SPC3 9 Amp in / 10 Amp out Solar Power Center

SPC3 9 Amp in / 10 Amp out Solar Power Center
A kit with the circuit board and parts for this circuit is available from CirKits.

SPC3 Circuit Board Kit


SPC3 9 Amp in / 10 Amp out Solar Power Center

(C) G. Forrest Cook 2007
Introduction
The SPC3 is a solar power center, it can handle all of the power functions for a solar charged 12 Volt DC system. The SPC3 contains a 9 amp photovoltaic charge controller, a 10 amp low voltage load disconnect circuit and a built-in white LED array for area illumination. The low voltage disconnect circuit has a load on-off switch, and a battery low voltage indicator. By using the SPC3 as the center of a solar powered device, long battery life is assured. The SPC3 can be used as a self-contained solar lighting system, it is also useful for making solar powered audio and radio devices and much more.

The circuit was designed with the following goals:

Single board smart solar power system with self-contained light.
Analog simplicity with common parts for ease of repair.
High efficiency: low-loss charging and minimal idle current.
Radio-quiet operation, low frequency charge control switching.
Capable of handling resistive, inductive and capacitive loads.

Specifications

Nominal battery voltage: 12V
Maximum solar panel current: 9 Amps
Maximum load current: 10 Amps, higher power loads can be connected directly to the battery.
Night time battery drain current: approximately 150 micro-amps
Temperature compensation for use in variable climates
Radio-quiet operation

See the full SPC3 kit specifications for more details.


Here are the SPC3 kit alignment instructions.
Charge Controller Theory
The charge controller is shown in the upper half of the schematic. When the PV panel's voltage rises above 12V, current flows through zener diode ZD1 causing transistor Q2 to turn on and send power to voltage regulator VR1. VR1 provides 5 Volt power to the rest of the charge controller circuitry. The charge controller power is supplied by the battery when the sun is shining on the PV panel. During the night, the Q2 circuit turns off and prevents the charge controller from draining battery power.

The upper half of IC1 is the heart of the charge controller. It acts as a comparator/oscillator circuit. When the battery voltage is well below the float voltage setting, IC1 turns on, this causes the LED to turn red and the 4N35 opto-coupler to turn on. The output of the 4N35 activates FET Q1, which connects the solar panel power to the battery through Schottky diode SD1. When the float voltage is reached, the circuit oscillates just above and below the float setting and charging current is switched on and off of the battery. The oscillation frequency is set by the battery charging characteristics and the current that is available from the solar panel. The maximum switching frequency of IC1 is limited by the hysteresis provided by R11.

The thermistor TM1 modulates the float voltage setting slightly, the full voltage setpoint rises in colder temperatures. The lower half of IC1 always produces the opposite output from the upper half of IC1, this is used for driving the bipolar state indicator, LED1. Shorting the equalize terminals causes the float voltage setting to rise, this is useful for occasionally overcharging (equalizing) a battery.

Schottky diode SD1 prevents battery power from leaking back into the solar panel at night. Diode D1 is wired as a crowbar circuit, if the battery is connected in reverse, the fuse to blow, saving the rest of the circuitry from destruction.
Low Voltage Disconnect Theory
The smart switch and low voltage disconnect circuitry is shown in the lower half of the schematic. The circuit operates like a solid-state version of a latching relay. Unlike simple voltage controlled switch devices, when the LVD circuit shuts off, it stays off until it is manually turned back on with a flip of switch S1. This action prevents the load from oscillating off and on due to the rise in battery voltage after the load is disconnected.

When momentary switch S1 is turned on, transistor Q5 is turned on. This activates the comparator circuits formed by IC2d and IC2c. When the circuit is active and battery voltage is above the LVD setpoint, the IC2d comparator output goes low and transistor Q4 is switched off. This allows gate drive voltage to reach Q3, Q3 connects battery power to the load. Resistor R16 bleeds off the gate drive voltage from capacitor C8 when the circuit shuts off.

When momentary switch S1 is turned off, the Q3 gate drive voltage is shorted to ground, causing load power to be switched off.

IC2a and IC2b form a square wave oscillator, the output of the square wave is fed to the D3,D4,D5 voltage tripler circuit to produce the gate drive voltage for Q3.

Once the LVD circuit has been turned on, diode D7 feeds the load power back to the circuit to keep it active. Power to LED3 and LED4, the two white LEDs is routed through R17, a current limiting resistor.

Regulator VR2 provides a reference voltage for the oscillator circuit and for the battery voltage comparator ladder IC2c and IC2d.

IC2c is the low battery sense comparator. When the battery reaches 0.6V above the shutoff point, the IC2c output goes high and turns on the yellow LED. Resistor R21 sets the difference between the low voltage indication and the power shutoff.
Charge Controller Alignment
Connect the PV panel and battery to the circuit, put the PV in full sun. Turn the float voltage setting fully clockwise, the dual color LED should turn red. Connect a volt meter across the battery and monitor the battery voltage. The battery voltage should gradually rise while the sun shines.

Leave the circuit connected until the battery voltage has reached or exceeded the desired full-charged setting, this is typically around 13.8V at room temperature. Turn the float voltage setting counter clockwise until the LED alternates red and green. Tweak the setting until the LED blinks and the battery voltage is where you want it to be at the full state. When the LED is alternating red/green, it is normal for the battery voltage to vary by about 10mV.

If a battery pack with a float voltage setting below 13V is used with the SPC3 (NiMH for example), zener diode ZD1 should be changed to a 1N4740 (10V) and resistor R6 should be changed to 250K.
Low Voltage Disconnect Alignment
Disconnect the battery from the SPC3 and connect a variable voltage power supply that can produce 10 to 15 Volts across the SPC3 battery connection. Observe the correct polarity. Set the variable supply to 11.6 Volts. Turn the LVD Setpoint pot fully counter-clockwise. Turn the power switch on. The White power LEDs should turn on. Turn the pot clockwise until the yellow low voltage LED just turns on. Monitor the supply voltage while you decrease it, at around 11V, the LVD should turn off the white LEDs. Repeat the adjustment if you wish to fine tune the shutoff voltage.
Use
Connect a 12V rechargeable battery, photovoltaic panel, and (optionally) a load to the circuit.

As sun shines on the solar panel, the circuit will pass charging current to the battery. The dual color LED will turn red while solar charging is taking place. When the battery voltage rises to the full setpoint, the charging current will be periodically cut off and the LED will alternate red and green.

The load can be operated during daytime charging and at night.

The on/off switch controls the load like a normal power switch. If the battery voltage drops to 0.6V above the shutoff point, the yellow LED will light up. If the battery voltage drops further, the circuit will shut the load off, preventing deep discharge of the battery. This greatly extends the life of the battery.
SPC3 Circuit Extensions
The SPC3 LVD function is automatic, when the battery voltage drops below the LVD setpoint, the load is turned off. The basic SPC3 circuit requires a manual operation of the switch to turn the load back on after the battery recharges and the voltage rises. For some applications, it may be desirable to have the circuit turn back on automatically. The following circuit can be used to perform this task. It is a simple voltage comparator circuit. When the battery voltage, which is tapped off after the SPC3 fuse from the PV+ line, rises above an adjustable setpoint the op-amp turns on the 2N3904 transistor. The transistor connects the SPC3 On switch to ground, turning on the SPC3 load control circuitry. The turn-on adjustment should be set to activate the circuit when the battery voltage rises somewhat above the SCC3 LVD setpoint to prevent oscillation.

SPC3 Turn-on circuit
Solar Charge Controller Kits For Sale
A kit version of this solar power center circuit is available from CirKits.com, buying the kit will save you time locating parts and wiring the circuit.

Solar Charger 2

SCC3 Circuit Board, Assembled SCC3 Wiring Diagram
Photo of an assembled SCC3 kit. SCC3 wiring diagram
SCC3 - 12 Volt 20 Amp Solar Charge Controller Kit
The SCC3 kit is the heart of a 12 Volt solar power system, it regulates the charging of batteries from photovoltaic (PV) solar panels. A charge control regulator is an essential part of any solar power system.

A 12 Volt solar power system can provide power to a wide variety of devices. Some examples include: lighting systems, CB and Ham radios, car stereos, cell phones, laptop computers, televisions, recording equipment, fans, water pumps and other 12V DC loads. With the addition of a DC to AC inverter, the DC power can be converted to 120 Volts AC for powering an even wider variety of devices.

The SCC3 is suitable for both permanently installed and portable power systems. It is an excellent choice for emergency backup lighting systems and independent building power supplies. Combine the SCC3 with a solar panel and rechargeable battery for a reliable source of DC power that's available, even when the power company is not.

Controls and indicators include a battery float voltage adjustment, a battery equalize (overcharge) switch and a red/green Charge/Float LED.

See the SCC3 specifications for details on the kit's capabilities.

The SCC3 Photo Gallery shows some real-world uses of the SCC3.

The SCC3 kit makes a great student project, it can be used as the foundation for many solar powered projects. The efficient design is suitable for charging large banks of lead acid batteries or small packs of rechargeable cells.

The kit includes:

* A high quality double sided, silk screened circuit board.
* All of the parts required for building the board.
* A schematic and wiring diagram.
* Easy step-by-step assembly, alignment and usage instructions.


Batteries, solar panels, and solder are not included with this kit.
Follow the Alternative Energy Web Sites link below for solar panel and battery suppliers.

12 Volt Toilet Tank Refiller

(C) G. Forrest Cook November 24, 2002 Rev 2: August 28, 2003.

This project can be used with a CirKits solar circuit kit.

The 12V pump on the side of the cistern

The rev 1 circuit in action

The rev 2 circuit board and sensor

The schematic

Introduction

A flushing toilet is something that most city dwellers take for granted, but it can be a luxury for those who live far away from utility water and electricity. This circuit controls a small 12 Volt pump that is used to fill a toilet tank from an external rainwater collection cistern. Automotive windshield wiper pumps work nicely in this application. The 12 Volt power in my application comes from a small solar power system, it may also be provided by a suitable wall-wart DC power supply. The cistern is located below the toilet tank, the pump moves the water up to the toilet's tank. The pump is switched on when the toilet tank is empty, it is switched off when the tank has filled.

Specifications

Nominal operating voltage: 12V Idle current: <>  
Theory
  The Panasonic hall effect sensor is the heart of the system. The hall effect sensor's output pulls to ground when in the presence of a relatively strong magnetic field.  When the magnet is pulled away from the hall effect sensor, the output goes high via the 10K pull up resistor.  This turns on the IRFZ34N MOSFET transistor, which pulls the negative lead of the 12V pump to ground, turning on the pump.  The LED is also turned on. 
 The 1N4004 diode snubs out potential spikes from the motor, and the 1000uF capacitor across the motor eliminates motor brush noise from the DC wiring. The 100uF capacitor filters noise from the 12V power source. As with all electrical circuitry, it is important to have a fuse and a switch in series with the power source, that is not shown in the schematic. 
 The 10 amp silicon diode is used in a crowbar circuit. Its purpose is to protect the circuit from reverse DC polarity on the power terminals.  Reverse polarity causes the fuse to blow. 
 This circuit will work with most momentary action (non-latching) hall effect sensors, you may want to experiment with the sensor and magnet to find the most sensitive orientation for both parts.    
Construction
  The rev 1 version of this circuit had all of the parts inside of the toilet.  This turned out to be a bad idea as water splashed onto the board and electrolysis corroded the electrical connections. 
 Rev 2 involved splitting the circuit into two parts, the hall effect sensor assembly, and the rest of the electronics.  The hall effect sensor was soldered to a small piece of circuit board, that was then screwed onto a piece of plumbing strap.  The entire sensor assembly was then coated in epoxy glue to make it waterproof. A 100nF capacitor was connected from pins 1-3 on the hall effect sensor and also covered with epoxy, it reduces the chance of the sensor picking up stray radio signals. 
 The rest of the circuit was built on another circuit board, that was mounted on a cover plate for a standard 4"x4" electrical box. Wires from the box connect to the sensor, the pump motor and the 12V supply. 
 The magnet was connected to the toilet tank float with duct tape.  A better magnet mount could certainly be fashioned, but this arrangement has held up for many years. Sometimes it is necessary to cheat when working in the field. The magnet was removed from an old miniature speaker.  The voice coil gap around the magnet's pole-piece was filled with silicone sealant to prevent rust.  People in damp climates may want to coat the entire magnet with epoxy paint or silicone caulk. 
 The pump inlet is connected to a valve and reducer assembly at the bottom of the cistern tank.  The pump outlet travels through a short section of conduit, into the building, and into the toilet tank via a piece of bent copper tubing.  The pump inlet should be near the bottom of the supply tank, it is a good idea to run the water source through a filter made with some metal screen in a PVC pipe to prevent debris from clogging the pump. The copper tubing output in the toilet tank should be above the tank's full water level, this prevents back-siphoning. 
 The pump output tube and wiring is built with connectors so that the pump can be removed when the building is unoccupied.  A more permanent installation can be done by mounting the pump in a metal box on the side of the building.   
Alignment
  Bend the metal strap that holds the sensor board so that the hall effect sensor is directly above the magnet.  Adjust the height of the PC board so that the circuit shuts off at the desired water level.   
Use
  Flush the toilet, the red LED will light up, and the pump will move water into the toilet tank.  As soon as the water level reaches the top, the pump will shut off.  Just like in the city. If you want to use this device in an area where the temperature gets below freezing, the water supply, pump, and water tubing will need to be mounted in an area that does not freeze, such as underground. This circuit has been in use for many years, it sure beats hauling buckets of water from the rainwater collection system.  
Failure Modes
  I have gone through a number of different pumps, mostly due to operation at temperatures below the freezing point of water. Applying power to a frozen pump will cause the pump motor to burn out. The rest of the circuit has managed to survive this abuse, a properly sized fuse may protect the motor from this problem. A useful revision to this circuit would be to include a cut-off circuit that prevents the motor from running when the outside temperature drops below freezing.  This problem was greatly reduced by moving the pump indoors to a location where the pump did not freeze.  Freezing of the supply tube is still an issue.  
 Another failure can occur if the supply tank runs dry.  In this situation, the pump will run continuously and the motor commutator will eventually wear out.  This problem could be corrected by either adding a pressure switch to the water line, or adding a timer that shuts off the motor power after a few minutes of operation.   

Solar Charger

Here's a neat little project that uses both your ham and carpentry homebrewing skills. (No jokes about my woodworking, now...)
About a year ago, I bought a 5 Watt solar panel on sale at Harbor Freight. It's an ICP Battery Saver Pro, and will supply about 15 Volts DC at 335 mA in full sunlight, which is about perfect for the 7 AH batteries I usually use for QRP portable. For a while, I just lashed-up some battery clips and wire, laid the solar panel on a lawn chair, and used a voltmeter to check the progress of the charging. I soon tired of hauling around all the piece-parts, and decided to consolidate battery, metering, and panel into a single enclosure. The result is what you see here, a 15" x 15" wood box about 5" high. This is not rocket-science, folks, so I'm not going to give dimensioned drawings, but I'll present the pictures with a description of what's going on, and you can duplicate it on your own from that point.





In the picture above, you can see what I'm trying to accomplish. I wanted to be able to store the battery and wiring inside the box, and hinge the top of the box so that it opens. The top of the box holds the solar panel, which can be propped at any convenient angle to maximize the solar collection (and so, the charging current). The box was built from 1x4" pine boards and 1/4" thick particle board. Cheap, real cheap...


The next picture (above) is a close-up of the method we use to prop the panel at the desired angle. I used two 1/2" dowels, about 3-1/2" long, one on each side of the solar panel. The sides of the box were then drilled at intervals, so that I could insert the dowels wherever I wanted along the side, to effect the desired angle. It works pretty well, and if I want the box closed (or near-flat), I just throw the two dowels inside the box, and the door-panel (solar-panel) serves as the top cover.

This image (above) shows the guts of the unit, and needs a little explanation. First, you'll see the 7AH, 12V battery. It connects with 1/4" quick-connect terminals, and can be swapped out readily (I keep 3 batteries standing by at all times). A little 1x1" wooden barrier keeps the battery from sliding around during transportation. Barrier strips were selected as tie-points for all wiring, in an attempt to keep things neat. Both current and voltage are monitored; current so I can verify charging is taking place, and voltage so I can see when to stop charging (around 14.4 volts maximum for a gell-cell lead-acid battery). I just used Radio Shack meters. I also installed a switch, and some circuitry for charging 2 NiCad D-Cells (the 4500 mAH type, which I use in my QRP battery booster accessory). The switch selects which battery is actively being charged (the lead-acid or the NiCad D-cells). This picture also clearly shows the hinges and holes for the propping dowels.


Here we see the front panel. The left meter reads the battery voltage, and the right reads charging current. The center switch selects which of the batteries is currently in the circuit. In this case, we see that the NiCad D-cells are in the circuit, that the voltage applied is about 2.5 volts, and the charging current is about 25 mA (from ambient indoor light)

Finally, here's a schematic of the electrical hook-up. The circuitry for charging batteries is unregulated, and depends on the operator to disconnect the battery before it gets overcharged. The circuitry for the NiCads is an especially crude regulator, but it keeps the batteries from over-charging. Here, two series silicon rectifiers limit the voltage to about 1.3- 1.4 Volts (1.43 Volts is about ideal for a NiCad to terminate charge), A planned improvement is to add real regulators so that over-charging cannot occur. A 14 Volt fixed-voltage-regulator would be ideal for the lead-acid battery, and maybe something a little more sophisticated for the NiCads.
Using this setup, I've found that I can charge a mostly-discharged 7-AH gell-cell in about 3 days of Texas sun. The NiCads take about 1-2 days.
Hope this gives y'all some ideas!
73, monty N5ESE