In this post we discuss the construction of a 5000 watt inverter circuit which incorporates a ferrite core transformer and therefore is hugely compact than the conventional iron core counterparts.
Written and Submitted By: Dhrubajyoti Biswas
DC Input Supply Prerequisite
First you need to find 60V DC power supply for powering the proposed 5kVA inverter circuit. The intention is to design a switching inverter which will enable change the DC voltage of 60V to a higher 220V at a lowered current.
The topology followed in this scenario is the push-pull topology which uses transformer on the ratio of 5:18. For voltage regulation which you may need, and the current limit – they are all powered by an input voltage source. Also at the same rate, the inverter expedites the current allowed.
When it comes to an input source of 20A it is possible to get 2 – 5A. However, the peak output voltage of this 5kva inverter is around 220V.
Ferrite Transformer and Mosfet Specifications
In regard to the architecture, Tr1 transformer has 5+5 primary turns and 18 for secondary. For switching, it is possible to use 4+4 MOSFET (IXFH50N20 type (50A, 200V, 45mR, Cg = 4400pF). You are also free to use MOSFET of any voltage with Uds 200V (150V) along with least conductive resistance. The gate resistance used and its efficiency in speed and capacity must be excellent.
The Tr1 ferrite section is constructed around 15x15 mm ferrite c. The L1 inductor is designed using five iron powder rings that may be wound as wires. For inductor core and other associated parts, you can always get it from old inverters (56v/5V) and within their snubber stages.
Using a Full Bridge IC
For integrated circuit the IC IR2153 can be deployed. The outputs of the ICs could be seen buffered with BJT stages. Moreover, due to the large gate capacitance involved it is important to use the buffers in the form of power amplifier complementary pairs, a couple of of BD139 and BD140 NPN / PNP transistors do the job well.
Alternate IC can be SG3525
You may also try to use other control circuits like SG3525. Also, you can alter the voltage of the input and work in direct connection with the mains for testing purpose.
The topology used in this circuit has the facility of galvanic isolation and operating frequency is around 40 kHz. In case if you have planned to use the inverter for a small operation, you don’t cooling, but for longer operation be sure to add a cooling agent using fans or large heatsinks. Most of the power is lost at the output diodes and the Schottky voltage goes low around 0.5V.
The input 60V could be acquired by putting 5 nos of 12Vbatteries in series, the AH rating of each battery must be rated at 100 AH
High Frequency 330V Stage
The 220V obtained at the output of TR1 in the above 5kav inverter circuit still cannot be used for operating normal appliances since the AC content would be oscillating at the input 40kHz frequency.For converting the above 40 kHz 220V AC into 220V 50 Hz or a 120V 60Hz AC, further stages would be required as stated below:
First the 220V 40kHz will need to be rectified/filtered through a bridge rectifier made up of fast recovery diodes rated at around 25 amps 300V and 10uF/400V capacitors.
Converting 330V DC into 50 Hz 220V AC
Next, this rectified voltage which would now mount up to around 310V would need to be pulsed at the required 50 or 60 Hz through another full bridge inverter circuit as shown below:
Update: An upgraded version of the above can be studied in this PWM sinewave 5kva inverter circuit
The terminals marked "load" could be now directly used as the final output for operating the desired load.
Here the mosfets could be IRF840 or any equivalent type will do.
How to Wind the Ferrite Transformer TR1
The transformer TR1 is the main device which is responsible for stepping up the voltage to 220V at 5kva, being ferrite cored based it's constructed over a couple of ferrite EE cores as detailed below:
Since the power involved is massive at around 5kvs, the E cores needs to be formidable in size, an E80 type ferrite E-core could be tried.
Remember you may have to incorporate more than 1 E core, may be 2 or 3 E-cores together, placed side by side for accomplishing the massive 5KVA power output from the assembly.
Use the largest one that may be available and wind the 5+5 turns using 10 numbers of 20 SWG super enameled copper wire, in parallel.
After 5 turns, stop the primary winding insulate the layer with an insulating tape and begin the secondary 18 turns over this 5 primary turns. Use 5 strands of 25 SWG super enameled copper in parallel for winding the secondary turns.
Once the 18 turns are complete, terminate it across the output leads of the bobbin, insulate with tape and wind the remaining 5 primary turns over it to complete the ferrite cored TR1 construction. Don't forget to join the end of the first 5 turns with the start of the top 5 turn primary winding.
E-Core Assembly Method
The following diagram gives an idea regarding how more than 1 E-core may be used for implementing the above discussed 5 KVA ferrite inverter transformer design:
E80 Ferrite core
Feedback from Mr. Sherwin Baptista
In the above project for the transformer, i did not use any spacers between the core pieces, the circuit worked well with the trafo cool while in operation. I always preferred an EI core.
I always rewound the trafos as per my calculated data and then used them.
All the more the trafo being an EI core, separating the ferrite pieces were rather easy than doing away with an EE core.
I also tried opening EE core trafos but alas; i ended up breaking the core while separating it.
I never could open an EE core without breaking the core.
As per my findings, few things i would say in conclusion:
---Those power supplies with non-gaped core trafos worked best. (i am describing the trafo from an old atx pc power supply since i used those only. The pc power supplies do not fail that easily unless its a blown capacitor or something else.)---
---Those supplies that had trafos with thin spacers often were discolored and failed quiet early.(This i got to know by experience since till date i bought many second hand power supplies just to study them)---
---The much cheaper power supplies with brands like; CC 12v 5a, 12v 3a ACC12v 3a RPQ 12v 5a all
such types ferrite trafos had thicker paper pieces between the cores and all failed poorly!!!---
In FINAL the EI35 core trafo worked the best(without keeping air gap) in the above project.
5kva ferrite core inverter circuit preparation details:
Using 5 Sealed Lead Acid batteries of 12v 10Ah
Total voltage = 60v Actual voltage
= 66v fullcharge(13.2v each batt)voltage
= 69v Trickle level charge voltage.
After calculation of battery voltage we have 66volts at 10 amps when full charged.
Next comes the supply power to ic2153.
The 2153 has a maximum of 15.6v ZENER clamp betwen Vcc and Gnd.
So we use the famous LM317 to supply 13v regulated power to the ic.
The lm317 regulator has the following packages;
1. LM317LZ --- 1.2-37v 100ma to-92
2. LM317T --- 1.2-37v 1.5amp to-218
3. LM317AHV --- 1.2-57v 1.5amp to-220
We use the lm317ahv in which 'A' is the suffix code and 'HV' is the high volt package,
since the above regulator ic can support input voltage of upto 60v and output votage of 57 volts.
We cannot supply the 66v directly to the lm317ahv package sice its input is maximum of 60v.
So we employ DIODES to drop the battery voltage to a safe voltage to power the regulator.
We need to drop about 10v safely from the maximum input of the regulator which is 60v.
Now the safe maximum input to the regulator from the diodes should be 50 volts.
We use the regular 1n4007 diode to drop the battery voltage to 50v,
Since being a silicon diode the voltage drop of each is about 0.7 volts.
Now we calculate the required number of diodes we need which would buck the battery voltage to 50 volts.
battery voltage = 66v
calc.max input voltage to regulator chip = 50v
Now, 0.7 * ? = 16v
We divide 16 by 0.7 which is 22.8 i.e., 23.
So we need to incorporate about 23 diodes since the total drop from these amounts to 16.1v
Now, the calculated safe input voltage to the regulator is 66v - 16.1v which is 49.9v appxm. 50v
We supply the 50v to the regulator chip and adjust the output to 13v.
For more protection, we use ferrite beads to cancel out any unwanted noise on the output voltage.
The regulator should be mounted on an appopriate sized heatsink in order to keep it cool.
The tantalum capacitor connected to the 2153 is an important capacitor that makes sure ic gets a smooth dc from the regulator.
Its value can be reduced from 47uf to 1uf 25v safely.
Rest of the circuit gets 66volts and the high current carrying points in the circuit should be wired with heavy guage wires.
For the transformer its primary should be 5+5 turns and secondary 20 turns.
The frequency of the 2153 should be set at 60KHz.
The High frequency ac to low frequency ac converter circuit using the irs2453d chip should be wired appropriately as shown in the diagram.