problem in 12v - 230v inverter

Replies

• 

  lal

  Actually pin 13 has an output at a different frequency - twice the frequency as that of outputs at pins 10 and 11.
  
  That is, if 't' is the time period of output at pin 10, then t/2 is the time period of output at pin 13. If one MOSFET has its gate connected to pin 13, in one complete cycle, both the MOSFETS will be 'ON' simultaneously for t/4 time and both will be simultaneously 'OFF' for another t/4 time. Which means that, the transformer output will be 0 for t/2 time.
  
  The gate connections should be from pins 10 and 11 itself. May be replace the IC and try again if pin 11 doesn't give any output.
• 

  Debashish Sahoo

  thank you lal.. i will try with a new IC and let you know.
• 

  Debashish Sahoo

  i replace the IC now i am getting output from transformer but not 230v it is around 80v. what should i do now? i double checked the construction but couldnt find the fault.
• 

  lal

  That is beautiful! Atleast we have a lead. We can work on that.
  
  The transformer is 12-0-12/230V in step-up configuration. So if there is 80V at output, a corresponding low voltage should be obatining at the input - between the centre tap and any other lead. For an 80V output, around 4V has to be input. Confirm if that is the case.
  
  And, if that is the case, we will have to figure out, why!
• 

  Debashish Sahoo

  at the input i.e at 0v input which is connected to +ve supply i am getting 12v and at 12v tapping i am getting 8v and at the other tapping i am getting around 6v. but voltage across drain and source of one mosfet is 5.4v and for other it is 8.5v
  voltage at 10th pin is 12v and at 11th pin it is 7v.
• 

  lal

  The voltage between Source and Drain of both the MOSFETS should be identical since the switching frequency is exactly the same.
  
  Wonder what could be the cause for 7V output at pin 11! A scope, if you have access to one, will be helpful to check the output waveforms and their time periods.
  
  Did you try adjusting the pot? That would change the switching frequency of MOSFETS and thus the output frequency (should change the voltage too). Try adjust the variable resistor to check if that makes any difference to the output at the transformer secondary. Theoretically, switching frequency of both MOSFETs should be 50Hz, each being in ON state for 10ms to get a 50Hz AC output.
  
  It might be a good thing to measure the current from battery with no load connected at the transformer secondary. If you have an ammeter or a multimeter that can measure up to 10A, that'll give a good picture about the total current consumption at idle condition.
• 

  Debashish Sahoo

  I had tried to adjust the variable resister but there is very little change in the voltage level. I am using 12v to 230v center tapped transformer whose current rating is 750mA. Do i have to change the transformer to higher current rating?
  I dont have any access to oscilloscope at home so cant not see the waveform of it.
• 

  lal

  Current rating of transformer won't help. A transformer with higher current rating is required if you need to transfer more power to load.
  
  What is your power source? A lead-acid battery?
  
  Check the outputs of pins 10 and 11 to ground using a DC voltmeter or the multimeter in DC mode. As the outputs at these pins will be +12V for exactly half the time period of a complete cycle, theorotically the meter should show 6V.
  
  Besides, try reducing the frequency to minimum by keeping the pot at its minimum position. The meter might show a value that is constantly changing at pins 10 and 11 rather than a constant +12V or 0V which would mean it is working as expected.
• 

  Debashish Sahoo

  yes sir i am using lead acid battery but now for testing i an using a rectifier.
  
  pin 11 is showing 5.8V and pin 10 showing 1.6V. there is no change if i change the resistance value.
• 

  lal

  Seems like the output at pin 10 is quite low. Pin 10 should also be at around 6V when measured with a DC voltmeter. Chance is that the FET doesn't get switched on for the gate pulse being feable. So only one cycle is recieved at the output. That might be the reason for the 80V output at secondary.
  
  One way to test (with limited testing facilities at home) if the FET, to which pin 10 is connected, gets turned on is to connect a 10A DC ammeter/multimeter between drain and 12V lead of transformer primary. Current will be zero if the FET doesn't get turned on.
  
  An LED may also be used in place of ammeter with proper resistances to limit the current flow. The LED should glow if the FET works as expected.
  
  PS: this doesn't allow to check if the outputs are at the levels as expected. But, should give a good image of what is happening.
• 

  Debashish Sahoo

  Sir after using my multimeter i got the following details
  pin 10 FET : drain to +ve - 11v
  drain to +ve - 2.47A
  gate to +ve - 2.1A
  source to +ve - 2.9A
  pin 11 FET : drain to +ve - 10.33v
  drain to +ve - 1.77A
  gate to +ve - 2A
  source to +ve - 2.89A
• 

  lal

  The values of voltage between Drain of both FETs and +12V terminal look alright. Current through Both Drains look alright too. I hope you measured the current by connecting the multimeter in series between Drain and 12V lead of transformer primary. Check the transformer output across secondary winding again, the primary voltage and current look normal now.
  
  By the way, how did you measure the current from Gate to +ve and Source to +ve? (mentioned in your post above) At which points exactly did you connect the multimeter?
  
  Connect the lead-acid battery instead of rectifier as the power source if you have access to one at the moment. That should help us know how the circuit behaves in actual condition.
• 

  Debashish Sahoo

  sir now when i checked the transformer output i am not getting any output which i was getting previously 80v ac. at the primary side i an getting 10v each at the tappings connected to mosfets. i really dont understand what to do. i am freaking out sir. 😡
• 

  lal

  Primary side looks like it is functioning as it is supposed to be.
  
  Try these
  1. Adjust pot.
  2. Make sure multimeter is in AC mode when measuring secondary.
  3. Check that the transformer winding is alright. Perform a continuity test/measure resistance across the secondary terminals (Circuit should be in OFF condition).
  4. Connect a resistive load (a low power incandescent lamp) to the transformer secondary and check if it works. (Take necessary safety measures when dealing with transformer secondary output)
• 

  Debashish Sahoo

  I tried everything as you said me.. but no response at secondary side.
  everything is perfect.. not if i adjust the pot there is no change in voltage level.
• 

  lal

  Where did the output suddenly disappear!
  
  Try this,
  Disconnect the transformer from the circuit. Connect mains AC supply to the 0-230V winding of transformer. Check if 12V AC is obtained across the center tap and both the other 12V leads.
  
  Take necessart safety measure while doing this.
• 

  Debashish Sahoo

  sir transformer is absolutely fine.. i checked it.
• 

  lal

  Cannot pin point the problem! Can only say, check the components and circuit again.
  
  Remove one FET and switch on the circuit. Check if that produces an output. Repeat with the other FET alone connected.
  
  Repeat the steps in the posts above to find any possible problems. Especially the current through FETs in ON state.
  
  A transformer will not work if the flux linked with its windings donot change. The current through the primary should be constantly changing to induce a voltage in the secondary winding. Since FETs are getting switched ON, a chance is that the FETs are in ON state constantly which makes a constant current flow through the primary. Check the outputs at 10 and 11 again with multimeter in DC mode to see if it is still around 6V.
  
  A scope would have given a better resolution.
• 

  Debashish Sahoo

  ok sir i will completely remove everything and try again and let you know
• 

  Debashish Sahoo

  Sir i have connected led in series with the drain pin of both the mosfet and one led i connected to the middle wire of transformer. after i change the preset there is no change in the led intensity..
• 

  lal

  That means, current is flowing as expected. We are still unaware of switching frequency of FETs.
  
  1. Disconnect any one of the FETs and check if there is an output available at secondary. (Keep the pot at maximum position, that gives the lowest frequency which is around 47Hz with 22K Ohms resistance)
  
  2. Since the transformer is not known to have any faults, should the FETs be constantly ON? May be try replacing 4047 with the first one you had.
• 

  Debashish Sahoo

  1. after disconnecting one fet still there is no output at secondary
  
  2. i replace the IC with the previous one and i tried with other new IC too but still no output.
• 

  lal

  1. Another thing to check will be the potentiometer and capacitor. If anyone of these get shorted, frequency of outputs will be theorotically infinite, which means, all the outputs will be constantly high. Check if these components are working fine.
  
  2. Can you try with a different transformer? (Though It might not be the reason for no output). It can be any transformer with a voltage rating at any one side greater than 12V and current rating 2A. No centre tap is necessary either, connect each MOSFET individually and see if there is an output at secondary corresponding to its voltage ratio.
• 

  Debashish Sahoo

  sir capacitor and potentiometer are fine i have checked it.
  and about transformer i dont have spare right now tomorrow morning i will get one and test it.
• 

  lal

  You don't have to get a new one for that purpose. You can use any transformer. An old disposed transformer in some very old DC supply will do. Just make sure the voltage rating of the side you connect the MOSFET is atleast 12V.
• 

  Debashish Sahoo

  ok sir
• 

  Debashish Sahoo

  hello sir,
  i have made another construction with all new component.. now i am getting 12v at drain of two FETs and 5.8v at gate terminal.. but still not getting any output..
• 

  Debashish Sahoo

  Sir i am getting 46v ac at the output... but not 230v
  what should i do now?
• 

  lal

  Do you recollect what modification helped you get an output?
  
  It is hard to say what exactly is the problem. What all modifications did you do, if any?
  
  I wish we had access to a scope!
• 

  Debashish Sahoo

  yes sir i remember... sir when i keep the potentiometer to minimum position transformer makes some sound..
  i think our circuit part is correct because we r getting the output.. but the desire output we r not getting from transformer.. so i think there might be problem in the transformer..
  how to check practically whether the mosfets are producing the desire frequency?
• 

  lal

  I cannot think of a way other than using a scope.
  
  The output produced by switching FETs are square waves. But, the transformer would actually be designed to deal with sine waves. When dealing with square waves, we cannot expect the transformer to exhibit similar performance as that of operating with sine waves. Still, it should have produced a better output than what is obtained right now.
• 

  Debashish Sahoo

  please see this image ...
• 

  Debashish Sahoo

  please see this image