# Question Regarding Input and Output of an AC Transformer

#### Benjamin0904

Joined Oct 3, 2020
32
Hi! My recent project involves the use of an AC Transformer, in which I have never used a transformer before. I think I understand that in an ""100% efficient"" circuit, the input and output of a transformer will always be the same, just in different ways. In a way, its like 5x10=50, and 25x2=50, and so on. Here is my question though:

If I have a supply of a constant 110 ACV, 10ma, what transformer would be most efficient at reducing the voltage and increasing the amperage? I tried using calculators online to calculate the power output given the power input, but failed because I didn't understand the terminology. In theory, by using the constant supply of power and putting it through a transformer, and a rectifier, I would like to power a small can/hobby motor

Thanks so much,
Benjamin

#### Ya’akov

Joined Jan 27, 2019
8,975
Hi! My recent project involves the use of an AC Transformer, in which I have never used a transformer before. I think I understand that in an ""100% efficient"" circuit, the input and output of a transformer will always be the same, just in different ways. In a way, its like 5x10=50, and 25x2=50, and so on. Here is my question though:

If I have a supply of a constant 110 ACV, 10ma, what transformer would be most efficient at reducing the voltage and increasing the amperage? I tried using calculators online to calculate the power output given the power input, but failed because I didn't understand the terminology. In theory, by using the constant supply of power and putting it through a transformer, and a rectifier, I would like to power a small can/hobby motor

Thanks so much,
Benjamin
Could you be more clear about the application? The required output voltage will determine the maximum current you will have available.

#### Benjamin0904

Joined Oct 3, 2020
32
Could you be more clear about the application? The required output voltage will determine the maximum current you will have available.
Hi Yaakov!
The power of the hobby motor that I will need to power is 3v, .450amps. I'm not to picky on what hobby motor i will be using. It can vary depending on how much output i get.
Thanks!

#### BobTPH

Joined Jun 5, 2013
8,688
You cannot have a constant voltage and constant current, so your question makes no sense as stated.

As for how you calculate the amperage and voltage of the secondary, you do it by equating the power

Power is voltage x current.

110V at 10 ma is 1100 mW or 1.1 W.

To figure out what current you would get at a different voltage, you have:

Pout = 11 x Iout

Iout = Pout / 11

Iout = 1.1 / 11 + 0.1 A = 100mA

Bob

#### Ya’akov

Joined Jan 27, 2019
8,975
Hi Yaakov!
The power of the hobby motor that I will need to power is 3v, .450amps. I'm not to picky on what hobby motor i will be using. It can vary depending on how much output i get.
Thanks!
It's a bit unusual to power a small motor from the mains, could you explain why you are doing this? Also, see #8 from @BobTPH for some good basic math to get an idea of what you can expect.

#### BobTPH

Joined Jun 5, 2013
8,688
Then y
The power of the hobby motor that I will need to power is 3v, .450amps
Then you need a transformer that can put out at least .45A at 3V. No mystery in that.

Get a 3V wall wart that can put out 1A, you are not knowledgeable enough to be making this yourself, or dealing with the lethal 110V.

Bob

Last edited:

#### BobTPH

Joined Jun 5, 2013
8,688

#### Ya’akov

Joined Jan 27, 2019
8,975
Then y
Then you need a transformer that can put out at least .45A at 3A. No mystery in that.

Get a 3V wall wart that can put out 1A, you are not knowledgeable enough to be making this yourself, or dealing with the lethal 110V.

Bob
3V, of course.

#### BobTPH

Joined Jun 5, 2013
8,688

#### Benjamin0904

Joined Oct 3, 2020
32
Then y
Then you need a transformer that can put out at least .45A at 3V. No mystery in that.

Get a 3V wall wart that can put out 1A, you are not knowledgeable enough to be making this yourself, or dealing with the lethal 110V.

Bob
I'm just so confused on all the information everybody is giving me. I will try to answer things in this paragraph. Of course you know I'm new to this stuff, but I would not mess with danger. The 110v Power supply has no more than a current of 10milliamps. That is because I am using a microwave oven plate motor that is 120v, 2-4Watts as the supply. When I Hand crank it it will easily produce 110+ ACVolts but max 10milliamps. I know your probably wondering why I'm trying to power a small dc motor with an ac generator. I just like to experiment, simply put. My #1 goal is to use the synchronous ac motor to power the 3v, .450amps motor to use as a portable fan. Maybe for camping, outside, etc. Hope this helps,,
Benjamin

#### Ya’akov

Joined Jan 27, 2019
8,975
I'm just so confused on all the information everybody is giving me. I will try to answer things in this paragraph. Of course you know I'm new to this stuff, but I would not mess with danger. The 110v Power supply has no more than a current of 10milliamps. That is because I am using a microwave oven plate motor that is 120v, 2-4Watts as the supply. When I Hand crank it it will easily produce 110+ ACVolts but max 10milliamps. I know your probably wondering why I'm trying to power a small dc motor with an ac generator. I just like to experiment, simply put. My #1 goal is to use the synchronous ac motor to power the 3v, .450amps motor to use as a portable fan. Maybe for camping, outside, etc. Hope this helps,,
Benjamin
The unloaded current from that motor doesn't tell you what it can produce into the motor. You will have to measure the output under load. I expect you will find you get far less from it.

Joined Jul 18, 2013
28,534
3v, .450amps motor to use as a portable fan. Hope this helps,,
Also helps to use Ma, the decimal is hard to see e.g. 450 ma

#### Benjamin0904

Joined Oct 3, 2020
32
The unloaded current from that motor doesn't tell you what it can produce into the motor. You will have to measure the output under load. I expect you will find you get far less from it.
I'm glad that I was actually taught how to measure load current. I just measured the load current of me cranking the synochronys microwave motor, and I got about 8-9ma on my meter

#### Benjamin0904

Joined Oct 3, 2020
32
I'm glad that I was actually taught how to measure load current. I just measured the load current of me cranking the synochronys microwave motor, and I got about 8-9ma on my meter
the load that i tested was a lightbulb, it did not light barely

#### SamR

Joined Mar 19, 2019
5,021
Get a 3V wall wart that can put out 1A, you are not knowledgeable enough to be making this yourself or dealing with the lethal 110V.
Sorry to jump in so late... Actually, any wall wart greater than 3V and 1A if you have one to hand. Then, learn how to apply a 3V regulator to the circuit such as an LM317 or LM337 1.5A, 1.2V TO 37V adjustable voltage regulator or LM350T 3A, 1.2-33V since I know of no 3V regulator. There is an IRU1010-33, 3.3V, 1A low dropout, positive, fixed regulator SMD. A transformer needs a cord set, fusing for safety, rectification from AC to DC, capacitive filtering and smoothing, and then regulation with perhaps some capacitive filtering and diode reverse voltage protection. By using a wall wart, you will at least learn about regulation.