Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

help with inverter circuit

Status
Not open for further replies.

elijah

New Member
hi,pls could you help me?how can i calculate the power output of a tranfomer winding.and again what wire guage will be suitablefor a 2000w power transformer.and how many tuens do i need.
 
HI!

This is how I see it. Someone to confirm?

The output power of a transformer depends on the Current drawn from it and the Voltage developped across it. Then, you just take their product (and you might divide by square root of 2 to get RMS values). The result would be the power of the winding, in VA.

The gauge of the wire, again, depends on the current drawn from that winding. At 2000W, the current could be 1A and the voltage will be 2000V, or the current could be 100A and the voltage 20V. In the first case, the wire shouldn't be as thick as in the second case. So, to determine the gauge, please specify the current.

About the number of windings, I'm not sure but I think that you should look into power transfer. Say, your transformer has 70% efficiency. Then, the output power will be 30% less than the input power (if input is 100Watt, the output will be 70Watt).
Also, the voltages depend through the ratio of number of windigs. If you put 10V on the primary with 10 windings and you take the output at the secondary with 100 windings, the output voltage will be 1V. The current will be bigger though. The formula is: n1V1 = n2V2, where V is voltage, n is the number of windings and numbers 1 and 2 are the primary and the secondary windings of the transformer.

With all that in mind, you should be able to figure out the number of windings and the thickness of the wire (there are tables on the internet that tell you the AWG of the wire for a particular current. Google for them).


Example:
output power needed 70Watt, then the input power will have to be 100Watt (70% efficiency).
input voltage: 100 Volts
output voltage: 10 Volts

So, the ratio of windings will be: for every winding of the secondary, there will be 10 windings on the primary.

Now, the input power is 100Watt, with 100Volts across it. So, there will be 1Amp flowing through the primary.
The output power is 70Watt, with 10Volts across it. So, there will be 7Amps flowing through it.
So, the secondary will have a thicker wire than the primary (more current flows through the secondary). Going to:

**broken link removed**

in Table 2, we can see that for 1Amp, wire should have AWG of 20 and for 7Amps, AWG of 14.

Hope this helps,
TI|CP
 
theimperia said:
This is how I see it. Someone to confirm?

You have a very good understanding of the principle of the the transformer already, except a few minor points which someone else can also comment if I am wrong.

theimperia said:
Then, you just take their product (and you might divide by square root of 2 to get RMS values). The result would be the power of the winding, in VA.

For VA rating, we do not divide the result by root 2. So, VA rating=voltagexampere and that's it. Sometimes we include the transformer efficiency for a little margin in our design.

theimperia said:
About the number of windings, I'm not sure but I think that you should look into power transfer.

Usually we refer to windings as for one set of voltage coil and what you really meant is the "number of turns" for that winding.

theimperia said:
Say, your transformer has 70% efficiency.

Only really bad transformer has efficiency as low as 70%. Usually they are around 90% or more for transformers below 1KVA and some 95% or more for rating above 1KVA for normal transformers. In case of inverter transformer, you are right, efficiency can be very low indeed.

theimperia said:
If you put 10V on the primary with 10 windings and you take the output at the secondary with 100 windings, the output voltage will be 1V. The current will be bigger though.

No, careless mistake you have made above. With 100 turns in the secondary, the voltage would be 100V, and the current would be 10 times smaller.
 
If the 2000W inverter operates at 80% efficiency, it draws 2500W from the battery. Therefore the low voltage winding must have wire thick enough to carry 208A from a 12V battery. BIG wire.
Even though the current flows through each half of the winding for only half the time, you shouldn't over-rate the wire, because it is confined in a tight space in the transformer. Wire's current is rated in open air. :)
 
In the ARRL Radio Amateur Handbook, it gives the Current Ratings for wire In a Transformer, Based on 700 CM per amp.

However for this kind of Current, you will require Multiple Strands of smaller wires.
 
audioguru said:
If the 2000W inverter operates at 80% efficiency, it draws 2500W from the battery. Therefore the low voltage winding must have wire thick enough to carry 208A from a 12V battery.

I'm sure I don't need to tell you?, but 2000W inverters would normally be fed from higher voltages than just 12V!.
 
Hi Nigel,
You're correct!
Since we only have 120VAC over here, it would take only 10 car batteries to do it with just a HV power oscillator, without a big transformer. :lol:
 
RE-HELP ON INVERTER

HI,
AM GRATEFUL AND HAPPY TO ALL OF YOU THAT CONTRIBUTED TO SEE TO MY SUCCESS IN BUILDING MY INVERTER.IT IS TRUE THAT I DID NOT SPECIFY SOME RELEVANT PONITS .
THE INVERTER IS A 12VDC TO 220VAC,2000W.I NOW WANT TO KNOW HOW MANY AMPS THAT FLOWS IN SUCH AN INVERTER.MOST IMPORTANTLY WANT ARE THE THINGS THAT I SHOULD GIVE DUE CONSIDERATIONWHILE BUILDING THIS KIND OF INVERTER.YOUR HELP IS NEEDED.
 
Re: RE-HELP ON INVERTER

elijah said:
THE INVERTER IS A 12VDC TO 220VAC,2000W.I NOW WANT TO KNOW HOW MANY AMPS THAT FLOWS IN SUCH AN INVERTER.

The following are very RELEVANT PONITS.

audioguru said:
If the 2000W inverter operates at 80% efficiency, it draws 2500W from the battery. Therefore the low voltage winding must have wire thick enough to carry 208A from a 12V battery. BIG wire.
 
Re: RE-HELP ON INVERTER

elijah said:
HI,
AM GRATEFUL AND HAPPY TO ALL OF YOU THAT CONTRIBUTED TO SEE TO MY SUCCESS IN BUILDING MY INVERTER.IT IS TRUE THAT I DID NOT SPECIFY SOME RELEVANT PONITS .
THE INVERTER IS A 12VDC TO 220VAC,2000W.I NOW WANT TO KNOW HOW MANY AMPS THAT FLOWS IN SUCH AN INVERTER.MOST IMPORTANTLY WANT ARE THE THINGS THAT I SHOULD GIVE DUE CONSIDERATIONWHILE BUILDING THIS KIND OF INVERTER.YOUR HELP IS NEEDED.

hi,
no need to post in all caps. we heard you the first time!
i think very important pointers have been said in order for you to get started!
you have to decide what batter voltage you are running your transformer, only then can you start working on the transformer.
if you insist on using 12volts, then be prepared to use a transformer with at least 2inch center leg, if you can get one with a 2.5 then winding will be easier! do you have access to such cores?
 
You're going to need to know quite a bit about magnetics- the different cores, frequencies, windings, copper losses, temp coefficients, and saturation. This is a LOT of power. For example, heat will always lower the saturation current substantially, and actually going into saturation may destroy things immediately.

You will also need to know a great deal about mosfet turn on/turn off behavior and the best way to drive them.

This is like 175 amps DC input to make 2kw out. You will need like 2 ga connections, probably 1/0 if it is a cable run of substantial length. The board will need very thick power rails on the 12v side.

Typically you would convert the 12v up to a DC rail. That high voltage DC is then switched in 4 phases via H-bridge: positive, then the output wires are disconnected from the DC supply and shorted together, then inverted, then shorted together again. This is closer to a sine wave than a square wave.

I don't know the exact "dead" time that makes it optimum, but this changes the DC value the rail needs to have to make 220v rms. It will be somewhat higher than 220v dc.

Most inverters than claim 2kw can only do something like that peak, and even then often cannot sustain that peak for any useful period of time. You might need to reassess how realistic this is. 2kw of transformer alone is massive even in well designed high freq toroids.

Most often, for high power converters like this, rather than use one large transformer, multiple cheap transformers are used. Finding a single core this large would not be an off-the-shelf item. Nor will you find a mosfet capable of handing 175+ amps of 12v input current so simply multiplying a bunch of independent transformers and drivers is very practical.

But one neat thing to do when you have multiple transformers is cut down on the battery drain by just "turning off" the drive to transformers you do not actually need at that power level. The drain in just keeping a transformer running is not insignificant when we're talking about leaving it on a battery for awhile. You can also revolve which transformer is working in order to spread the heat around and keep it as cool as possible.

I don't want to discourage you in any way, just to give you a realistic impression of what is required to do this. It can be a very worthwhile experience that requires so much knowledge in magnetics, mosfets, controls, bridges, and thermal design you will learn a LOT if you actually pull it off.

I am quite disappointed by the quality of most inverters I find off-the-shelf today. Many pull far, far more idle current than they should (I've seen it take amps!) and I've smoked several. I'd love to see one properly overbuilt, able to shut down faulty paralleled converters AND report it via LEDs, and manage idle current better.
 
You still haven't mentioned what you want the inverter to feed, what 12V batteries you are hoping to feed it from, and how long you expect the battery to last?.

As I mentioned previously (and as everyone else has also mentioned), 2000W from a 12V supply isn't practical - due to the massive currents required!. To provide these currents would require multiple batteries, so why not place the batteries in series?, rather than parallel, and run from a higher voltage.
 
Nigel Goodwin said:
As I mentioned previously (and as everyone else has also mentioned), 2000W from a 12V supply isn't practical - due to the massive currents required!. To provide these currents would require multiple batteries, so why not place the batteries in series?, rather than parallel, and run from a higher voltage.

I have a power inverter that can actually power a window a/c unit to make a rear a/c for my van. That thing consumes about 70 amps from the battery system and the starting current must put it in the 2 kw range. I haven't really run it that way though, the alternator is quite beefy but I'm still not sure how well it would handle the heat from another 70 amps continuous in the summer. Its main function is just something to plug in when 120v power is handy.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top