# Where to find cheap transformers? 220v to 24/48v

#### mmocz

Joined Apr 26, 2017
14
Hi,

I am thinking about building some simple power supply units. I want to take 220v ac from the power socket and transform it to 24/48v ac, and then rectify to dc. But I can not find ANY ac-ac transformers on eBay or aliexpress. All I can find are assembled power supplies, but thats not what I want. What should I be looking for? I have spent a day looking for sth, but I must be looking for some wrong keywords.

Thanks!

#### mmocz

Joined Apr 26, 2017
14
I managed to find only a few transformers, but they cost around 20 USD. I would like to find those, which are in the cheap 1USD power supplies. Or some similar.

#### Kermit2

Joined Feb 5, 2010
4,163
Try "EI power transformer"

That is not the letter L, but is a capital letter i

Joined Jul 18, 2013
19,414
If $20 is high then about the only option is to seek out surplus equipment, probably older equip. as much of today's uses SMPS. There is Antek for toroidal versions which can easily be modified, but they are above your price range. Also the shipping on most of a suitable size will be ~$20 to boot.
Max.

Joined Jul 18, 2013
19,414
That link is a SMPS so a standard AC linear transformer is no good.
Wall Wart style.
Max.

#### tcmtech

Joined Nov 4, 2013
2,868
That EI power transformer search seems usable, thanks! But I still don't get how I can buy 1 AC-DC transformer power supply for a dollar and the cheapest transformer is for 20 USD? Because basically I want to make sth like this.
I'm guessing you didn't use the most obvious search criteria as " 24/48 transformer" being I came up with half a million hits with price ranges for ~$5 to several hundred dollars depending on size, type and quantity. Thread Starter #### mmocz Joined Apr 26, 2017 14 Oh, silly me. Thanks for pointing that out. I didnt realize that these power supplies work first by rectifying AC to DC and only then they lower the voltage. I have a slightly different question then. What is this block in the middle and under what name I can buy it? Thread Starter #### mmocz Joined Apr 26, 2017 14 I'm guessing you didn't use the most obvious search criteria as " 24/48 transformer" being I came up with half a million hits with price ranges for ~$5 to several hundred dollars depending on size, type and quantity.
I am getting a lot of fully working power supplies, but I am just looking for one component, to make it myself to learn something. At least I hope I am getting the same results as you are.

https://www.dropbox.com/s/dissj1803mz6slz/Screenshot 2017-05-26 23.13.44.png?dl=0

Joined Jul 18, 2013
19,414
Oh, silly me. Thanks for pointing that out. I didnt realize that these power supplies work first by rectifying AC to DC and only then they lower the voltage.

I have a slightly different question then. What is this block in the middle and under what name I can buy it?
They are usually ferrite core transformers, often custom designed for a particular design.
You would need to look up some of the manufactures of semiconductors app notes aimed at SMPS supplies.
Such as Linear Technology etc.
Max.

Joined Jan 15, 2015
4,698
Oh, silly me. Thanks for pointing that out. I didnt realize that these power supplies work first by rectifying AC to DC and only then they lower the voltage.

I have a slightly different question then. What is this block in the middle and under what name I can buy it?
Not quite. We start with a high voltage AC which we "step down" (step down transformer) to a lower voltage AC and then we rectify that lower stepped down AC to DC. Transformers can be step down, step up, isolation as in 1 to 1 ratio and several other flavors but we are referring to a step down transformer in this case. Other power supplies use different techniques and designs but what you describe in your original post:

I am thinking about building some simple power supply units. I want to take 220v ac from the power socket and transform it to 24/48v ac, and then rectify to dc. But I can not find ANY ac-ac transformers on eBay or aliexpress. All I can find are assembled power supplies, but thats not what I want. What should I be looking for? I have spent a day looking for sth, but I must be looking for some wrong keywords.
That would be a step down transformer and the reduced or stepped down AC would then be rectified to DC. This is generally followed by some filtering.

Ron

Joined Jan 15, 2015
4,698
I have a slightly different question then. What is this block in the middle and under what name I can buy it?
Uh, the block in the middle is a transformer if we are looking at the same picture.

Ron

#### tcmtech

Joined Nov 4, 2013
2,868

#### AlbertHall

Joined Jun 4, 2014
8,780
I managed to find only a few transformers, but they cost around 20 USD. I would like to find those, which are in the cheap 1USD power supplies. Or some similar.
If you are prepared to work at it then you could get a defunct microwave oven and rewind the transformer. There are lots of articles and videos on www on how to do this.

Joined Jul 18, 2013
19,414
In post 5 the OP says he want to build a SMPS.
Max.

#### GenJacks

Joined May 15, 2016
19
Have you tried ordering online? Coz they also give great deals.

#### AlbertHall

Joined Jun 4, 2014
8,780
I managed to find only a few transformers, but they cost around 20 USD. I would like to find those, which are in the cheap 1USD power supplies. Or some similar.
I have discovered many times that, if something is available to buy ready made, that it will be more expensive to buy the parts than to buy the complete thing and then you have to add the cost of all your designs that didn't work.