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how to make high current Transformerless powersupply

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Qaisar Azeemi

Qaisar Azeemi

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Hi Friends;

i have made a battery charger successfully with a maximum output of 20A. i used 20A transformer in it but it is too bulky and having larger in size and having cost double than the original circuit... so i want to replace the transformer with an Electronic circuit....

How should i design its schematic ... kindly help me... formulatic evaluation and related links will be very appreciated.

sincere regards;
Qaisar Azeemi
 

You could draw 20A directly, but it will trip circuit breakers. Or you could draw 40A at a 50% duty cycle (using a buck converter, etc.)... but that would also trip breakers.

So a transformer is a comparatively efficient way to draw power in one form and convert it to another.

Theoretically you could charge a capacitor stack during the positive cycle, then switch them so they're parallel, and obtain ample battery charging voltage at several times the current. But in real life this would involve a number of components which would probably wind up being just as costly as the transformer, take up as much (or more) space, and dissipate the same (or greater) amount of power.
 

So you mean there is no way at all to make a transformerless powersupplies for high currents??? :-(

I think Chinees are making such type of power supplies. Do you know anything about that? i also hear about some UPSes (1KVA or 2KVA) in our country that are using Transformerless approach. :-(
 

Hi Qaisar

Perhaps you could use a switched-mode power supply (SMPS) for this. There is a lot of information and links here: Switched-mode power supply - Wikipedia. This thread has links too.

SMPS uses a small high frequency transformer instead of a large mains transformer. This is how the power supplies in desktop computers work. Many computer power supplies can give more than 20A at 12V.

Regards - Godfrey
 
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Hiya Qaisar!

Aye - the direction suggested by godfreyl's the way to go, and what I suspect you meant by an 'electronic replacement'. Switch(ed) mode power supplies are able to employ a smaller (lighter) transformer by operating at a higher frequency (typically 10's - 100's of kHz) than the giant lumps of steel required at the 50/60 Hz mains frequency.

There's an abundance of information on the net under the heading 'off-line switch mode power supplies' that might help, as well as articles on how to modify (cheap) PC power supplied to obtain low-voltage, high current outputs - such as this one: https://www.qsl.net/vk4ba/projects/ps.pdf.

If you wanted to build something rather than buy it, I'd recommend the option of modifying an existing (junked PC) switcher design to meet your needs rather than starting from scratch. I can guarantee it'll cost you a whole lot less in the long run!! (I have winced, watching sets of $30 IGBT's go up in smoke on so many, painful occasions ;) Horowitz and Hill say it so nicely in their book "The Art of Electronics":
27_1335162221.jpg



Enjoy :)
 
Qaisar Azeemi said:
So you mean there is no way at all to make a transformerless powersupplies for high currents??? :-(

I think Chinees are making such type of power supplies. Do you know anything about that? i also hear about some UPSes (1KVA or 2KVA) in our country that are using Transformerless approach. :-(
Click to expand...

What you need is a switched mode power supply which does use a transformer, but a small ferrite transformer working at high frequency, and thus avoids the bulky iron transformer.
You can start by going through a few resources posted here:






You should get some books, start reading on SMPS and then move on to designing it.

Hope this helps.
Tahmid.
 

i have made a battery charger successfully with a maximum output of 20A. i used 20A transformer in it but it is too bulky and having larger in size and having cost double than the original circuit... so i want to replace the transformer with an Electronic circuit....
Click to expand...
It is not possible to make a supply with such a large current supply. I think what you are assuming a TRANSFORMERLESS power supply is the Switch Mode power supply (SMPS) as said in post #5 and #7. The reason for assuming is that it is almost weightless as compared to the Transformer power supply. In post #7 many references are given for good guidance.
 
Please refer the following article to know how to make a CHEAP, high current transformerless power supply circuit:

**broken link removed**

Thanks,
Swagatam
 
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Please refer the following article to know how to make a CHEAP, high current transformerless power supply circuit
Click to expand...

How can that be scaled to supply 20A as requested in post#1?
The circuit requires just 1 of any of several components to fail
for the user to experience 220V at the output instead of the desired 12V.
 

transformer less circuitory in high current rating is not possible in real time even smps follows some form of power transformations only SO IT IS PRACTICALLY NOT POSSIBLE in current world scenario
 

jeffrey samuel said:
transformer less circuitory in high current rating is not possible in real time even smps follows some form of power transformations only SO IT IS PRACTICALLY NOT POSSIBLE in current world scenario
Click to expand...


It is possible. I have done this with a mosfet a transistor and a zener, basically I control the switching of the mosfet so as to charge a capacitor only from 0 to 12v of the sine wave. It provides good power and no inductor or transformer is used. So yes, its possible and I've done this before.
 

It is possible. I have done this with a mosfet a transistor and a zener, basically I control the switching of the mosfet so as to charge a capacitor only from 0 to 12v of the sine wave. It provides good power and no inductor or transformer is used. So yes, its possible and I've done this before.
Click to expand...
The original post is asking about a 20 A battery charger. Providing 20 A by the suggested method involves peak currents of several 100 A and > 50 A rms current. That's effectively impossible.
 
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    tpetar

    tpetar

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About getting 20 A out of a buck converter, by drawing from rectified mains AC...

Here is a screenshot of a buck converter dropping 120 VDC to 40 V at 20 A. (In theory.)



The scope traces tell the story.

Notice that you need to draw 20 A from the supply (average), in order to get 20 A at the load.

It can be no other way with a buck converter topology.

There is a way you can input 10 A, and get 20 A out...

namely by using a flyback, etc., which contains a transformer.

- - - Updated - - -

Okay, looking closer...

The supply does not need to provide 20 A average. It looks more like 8 or 9 A average.

Additional interleaved buck converters could help the situation further.

Being connected to mains AC, this will still have the hazard of explosion if you connect a battery (particularly lead-acid type).

- - - Updated - - -

Screenshot of triple interleaved buck converter.

Load gets 40V at 20 A.

Supply is 120 VDC. Draw is about 7 A average.



This is all theory of course. Losses are not depicted.
 

Hello Mr
i have 220v source with max 0.5a
can i use this anyway to drive a transformer then connect it to an inverter to supply higher current ?
thx
 

janosandi said:
Hello Mr
i have 220v source with max 0.5a
can i use this anyway to drive a transformer then connect it to an inverter to supply higher current ?
thx
Click to expand...

In another thread you state your generator produces 220 VAC.

It would be typical to feed it to a transformer, to step down voltage, and step up Amperes...

However it would be a tough job to construct (or find) a transformer that is exactly suited to your task.

Then there is the question whether your frequency is unchanging, or whether it varies.

A transformer operates best at a particular frequency. If your frequency varies, then it is difficult to design a transformer that will convert power efficiently.

You probably will do better to full-wave rectify it, then send it to a flyback converter. A flyback contains a transformer, but you can run it at optimum frequency.
 

thx for u reply Brad
about a generator i think the frequency would change but i never measure it
im thinking about using this to charge a battery when its used to suplly 12v to DC-AC inverter
any good idea ? or search for another thing ?
 
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350W PC power supplies can be bought in bulk for $20You need how many at 300W , for what cost?

- - - Updated - - -

atwoz said:
It is possible. I have done this with a mosfet It provides good power and no inductor or transformer is used. So yes, its possible
Click to expand...


If you pulse the primary line to step down 220V to 14V with a 20A DC load, your primary current pulses are short in duration going into a battery with low ESR and many Farads of capacitance, so the charge pulse current might be 20x Idc at <5% duty cycle when AC is between 12 & 15 V and then you need 400A rated Mosfets. Thus a series 25A choke is needed to run in continuous mode with value of 10 Henry and 0.1 Ohm resistance. ... Ballpark such as an MOT for $10.
 

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