12 V DC to 220 VAC inverter

[abdoalghareeb]

I am trying to build my 900 VA inverter
My problem is in charge battery phase, I don't use external rectifier diodes but I depend on body diode of mosfet transistor (IRF3205).
In case of 220 V on primary, the secondary is 16 V but the maximum battery voltage was 12.2 V, and the charge current is 100 mA.

What is the wrong ?

?

 

[Audioguru]

Your battery is being charged with rectified pulses, not DC. The average voltage of the rectified pulses is reduced by the body diodes and is much less than 16V. Since the voltage of the pulses is low then the battery charging current occurs only when the voltage of the pulses exceed the voltage of the battery so the average charging current is low.

As an inverter with a 32V center-tapped transformer being fed pulses of a 13.2V battery by the Mosfets then the output voltage of the inverter will be only about (13V/16V) x 220V= 179V.

 

[chuckey]

16V RMS = 17V P, so when your FETs conduct they should be switching half wave rectified pulses of 17 V into a 12 V battery, so either there is some thing that is limiting the current to .1 A or your timing is way off and the switching is not co-incident with the mains .
Frank

 

[KlausST]

Hi,

16V RMS = 17V P

How this?

Klaus

 

[Audioguru]

The peak voltage of 16V RMS is 16 x 1.414= 22.6V but it is not steady DC, instead it is rectified pulses that the rectifiers reduce to about 21.8V peak. The peak voltage and current occurs only for a moment for each pulse and the average voltage is about 13.9V then the charging current is low and the battery will take a long time to be fully charged.

 

[chuckey]

10 out off ten for being awake KlausST
, sorry about that!, but the real figure only underlines my statement, you have loads of volts and no current. With 22.6 V peak (thanks Audioguru), and a battery voltage of about 12V, from Audiogurus figure you can see that the incoming voltage pulses exceed the battery voltage for 50% of the time. If you had a conventional battery charger (that is where I got my 17V from) you have massive charging currents, err, like 20 Amps not .1A
Frank

 

[Audioguru]

A car overcharges the battery continuously at 14.4VDC. Which is one reason a car battery lasts only about 5 years.

 

[Tahmid]

I am trying to build my 900 VA inverter
My problem is in charge battery phase, I don't use external rectifier diodes but I depend on body diode of mosfet transistor (IRF3205).
In case of 220 V on primary, the secondary is 16 V but the maximum battery voltage was 12.2 V, and the charge current is 100 mA.

What is the wrong ?

View attachment 107115?

In inverters of this type, there are large capacitors across the battery which help filter the pulsating output DC to a more steady DC (depending on the size of the capacitance). These capacitors also help while the inverter is running, but that's not your concern here.

Additionally, in these types of inverters, there is a separate tapping on the primary, a lower voltage one: 140V to 160V is common. Then a triac is used for phase angle control to alter the voltage entering this tapping from the live mains. This is then used to increase the voltage at the output to increase charging current. The firing angle is controlled to control the charging current.

While this isn't the best option to charge the battery, it's widely used in inverters since this allows the same transformer to be used for stepping voltage up for the inverting as well as down for battery charging with minimal external components.

Hope this helps.
Tahmid.