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From: tmpstr on 20 Jul 2010 13:45
I would like to build a pure sinewave inverter and need some help in
designing & component selection.

What ?
A 100-200 Watts, 230 V pure sinewave inverter
Input: preferably one 12V SMF battery. two if absolutely needed.
Output: 230V RMS sinewave capable of 100 ~ 200 watts
Load: 19" LCD TV for now.

Constraints:
Design should be simple as this is my first hi-wattage supply.
Would like to use standard off-the-shelf transformer and other
component.(as i have no experience designing transformers)
Should be very fault tolerant (overload/SC etc) and safe to use as i
am the one who will use it.

Why ?
Primarily for learning.Yes, i know building one may cost more than
buying. Yes i also know that
lethal voltages will be present.

What i can:
i am an electronics hobbyist and design digital ckts regularly, but
have not embarked on a high wattage power supply before. Have the
standard tools like DMM/DSO and use LTSpice, gEDA and such tools. Have
designed and programmed PIC18F micros.

My proposed block diagram:
12/24V --> [ DC-DC boost converter] --> 320 VDC --> [ 100 KHz PWM/H-
bridge ] --> [ Filter ] --> 230V RMS sinewave.

What help i need:
Topology: How to get the 325V peak DC in the first place ? does it
require multiple boost stages ?
Transformer: I guess a transformer would invariably be needed. how to
select one (off the shelf one) ?
Snubber: How do i go about design a snubber ?

Any answers or even pointers to above questions would be much
appreciated..
Thanks
From: Michael Black on 20 Jul 2010 14:02
On Tue, 20 Jul 2010, tmpstr wrote:

> I would like to build a pure sinewave inverter and need some help in
> designing & component selection.
>
> What ?
> A 100-200 Watts, 230 V pure sinewave inverter
> Input: preferably one 12V SMF battery. two if absolutely needed.
> Output: 230V RMS sinewave capable of 100 ~ 200 watts
> Load: 19" LCD TV for now.
>
You're going about it wrong.

Find an LCD tv set with an external power supply, or modify the existing
set. Then figure out the voltages it needs, and supply those directly.

What you propose is to convert a 12v DC source to high voltage AC, so the
tv set can then convert that AC to a low voltage DC source. Chances are
good that the tv set is using a switching supply.

Figure out how to run the set off 12vdc directly, and feed a battery into
it. You may need some regulators to supply some other voltages, depending
on what's in the tv set. Or, replace the existing switching supply with
a supply that takes 12vdc and supplies the needed voltages.

Michael
From: JW on 21 Jul 2010 05:35
On Tue, 20 Jul 2010 14:02:21 -0400 Michael Black <et472(a)ncf.ca> wrote in
Message id: <Pine.LNX.4.64.1007201358400.25889(a)darkstar.example.net>:

>On Tue, 20 Jul 2010, tmpstr wrote:
>
>> I would like to build a pure sinewave inverter and need some help in
>> designing & component selection.
>>
>> What ?
>> A 100-200 Watts, 230 V pure sinewave inverter
>> Input: preferably one 12V SMF battery. two if absolutely needed.
>> Output: 230V RMS sinewave capable of 100 ~ 200 watts
>> Load: 19" LCD TV for now.
>>
>You're going about it wrong.
>
>Find an LCD tv set with an external power supply, or modify the existing
>set. Then figure out the voltages it needs, and supply those directly.
>
>What you propose is to convert a 12v DC source to high voltage AC, so the
>tv set can then convert that AC to a low voltage DC source. Chances are
>good that the tv set is using a switching supply.
>
>Figure out how to run the set off 12vdc directly, and feed a battery into
>it. You may need some regulators to supply some other voltages, depending
>on what's in the tv set. Or, replace the existing switching supply with
>a supply that takes 12vdc and supplies the needed voltages.

But the OP said:

>>Why ?
>> Primarily for learning.Yes, i know building one may cost more than
>>buying. Yes i also know that
>>lethal voltages will be present.
From: George Jefferson on 21 Jul 2010 06:08


"tmpstr" <mahesh_nkr06(a)yahoo.co.in> wrote in message
news:0c0db393-62ab-4b72-b11f-adf13e0c275b(a)u36g2000prg.googlegroups.com...
> I would like to build a pure sinewave inverter and need some help in
> designing & component selection.
>
> What ?
> A 100-200 Watts, 230 V pure sinewave inverter
> Input: preferably one 12V SMF battery. two if absolutely needed.
> Output: 230V RMS sinewave capable of 100 ~ 200 watts
> Load: 19" LCD TV for now.
>
> Constraints:
> Design should be simple as this is my first hi-wattage supply.
> Would like to use standard off-the-shelf transformer and other
> component.(as i have no experience designing transformers)
> Should be very fault tolerant (overload/SC etc) and safe to use as i
> am the one who will use it.
>
> Why ?
> Primarily for learning.Yes, i know building one may cost more than
> buying. Yes i also know that
> lethal voltages will be present.
>
> What i can:
> i am an electronics hobbyist and design digital ckts regularly, but
> have not embarked on a high wattage power supply before. Have the
> standard tools like DMM/DSO and use LTSpice, gEDA and such tools. Have
> designed and programmed PIC18F micros.
>
> My proposed block diagram:
> 12/24V --> [ DC-DC boost converter] --> 320 VDC --> [ 100 KHz PWM/H-
> bridge ] --> [ Filter ] --> 230V RMS sinewave.
>
> What help i need:
> Topology: How to get the 325V peak DC in the first place ? does it
> require multiple boost stages ?
> Transformer: I guess a transformer would invariably be needed. how to
> select one (off the shelf one) ?
> Snubber: How do i go about design a snubber ?
>
> Any answers or even pointers to above questions would be much
> appreciated..
> Thanks

1. Topology - how about inverting the 12V into AC then into a transformer.
Then you can simply run the transformer "backwards".

e.g., if I was going to do it:
12VDC->PWM->Step Up-> Filter->sinewave

It shouldn't be hard to find a 230V:12V transformer and hence you just run
it in reverse(although you might get a higher voltage since it won't be
exact).

This method uses cheaper mosfets because of the low voltage(as it is easier
to drive as there is no HS gate... you'll be able to use both n-ch and
p-ch). Of course th current is larger but shouldn't be a bit problem.

In the US I could just take a basic wall-wart and use that. (The difficult
thing is you'll need a 10A wall-wart which I've not ever seen... but you
could take a few and parralel them)

2. Snubber - For AC these are basic cap + res in series. It acts as a simple
HP filter and shunts HF spikes across the switches. There are other methods.
For DC one can use diodes as any reverse spike will flow through the diode
instead of trying to flow through the switch. Most mosfets have built in
diodes and depending on the currents involved you don't have to do anything
but makes sure you get the direction right.

There are lot's of inverter circuits out there that you might want to take a
look at. If I were really going to do this I would follow what you suggest
and simply use a boost converter. Getting the 325V shouldn't be an issue.
The duty cycle will be about 3% which is a bit low but doable.

To get the inductor/transformer for these circuits you have to worry mainly
about three things. DC resistance, Inductance(many calculators on the net
for it), core saturation. (this is assuming your buying off the shelf)

You can compute the total magnetic flux based on the core type and current.

http://en.wikipedia.org/wiki/Saturation_%28magnetic%29

Should help.

If you use wall-warts or they may saturate and not be as effective but by
paralleling them you'll reduce the current and hence the total flux through
each individual core.




From: John Larkin on 21 Jul 2010 11:39
On Tue, 20 Jul 2010 10:45:05 -0700 (PDT), tmpstr
<mahesh_nkr06(a)yahoo.co.in> wrote:

>I would like to build a pure sinewave inverter and need some help in
>designing & component selection.
>
>What ?
>A 100-200 Watts, 230 V pure sinewave inverter
> Input: preferably one 12V SMF battery. two if absolutely needed.
> Output: 230V RMS sinewave capable of 100 ~ 200 watts
> Load: 19" LCD TV for now.
>
>Constraints:
> Design should be simple as this is my first hi-wattage supply.

Some things just aren't ever going to be simple.

John

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