In this article we discuss a 1000 watt UPS circuit powered with a +/- 220V input, using 40 nos of 12V/4 AH batteries in series. The high voltage operation renders the system relatively less complex and transformerless. The idea was requested by Aquarius.
The Circuit Request
Hi dear Swagatam,
I am ur fan & have built many projects for my personal use with success & had a lot of pleasure. God bless you. Now I intend to build a 1000 watt UPS with a different concept (inverter with high voltage input dc).
I will use a battery bank of 18 to 20 sealed batteries in series each 12 volts/ 7 Ah to give a 220+ volts storage as input to a transformerless inverter.
Can you suggest a simplest possible circuit for this concept which should include a battery charger + protection and auto switching by mains failure. Later I will include a solar power input too.
The proposed 1000 watt UPS circuit can be built by using the following two circuits where the first one is the inverter section with the required automatic changeover relays. The second design provides the automatic battery charger stage.
The first circuit which depicts the 1000 watt inverter consists of three basic stages.
T1, T2 along with the associated components form the input differential amplifier stage which amplifies the input PWM signals from a PWM generator which could be a sine generator.
R5 becomes the current source for providing optimal current to the differential stage and to the subsequent driver stage.
The section after the differential stage is the driver stage which effectively raises the amplified PWM from the differential stage to sufficient levels for triggering the subsequent power mosfet stage.
The mosfets are aligned in a push pull manner across the two 220V battery banks and therefore switch the voltages across their drain/source terminals to produce the required AC 220V output without incorporating a transformer.
The above output is terminated to the load via a relay changeover stage consisting of a 12V 10amp DPDT relay whose triggering input is derived from the utility mains via a 12V ac/DC adapter. This triggering voltage is applied to the coils of all the 12V relays that's used in the circuit for the intended mains to inverter changeover actions.
Parts List for the above 1000 watt UPS circuit
All resistor CFR 2 watt rated unless stated.
R1, R3,R10,R11,R8 = 4k7
R2,R4, R5= 68k
R6, R7 = 4k7
R9 = 10k
R13, R14 = 0.22 ohms 2 watt
R12,R15 = 1K, 5 watt
C1 = 470pF
C2 = 47uF/100V
C3 = 0.1uF/100V
C4, C5 = 100pF
D1, D2 = 1N4148
T1, T2 = BC556
T5, T6 = MJE350
T3, T4 = MJE340
Q1 = IRF840
Q2 = FQP3P50
relay = DPDT, 12V/10amp contacts, 400 ohm coil
Battery charger circuit for charging the 220V DC battery banks.
Although ideally the involved 12V batteries should be charged individually via a 14V supply, keeping simplicity into account a universal single 220V charger was finally found to be more desirable and easy to build.
As shown in the diagram below, since the required charging voltage is within the vicinity of 260V, the mains 220V output could be seen directly used for the purpose.
However applying the mains directly could be dangerous for the batteries due to the massive amount of current it involves, a simple solution using a 200 watt series bulb is included in the design.
The mains input is applied via a single 1N4007 diode and through a 200 watt incandescent bulb which passes through a switching relay contacts.
Initially the half wave rectified voltage is unable to reach the batteries due to the relay being in the switched OFF mode.
On pressing the PB1, the supply is momentarily allowed to reach the batteries.
This prompts a corresponding level of voltage to be generated across the 200 watt bulb and is sensed by the opto LED.
The opto instantly responds and triggers the accompanied relay which instantly activates and latches ON and sustains it even after PB1 is released.
The 200 watt bulb could be seen glowing slightly whose intensity would depend on the charged condition of the battery bank.
As the batteries begin charging, the voltage across the 200 watt bulb begins dropping until the relay is switched OFF as soon as the battery full charge level is reached. This could be adjusted by setting up the 4k7 preset.
The output from the above charger is fed to the battery bank through a couple of SPDT relays as shown in the following diagram.
The relays make sure that the batteries are put into the charging mode as long as the mains input is available and is reverted to inverter mode when mains input fails.