Help in using transformer and voltage regulator...

[SgtWook]

Yes, that does look mighty small. A decent quality 18-0-18 500mA transformer would be roughly:
3" x 2" x 2" or 75mm x 50mm x 50mm and weigh at least 1 lb (0.455kg)

That one would be badly saturated at 500mA out.

[eta]
It would be quite helpful if our OP would measure the transformer output under both no-load and a fixed load, so that we can get an idea of the transformer impedance.

It would also be helpful to know the peak output voltage, both loaded and not loaded. However, since they apparently don't have a supply already...

 

[crutschow]

Yes, that does look mighty small. A decent quality 18-0-18 500mA transformer would be roughly:
3" x 2" x 2" or 75mm x 50mm x 50mm and weigh at least 1 lb (0.455kg)

That one would be badly saturated at 500mA out.

..................

A transformer core doesn't saturate due to high load current. It saturates due to an input voltage over its rating. But excess current will cause a large output voltage drop and high power dissipation in the transformer due to the winding impedances.

 

[yusuf]

Thanks all friends for replying me !!!!
Friends which circuit should I use .... Eric's or Sgtwook !!

And other thing while talking on efficiency... will it give 12v and 8v output voltage !

And if suppose (just for knowledge only)..

If I remove the R4 & R3 resistors...
And the output load will remain at 12, 8v 200ma ......
It will not increase....

So what would happened at output !

 

[ericgibbs]

Thanks all friends for replying me !!!!
Friends which circuit should I use .... Eric's or Sgtwook !!
Its your choice.!

And other thing while talking on efficiency... will it give 12v and 8v output voltage !
What do you think?

.......................
E

 

[yusuf]

And if suppose (just for knowledge only)..

If I remove the R4 & R3 resistors...
And the output load will remain at 12, 8v 200ma ......
It will not increase....

So what would happened at output !

Friend I am new in electronic so I hope it seems foolish questions... which I am asking to you friend..
But I am getting questions and doubt so I am asking here because I am newbie in this field...

 

[yusuf]

and Can I use C1 at 330uf 16v...
and C7 220uf 10v..

BECAUSE I HAVE ONLY THIS CAPACITOR WITH THEIR VOLTAGES..

 

[ericgibbs]

And if suppose (just for knowledge only)..

If I remove the R4 & R3 resistors...
And the output load will remain at 12, 8v 200ma ......
It will not increase....

So what would happened at output !

Friend I am new in electronic so I hope it seems foolish questions... which I am asking to you friend..
But I am getting questions and doubt so I am asking here because I am newbie in this field...

Sorry,I dont see any purpose in discussing, what if I do this or that, for removing components.
If they were not necessary the circuit design would not include them.

and Can I use C1 at 330uf 16v...
and C7 220uf 10v..
You cannot use these capacitors, their working voltage is too low.
Ideally you want 35V working.

 

[audioguru]

Sorry,I dont see any purpose in discussing, what if I do this or that, for removing components.
If they were not necessary the circuit design would not include them.

The student (and every kid in his class) should be taught about power dissipation (heating) and the reasons for including R3 and R4.

 

[ericgibbs]

The student (and every kid in his class) should be taught about power dissipation (heating) and the reasons for including R3 and R4.

hi 'agu' and a Happy 2012.

Normally I would agree, but all the OP's multiple Threads seem finish up this way,,, as what ifs.?

 

[audioguru]

hi 'agu' and a Happy 2012.

Normally I would agree, but all the OP's multiple Threads seem finish up this way,,, as what ifs.?

Thanks Eric and a Happy New Year to you too.

One problem with an international forum like this one is that some people like Yusuf are different from us. His name indicates that he is probably an Arab. Different language, different customs, different religion, different clothes, different food and different education.

He hasn't been taught and doesn't understand the basics of electronics and asks "what ifs" because I guess he cannot obtain parts in his country that are inexpensive, common and available anywhere in our countries.

I think he should ask on a forum in his own country where people know that common 5W resistors and ordinary semiconductors are not available.

 

[yusuf]

Hi friends happy new year..........

Friends If suppose I remove the R3 and R4.. and now the load current will not exceed 100ma then... what will happen...
Will the regulator overheats or it works normal...
and in the normal working condition will the regulator will heat or not...

 

[ericgibbs]

Hi friends happy new year..........

Friends If suppose I remove the R3 and R4.. and now the load current will not exceed 100ma then... what will happen...
Will the regulator overheats or it works normal...
and in the normal working condition will the regulator will heat or not...

Yusuf,
The problem is your unsuitable 18/0/18v transformer.!

If you remove the series power resistors,. ALL the 'excess' voltage will be across the voltage regulators.
If you multiply the 'excess' voltage times the current thru the regulators this will give the Power dissipation in the regulators.

Example: assume the Voltage on the smoothing caps is 25volts and the current is 200mA in the 12V and 8V circuits.

For the 12V regulator thats 25v-12v = 13v * 0.2 = 2.6 Watts

For the 8v regulator thats 25-8 = 17v * 0.2 = 3.4 Watts

Reducing the current to 100mA maximum will HALF those wattage figures, you will require a Heat sink on both regulators.

 

[yusuf]

thanks for your reply...
so by removing series power resistors... and by adding a heat sink to both regulator .... I can use below 200ma that's 100ma current at 12v & 8v... without any problem...;;;

or is it necessary to give series power resistor to it...
or it can work fine at max load 100ma without series power resistors...

and friend I have made your circuit diagram..... the series power resistor is not getting hot but the regulator and relay is getting hot...
so, on working will the regulator and relay will heat little bit.. or not...

The problem is your unsuitable 18/0/18v transformer.!

I have two smps mobile chargers circuits..
when i connect this circuit in series I get 12v and 200ma at output...

each circuit deliver 6v and 200ma current ... so to gain 12v and 200ma current i have connected this both circuit in series....

and the relay is also energizing with it..

So, while talking on unsuitable ....... can we use this mobile circuit in series to work properly !


thanks in advance...

friends I dont know whether this is stupid questions or not... but i am new in this field so as i am getting any Idea or any doubt , i am posting here for help..
so please dont be angry on my any questions friend..

 

[ericgibbs]

thanks for your reply...
so by removing series power resistors... and by adding a heat sink to both regulator .... I can use below 200ma that's 100ma current at 12v & 8v... without any problem...;;;
Both regulators require a suitable sized heat sink.

or is it necessary to give series power resistor to it...
or it can work fine at max load 100ma without series power resistors...
Read my last post, with big heat sinks

and friend I have made your circuit diagram..... the series power resistor is not getting hot but the regulator and relay is getting hot...
If the relay is getting HOT you are most likely over voltage driving it.!

so, on working will the regulator and relay will heat little bit.. or not...



I have two smps mobile chargers circuits..
when i connect this circuit in series I get 12v and 200ma at output...

each circuit deliver 6v and 200ma current ... so to gain 12v and 200ma current i have connected this both circuit in series....

and the relay is also energizing with it..

So, while talking on unsuitable ....... can we use this mobile circuit in series to work properly !
Yes for the +12V, also drive the 7808 regulator from that 12Vdc

thanks in advance...

friends I dont know whether this is stupid questions or not... but i am new in this field so as i am getting any Idea or any doubt , i am posting here for help..
so please dont be angry on my any questions friend..

You really must make up your mind which solution you are going to use, otherwise this project is never going get started/finished.

 

[yusuf]

Friend the relay is not getting very hot... it is little hot... will be this a problem or it is normal heat...
the voltage I am getting at the output of 7812 is 12.30v

and the mobile smps charger circuit will be better or this regulator circuit...... will be the better..
Among this both circuit which one will work good and for longer timer.. because this circuit will going to work 24hr.....

 

[crutschow]

And if suppose (just for knowledge only)..

If I remove the R4 & R3 resistors...
And the output load will remain at 12, 8v 200ma ......
It will not increase....

So what would happened at output !

Friend I am new in electronic so I hope it seems foolish questions... which I am asking to you friend..
But I am getting questions and doubt so I am asking here because I am newbie in this field...

If you are interested in answers to all those "what ifs" then I suggest you simulate the circuit with a Spice program such as LTspice (free) and you can answer those questions for yourself.