit day, the solar panel (150mA current set by the charge controller resistor R2) will pump about 600 – 750 mAh into the battery pack. When power switch S1 is turned on, dc supply from the Ni-Cd battery pack is extended to the white LED (D3). Resistor R3 determines the LED current. Capacitor C1 works as a buffer.

Note: After construction, slightly change the values of R1,R2 and R3 up/down by trial&error method, if necessary.
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Solar Powered Lithium-Ion Battery Charger

Category: Battery Charger, Solar Power
The circuit below feeds a controlled current and voltage to a 3.6v lithium ion battery. The current is limited to 300ma and the voltage is limited to 4.2 volts. The circuit uses a LTC1734 IC from Linear Technology. No diode is needed between the circuit and a 6 volt solar panel. Some very nice 6 volt solar panels are available from www.plastecs.com Their SP6-200-12 cranks out about 1 watt while the SP6-300-12 can produce about 2 watts. Assuming a 6 hour sunlit day, the 2 watt panel will pump about 1.8 amp-hours into a battery.

Circuit Project: Circuit Solar Powered Lithium Ion Battery Charger
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Solar Powered Animal Scarer

Category: Animal Repellent, Solar Power
Here is a solar powered Flasher to scare away the nocturnal animals like bats and cats from the farm yard or premises of the house. The brilliant multicolored flashes confuse these animals and they avoid the hostile situation. It is fully automatic, turns on in the evening and turns off in the morning.

The circuit has an LDR controlled oscillator built around the Binary counter IC CD 4060.The functioning of the IC is controlled through its reset pin 12. During day time, LDR conducts and keeps the reset pin of IC high so that it remains dormant. During night, LDR cease to conduct and the reset pin will be grounded through VR1. This triggers the IC and it stats oscillating using the components C1 and VR2. Output pins 7, 5 and 4 are used to power the LEDs strings.

VR1 adjusts the sensitivity of LDR and VR2, the flashing rate of LEDs. High bright Red, Blue and White LEDs are used in the circuit to give brilliant flashes. Red LEDs flash very fast, followed by blue and then White. White LEDs remains on for few seconds and provide light to a confined area. More LEDs can be added in the strings if desired. The circuit can also function with 12 volt DC.

Animal Repellent Circuit Diagram

Circuit Project: Solar Powered Animal Scarer

The circuit uses a solar powered battery power supply. During daytime, battery charges through R1 and D1.Green LED indicates the charging mode. During night time current from the solar cell decreases and D1 reverse biases. At the same time D2 forward biases to provide power to the circuit. Resistor R1 restricts the charging current and the high value capacitor C1 is a buffer for current.

Animal Scarer Solar Power Supply

Circuit Project: Solar Powered Animal Scarer
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Solar Powered SLA Battery Maintenance

Category: Battery Tester, Solar Power
This circuit was designed to ‘baby-sit’ SLA (sealed lead-acid or ‘gel’) batteries using freely available solar power. SLA batteries suffer from relatively high internal energy loss which is not normally a problem until you go on holidays and disconnect them from their trickle current charger. In some cases, the absence of trickle charging current may cause SLA batteries to go completely flat within a few weeks. The circuit shown here is intended to prevent this from happening.

Two 3-volt solar panels, each shunted by a diode to bypass them when no electricity is generated, power a MAX762 step-up voltage converter IC. The ‘762 is the 15-volt-out version of the perhaps more familiar MAX761 (12 V out) and is used here to boost 6 V to 15 V. C1 and C2 are decoupling capacitors that suppress high and low frequency spurious components produced by the switch-mode regulator IC. Using Schottky diode D3, energy is stored in inductor L1 in the form of a magnetic field.

Solar Powered SLA Battery Maintenance Circuit Diagram
Solar Powered SLA Battery Maintenance Circuit Diagram

When pin 7 of IC1 is open-circuited by the internal switching signal, the stored energy is diverted to the 15-volt output of the circuit. The V+ (sense) input of the MAX762, pin 8, is used to maintain the output voltage at 15 V. C4 and C5 serve to keep the ripple on the output voltage as small as possible. R1, LED D4 and pushbutton S1 allow you to check the presence of the 15-V output voltage.

D5 and D6 reduce the 15-volts to about 13.6 V which is a frequently quoted nominal standby trickle charging voltage for SLA batteries. This corresponds well with the IC’s maximum, internally limited, output current of about 120 mA. The value of inductor L1 is not critical — 22 µH or 47 µH will also work fine. The coil has to be rated at 1 A though in view of the peak current through it.

The switching frequency is about 300 kHz. A suggestion for a practical coil is type M from the WEPD series supplied by Würth (www.we-online.com). Remarkably, Würth supply one-off inductors to individual customers. At the time of writing, it was possible, under certain conditions, to obtain samples, or order small quantities, of the MAX762 IC through the Maxim website at www.maxim-ic.com.

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Solar Panel Voltage Regulator

Category: DC Power Supply, DC to DC Converter, Solar Power
Our energy-hungry and environmentally aware society has been slow to make good use of the sun's "free" power. But now it's finally taking off. Using the sun's heat directly, for cooking and other applications, is already a common and popular technology in countries that have good weather. Hot-water panels are nowadays used in many parts of the world, in combination with a gas or electric powered water heater to help out when the weather doesn't help.

Solar Panel Voltage Regulator Circuit Diagram
Solar Panel Voltage Regulator Circuit Diagram

But at the same time, electric solar panels are still expensive, justifying their use only as a novelty, or in locations where little power is needed, and bringing in commercial power would be even more expensive. A solar electric power system needs panels for generation, batteries for storage, a regulator to keep the batteries within a safe operating range, and in some cases a power converter for AC output. For those who need to set up a few panels for a summer cottage, a boat, a remote mountaintop installation, or whatever, I'm herewith providing a version of the regulator circuit that I have used in a lot of such installations.

Such a solar panel regulator should perform at least two operations: The obvious one is protecting the battery from overcharge at times of strong sun and little consumption, and the other is protecting it from excessive discharge in bad weather conditions. Both overcharge and deep discharge are harmful to a battery. For regulating a solar panel's output, there are several possible ways. A linear series regulator can be used, but has the disadvantage of causing some voltage drop and having some internal power consumption at times when the sun is weak and the load is heavy.

It's much better to use a shunt regulator, which is inactive at such times, and springs to life only when there is excess energy. For this reason, most solar panel regulators use the shunt scheme, the one presented here being no exception. But such shunt regulators come in two flavors: Most commercial units are ON-OFF regulators. That means, they have a simple switch device, most often a transistor or MOSFET, sometimes even just a relay, that stays off until the battery reaches over voltage, and then switches in, shorting out the panel until the battery voltage has dropped off. Then the full panel current is switched on again.

The only advantage of this method is that's cheap. The power switch operates with very low power dissipation, allowing a small, low cost construction. But the disadvantages of this system are major: The voltage output is all the time fluctuating between about 13 and 14.5V. The battery is cycling between getting overcharge and having to deliver all the load current, which severely reduces the battery's lifetime. And in the event of battery disconnection or failure, the regulator cycles quickly, applying pulses of full panel voltage to the output, which can destroy sensitive equipment powered by the system!

The circuit presented here uses linear shunt regulation. Simply spoken, it burns off all excess energy from the panel, keeping output voltage constant. At times when the solar panel output is equal or greater than the load, and the battery is fully charged, the load gets its power from the panel, while the battery rests at full charge. Five years battery lifetime are entirely normal with this system, while the same batteries last only two to three years when used with pulsing regulators!

The second responsibility of the regulator is watching over the battery voltage, and dropping off the load when the battery gets discharged too much. Lead batteries are severely damaged by deep discharges, so it's far preferable to drop off the load, then to have the battery die in a bad weather spell. This regulator is designed for 12V systems employing panels of up to 7A total current, and loads of not over 20A. It can be easily modified for greater currents.

U1A compares an adjustable sample of the present battery voltage to a 5V reference from a highly stable source. According to the result, it controls the power transistors Q1 and Q2, which shunt off the excess power generation from the panel. A diode (D1) avoids battery voltage to go back to the panel under no-light condition. To avoid imprecise voltage control due to varying diode drop, the sample is taken from the battery side, even if this means a very small power waste.

The power resistors R1 and R2 are dimensioned in such a way that under maximum shunting, these resistors will dissipate almost all power (about 100W total), leaving the transistors running cool. The highest dissipation in the transistors happens when the regulator is dissipating half of the panel output; in this case, each transistor will dissipate about 12W.

U1B is a Schmitt trigger that compares the battery voltage to the same stable reference of the other section, but for another purpose: It controls the load switch Q3. This circuit will disconnect the load if the battery gets close to deep discharge, and reconnect it only when recharge is well underway. The negative side of the load is switched, simply because N-channel MOSFETs are much cheaper and better than P-channel ones.

Component notes:


D1 can be any diode that can safely survive the panel's current. If the panel has a very low voltage output (less than 33 cells in series), it is an advantage to employ a Schottky diode in this place. Q1 and Q2 are common power Darlington transistors. They need to be heatsinked for safe long-term operation at the 12 Watt dissipation level. That's easy enough to do, but many newcomers misjudge how much thermal resistance is introduced by a mica insulator! Plan on 1K/W thermal resistance inside each transistor, two times as much in the insulator (if you use any), and 370K safe junction temperature.

For typical environmental conditions, this makes you need a heatsink having a thermal resistance of about 1.3K/W. If it is larger, you get more safety margin. R1 and R2 will have to be made by combining a number of power resistors in parallel. Yes, you need to make two resistor arrays of 4 Ohm, 80W each! This 80W figure includes a reasonable safety margin. These resistors will produce a lot of heat, and you may cook your coffee on them! Be sure to mount them in such a way that they have lots of ventilation, and that the heat from them will not reach the other components.

R3 and R4 may to have be built from parallel combinations too, because of the low value of only 0.15 Ohm. U2 is a voltage reference IC. You cannot replace it by a standard Zener diode! Zeners are much too unstable! If you can't find this chip locally, you may use the ubiquitous 7805 regulator instead, but the power drain from the battery will be higher. In this case, of course you don't need R8, but you would need a 1uF capacitor at the 7805 output.

Q3 is a power MOSFET that has a very low Rds(on). You may use a different one, provided that it has a resistance that's low enough for your application. You may use several in parallel. The one I used has low loss even at loads of 20A, and can handle much more!

Calibration:


Once the circuit is assembled, calibration is quite easy. Connect the panel, leave the battery and load disconnected. With a nice sun on the panel, adjust RV1 for the desired voltage at the battery output. I recommend 13.8V for sealed batteries, and 14 to 14.2V for open cell ones, to which water can be added if necessary. Now you need either a variable power supply connected to the battery lines, or some kind of variable load. You may also use your panel as variable power supply, by tilting it away from the sun while a fixed load is connected to the battery lines.

The idea is to adjust the voltage at the battery lines to the desired shut-off value (I recommend 11.5V), and then move RV2 until Q3 shuts off, as indicated by a voltmeter across the load output, a 12V light bulb, or whatever you can use to detect it. After Q3 has shut off, increase the voltage across the battery lines and see at which level Q3 switches on again. This should happen above 12.6 and below 13.4 V. You may have to retouch RV2 and look for a compromise between ON and OFF voltages. If your components are not too much out of value, then both potentiometers should have ended up reasonably close to the center position.

Using more panels:


You can use this regulator for larger installations. Simply add one group like R1-Q1-R3 for each additional 3.5A panel, and use a diode for D1 that handles the total current. Remember that large diodes need heat sinks! U1A can drive at least 8 such transistors. If you intend to build a really large system, you may want to add an emitter follower between U1A and the power transistors. If you need to handle large load currents, you can place as many MOSFETs in parallel as you need. There is no practical driving limitation in this case.

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