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 12/120V inverter again
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tt1493
Apprentece

Hong Kong
15 Posts

Posted - Apr 19 2005 :  05:33:31 AM  Show Profile  Reply with Quote
I have a question. i find that a transformer is 220v input 12v-0-12v output.
Can it use for 12v-0-12v input, 220v output?
The sales told me can't, is he right?

Thanks
TT




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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 19 2005 :  06:44:52 AM  Show Profile  Reply with Quote
Of course the transformer will work fine.

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wasssup1990
Nobel Prize Winner

A Land Down Under
2261 Posts

Posted - Apr 19 2005 :  06:49:46 AM  Show Profile  Visit wasssup1990's Homepage  Reply with Quote
G'day John! You replied whilst I was typing a reply to this topic. Just reply again if you think anything i've said below is a bit off.

He would be right if the resistance is too low on the Secondary coil of the transformer. If it was like 1-2 ohms then you'd consider checking a different transformer. Also make sure the Origional Secondary coil can handle the current it's consuming.

Oscillating 12V on each side of the CT one turn at a time on the Secondary coil will produce a square-wave 220VAC on the origional Primary Coil.

The transformer's secondary coil would consume too much current if the resistance across it is too low. If this is the case then the efficiency is too low, and would consume lots of current while in 'idle' mode (switched ON but no load).

It's best to keep inverters efficient as possible, so transformers are what you should be focusing on in an inverter. Get, or make the best one for the job.

Good luck!

J.C.
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 19 2005 :  07:07:46 AM  Show Profile  Reply with Quote
Hi Johnny,
You are correct, the transformer must be rated to do the job. You can't use a little 100W transformer to pass 500W continuously.

You want windings with low resistance (thick wire) so they don't heat too much. But you also want enough inductance so the 12-0-12 winding is not like a dead short.Your microwave-oven transformer didn't have enough turns on its windings because a microwave oven never idles, it is always fully-loaded. Without enough turns on its windings, it was approaching being like a dead short (low inductance) when your inverter was idling or driving a light load.

A purchased power transformer usually has enough turns in its windings to be fairly efficient without a load or when lightly loaded.

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wasssup1990
Nobel Prize Winner

A Land Down Under
2261 Posts

Posted - Apr 19 2005 :  07:13:08 AM  Show Profile  Visit wasssup1990's Homepage  Reply with Quote
Yeah if you do the math, there was nothing I could really do about it. More turns would equal a lower voltage on the 'new' secondary. You've just gotta basicly use your common sense about this stuff.

So good to talk to you again John.

See ya.

J.C.
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sule
Apprentece

6 Posts

Posted - Apr 22 2005 :  4:09:24 PM  Show Profile  Reply with Quote
pls can anyone send me the schamatic of inverter of about 2000watt which would be able to carry ceiling fan ,tv of 75 watt and so on.i used the diagram of this site and it didnt work.when i used a small transromer of about 500watt it only lighted a bulb of 40wattand i thought the fault was from the transformer ,i changed the tranformer to 2000watt and it could not even light a bulb.pls i need a help and send me the schematic of 1000-2000watt.the transistor i used was 2N3055.this is my address.............suledes@yahoo.com
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - Apr 22 2005 :  6:52:22 PM  Show Profile  Reply with Quote
Let's see. Inverters are about 80% efficient so a 2kW inverter would heat with about 400W, a lot of heat to get rid of.
It would draw 2.4kW from the battery. If the battery is 12V, the inverter would draw a whopping 200A. A car battery might boil or explode when trying to deliver so much continuous current, and its voltage will probably drop to about 8V immediately. It might last about 1/2 hour before needing a re-charge.

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wasssup1990
Nobel Prize Winner

A Land Down Under
2261 Posts

Posted - Apr 22 2005 :  7:22:36 PM  Show Profile  Visit wasssup1990's Homepage  Reply with Quote
I can tell that this would be a huge, heavy inverter. According to audioguru's calculations you would need 8 car batteries paralelled at equal charge to supply that inverter for only 4 hours. Or you could just connect the inverter up to a car battery whilst the engine is running, so the battery stays charged. BUT I think the battery and the alternator in the car would overheat when the inverter is on full load. Also in this case you might get a very unstable voltage and current supply from the battery because the alternator and the battery can't cope. You might use a 4WD or a truck's battery and alternator to run your inverter! LOL That seems powerfull enough. Come on, why do you really need this much power? I don't even think there's a schematic out there on the net to find! Unless you have access to some Super Battery or want to power your inverter off a petrol or LPG guseler, why bother? Where are you planning to use this device? An isolated area? If in that case just buy a ???VAC electric generator. If it's just for hobby use, build a 300W inverter like I did.

J.C.
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blah
Apprentice

Australia
75 Posts

Posted - Apr 23 2005 :  9:06:15 PM  Show Profile  Reply with Quote
Hi, I'm a newb and i found this forum after looking for a way to invert 12v to 40V at a about 40Amps to use as a portable thin rod welding setup, just for fun. I have used 2 12V batteries in series and it worked well, but an inverter that i could clamp on my car battery would be more fun, i know you can buy alternator welders and there's a 12V mig welder on the market but i like the challenge of building something myself.
Sule, Why do you want a 2000W inverter to drive a ceiling fan, 75watt TV and a Lightbulb? why not open a window, use a fluro and build a ~200W Inverter to run a fluoro and your TV. Anyway, I found a circuit that claimed to be able to handle 2000-5000W.
http://www.theverylastpageoftheinternet.com/forsale/plans/inverter/inverter.htm

However, after reading this entire thread and using what i have learnt from it so far, i believe the IRFZ44's driving the 24CT windings will only be capable of delivering ~600W and they would get pretty warm. Stranger still is the suggestion they give of using smaller IRF640's? You could try 3xIRFZ44NS's in parallel in conjunction with a rewound Arc Welder as a transformer? I look forward to hearing what some of the more knowledgeable guys have to say about this design.

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Robert Hedan
New Member

Canada
2 Posts

Posted - Apr 23 2005 :  10:34:47 PM  Show Profile  Reply with Quote
I've read the entire thread, and now I'm TOTALLY confused. :D

I am searching for a schematic that I can modify to power the EL on a Seiko L2432 LCD; specs on page 38:
http://www.iweil.com/devices/lcd%20drivers/seiko%20manual.pdf

In:
5V DC, 45mA

Out:
350Hz, 95V, 1.5mA

Any help would be greatly appreciated. The circuits discussed above are WAY too powerful for my rinky dink application. Generating a stable 5V DC 1A supply with 7805s is not a problem, it's the other end that I need help with. Personal background so you know what kind of newb you are dealing with: :) (sounds like a CV :D )

- can draw 5V and 12V power supplies with the bypass caps on QCAD.
- can fabricate PCBs using UV process and etching acid.
- can program PICs using BASIC.
- can download a linked database (built in Excel) via RS232 from PC onto memory chips like the 24C128.
- hacked a USB keyboard matrix so I can generate any keystroke I want, or combination like CTRL-A (using a PIC and some MCT6 opto-couplers).

Note that I'm on medication right now, I can't remember stuff I read like in books and such. But I remember stuff I build, weird, that's why I use sites like Aaron's as tutorials.

I just need a slight push in the right direction and I usually figure stuff out on my own. But please don't push too hard, it doesn't take much to make me look like Homer in that skit with the ambulance dropping him off a bluff.

Robert
:)

P.S.: AudioGuru, where in Canada?


Not as dumb as yesterday, but stupider than tomorrow!

D'uh, never mind, I just clicked on your profile. :)

Edited by - Robert Hedan on Apr 23 2005 10:40:39 PM
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Robert Hedan
New Member

Canada
2 Posts

Posted - Apr 24 2005 :  12:47:12 AM  Show Profile  Reply with Quote
I've just found this gem:
http://www.elecdesign.com/Articles/ArticleID/6400/6400.html

What do you folks think of it? Are there design flaws? It's kinda too good to be true at this point. I've been searching for this circuit for several months now.

Robert
:)


Not as dumb as yesterday, but stupider than tomorrow!
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sule
Apprentece

6 Posts

Posted - May 03 2005 :  08:51:34 AM  Show Profile  Reply with Quote
SEND ME A SCHEMATIC OF HOW I CAN CHARGE AND ALSO SAME TIME BE USING MY INVERTER.THE I BUILT WHEN I WAS USING IT AT SAME TIME I WANTED TO CHARGE IT .THE TRANSISTORS JUST BURNT OFF.PLS HELP EVEN IF I NEED TO USE RELAY.

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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - May 03 2005 :  09:44:48 AM  Show Profile  Reply with Quote
You are using the inverter to power a battery charger that is charging the same battery? Same thing as connecting the shafts of a gererator and a motor togerther.
The circuit losses prevent them from running very long.

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hobby16
New Member

France
3 Posts

Posted - May 04 2005 :  6:31:58 PM  Show Profile  Reply with Quote
Audioguru,
To my humble opinion, the circuit based on 2N3055 is fine ... 20 years ago.
Yeah, npn transistor is OBSOLETE for switching.
It's bulky, fragile and pricy (even if you have it for free when considering the amount of time for assembling a bunch of it, not to say making a so low gain oscillator work).

Mosfet used like in http://www.theverylastpageoftheinternet.com/forsale/plans/inverter/inverter.htm
IS the right way. The control stage can be greatly simplified of course (beware, 555 does NOT ouput a 50% duty cycle square wave).

Simple considerations show the superiority of mosfets
- No load balancing resitor when paralleling: just add another mosfet (but with 120A mosfet off the shelf, WHY paralleling!)
- at 50 hz, nearly infinite gain (compare to 30-50 on 2N3055!)
- nearly zero loss: with a common 0.004 ohm (yes, 4 milli-ohm) mosfet, when switched on 50A (600W at 12V), the dissipation at the transistor is... 10W.
With 2 mosfets as in the above schematics, each transistor takes 5W. Try to do the same with npn: NO WAY!
- With a small microcontroller (around 1 euro/unit), you can generate a pwm signal to reproduce a 220V sinus output. And no more heat dissipation since transistors work in on/off mode. DON'T say that sinus inverter are bulky, it's false.

Please, be in touch with modern electronics and avoid old age solutions. Go to manufacturer sites (ti, ir, national, maxim, vishay...) on your spare time and do some fundamental readings, it helps!
Anyway, your dedication, misleading as it may be sometimes is FORMIDABLE.

P.S. toroid transformers are best (excluding microware transformer ) because they are small and silent both accoustically and electrically.

(Edit...Remove notification)

Edited by - Aaron Cake on May 31 2005 10:21:51 AM
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audioguru
Nobel Prize Winner

Canada
4214 Posts

Posted - May 04 2005 :  7:14:49 PM  Show Profile  Reply with Quote
Hi Hobby,
I didn't design this 2N3055 inverter with its low output and exploding capacitors, I'm only trying to fix it. If I could post a sketch on this site it would show how easy it is to add driver transistors, diodes to protect the base-emitters and the correct polarity of the capacitors.
I also didn't design the 500W inverter, I simply discovered its shorts and helped make it work. In Indonesia where it is needed they had a bucket full of 2N3055 transistors but no money to buy Mosfets.
I agree that a microcontroller driving Mosfets in a sine-wave inverter like in the inexpensive inverters that are sold today is the proper way to do it. If I needed an inverter I would just buy one of them instead of designing and purchasing some expensive parts. But I don't need an inverter today, probably never.

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