The other day i was looking to improve my current set-up/way of powering my 12v-24v DC motor with a power rating of 130W.
My current set-up a switching power supply like this then to a PWM then to my DC motor, but I don't like it since I have 4 live leads of AC and DC.
This is my actual power supply, sorry i'm using pictures from the internet because my phone camera lens cracked and i dont have any cameras.


I have wires straight from the plug to the ac input and wires straight from dc output to the pwm and to my dc motor.

however, the other day i was looking at other options and saw this board which does 220V ac to 12V dc.







and here is the description:
Input voltage:AC85-265V
Frequency:50HZ/60HZ
Output voltage: DC 24V
Output current:4A-6A
Output power:100W
Overvoltage protection:yes
Over current protection:yes




today i looked it up and can't believe this.
My only question is, how can this small of a board do what my giant of a power supply also do?
Pardon me and my dumb questions but from the pictures it looks really really small, but does what my gigantic power supply does.
can someone explain to me how it works if it is real, and is it reliable. Thanks, again I'm sorry if I'm asking really dumb questions, I'm sorta new to electronics and stuff.

 

Your psu is rated at 12V @ 20A, that's 240W, whereas the smaller pcb is 100W..

 

Your psu is rated at 12V @ 20A, that's 240W, whereas the smaller pcb is 100W..

But would that small of a board really work at stepping down and rectifying 220ac?

 

Yes it's a switchmode psu rated at 5Amps..

Look at how small a mobile phone charger is..!

 

Just think of a lawnmower motor as against a Mac Truck motor. They are basically the same, just different sizes relating to their power outputs.
Same with power supplies.
I would stay with the supply in a case, keep away from the bare board one.

 

You are much better off, reliability wise, to use a simple transformer and bridge rectifier for motor control.
SMPS are not the ideal for this application.
Max.

 

The size of a power transformer, for a given power rating, is determined by its operating frequency, with lower frequencies requiring a larger transformer.
The transformer in a linear supply, as yours is, operates at the line frequency (50-60Hz), so requires a relative large transformer which occupies a significant part of the volume of the supply.
A switch-mode power supply typically operates in the tens of killohertz region, so the transformer can be much smaller.

 

Yes it's a switchmode psu rated at 5Amps..

Look at how small a mobile phone charger is..!

Oh right, a phone charger is much more smaller than this. Sorry, I was just amazed at how small this switching power supply is. Thanks!

 

Just think of a lawnmower motor as against a Mac Truck motor. They are basically the same, just different sizes relating to their power outputs.
Same with power supplies.
I would stay with the supply in a case, keep away from the bare board one.

Yes, I missed the current factor, although that it is small, it barely could handle amperage if I were to switch to this. Sorry again, i was awed in comparing sizes.

 

You are much better off, reliability wise, to use a simple transformer and bridge rectifier for motor control.
SMPS are not the ideal for this application.
Max.

Hi max! you helped me a lot in my last thread I hope you remember me! Thanks, also I wanted to ask you if i were to get this SMPS, can i use a buck converter that takes DC 6V-40V and outputs DC 1V-35V and supports up to 20A? or if i do that would I be limited to the 6A current rating of the SMPS? Thanks again!

 

The power rating/limit of the SMPS applies to any further application, downstream.
I don't recall the previous issue, but one, are you going to vary the rpm of the motor? Or what exactly is the application?
It may cost a little more to go the linear supply route, but IMO that is the better option.
Max.

 

The power rating/limit of the SMPS applies to any further application, downstream.
I don't recall the previous issue, but one, are you going to vary the rpm of the motor? Or what exactly is the application?
It may cost a little more to go the linear supply route, but IMO that is the better option.
Max.

Yes, I will be varying the rpm of the motor because I want to drill .6mm holes through 1/2 inch steel plate at different speeds and study the quality of the holes, and I want to make sure that power supply can give the current needed by the motor to drill through 1/2 inch steel plate at different rpm.

 

If doing a qualitative test, then you may need some kind of feed back to maintain RPM, alot depends on the controller also.
Max.

 

If doing a qualitative test, then you may need some kind of feed back to maintain RPM, alot depends on the controller also.
Max.

Hi, I've decided that I will be sticking to my 12v 20 amp psu although i plan on making it a bench supply. supposed a power supply has 3 outputs like mine, 3 negatives and 3 positive leads, if i were to use all of those at the same time would it provide the 12v 20amp dc rating or will it be split evenly across the three outputs? Thanks again!

 

One thing that makes SMPS power supplies smaller is the frequency they operate at. e.. 300 kHz to 1 Mhz is common. Transformers are much smaller. Aircraft operates at 400 Hz instead of 50 or 60 Hz because of weight.

 

if i were to use all of those at the same time would it provide the 12v 20amp dc rating or will it be split evenly across the three outputs? Thanks again!

Usually the rating applies to a total load of all sources combined.
Max.