Going to build a circuit!

All right people! It is time

http://www.next.gr/automations/motor-control-circuits/Universal-motor-speed-control-l12865.html

Is planing to build this circuit but not sure if it will fit my specifications
can someone help me ?

Am needing about 10-12 amps power for a universal motor at around 120-80 volts ac.( The diagram doesn't show anything about varying the speed with a switch so I would like to put a sliding potentiometer somewhere.)

Ok it says max current is 1.5amps but will a vacuum cleaner run at that?

How about this circuit? **broken link removed**

Omm so many circuits.. Ok I need to know this peoples , maybe I will just make my own but I don't really know how it all works yo :/ .

For instance in all those two circuits they all use some kind of capacitors , resistors and SCR etc; why are they even used to lower the voltage and current? How do they do it?
Someone please help explain?

You can give this a read.
https://www.circuitstoday.com/scr-control-circuits
It needs to be what is called a universal motor. They are commonly found in washing machines, mixers and other small appliances.

ronv said:

You can give this a read.
https://www.circuitstoday.com/scr-control-circuits
It needs to be what is called a universal motor. They are commonly found in washing machines, mixers and other small appliances.

Click to expand...

Ronv hello, thanks for the link dude.
I got a question not related to this can you help ? ( How do people determine what specific type of electrical component to use for a specific type of job in a circuit and does it matter if the non-correct specifications are used?)[Like in a diagram it says to use a C106B1 SCR for a 120v circuit, how was using a C106B1 SCR determined?]

In this case they were looking for a part that would work on 120 volts AC, which is about 170 volts peak, So they chose one good for 200 volts.
Then the maximum current, in this case 20 amps, was chosen. This would depend on the current your motor needs and the size of the heat sink you use.
https://pdf1.alldatasheet.com/datasheet-pdf/view/97088/CENTRAL/C106B1.html

ronv said:

In this case they were looking for a part that would work on 120 volts AC, which is about 170 volts peak, So they chose one good for 200 volts.
Then the maximum current, in this case 20 amps, was chosen. This would depend on the current your motor needs and the size of the heat sink you use.
https://pdf1.alldatasheet.com/datasheet-pdf/view/97088/CENTRAL/C106B1.html

Click to expand...

Oh Oh I see I see, so the electrical component can be( best to be) over what it can handle just in-case it needs to handle higher quantities.

So does that mean if a circuit needed a( 50uf 30 volt) capacitor to handle 30vdc and I used a ( 50uf 40volt) one instead.It would be safer because if the voltage were to fluctuate it wouldn't breakdown.[Does this also apply to other electrical components; resistors,transistors,diodes ..etc ?]

[Would having it as a 40volt instead of 30volt capacitor effect the rest of the circuit? or will the changes be negligible? ]

onetwothree4 said:

Oh Oh I see I see, so the electrical component can be( best to be) over what it can handle just in-case it needs to handle higher quantities.

So does that mean if a circuit needed a( 50uf 30 volt) capacitor to handle 30vdc and I used a ( 50uf 40volt) one instead.It would be safer because if the voltage were to fluctuate it wouldn't breakdown.[Does this also apply to other electrical components; resistors,transistors,diodes ..etc ?]

[Would having it as a 40volt instead of 30volt capacitor effect the rest of the circuit? or will the changes be negligible? ]

Click to expand...

In general, yes. A higher voltage capacity for a component than what would be the "normal" operating voltage that component would be subjected to in the circuit is a good practice, for the reasons you noted.

To your last question: a capacitor with a higher voltage rating will have no effect on the rest of the circuit.

Yes, the more factor of safety you have the safer circuit is. You can use capacitors with higher voltage rating and it will work fine in almost all circuits. The only cons of this is that they are bigger, more expensive, and may have greater ESR (this doesn't matter in your circuit)

>Does this also apply to other electrical components; resistors,transistors,diodes
Yes, it's usually good idea to have some reserve. But not always this is reasonable, there is no need to have 1W resistor where only 0.1W of heat is dissipating, or to use 1000v 10A transistor to drive small led from battery.
Selecting parts voltage/current/power rating is usually a choice between reliability and size/price.

Thank you Cowboybob and Nyaknyan

My vacuum cleaner motor draws 12A when it is working hard. It will blow up that weak circuit to kingdom come.

Don't forget about inrush current when the motor first starts, it can be several times the normal running current.