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From: John Larkin on 21 Jul 2010 11:43
On Wed, 21 Jul 2010 05:08:29 -0500, "George Jefferson"
<phreon111(a)gmail.com> wrote:

>
>
>"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.
>

Paralleling the primaries does not reduce flux density. Reducing
excitation voltage, or increasing frequency, does.

All others things being constant, reducing the load current taken from
a transformer secondary *increases* flux density in the core.

John

From: George Jefferson on 21 Jul 2010 13:19
>>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.
>>
>
> Paralleling the primaries does not reduce flux density. Reducing
> excitation voltage, or increasing frequency, does.
>
> All others things being constant, reducing the load current taken from
> a transformer secondary *increases* flux density in the core.
>


Haha, you really have no knowledge of electronics do you? When are you going
to learn the difference between current and voltage?


From: Tim Wescott on 21 Jul 2010 13:35
On 07/21/2010 03:08 AM, George Jefferson wrote:
>
>
> "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).

Given 12VDC and an H-bridge, the best you'll get out will be about
8.5VAC rms.

But you can probably find catalog transformers that'll come close to
that, and can be used.

> 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.

Less expensive MOSFETs, but a much more expensive (and bigger)
transformer. Most switching circuits that I see for 12V use all
N-channel MOSFETs with high-side drivers, because good high power
N-channel FETs are enough easier to find than good high power P-channel
FETs it makes the driver circuit worthwhile.

> 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)

It'd be cheaper & smaller to find one power transformer, though.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: Tim Wescott on 21 Jul 2010 13:41
On 07/20/2010 10:45 AM, 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.
>
> 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 ?

A flyback transformer is probably your best bet; get most of your
step-up from the transformer, and the last little bit from the flyback.

Alternately, use a transformer with a turns ratio greater than 320:12,
and control the duty cycle down.

(Come to think of it, you could do the latter with a self-oscillating
circuit and avoid the need for a controller -- just accept that your
320VDC rail will be unregulated and be happy).

> Transformer: I guess a transformer would invariably be needed. how to
> select one (off the shelf one) ?

For this you may find it easiest to wind your own. Cores are available
for just this sort of thing.

Get isolated 320VDC, drive your AC with an H-bridge, and you shouldn't
need a transformer on the HV side -- just output filtering.

> Snubber: How do i go about design a snubber ?

Find similar circuits and copy them shamelessly. It helps if you
understand them before you copy them.

If you can find copies of the ARRL Handbook there's a big line-to-12V
switcher that appears in there -- many of the principals of design are
the same, even if you're going in the opposite direction.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: tmpstr on 21 Jul 2010 14:52

> 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).

Did you mean PWM -> Filter -> Step Up ?
this would allow me to use a 50Hz transformer (quite bulky for 50 Hz,
100 Watts. may need a trolley ;-) ).
If you did mean PWM->Step Up-> Filter,
then i am not sure if we get off-the shelf transformers that do 12:230
at the PWM freq.
I am now doing a search on Coilcraft/Pulse/Magnetica.eu etc
The Magnetica.eu site has a 1KW inverter designed by ST ! having a
look at it now.
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