SOLAR BATTERY CHARGER CIRCUIT

Solar charge controller circuit that is used to charge  inverter batteries and car batteries using the solar energy.

12V, 24V, 36V, 48V, 72V SOLAR SOLAR BATTERY CHARGER CIRCUIT.

A solar battery charger is a charge controller device that controls the charging state of a battery when using solar panels. Solar chargers comes in different forms and types. But the most important aspect of it is to get your batteries charged without over charging them or under charging them since any of the two conditions can reduce your battery life. Also, the charger should not waste power and in that case must be highly efficient.

Today am going to show you how to make for your self a highly efficient two stages solar charger (solar charge controller).

HOW THE SOLAR BATTERY CHARGER CIRCUIT WORKS

The circuit is built around LM358, CD4013 and N-Mosfets. The charging current of this circuit is 60A but can be increased to handle 80A by using appropriate Mosfets or connecting more mosfets in parallel.

The op amp LM358 has two independent comparator within the 148 pins single package. Please download the data sheet from https://www.onsemi.com/pub/Collateral/LM358-D.PDF

The second  part of the op amp is configured to give a high output when the battery is low. The high output is sent to pin 5 and pin 9 of CD4013 digital IC which is called data pin. This causes pin one of the CD4013 to go high and turn optocoupler U10 on. When U10 turns on, Q13 also turns on and positive voltage is applied to the gates of the N-Mosfet to turn it on for charging to start.


When solar battery Charging is complete, pin 7 of LM358 which is the op amp 2nd output pin goes low. As the op amp goes low, pin 2 of CD4013 goes high whiles its pin 1 goes Low. The high output from Pin 2 of CD4013 turns U14 on and this turns of the mosfet to stop the charging. I did not add hysteresis because i want the output to be always stable at my set battery full value.


whiles pins 1 and 2 of CD4013 takes care of switching the mosfets, pins 13 and 12 of CD4013 will turn on LED 2 and LED 1 to indicate charging and floating respectively.


The second op amp is configured to generate square wave clock signal and its output is fed to the clock pins of CD4013 flip-flop IC. Download CD4013 datasheet.When clocking is working, output pin 1 of the op amp will measure 2.5V or close.

12V 24V 48V 96V

SOLAR BATTERY CHARGER CIRCUIT

Updated Circuit

To set floating level ( battery full level), connect the battery to the circuit and connect your solar panels to the part labeled panel. Please ensure correct polarity though the circuit has reversed polarity protection.

monitor the charge level with a voltmeter and when battery reaches your desired battery full level, adjust U13 variable 10k resistor until float indicator turns on. In that case, the battery voltage will neither go up nor down but stable. That is called floating, this kind of charging ensures that your battery is always charged.


Other voltage designers should leave their designing voltages in the comment section below and i will be ready to support them. All other comments are also welcome.

Update: U5 should be replaced with LM7812 or any 12V voltage regulator.

OVERLOAD PROTECTION CIRCUIT AND LOW BATTERY ALARM

How to connect the low battery protection circuit and an overload protection circuit to any circuit that uses pulse width modulation IC such as SG3525, SG3524, UC3842, 43,44, TL494 etc.

Its Good to know and understand the functions of the pins of the PWM IC that you are going to add this function to. I therefore advice that you google the IC number and download its datasheet in PDF or any readable format.

Every pulse width modulation IC has either of these functional pins: Shutdown or current sense (Is) or even both in some ICs. 

 This post was requested by Mr. Amon from Asamankese (E/R). 

LOW BATTERY AND OVERLOAD PROTECTION FOR PWM IC

FUNCTIONS OF SHUTDOWN PIN

The function of the shutdown pin of any pulse width modulation (PWM) IC is to safely stop or turn off the PWM IC when the pin senses voltage higher than its operating point (threshold). After the IC has turned off, the system will turn on only when the cause for increased pin voltage is removed or reset.

FUNCTION OF CURRENT SENSE (Is) PIN

The current sense pin works the same way as the shutdown pin. When the pin dedicated for current sensing sees voltage higher or equal as the threshold voltage, the IC temporally, stops operating in other to save the system. The IC will begin to work normal again after the cause of overload is removed.


Current sense and shutdown pins responds to voltage within 0.3V to 5V with little current in milli ampere (mA). This means that if we are able to provide a circuit that will deliver 0.3V to 5V or above during low battery or overload, our aim of designing a low battery and overload protection circuit will be fulfilled.
 

HOW TO SENSE OVERLOAD CURRENT

Many people have the problem of sensing overload current in power system circuits. Their main problem has been either they are not getting a small resistor value which is usually called SHUNT or They are not getting a good length of AWG to provide a resistance value in Milli ohm. Personally, i prefer using AWG copper since its always common than real shunt resistors.


Overload current can be sensed either at the DC side or AC side. Its advisable to sense inverter overloads at the DC side. In that case, Mosfets can be used as Shunt resistors since they have some resistance in milli ohms even when they are fully turned on. Connecting the mosfets in parallel is same as connecting its internal resistance in parallel and hence forming low resistance shunt.


One thing to know is that before you can choose a good shunt value, you have to know the maximum current you want to switch and the voltage drop that must occur. This can be known using simple ohms law: V=IR where V is the maximum voltage drop that should occur at maximum current I. R is the shunt resistor value. Read the power drive stage of this post to learn how to calculate max current.


The circuit below shows how to sense overload DC current and connect it to the current sense pin of a PWM IC. 

ADDING LOW BATTERY PROTECTION TO PWM IC

I have already writing about low battery protection for battery powered devices and explained the circuit operation. I will therefore move on to show you how to connect this updated circuit to any pulse width modulation IC to shut your system off when battery runs low so that your battery doesn't over drain.
 

overload protection, low battery alarm and low battery shutdown circuit for inverters

A shunt resistor is a small value resistor or resistive device connected in a circuit mostly for the purpose of current sensing.

In the above circuit, the mosfet stage is connected to the shunt resistor which is connected in series with the negative supply of the battery. Please ensure that only the mosfets are connected to this part. all other sections of your inverter should be connected before your shunt. shunt size should be calculated by you based on your max current as discussed earlier.

Adjust U3 to set your low battery shutdown.

Adjust U2 to set your battery low alarm

POWER STABILIZER CIRCUIT

In this tutorial we are going to design an AC Voltage stabilizer using auto transformer. Auto transformer is a transformer with its primary and secondary connected together. This type of transformer is mostly used for AC voltage regulators (stabilizer).

100VA TO 10KVA POWER STABILIZER CIRCUIT

 

CLICK TO ENLARGE

Circuit Explanation

The circuit above is a Voltage stabilizer circuit designed and tested by me. The circuit uses an auto transformer for voltage stabilization. It has same useful functions as stabilizers currently on our markets. It has built in Delay, delay indicator, working indicator  and automatic switching.

The design accepts a wide range of input voltage ( 140V to 260V AC ). This does not mean that the circuit will fail when those voltage ranges are exceeded but its within these range that the AC voltage regulator will give constant 220V .

When power is applied to the unregulated input and S1 closed, Diodes D1 and D2 rectifies the 20V from the transformer and IC LM317 regulates its to 13V DC which is used to run the system. when the system starts working and the delay switch is closed, the output relay U2 will not switch until the delay time has passed. When delay time set by R1 and C5 is over, Q4 switches the output relay and the working indicator will now turn on to indicate working state.

To use the design for high power applications, use high current handling relays, else relay will fail.

HOW TO SET AUTOMATIC VOLTAGE REGULATION 

Automatic regulation is done using LM324 and LM358 configures as voltage comparators. To configure the system to work automatically, use a variable AC of 140V to 240V and adjust the variable resistors until their corresponding relays turn on at the voltages written on the variable.

Another way is to use a variable supply AC supply of 12V to 25V AC. when using this method, set your supply to 21.8V and adjust  the 240V variable until its relay turns on. Next, Adjust your variable supply to 20V and adjust 220V variable until its relay turns on. .....do the same for 200V at 18.1V, 180V at 16.4V, 160V at 14.5V and 140V at 12.7V AC. 

Please connect your variable supply at the 20V point.

Another way of setting up the system is to use variable DC supply of 33V-15V DC and adjusting the variable resistors to turn the relay on. At 31V adjust 240V variable until it turn on, at 28V adjust 220V, at 25.5V adjust 200V, at 23.2 adjust 180V variable, at 20.5DC adjust 160V variable and at 18V adjust 140V variable.

How to repair inverter part 1

Learn this simply way of repairing an inverter.

 

How to repair inverter

Inverter repairs  is not common and repairing a faulty inverter has not been an easy task for the local electronic repairers. This has made the few of us who does professional repairs to charge more especially when the inverter is a foreign made. I particularly do this to promote local inverter manufacturers as well as my products and discourage others from buying inferior foreign inverters which can even fail on same day. Lets start this first part of inverter repairs by knowing the types of inverters we currently have on market.

TYPES OF INVERTER

On the commercial market, the types of inverters seen are square wave two stages inverters, square wave single stage low frequency inverters, modified sine wave two stages inverters , modified sine wave single stage low frequency inverters, pure sine two stages inverters, pure sine single stage low frequency inverters.


TWO STAGES INVERTERS



Two stages inverters are inverters that first converts the input battery voltage to 300V - 310V DC using high frequency. This is achieved by switching ferrite transformers at high frequency. The square wave output of the ferrite transformer is then rectified using diode bridge rectifier and filtered using 400V electrolytic capacitors. This ends the first stage of the two stages inverter.
Before we go to the second stage, please know that the components in the second stage is powered by a separate 15- 25V winding on the ferrite transformer used for the 310V switching.
The second stage of two stages inverters works by converting the 310V DC to 220V AC pure sine or PWM or Square Wave using mosfet bridge or mosfet half bridge with an appropriate control drive circuit.


SINGLE STAGE (LOW FREQUENCY CONVERTERS)


This type of inverters consists of a driver stage (oscillator stage) and mosfet switches arranged in either a push pull ( for center tap transformer inverters ) or H-bridge ( for inverters without center tap transformers. This type has mosfets fixed on three different heat sinks.)

OSCILLATOR STAGES OF ALL CONVERTERS

Every inverter is made up of a control signal generation stage called the oscillator. The oscillator in lay mans term can be explained as an electronic signal that goes on and off at a set frequency. For inverters, the set frequency may be either 50 times in one second (50Hz) or 60 times in a second (60Hz)

Currently, inverters on market uses either a pulse width modulation (PWM) IC for their oscillation stage or a microcontroller with built in PWM.

COMMON INVERTER OSCILLIATOR ICS


commercial inverters and UPS are built around the following ICs.


SG3525

SG3524

TL494

CD40..

MICRO CONTROLLERS

Common Decision making ICs (OP AMPS) used in commercial inverters



LM324

LM358

LM339

LM471

LM258

ETC.
FUNCTIONS OF THE OP AMPS IN INVERTERS

Every good inverter has a number of operational amplifiers (OP AMPS) configured or designed to take simple decisions for the inverter. These decisions may include:


Battery Low

Battery Full

overload in some cases

high and low temperature

Fault.

In How to repair inverter part 2, I will tell you how these op amps can cause fault and how to remove or solve the faults in few minutes.
Now that you have idea of the compositions of an inverter, lets start our troubleshooting and repairs by reading INVERTER REPAIRS 2.

LOW BATTERY ALARM CIRCUIT

The circuit below will provide you a beeping alarm when your battery is low (below your low battery set point) and also turn off any circuit or device connected to it when battery goes below your second set point.

The beeping circuit consists of two transistor astable multi-vibrator which turns the buzzer on in short pulses avoiding continues high pitch noise.

Low Battery protection and alarm for Inverters and battery powered applications

LOW BATTERY PROTECTION AND ALARM CIRCUIT USING P-MOSFET

LOW BATTERY PROTECTION AND ALARM CIRCUIT USING RELAY

The circuit is designed around LM358 operational amplifier configured as comparator (click here to download data sheet). The IC has two different op amps (A and B) in a single package. Both op amps are given a common reference voltage of 4.7V or 5.1V using zener diode D2. Variable resistors U3 and U4 are used to set the operating points (thresholds) of their corresponding op amps.

low battery alarm Setting

When setting low battery alarm, monitor the battery voltage using voltmeter. Now let the battery run down to the point where you always want to be notified and adjust U4 until the buzzer start beeping and LED2 starts blinking.
Setting low battery protection or shutdown

After the alarm, let the battery drain some little more and adjust U3 until the output light and the alarm goes off. These settings are done once and it will always work for u as set.


Please note that, when the system turns off, it may not be able to turn on instantly unless the battery level has increased beyond a certain level which is set by R7. (Hysteresis). This functions sees to it that the circuit does not turn on and off unnecessarily.

To increase the turn off / turn on time, please decrease or increase R7.

PRESS ON OFF SWITCH CIRCUIT

Simple soft press switch using an NPN transistor, N mosfets, and either a P mosfets or a relay depending on your load.

The soft press switch in this circuit is similar to our computer, monitor and some phone switches. I like it most because of its durability and nice look when fixed.

SOFT PRESS SWITCH CIRCUIT DIAGRAM

PRESS SWITCH CIRCUIT OPERATION

IRF5210 can be replaced with a 12V relay to control heavy loads. The relay is connect to point A and B. Connecting a 100uf capacitor across the relay coil will ensure better operation.

When an input voltage is applied, the circuit stays off until the switch S1 is pressed because Q8 has turned on and connected the base of Q10 close to ground.

Because U23 is not charging, it’s shorted, hence, pressing the switch S1 shorts the base of Q8 and connects it to ground through R30 and U23. This actions turns Q8 off to remove its latch and allows Q10 to turn on and Q9 or the relay is turned on and latched until the switch is pressed again.

As Q10 turns on, U23 is charged through R47 and R46 at time constant 2RC. When U23 is charged and the switch is pressed again, the voltage stored in capacitor U23 is connected to the base of the NPN transistor through the 220 ohms resistor and the circuit turns off again and stays off until next press or infinity.

Capacitor U21 ensures that the circuit operation is not affected by electrical noise.

 To let the circuit turn on automatically at DC in or power restored, remove U24 from the circuit. Else leave it as it is for the function explained above.

The circuit is tested and is in use.

INVERTER BATTERY CHARGER CIRCUIT

In inverter designing, one of the most required tasks is a good charging system. A good inverter charger will increase battery life span and will also increase the run time of the inverter. 

Many inverter chargers exist but one that will keep the battery always fully charges is the best. These type of chargers are known as float chargers. 


A float charger is a charger that keeps the battery always under its float voltage level or fully charged level without over charging it.

Many poor or basic chargers consists of relays that disconnects the power supply line when the battery reaches its full state. This is not best because the relay contacts may stack and the battery will be overcharged and even swell up.

Many home made inverter chargers also lacks current regulation and also make heavy humming noise during charging.

The circuit below shows an inverter charger circuit for all battery sizes. The circuit is based on Iron transformer, SG3524, Mosfets, fast switching diodes and filter capacitor.

INVERTER  CHARGER CIRCUIT FOR ALL BATTERY SIZES

CLICK TO ENLARGE

LEARN HOW TO MAKE INVERTER TRANSFORMER 

INVERTER  CHARGER CIRCUIT OPERATION

The power conversion technique employed here is bridgeless boost power factor correction (boost PFC).  This technique ensures minimum parts count and high reliability.

One adorable advantage of this circuit is that, a smaller transformer can charge a battery of any ampere hour (AH) rating.

The circuit is based on SG3524 PWM IC. The datasheet of the SG3524 can be downloaded from here.

The inverter float charger works by supplying 220V or110V AC to a step down transformer T1.

This produce a stepped down voltage at the secondary side of the transformer.

D1, D2, Q1 and Q2 forms a bridge circuit which is connected to the secondary side of the transformer. The secondary winding coil forms an inductor connected to the bridge circuit. This means that if we are able to switch Q1 and Q2 alternatively at a higher frequency, the circuit will behave as a boost converter which will boost the stepped down AC to a high voltage DC.

Example, if a 12V transformer is used, more than 36V DC can be obtained from the output. This means that, a small 12V transformer can be used to charge 24V battery bank or 36V battery bank.

Best practice is to use a transformer with half of your battery bank ratting for charging or little higher than half. That is select 6V-10V for 12V battery banks, 12V -18V for 24V battery banks, 28V to 19V -24V for 36V battery banks etc. 

D1 and D2 can be any fast switching diode which can handle your desired output current. 

Q1 and Q2 is any N-mosfet which can handle your maximum charging voltage and current. 

NB. the mosfet voltage should be higher than your floating voltage by minimum of half.

The duty of the SG3524 is to switch Q1 and Q2 alternatively at a frequency set by U4 and R12.

U4 is 103 fixed capacitor and R12 is 100K.  This set the operating frequency to f = (1.3/RtCt) where Rt =100k and CT = 0.01uf.

If the value for RT and CT does not work for you, you can use 104 capacitor and 4.7k

T2 is a current transformer which is used for setting the maximum charging current. The current transformer is done by removing all the secondary winding of any transformer (smaller ones preferred ) and using a cable to rewind the part you removed by 2 turns. After winding, connect it as shown in the diagram above.

The output from the current transformer is rectified using normal diodes and fed to pin 10 for current regulation. U3 is used for setting the charging current. PLEASE ENSURE THAT U3 IS CONNECTED BEFORE TESTING YOUR CIRCUIT IF NOT, THE HIGH VOLTAGE FROM THE CURRENT TRANSFORMER WILL CAUSE THE SG3524 TO FAIL.

U2 is used for setting the floating voltage or battery full level.

READ ALL MY POSTS FROM THE LINK BELOW

DSPIC30F2010 inverter with charger circuit

SG3524 INVERTER WITH CHARGER

MAKE FERRITE TRANSFORMER

MAKE INVERTER TRANSFORMER

https://manycircuits.blogspot.com/

SG3524 PWM INVERTER CIRCUIT

PWM Inverter circuit  with charger  using a single transformer. The circuit is based on SG3524 IC.

Inverters are electronic devices which converts battery power (DC) to alternating current (AC) which is clean enough to power our useful appliances.

Inverters can be expensive but going through this tutorial can give you enough ideas to build your own solar inverter at home without spending much.

Let’s go through the designing and construction of 100W to 6000W single phase PWM inverter or UPS with charger using a single transformer, since two transformer systems requires much money and also much space.


The PWM inverter circuit is made up of three sections:

1. Oscillator section

2. Power driver stage

3. Change over and charging stage

THE OSCILLATOR STAGE 

FOR PWM INVERTER CIRCUIT WITH CHARGER

Credits to Nick_Zouein of instructables.com who provided the driver stage. which was later updated by me base on testing.

This is the heart of the solar inverter design. The main inverting work is done by this section using pulse width modulation IC (SG3524 or KA3524) or similar. Below is a 12V inverter circuit but few components can be changed or added to work for 24V, 48V and 96V systems whiles the concept still remains unchanged.

In this design the oscillator section is powered by a nine volts regulator IC (LM7809) when switch S1 is closed. The output frequency of the inverter is determined by R22, R23 and U12 (104 fixed cap). Theoretically, total resistance values should be higher but practically these values works best without humming in inductive loads such as fans. The output of the inverter/UPS is regulated using U3 which is 10K variable resistor or pot. This ensure that the output is always stable or within accepted range when loaded.

POWER DRIVE STAGE FOR PWM INVERTER CIRCUIT WITH CHARGER

This stage switches the transformer on/off 50 times is a second. That is 50Hz frequency base on the output from pin 11 and 14 of SG3524. 
The main components used here are N-Channel mosfets connected in parallel to deliver the required current to the transformer as shown in the circuit. In my designs I always assume that each pair will switch 20A of DC current. So if I want to switch 1000W using 12V DC supply, I calculate the max current to switch, which is 1000/12 = 83.3A. I then divide 83.3 by 20A which is my assumed current for each pair of mosfets and get 4pairs as the number of Fets to use.

Another great function of this section is to act as a half bridge rectifier during charging. During inverter charging, pin 10 of SG3524 receives positive signal from optocoupler U17 and shut down the SG causing the mosfets to turn off. The internal body diode of the mosfets then acts as rectifier to achieve DC battery charging.

PWM Inverter circuit with charger

INVERTER CHARGING

Battery charging is controlled automatically by LM358. It is configured such that the output pin 1 goes high when the battery voltage drops from a set value using U19. The high output turns Q10 on, but since Q10 and Q11 are connected to form an AND gate, when optocoupler U16 senses the presence of 220V input, Q11 also turns on and relay U14 switches and charging begins. When the battery is full adjust U19 until the relay switches and the full indicator turns on to set battery full.

 Relay U15 provides output from the inverter as well as your nation grid for the inverter to work as UPS. Output is filtered using 335 by 400V capacitor. In some cases without filter some inductive loads will not run. The system is protected from power surge using NTC 8 ohms or better. You can add NTC in parallel when handling higher wattage. this will cause the NTC not to over heat.

How to wind PWM Inverter Transformer

The transformer secondary coil must be Thick enough to handle the high current at the DC side else undue voltage drop will occur when loaded with little load. A center tap transformer is to be used for this project with the following specifications:

SECONDARY: 12-0-12

24-0-24

48-0-48

PRIMARY: 0-220-250

0-110-140 for US

NB: use 0-200-250 secondary for places with low line voltages else charging won’t occur.

AWG for primary should be 11 and below depending on the wattage. (You can double AWG or use higher voltage design for high output power)

NB. You can lower or increase charging current by reducing the secondary turns and voltage. E.g. To lower 12-0-12 charging current…make it 11-0-11 and vice versa.

Feedback winding: this should be a separate winding on the same transformer in the range of 12V to 16v. Winding gauge should be smaller…AWG…..18 to 28.

H BRIDGE

H Bridge circuit is the arrangement of electronic switches in a pattern that forms the letter ''H'' during switching. The switches may be bipolar transistors, Mosfets, IGBTs, etc. 

These switches are controlled by logic signals in such a way that the four arranged switched connected in "H" turns on diagonally as shown below:

In H bridge circuit, never should two switches on the same side eg. A and C or B and D be turned on at the same time.

Turning A and B or C and D on at the same time will create a bombing sound and all your mosfets or transistor will produce beautiful smoke with a nice smell......Hahaha

H BRIDGE CIRCUIT FOR INVERTERS

In inverter systems, H bridges are mostly used for pure sine inverters with only few modified sine wave inverters using them.

H bridge inverters are best for me especially when it comes to their way of charging your batteries until float level. The circuit below is an H bridge circuit which can handle 1000W to 3000W 12V, 1000W to 4000W 24V, 1000W to 5000W 48V.  

Before you use any mosfet, please make sure your highest switching voltage is less than the maximum operating voltage of your mosfets by at least half. 

Example 48V inverters should use at least 100V mosfets using 75V may result in failure.

H BRIDGE DRIVER CIRCUIT

Click to View

CLICK TO VIEW

NB. without the addition of surge capacitors or not adding enough, your pure sine inverter will fail on inductive loads eg. fridges, air conditioners etc.

You can assume that 10000uf is for every 1000W.

There is something I omitted, that is a fast switching diode paralleled with a 47ohms resistor to feed the high sides and the low sides gates. 

Connect this in series to the output of your driver stage before connecting it to this H bridge. Its another form of protection against failure. 
Read more about this by clicking this link
http://manycircuits.blogspot.com/2017/05/mosfet-heating-solution-for-h-bridge.html

Types of inveter protection

Inverters must have various protections so that they can withstand the tests of time. At times, the inverters you design or build are not used by only you. Therefore its advisable to include some basic decision making functions for the inverter to behave at every point as though you are making those decision at those points in time.

Below are some basic inverter protections which can be achieve by using op amps configured as comparators. If you are into programing, you can also include them in your programs, else its advisable to use op amps. 

 INVERTER PROTECTIONS

• Overload warning alarm with indicator
  

• Overload shutdown

• Low battery alarm

• Low battery shutdown

• Over temperature protection with indicator

• Over battery protection

• Float charging system

• Temperature based fan control

INVERTER PROTECTIONS FUNCTIONS EXPLAINATION

•    Overload warning alarm with indicator: This function monitors the amount of load powered by the inverter.  When the total load connected to the inverter reaches 90% of the rated inverter system, the system alarm triggers with an indicator on. This prompts the user that He or She is about to overload the system.

• Overload shutdown: This function takes care of overloads and short circuit instances. When overload or short circuit occurs, this function turns off the inverter output to protect the inverter from damage.

• Low battery alarm and shutdown: This function takes care of battery protection. It is always good to ensure that, the battery of an inverter is not deeply drain to prolong the battery life. During inverter usage, this function monitors the battery level and triggers the system alarm when the battery level reaches a set level. After the alarm, the inverter turns off to protect the battery from over draining.

•  Over temperature protection with indicator: Every electronic system as well as inverters produces some amount of heat as a result energy conversion and power loss. But this heat should always be in an acceptable level to ensure high efficiency and avoidance of failure.

    The over temperature protection system monitors the system temperature and turn system function (charging or working as inverter) off when system temperature is above acceptable level which is a sign of possible problem.

• Over battery protection: This function is included to ensure that, if a customer buys the inverter and uses the wrong number of batteries (uses 24V instead of 12V), the system will never turn on until the correct battery system is used.

• Float charging system: When this charging technique is employed in designing, it ensures that the batteries are always charged without ever overcharging them.

• Temperature based fan control: The system fan should be designed to turn on only when the system begins to gain heat and turn off after extracting the heat. This function ensures that the inverter system is always silent.