Another INVERTER we can talk about..

[audioguru2]

Hi Alun,
You must keep the Q high on a tuned transformer for it to continue to ring at the reonant frequency and convert a square-wave to a sine-wave. Therefore a load ruins it.
I was thinking of hitting the tuned circuit with a brief pulse of the proper direction at zero crossings and the voltage will build to infinity without a load.

There is a lot of discussion on the web about the pros and cons of ferroresonant transformers also called a CVT (constant voltage transformer). They convert a 15% change in voltage at the primary to a 3% change at the output. They are said to hum badly, heat-up with a low input voltage and a high one and slowly reduce their output when the input is cutoff (blowing-up SMPS).
You could probably use one with a push-pull inverter drive and get a reasonable sine-wave out.

View attachment 36690

 

[blitznet]

Hi,
Is your inverter suitable for a personal computer?

 

[Alun]

Yes this inverter is perfect for a PC.

Whoops I made a mistake transposing the formula for C here's the correct formula.

 

[blitznet]

Hi Sasi,
I've just finish my inverter. I use a 40 A transformator. But when I try this inverter for my computer, the mosfets become overhead and then burned. :-[
What's going on with my inverter ???
Now I'm trying to use transistors to change the mosfets.

thank's

 

[audioguru2]

Maybe the Mosfets are both turning on at the same time.
Maybe the Mosfets are trying to pass too much current for their rating because the load current of the inverter is too high.

 

[Alun]

Are they mounted on a suitable heatsink?

 

[audioguru2]

Hi Alun,
Maybe he was feeding a 40A sine-wave into his Mosfets. Then they will make lots of smoke!  ;D

 

[blitznet]

Hi Audioguru,
Yes, they mounted on a suitable big headsink.
Do you have any suggestion?  ???

 

[audioguru2]

Hi Blitznet,
Which inverter circuit did you build?

 

[blitznet]

Hi Audioguru,
I've build the Sasi's Inverter that using six IRFZ44.
Here it is. Before I tried to use for my computer, when I measure the voltage, i've got 220 V. And finally I tried for my computer, then the MOSFETs becoma overhead and the power was going down.

 

[CheeseE]

Hello!

Can I use sasi's inverter for my desktop computer?

Or can anybody help me building a modified square- or pure sin- wave inverter?

THX!

 

[Alun]

Why not?

The PC's power supply converts the mains input voltage to DC before the switching regulator so the shape of the wave makes no difference whatsoever, you could run a PC off 290VDC if you wanted to.  Most of my monitors are international and are rated for 100-240VAC so  they have internal switch mode power supplies similar to that in my PC, if you don't like the idea of powering a monitor of one of these inverters, you could just use a TFT screen as they often are rated for 12V input, and even if they're not they certainly do have an internal switched mode power supply.

 

[CheeseE]

Ok! so I can use it
Now...I will build sasi's inverter with mosfets...
But what are these 0.01 Ohm/5W resistors?
And what is that MOV after the transformer?

 

[Alun]

Hang on I wasn't thinking earlier on, just because my monitor might beable to handle squarewave it doesn't mean yours will, I'm sorry if I've confused you ???, I've done my best to exmplain this in the other thread:
http://www.electronics-lab.com/forum/index.php?topic=3113.14

 

[Kasamiko]

@Sasi
What's the update of your inverter..

rhonn 

 

[Alun]

I am not recommending it not because of its squire wave output, but because of its switching between Mains and inverter. When mains power fails the inverter will start automatically after a fraction of seconds because of the relay switch. For PC cant sustain that time, it will get restarted.

I'm sorry - hadn't read this thread from the beginning.

This would be a big problem.

However if you just used the inverter part of the circuit with out the mains switching relay, you could still use it to power a PC from a car battery providing the monitor can take the squarewave input.

There are also ways to avoid this problem, one would be to increase the size of the filter capacitors in the PC's power supply so it can remain on during this short power cut. You could connect it up so mains transformer steps down the mains voltage to both charge the battery and power the inverter at the same time like in a proper UPS, then when the mains power goes down the battery power will immediately kick in and power the circuit.

 

[CheeseE]

I won't use the switching relay, i will only use the inverter part in my car...so that not a problem...
But what are these 0.01 Ohm/5W resistors? Is it 0.01 os 0.1?
And whats's that MOV after the transformer?

 

[Alun]

CheeseE,

They are 0.01ohm resistors, or you could use 10 0.1ohm resistors in paralell.

I think it might be better to use a large inductor instead of these resistors. The resistors are there to absorb the large current transients when both of the transistors turn on at once, a choke might be better as it would do the same job without dissipating energy all the time.

The MOV thingy (I can't remember what MOV stands for) is a surge suppresser that absorbs any high voltage spikes that might be present on the output of the transformer.


Did you read my post in the thread the following link leads to?
http://www.electronics-lab.com/forum/index.php?topic=3113.14

MP expresed a concern that your monitor might not like the squarewave output of this inverter. While my monitor will probably work from the square wave output yours might not.

What sort of monitor do you plan to use with this inverter?

If it's an TFT flatscreen then it'l work for sure, but if it's an old CRT you might not be so lucky.

What does the label on the back of the monitor say?

Does it say 100-240VAC 50/60Hz, or 230VAC 50Hz, or something completely different?

Mine says 100-240VAC 50/60Hz so I know it'll work because the internal power supply in my monitor is like the one in my PC, it converts the AC to DC before it powers the device.

If the label says 230VAC 50Hz you might not be so lucky but it's still worth a go, monitors aren't that expensive so you could easily pick one up that will work with this inverter at a very resonable price, you could always try ebay.

 

[audioguru2]

Hi CheezE,
If you use 0.1 ohm resistors instead of the required 0.01 ohms ones, they will each waste 28W of heat and cause the output voltage to be about 24V less at full load.
The same applies to the resistance of your battery connectors and wiring if they are only 0.03 ohms. You're going to draw about 50A from a 12V battery!

 

[Alun]

I agree with audioguru, if you must use 0.1ohm resistors use 10 in parallel, make sure each resistor is rated to at least 0.5W.

What do you think of my idea to use an inductor instead of resistors audioguru?