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Not working 12v dc to 220v Ac

teja4

Jan 23, 2023
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i am trying to make a circuit for 12v battery to 220v ac.
its runs for 1 second after its off
and the mosfets irfz44 heating too much
here is full circuit diagram (i didn't add 1k resistor and led]
 

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Bluejets

Oct 5, 2014
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Use a mosfet driver or buffer the drive from 12v to the 2 mosfets with a couple of transistors.
 

crutschow

May 7, 2021
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The transformer magnetizing current is proportional to the average value of it's input waveform, not the RMS.
This means a 12.6V square-wave (from a lead-acid battery) causes about a 16% higher transformer magnetizing current than a 12Vrms sinewave voltage, which may be saturating the transformer.

Try operating the circuit from about 10Vdc and see if that makes a difference.
 
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teja4

Jan 23, 2023
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The transformer magnetizing current is proportional to the average value of it's input waveform, not the RMS.
This means a 12.6V square-wave (from a lead-acid battery) causes about a 16% higher transformer magnetizing current than a 12Vrms sinewave voltage, which may be saturating the transformer.

Try operating the circuit from about 10Vdc and see if that makes a difference.
i am tested with 12v dc and 500Ma current adapter. then the output voltage is 33v ac
before i tested with 12v dc 7 amps lead acid battery (known as ups batter)
should i use 4 lithium ion batteries
 

AnalogKid

Jun 10, 2015
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The only thing limiting the current through the FETs is the impedance of the transformer. A 5 A rating does not mean that the current through the winding is limited to 5 A. You do not say how hot the FETs are getting. Can you post a scope shot of a FET drain voltage?

ak
 

teja4

Jan 23, 2023
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The only thing limiting the current through the FETs is the impedance of the transformer. A 5 A rating does not mean that the current through the winding is limited to 5 A. You do not say how hot the FETs are getting. Can you post a scope shot of a FET drain voltage?

ak
can you tell in more detailed?
 

Alec_t

Jul 7, 2015
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Your circuit does not provide any dead time between the two gate drive voltages. Because of the finite turn-on and turn-off tmes of FETs there will be brief moments when both FETs are conducting simultaneously. This results in high 'shoot-through' current which causes the FETs to heat up.
Also, because a 4017 has an internal impedance comparable to the gate resistor value, its output voltage will be considerably less than its 9V supply voltage, so may not be switching the FETs on fully. As Bluejets said, use a FET driver/buffer.
 
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crutschow

May 7, 2021
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because a 4017 has an internal impedance comparable to the gate resistor value, its output voltage will be considerably less than its 9V supply voltage,
That resistance only effects the gate signal rise and fall times, it has no effect on the final gate voltage.
 

Alec_t

Jul 7, 2015
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True, but the rise and fall times would be shorter with a lower-impednce driver.
 

crutschow

May 7, 2021
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but the rise and fall times would be shorter with a lower-impednce driver.
Of course. But I don't think the high dissipation he is seeing is due to slow MOSFET gate rise and fall times @ 50Hz.
 

Alec_t

Jul 7, 2015
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Do you have thermal paste between the FETs and their heatsinks?
 

teja4

Jan 23, 2023
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Did you double-check all the connections, particularly those to the transformer?
i am checked all wirings all are connected good.
i am testing with a lead acid battery which has 13.5v dc output and 7.5 ah amps. is the battery problem ?
 

teja4

Jan 23, 2023
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But are they all connected to the correct terminals?

That could be a problem with a 12V transformer.
That's why I suggested the test with a lower voltage.
when i testing with that bettery the positive wire was burning both battery and transformer a little bit
the red wire is positive on blue mark, its directly connected
 

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