12vdc - 220vac inverter not working

Dodgydave

Joined Jun 22, 2012
11,284
So the first chip is not working,you said the first chip was working at the first posts,

right what is the voltage on pin 4 of the first chip,?
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
It's right.
Now the circuit is that of first post.
The first stage is working on pin 4 of first tl494 there is 0 volt and on pin 3 there is 0,06v.
The battery voltage is 12,34 v.
In output have two square waves as previous pictures (40khz and 11 volt about)
The buzzer is off. Nothing sound, and there is voltage in capacitors (in this moment 440 vdc)
In this way i can leave the inverter live for an hour also and nothing other problem i seen.
On the second ic tl494 i have 4,28 v on pin4 and 4,86 v on pin3.
The its output have the fixed signals continued of 11,15 v on pin 8 and 8,78v on pin11.
 
Last edited:

Dodgydave

Joined Jun 22, 2012
11,284
So your the first ic U1 is working at 40khz, the problem is the second ic U2, its not oscillating, have you replaced the ic Tl494?
 

tcmtech

Joined Nov 4, 2013
2,867
U1 is not seeing the feedback voltage from the secondary output. Thats why the HV DC rail is so far above what it should be.

Looking at the schematic U2 has a interlock with the HV rail that pulls pin one to ground preventing it from running.

Fix the feedback loop to U1 and get the HV rail voltage back down to where it should be before your 400 volt capacitors blow up.
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
Yes, i replaced all three ic (two tl494 and one lm324)
I'm trying to complete the pattern of my inverter following the tracks of the circuit. I found many diverse parts LM324. As soon as I finished I attach the picture since we can see better the connections.
there are many components reversed!!!
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
Ok, i just finished in This moment...How exhausting!
If i did not do some error, this should be the diagram of my inverter.
I followed step by step all the tracks and redesigned the pattern.
As can you see there are many differeces from the diagram posted at first.
i hope that in this way is more clear.
Thank you much for suggestions
 

Attachments

Thread Starter

kyu9971

Joined Mar 28, 2015
90
Maybe I explained badly.
The differences were with the diagram posted top.
Now the pattern and same to that of my inverter.
Can you give me some advice on what to check too.
Thanks to all
 

tcmtech

Joined Nov 4, 2013
2,867
Until you get the the primary feedback circuit working so the HV rail voltage regulates itself to around 310 volts there is not much advice I can give you.
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
hi,
i have some news from my circuit.
before shorting R15 i measured the voltage on its pin and i see the this was zero.
so i removed the R32 (620k) and i found it broken.
now i search this resistor and i give you the response.
i hope a good response.
see you later.
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
Ok, i replaced the resistor R32 (620k) with 2 resistors in serial (470k+150k).
Now the second stage working and there is output voltage, but i not understand some things:

1) Because the voltage on capacitors is 240/250 volts instaed 300/310 volts?
2) with the scope i see an perfect modified sine wave but its max value is 250v.
3) in output with my tester i read 216 volts (AC position).
Maybe there is some problem still?
Thanks everyone for your help
 

Attachments

tcmtech

Joined Nov 4, 2013
2,867
Told you it had a HV safety built into the secondary circuit.

Now being you have a ~250 VDC rail and a working square wave output I would be working on changing out the feedback loop resistors to get the DC rail up around your 310 - 320 VDC level and then adjust your square wave duty cycle down a bit to get the output to be more like a proper sine waves RMS to peak voltage ratios.

Right now I am guessing that R46 and R47 may be what set the primary output PWM duty cycle.
 

Thread Starter

kyu9971

Joined Mar 28, 2015
90
Thank you so much for your suggestions.
On the diagram taken from web, there is only one R620k . instead in diagram that i redesigned there are two R620k.
I had checked only one of these,
And that led me astray.
If i understood good, the pin 14 is ref 5v and R46 e R47 form a voltage divider. If before failure of the inverter , it worked ok, what is happend to the resistors ?may be broken?
I tryed the inverter without load, first thing because it have only 4 final mosfets and it is without heat sink.
Can be this problem, maybe with load is ok?
Thanks, you are giving me a great help.
 
Last edited:

Thread Starter

kyu9971

Joined Mar 28, 2015
90
i measured the voltage on pin 2 of second tl494 (between the resistors R46 and R47) and is 1,49 volts.
it should be correct, being the vref=5 volts on pin 14.
correct me if I'm wrong
 

pedja101

Joined Sep 5, 2015
2
Did you solve your problem? I have same inverter with same problem :-( Now I trying to replace R32 resistor (i do not have any on my stock). So far I replaced Ka7500 and two CS740 but still output from KA7500 is 11VDC (there is no 50Hz) and I have 450V on 400V capacitors (instead 310V).
 
Top