Build a 10 Amp Solar Charge Controller SCC2 Circuit

The SCC2 is a solar charge controller, it’s function is to regulate the power flowing from a photovoltaic panel into a rechargeable battery. It features easy setup with one potentiometer for the float voltage adjustment, an equalize function for periodic overcharging, and automatic temperature compensation for better charging over a range of temperatures.

10 Amp Solar Charge Controller Circuit Diagram With Parts List

The goal of the circuit design was to make a charge controller with analog simplicity, high efficiency, and reliability. A medium power solar system can be built with a 12V solar panel up to 10 amps, the SCC2, and a lead acid or other rechargeable up to a few hundred amp hour capacity. The SCC2 can be operated at battery voltages other than 12V, it can work at 6V and 24V by changing a few parts. Operation at voltages between 6V and 24V is also possible.

Specifications

Maximum solar panel current: 10 Amps
Night time battery drain current: approximately 1ma
Nominal battery voltage: 6V, 12V or 24V.

Theory

The SCC2 acts as a medium power DC current switch between the + terminals of the PV and battery. Diode D1 prevents reverse night time current flow from the battery back to the PV panel.

When the PV voltage is high enough to charge the battery, zener diode D2 conducts and turns on transistor Q2. Q2 switches the power for the rest of the circuit on. The circuit is switched off at night. IC2 provides a 5 volt regulated voltage to power the comparator circuits, it also provides a reference voltage for comparator IC1a.

When the battery voltage is below the desired full voltage and needs charging, comparator IC1a turns on and activates Q1 and Q3, this allows the solar charging current to flow into the battery. Note that Q3 is a P-channel mosfet, this allows the circuit to be wired with a common ground for the solar panel and battery. The solar current loop is drawn in heavy lines on the schematic.

When the battery reaches the full charge point, IC1a operates as a comparator based schmidt trigger oscillator, it switches the solar current off and on. The switching causes the battery voltage to oscillate a few tens of millivolts above and below the desired set point. A rail-to-rail op-amp is required for proper operation, 741 style op-amps will not work in this circuit.

The red/green charging/full LED is driven between the output of IC1a and IC1b. IC1b has an inverted version of the IC1a signal. Pin 5 of IC1b only needs an approximate center point to work as an on-off comparator, it is connected to the varying IC1a pin 2 so that it does not require another reference divider circuit.

The resistors and thermistor on the input side of IC1a form a resistive bridge circuit that is used to compare the battery voltage to a reference voltage coming from IC2/R8/R9. The potentiometer adjusts the voltage point around which the circuit will oscillate on full charge. Resistor R7 adds positive feedback to IC1a for a schmidt trigger characteristic. The thermistor provides thermal compensation, as the temperature goes down, the full voltage goes up.

The equalize switch, S1a, forces the circuit on for intentional overcharging. Switch S1b and R1 can be used to select a different float voltage range, you can experiment with this by using different values of R1, typically R1 should be greater than 1M.

Alignment

    Start with a charged battery, connect the solar panel directly to the
    battery until the battery voltage is at or above the desired full setting,
    this also that the panel is capable of charging the battery.
    While measuring the battery voltage, adjust VR1 clockwise to align the
    float voltage set point.  If the LED turns red before it reaches the
    desired float voltage, the battery will need to charge for a while.
    When the battery is fully charged, it should be at the float voltage and
    the led should show alternating colors.

    The float voltage should be set when the board and battery are at room
    temperature. Typical 12V set points are 13.8V for a gell cell and 14.5V
    for a wet cell.  For 6V, divide those by two, for 24V, multiply by 2.
    Follow your battery manufacturers recommendations for the best settings.
    Readjust the float voltage after the battery has reached a full charge.The float voltage should be set when the circuit is at room temperature.

Use

Connect the solar panel to the SCC2 solar panel input connectors, connect the battery to the SCC2 output connectors. Put the solar panel in the sun, and watch the battery charge up. Systems where the battery is frequently discharged way down should occasionally be run in equalize mode for a few hours or a full day. It is best to monitor the battery voltage during this operation, disable equalization if the battery voltage goes above 16V (12V version).

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Controlling A Relay With A Digital Logic Level Circuit

Description 

The schematic below illustrates 4 methods of controlling a relay with a digital logic signal. Figure (A) can probably be used in most cases where the relay coil requires 100 mA or less and the input current is 2 milliamps or more. The resistor value (R) is determined from the input voltage and the available current. For example, a 5 volt input signal supplying 2 milliamps would require (5-.7)/.002 = 2150 ohms, or a 2.2K standard value. If the transistor has a minimum current gain of 50, there will be 100 mA of current available for the relay coil. The following table shows various resistor values that can be used to obtain various relay coil currents assuming a transistor current gain of 50 such as the 2N3053. 74XX refers to standard TTL logic, 74LSXX refers to low power TTL logic, 74HC is high speed CMOS and CD40XX is the older CMOS devices. The currents given are approximate values and may not be correct for all devices but should be close. 

Input Voltage - Input Current - Relay coil current - Standard Resistor

• 4 - 74LSXX .0004 - 20 milliamps - 8.2K
• 4 - 74XX .0008 - 40 milliamps - 4.3K
• 4 - 74SXX .001 - 50 milliamps - 3.3K
• 5 - 74HCXX .004 - 200 milliamps - 1K
• 6 - 74HCXX .004 - 200 milliamps - 1.3K
• 5 - CD40XX .0003 - 15 milliamps - 13K
• 12 - CD40XX .0006 - 30 milliamps - 18K

Figure B can be used when the input voltage is the same as the relay coil voltage. The voltage on the emitter of the transistor will be about 0.7 volts less than the input, so a 12 volt relay would operate on 11.3 which should be close enough. No resistor is needed since the emitter follower configuration presents a high impedance at the input. The input current will be the relay coil current divided by the transistor gain. For example a 120 ohm relay coil will draw 100 mA at 12 volts and if the transistor gain is 50, the input current will be about 2 milliamps.

Figure C can be used to provide additional gain when the input current is very small. You can also use a Darlington transistor in place of the two transistors which is a better approach, but this idea works just as well when you dont have a Darlington transistor handy. The overall gain will be the product of the individual gains of the two transistors or about 2500 for two transistor with a gain of 50 each. This will enable supplying over 250 mA to the relay with only 100 microamps of input current. The R value will depend on the input voltage and current and gain of the first transistor. For example, using a 5 volt input and 100 microamp current and transistor gain of 50, the R value will be 5 minus two diode drops (5 - 1.4) divided by the input current times 50, or about (5 - 1.4) / (.0001 * 50) = about 750 ohms. So this setup can be used when controlling heavy duty relays with low power CMOS logic signals.

Figure D can be used to reverse the relay action so that it engages when the input is low and disengages when the input is high. The R value is determined the same as in Figure A. The R1 value should be high enough to ensure saturation of the first stage and low enough to saturate the second stage. For example, if a 12 volt relay coil requires 100 mA and the driving transistor gain is 50, then the base current will be 100/50= 2 mA and the R1 value must be less than 6000 ohms so that 2 mA does not drop more than the supply voltage of 12. If the first transistor gain is 50 and the input current is 100 microamps, the collector current will be 5 mA and the R1 value must be greater than 2400 ohms so that 5 mA drops the entire supply voltage of 12. So we need to select something between these two limits of 2.4K to 6K, something around 4.3K would be near the midrange.

Circuit Diagram

Source http://www.bowdenshobbycircuits.info/r_ctrl.htm

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Converting a DCM Motor

We recently bought a train set made by a renowned company and just couldn’t resist looking inside the locomotive. Although it did have an electronic decoder, the DCM motor was already available 35 (!) years ago. It is most likely that this motor is used due to financial constraints, because Märklin (as you probably guessed) also has a modern 5-pole motor as part of its range. Incidentally, they have recently introduced a brushless model. 

The DCM motor used in our locomotive is still an old-fashioned 3-pole series motor with an electromagnet to provide motive power. The new 5-pole motor has a permanent magnet. We therefore wondered if we couldn’t improve the driving characteristics if we powered the field winding separately, using a bridge rectifier and a 27 Ω current limiting resistor. This would effectively create a permanent magnet. The result was that the driving characteristics improved at lower speeds, but the initial acceleration remained the same. But a constant 0.5 A flows through the winding, which seems wasteful of the (limited) track power. A small circuit can reduce this current to less than half, making this technique more acceptable. 

Circuit diagram :

Converting a DCM Motor Circuit Diagram

The field winding has to be disconnected from the rest (3 wires). A freewheeling diode (D1, Schottky) is then connected across the whole winding. The centre tap of the winding is no longer used. When FET T1 turns on, the current through the winding increases from zero until it reaches about 0.5 A. At this current the voltage drop across R4-R7 becomes greater than the reference voltage across D2 and the opamp will turn off the FET. The current through the winding continues flowing via D1, gradually reducing in strength. When the current has fallen about 10% (due to hysteresis caused by R3), IC1 will turn on T1 again. The cur-rent will increase again to 0.5 A and the FET is turned off again. This goes on continuously.

The current through the field winding is fairly constant, creating a good imitation of a permanent magnet. The nice thing about this circuit is that the total current consumption is only about 0.2 A, whereas the current flow through the winding is a continuous 0.5 A. 

We made this modification because we wanted to convert the locomotive for use with a DCC decoder. A new controller is needed in any case, because the polarity on the rotor winding has to be reversed to change its direction of rotation. In the original motor this was done by using the other half of the winding.

There is also a good non-electrical alter-native: put a permanent magnet in the motor. But we didn’t have a suitable magnet, whereas all electronic parts could be picked straight from the spares box. 

Source By : Streampowers

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Track Your Distance Through a Bicycle Odometer

Just like cars that measures the distance it can travel, you can also do it with your bicycles. We usually keep track of our mileage to see how far our strength can go but would it be of great use if we track it because we are maintaining a workout everyday considering the calories we are burning.

If you want to make your own odometer, you will need a micro controller that generates pulse and a MOSFET that converts those voltage pulses. Just remember to check your batteries all the time.
The best way of burning calories is to move those muscles everyday! Set your bikes and your odometer! Burn fats!

 

 

Streamcircuits

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Use A DAC To Bias Your Varactor Diode

Varactor (or “varicap”) diodes are used primarily in radio-frequency (RF) circuits to provide a capacitance that can be varied by changing the applied voltage. These types of diodes often are used for tuning circuits, such as RF oscillators and filters found in wireless applications like wireless microphones and radios. Designers, then, should know about the benefits of using a nonvolatile digital-to-analog converter (DAC) to provide the biasing voltage of a varactor diode used as a voltage-controlled capacitor.

The varactor diode is operated under reverse bias, which creates a depletion zone around the P-N junction. Changing the level of the reverse bias changes the thickness of the depletion region and, thus, the effective capacitance of the diode. Increasing voltage causes a decrease in capacitance.

Varactor diodes are specified with a nominal capacitance value and the range of capacitance that can be achieved with a maximum and minimum voltage level. Increasing the bias voltage range increases the capacitance range available, but designers can also look for varactors with a larger capacitance- to-voltage ratio.

A convenient solution for creating a varying bias voltage is to use a DAC. Most DACs have an output voltage range of 0 V to +5.5 V. If a higher voltage bias is required, though, then a high-voltage DAC can be used. However, it may be more cost-effective to use a low-cost, high-voltage operational amplifier in a non-inverting configuration to provide level shifting of the output voltage from a common 5.5-V DAC.

 

The LC-tank circuit portion of a voltage-controlled oscillator allows for FM modulation in wireless microphones and radios. Its back-to-back varactor configuration minimizes the effects of RF modulation.

Using a DAC does introduce sources of potential error. The varactor is affected by any form of amplitude variation of the bias voltage, resulting in an undesired shift in capacitance. Deterministic errors can be accounted for when using the microcontroller to program the DAC output voltage. The primary sources of error that should be considered include varactor nonlinearity, offset errors, and DAC integral nonlinearity (INL). RF modulation may also be caused by voltage induced from a noise source – perhaps from an antenna in the system. The figure shows an LC-tank circuit portion of a voltage-controlled oscillator. This circuit allows for FM modulation in the aforementioned wireless microphone or radio.

Here, a back-to-back varactor configuration minimizes the effects of RF modulation. If a varying signal is injected, the bias across one diode increases as the other decreases, keeping overall capacitance unchanged. Note that the two diodes are in series with each other, so capacitance is half of a single varactor setup.

To also prevent RF signals from affecting the circuitry outside the tuning circuit, the bias voltage is fed through an isolation resistor or an RF choke. There are other benefits to using a DAC to bias a varactor diode. For example, multiple-output-channel DAC devices can be used in a multistage application. Additionally, in a four-channel DAC, three channels could potentially be used for separate band-pass filters for low-, mid-, and high-frequency filtering. The fourth output could be used for offset voltage calibration elsewhere in the circuit, or it could be turned off when it isn’t in use. Space and design time can be saved by avoiding having to set up separate biasing schemes.

Some DACs, such as the MCP4728, also offer on-board nonvolatile memory, which can store configuration data such as output-voltage levels and channel status (on/off). This enables the device to be reset or powered up into a known set state, which could allow a pre-programmed tune to be stored. The tune could be recalled when a desired event or input occurs or when power is lost and restored.

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Designing A Li Ion Battery Charger with Load Sharing MCP73837

Batteries often serve as the main energy source for portable electronic devices. Although they depend on batteries, portable consumer electronic products, such as GPS devices and multi-media players, often consume energy directly from an ac-dc wall adapter or accessory power adapter (or “Auto Adapter”) when the battery is low or the device is in a stationary mode. Due to their cost effectiveness over their useful life, rechargeable batteries are often used for the power source of the portable electronic device.

Attributes such as “relatively high energy density” and “maintenance free” make Lithium-Ion (Li-Ion) batteries popular in the portable consumer electronic products. Refer to the application note, AN1088, “Selecting the Right Battery System For cost Sensitive Portable Applications While maintaining Excellent Quality” (DS01088) for characteristics of Li-Ion batteries. Some examples of how to properly design with Li-Ion batteries will be discussed in this application note. [Link] 

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A Bipolar Regenerative Receiver

Contrary to what some radio experimenters think, a bipolar regenerative design can be made to work efficiently. The major concern is the low input impedance of the detector-amplifier bipolar stage. Nevertheless, it can be easily compensated with positive feedback or regeneration. A sufficient amount of regeneration can make tuning astonishingly sharp. Another concern is the quality of the detected audio. This, to my knowledge, is subjective. The quality of sound coming out from an earphone can be rated good or fair by two different people. I would suggest that you decide by yourself. So, come on and try the following schematic for the 530 kHz to 1650 kHz AM Broadcasting Band.

A Bipolar Regenerative Receiver Circuit Diagram

Please notice that the 475 pF variable capacitor tunes in the stations whereas the 200 pF variable capacitor controls regeneration. The latter is known as the throttle capacitor. L2 is the tickler coil. In order to regeneration to take place, L1 and L2 must be correctly phased ( very important! ).

The power consumption is very low. The 2N3904 drains some 60 uA from the 9 volt battery and the AC126, about 0.5 mA.As a benchmark, medium powered ( 5 to 10 kw ) local stations within 25 km from my site are heard as fair to loud audio signals.

The audio output stage has no external bias, and doesnt need any. This is because Iceo, the leakage collector current ( about 0.5 mA in my prototype ), is sufficient to build up a usable Beta ( or current amplifying factor ) in the germanium AC126 transistor. This is a bit unusual but it works fine. Also, the signal detection is carried out by the 2N3904 transistor, as it is driven, thanks to regeneration, into its non-linear region. In other words, it works as an amplifier-detector.

Photographs of Ramons Prototype

Email: rvargas@inictel.gob.pe

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How to Use IC 741 as a Comparator

Weve been using this IC probably since we were kids, I am referring to this wonderful little IC 741, through which virtually any circuit designing becomes feasible. It almost alone is able to handle many complex functions and makes circuit configuration very easy, thats why its one of the favorite chips not only with the new electronic hobbyists but also with the experienced engineers.
Here we are discussing one of the simple application circuits of this IC where it is being configured as a comparator, no surprise the following applications can be modified in numerous different ways as per the user preference.
As the name suggests, comparator means the function of comparing between a particular set of parameters or may be just a couple of magnitudes as in the case.

Since in electronics we are primarily dealing with voltages and currents, these factors become the sole agents and are used for operating or regulating or controlling the various components involved.

In the proposed design, where the IC 741 is being used as a comparator, basically different voltage levels are used as the referring and comparaing parameters by the IC.

The two input pins named the inverting (with a minus sign)and the non-inverting pin (with a + sign) become the sensing inputs of the IC 741.

When used as a comparator, one of the pins out of the two is applied with a fixed reference voltage while the other pin is fed with the voltage whose level needs to be monitored.

The monitoring of the above voltage is done with reference to the fixed voltage thats been applied to the other complementary pin.

Therefore if the voltage which is to be monitored goes above or falls below the fixed reference threshold voltage, the output reverts state or changes its original condition or changes its output voltage polarity.

Letsanalyze the above explanation by studying the following example circuit of a light sensor switch.

Looking at the circuit diagram we find the circuit configured in the following way:

The IC 741 is at the center.

Its Pin #7 which is the +supply pin is connected to the positive rail, similarly its pin #4 which is the negative supply pin is connected to the negative or rather the zero supply rail of the power supply.

The above couple of pin connections powers the IC so that it can carry on with its intended functions.

Now as discussed earlier, pin #2 of the IC is connected at the junction of two resistors whose ends are connected to the power supply positive and negative rails. This arrangement of the resistors is called a potential divider, meaning the potential or the voltage level at the junction of these resistors will be approximately the half of the supply voltage, so if the supply voltage is 12, the junction of the potential divider network will be 6 volts and so on.

If the supply voltage is well regulated, the above voltage level will also be well fixed and therefore can be used as the reference voltage for the pin #2.

So if we take 6 as the junction voltage of the resistors, this voltage becomes the reference voltage at pin #2 which means the IC will monitor and respond to any voltage that might go above this level.

The sensing voltage which is to be monitored is applied to pin #3 of the IC, in our example it is via an LDR. The pin #3 is connected at the junction of the LDR pin and a preset terminal.
That means this junction again becomes a potential divider, whose voltage level this time is not fixed because the LDR value cannot be fixed and will vary with the ambient light conditions.
Now suppose you want the circuit to sense the LDR value at some point just around when dusk falls, you adjust the preset such that the voltage at pin #3 or at the junction of the LDR and the preset just crosses above the 6 volt mark.

When this happens the value rises above the fixed reference at pin #2, this informs the IC about the sense voltage rising above the refefnce voltage at pin #2, this instantly reverts the output of the IC which changes to positive from its initial zero voltage position.

The above change in the state of the IC from zero to positive, triggers the relay driver stage which switches ON the load or the lights which might be connected to the relevant contacts of the relay.

Mind you, the values of the resistors connected to pin #2 may also be altered for altering the sensing threshold of pin #3, so they are all inter-depended, giving you a wide angle of variation of the circuit parameters.

Another feature of the R1 and R2 is that it avoids the need of using a dual polarity power supply making the involved configuration very simple and neat.

As shown below, the above explained operation response can be just reversed by interchanging the input pin positions of the IC or, by considering another option where we only inter-change the positions of the LDR and the preset.

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A Simple Tan Timer Circuit Diagram

Six timing positions suited to different skin types, Timing affected by sunlight intensity

This timer was designed for people wanting to get tanned but at the same time wishing to avoid an excessive exposure to sunlight. A Rotary Switch sets the timer according to six classified Photo-types (see table). A Photo resistor extends the preset time value according to sunlight brightness (see table). When preset time ends, the beeper emits an intermittent signal and, to stop it, a complete switch-off of the circuit via SW2 is necessary.

Circuit diagram:

A Simple Tan Timer Circuit Diagram

Parts:

R1 = 47K - 1/4W Resistor
R2 = 1M - 1/4W Resistor
R3 = 120K - 1/4W Resistors
R4 = Photo resistor (any type)
R5 = 120K - 1/4W Resistors
C1 = 10µF - 25V Electrolytic Capacitors
C2 = 220nF - 63V Polyester Capacitor
C3 = 10µF - 25V Electrolytic Capacitors
D1 = 1N4148 - 75V 150mA Diodes
D2 = 1N4148 - 75V 150mA Diodes
Q1 = BC337 - 45V 800mA NPN Transistor
B1 = 3V Battery (two 1.5V AA or AAA cells in series)
IC1 = 4060 - 14 stage ripple counter and oscillator IC
IC2 = 4017 - Decade counter with 10 decoded outputs IC
SW1 = 2 poles 6 ways Rotary Switch (see notes)
SW2 = SPST Slider Switch
BZ1 = Piezo sounder (incorporating 3KHz oscillator)

 

Photo-type	Features	Exposure time
I & children	Light-eyed, red-haired, light complexion, freckly	20 to 33 minutes
II	Light-eyed, fair-haired, light complexion	28 to 47 minutes
III	Light or brown-eyed, fair or brown-haired, light or slightly dark complexion	40 to 67 minutes
IV	Dark-eyed, brown-haired, dark complexion	52 to 87 minutes
V	Dark-eyed, dark-haired, olive complexion	88 to 147 minutes
VI	The darkest of all	136 to 227 minutes
Note that pregnant women belong to Photo-type I

Notes:

• Needing only one time set suitable for your own skin type, the rotary switch can be replaced by hard-wired links.
• A DIP-Switch can be used in place of the rotary type. Please pay attention to use only one switch at a time when the device is off, or the ICs could be damaged.

Source : www.redcircuits.com

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A Jogging Timer Circuit

3V Battery powered, Beeps after a fixed minutes delay

This circuit was developed since a number of visitors of this website requested a timer capable of emitting a beep after one, two, three minutes and so on, for jogging purposes. As shown in the circuit diagram, SW1 is a 1 pole 9 ways Rotary Switch. Setting the switch in position 1, the Piezo sounder emits three short beeps every minute. In position 2 the same thing happens after a 2 minutes delay, and so on, reaching a maximum interval of 9 minutes in position 9.

Circuit diagram:

A Jogging Timer Circuit Diagram

Parts:

R1_____________47K 1/4W Resistor
R2_____________10M 1/4W Resistor
R3______________1M 1/4W Resistor
R4_____________12K 1/4W Resistor (see notes)
C1,C3__________10µF 25V Electrolytic Capacitors
C2____________100nF 63V Polyester Capacitor
D1___________1N4148 75V 150mA Diode
IC1____________4093 Quad 2 input Schmitt NAND Gate IC
IC2____________4060 14 stage ripple counter and oscillator IC
IC3____________4017 Decade counter with 10 decoded outputs IC
Q1____________BC337 45V 800mA NPN Transistor
SW1___________1 pole 9 ways Rotary Switch (see notes)
SW2___________SPST Slider Switch
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
B1____________3V Battery (two 1.5V AA or AAA cells in series etc.)

Notes:

• Needing only one time set, rotary switch can be replaced by an hard-wired link.
• A DIP-Switch can be used in place of the rotary type. Please pay attention to use only one switch at a time, or the device could be damaged.
• Varying R4 from 10K to 15K you can obtain more or less than three short beeps after the preset time delay.
• To obtain a one-second beep only, after the preset time delay, disconnect pin 9 of IC1C from pin 9 of IC2 and connect it to pin 8 of IC1C.

Source : www.redcircuits.com/Page32.htm

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