# 12v - 36v DC motor to wall plug 220v ac

#### James Ibarra

Joined Apr 26, 2020
23
Hi, i have a DC motor and wanted to make it into drill press for PCB fab. I'm kinda new to electronics and just started to learn about PCBs. I wanted to ask if what i had in mind is feasible.

I thought this project would do me good in terms of increasing my knowledge and practicing my soldering skills.

Now this is a dc motors which means I need to convert ac to dc, what i wanted to ask is what diode/s, capacitors, and switches do you recommend.
I also want to ask if i can control rpm on a DC motor,if yes then what do i need to do that?

sorry if I'm asking too much, this pandemic bores me and i just got a sudden interest in PCBs
thanks to anyone that notices

Here are pictures:

#### djsfantasi

Joined Apr 11, 2010
6,501
There are two parts to your question. Converting AC to DC and controlling a motor.

With the voltages you are dealing with, AC to DC is best done with a transformer.

Firstly, an 8:1 transformer will drop the line voltage to approximate 25VAC. Once rectified and filtered, you’ll get ~36VDC.

Secondly, to vary the voltage to the motor, you’ll use PWM. that varies the voltage by turning it in and off quickly. If the pulse width is 20%, then the average voltage the motor sees is ~8VDV (7.8vdc)

#### James Ibarra

Joined Apr 26, 2020
23
There are two parts to your question. Converting AC to DC and controlling a motor.

With the voltages you are dealing with, AC to DC is best done with a transformer.

Firstly, an 8:1 transformer will drop the line voltage to approximate 25VAC. Once rectified and filtered, you’ll get ~36VDC.

Secondly, to vary the voltage to the motor, you’ll use PWM. that varies the voltage by turning it in and off quickly. If the pulse width is 20%, then the average voltage the motor sees is ~8VDV (7.8vdc)
I can't find a transformer to bring down 220v AC to 25v AC however i have a 220v AC to 110v AC transformer and I'm thinking of using resistors to bring the voltage down even more, is it recommendable?
sorry for asking questions that seem a little dumb.

#### djsfantasi

Joined Apr 11, 2010
6,501
I can't find a transformer to bring down 220v AC to 25v AC however i have a 220v AC to 110v AC transformer and I'm thinking of using resistors to bring the voltage down even more, is it recommendable?
sorry for asking questions that seem a little dumb.
Using resistors won’t work. Can you find a 110VAC to 25VAC? Then hook both transformers in series to get 25VAC? But it’s inefficient.

I don’t deal with 220VAC. Can you get a switching power supply for your needs? A Google search for 220VAC to 36 VDC switching power supply?

#### James Ibarra

Joined Apr 26, 2020
23
Using resistors won’t work. Can you find a 110VAC to 25VAC? Then hook both transformers in series to get 25VAC? But it’s inefficient.

I don’t deal with 220VAC. Can you get a switching power supply for your needs? A Google search for 220VAC to 36 VDC switching power supply?
I found a power supply that takes 110v-240v then output is 1.5v to 12v, however i don't it if takes input AC or DC.

here is a picture:

#### djsfantasi

Joined Apr 11, 2010
6,501
I found a power supply that takes 110v-240v then output is 1.5v to 12v, however i don't it if takes input AC or DC.

here is a picture:
View attachment 205876
That picture shows a 110VAC NA line cord. So I’d say it’s input is AC.

#### James Ibarra

Joined Apr 26, 2020
23
That picture shows a 110VAC NA line cord. So I’d say it’s input is AC.
So this would work if i only needed 12v right? how could i say upgrade this to output more volts?

Joined Jul 18, 2013
20,875
Where are you located?
If you have a 220v service then this is what you need for a suitable transformer/supply.
You can seek out bell transformers, often they will rectify to ~24vdc with suitable bridge and capacitor,
Max..

#### James Ibarra

Joined Apr 26, 2020
23
Where are you located?
If you have a 220v service then this is what you need for a suitable transformer/supply.
You can seek out bell transformers, often they will rectify to ~24vdc with suitable bridge and capacitor,
Max..
I'm from Philippines and i can't find any 24v DC bell transformers only 12v DC ones, I guess i'll just have to make do with 12v DC, Thanks djsfantasi and MaxheadRoom for answering my question

#### djsfantasi

Joined Apr 11, 2010
6,501

220 VAC TO 36 VDC Power Supply​

36VDC is a common requirement for medical equipment, so you should find a variety of supplies.

The one question I haven’t asked yet is what power/amperage do you need on the output?

#### djsfantasi

Joined Apr 11, 2010
6,501
Remember that when you use a switching power supply, you need to specify the maximum voltage. When you are rectifying AC, the transformer needs to specify an output that is the required voltage divided by 1.414 because of the differences in how AC and DC are measured.

Joined Jul 18, 2013
20,875
I'm from Philippines and i can't find any 24v DC bell transformers only 12v DC ones, I guess i'll just have to make do with 12v DC, Thanks djsfantasi and MaxheadRoom for answering my question
They do not make dc bell transformers!
They most likely are 12ac, but open circuit, they will be higher, if using a 12v and rectifying and smoothing it will be ~15vdc at least under load.
Max.

#### James Ibarra

Joined Apr 26, 2020
23
They do not make dc bell transformers!
They most likely are 12ac, but open circuit, they will be higher, if using a 12v and rectifying and smoothing it will be ~15vdc at least under load.
Max.
Sorry, yes i meant 12v AC bell transformers. I would rectify it myself but I don't think i have the knowledge, confidence, and skills to do it.

#### James Ibarra

Joined Apr 26, 2020
23

220 VAC TO 36 VDC Power Supply​

36VDC is a common requirement for medical equipment, so you should find a variety of supplies.

The one question I haven’t asked yet is what power/amperage do you need on the output?
The DC motor's current rating floats between .14A to .20A depending on the voltage ofc.

#### James Ibarra

Joined Apr 26, 2020
23
Remember that when you use a switching power supply, you need to specify the maximum voltage. When you are rectifying AC, the transformer needs to specify an output that is the required voltage divided by 1.414 because of the differences in how AC and DC are measured.
thanks for the tips! I'm already learning a lot and I haven't even started on the project haha, I'd be sure to keep that in mind.

#### James Ibarra

Joined Apr 26, 2020
23

220 VAC TO 36 VDC Power Supply​

36VDC is a common requirement for medical equipment, so you should find a variety of supplies.

The one question I haven’t asked yet is what power/amperage do you need on the output?
Hi, I've found a stepdown transformer laying about in our garage 220v AC to 20v AC however it does has a marking saying "2000 ma" and I wanted to ask what it means before I plug it to the wall to test if it's working.

Joined Jul 18, 2013
20,875
It means the rating is 2000 ma = 2amps.
Are you sure is is not VA rating?
Max.

#### djsfantasi

Joined Apr 11, 2010
6,501
It means the rating is 2000 ma = 2amps.
Are you sure is is not VA rating?
Max.
...before you ask, it’s ok to have a supply rated for more than the load, because a load (the motor) only takes what it needs. The transformer can’t / won’t force 2A into a 200mA motor.

#### djsfantasi

Joined Apr 11, 2010
6,501
Sorry, yes i meant 12v AC bell transformers. I would rectify it myself but I don't think i have the knowledge, confidence, and skills to do it.
Rectifying AC is connecting two wires from the transformer to a bridge rectifier and taking two wires from the other or DC terminals of a bridge rectifier to your load. Since your load is a motor, you may not need filtering, which is just a capacitor across the DC terminals.