so , how much the ampere handling for one mosfet?, in this design for 2200 kva machine, and 1320 watt?
the designer selected p65nf06 mosfet, which is Id of 60 A , and 60v
for us , how can we calculate the maximum drain ampere at full load?
is there any online calculator tools?

 

It is NOT a 2200 Kilo Volt Ampere (KVA)machine. Get your ratings right. It is a 2.2 KVA, that is, 2200 VA; that is 10 Amps @ 220 Volts, all RMS.
There is no need for any Calculator Tools, simple Arithmetic will do.
Convert all values to Peak, so 2200 VA is at 310 volts and 14 Amps peak.
Assuming the overall conversion efficiency of 80 %, the input VA will be 2750 VA.
The Peak voltage here is 48, so the Peak current will be 57 Amps.
This peak current will be shared by 3 MoSFeT's, that is about 20 Amps each.

 

Yes it's 2200 VA, sorry again
Why you don't consider the step up transformer in your calculations for the inverter and mosfet ampere handling?

 

Yes it's 2200 VA, sorry again
Why you don't consider the step up transformer in your calculations for the inverter and mosfet ampere handling?

I have not spelt it out in words, but the transformer is in the picture.. Check the calculations again.

 

I have not spelt it out in words, but the transformer is in the picture.. Check the calculations again.

Ok

 

so 2200 VA is at 310 volts and 14 Amps peak.
Assuming the overall conversion efficiency of 80 %, the input VA will be 2750 VA.

Where from the 310v came from?,, can you more clarify?

 

Here is the circuit for UPS 2200 va capacity, use 4 batteries 12v in series, so total is 48v, 7AH
im replacing these 12 mosfets
View attachment 335907in the inverter circuit of UPS
The original mosfets are p65nfo6, attached datasheet
I have 75nf75 available for replacement
Attached datasheet
The inverter output goes to step up transformer
The output signal is modified sine wave, 50hz, not pure sine wave
220vac
I can see that every 3 mosfets Re connected in parallel, and that's for high current handling under load which is up to 2kw almost
What I need understand is how the switching work in this inverter?
As I see that the mosfets into two groups, each group is symmetric to other, why not all symmetric?
Can we calculate how much ampere go through mosfets under full load?, Id?
Can we estimate dead time between switching from high to low?, so we are safe when changing mosfets with little slower speed?
Attached the whole UPS circuit
What calculations we can do having these info!, of battery voltage, mosfets chosen, UPS capacity, inverter circuit, driver circuit, etc to help in choosing right replacement mosfets?

Hi,

Are you mostly interested in repairing this device or just want to know more about the theory of operation?

When replacing the MOSFETs, one of the things to check is the gate charge. That is part of what determines the switching speed and therefore the required dead time. The original driver will be able to turn on and off the MOSFETs at a certain speed because they will be able to supply enough current especially at the start of the transition and allow it to turn off completely near the end. If any MOSFET was to have a larger gate charge spec, that would mean it would switch slower given the same gate driver. That could mean the new MOSFET would need a better driver. There is a chance that the driver works with the newer MOSFET though, if it was over specified to begin with. To check for this you could look at the MOSFET drain current looking for spikes near the end of a pulse, but at reduced buss voltage so the MOSFETs do not blow out.

The output pulses would have to supply the same RMS values that a sine wave would supply. The RMS value is the root of the mean of the square, which mathematically looks like this:
s(t)=v(t)^2
mean=integrate(s(t),t,0,Tp)/Tp
RMS=r(t)=sqrt(mean)
where Tp is the total time period that is the 'on' time plus the 'off' time.
It's easier to see in multiple statements like that rather than put it all in one statement, which you can do though:
RMS=sqrt(integrate(v(t)^2,t,0,Tp)/Tp)

 

Are you mostly interested in repairing this device or just want to know more about the theory of operation?

Know more about theory and calculations

 

Know more about theory and calculations

Hi,

What have you studied so far?
There are different aspects of this kind of device that can be discussed.

 

Where from the 310v came from?,, can you more clarify?

2200 VA is 220 Volts RMS * 10 Amps RMS. What are the peak Values? The MoSFeTs will have to handle the peak values.

 

2200 VA is 220 Volts RMS * 10 Amps RMS. What are the peak Values? The MoSFeTs will have to handle the peak values.

Surely you must know the peak values are sqrt(2) times the RMS values right?
But that's not exactly right either because when dealing with the line power, we have to take into consideration low line and high line. Low line is 15 percent lower than the nominal line (220vac for example) and high line is 15 percent higher than the nominal line voltage. I've never seen it go as high as 15 percent higher, but converters are usually tested at that voltage anyway. I have seen it go as low as 15 percent lower many times though, and sometimes even a little lower depending on location (in the USA that is).

What this means is that the high line peak voltage can be 220*1.15*sqrt(2) as a minimum. Transistor ratings should be even higher than that though. Also verify the line voltage is 220vrms and not 230vrms or 240vrms.