Sciencemadness Discussion Board

Help with a circuit and a toroidal transformer

Organikum - 24-2-2013 at 10:06

First the transformer, picture is attached. It is a 220V AC to 22V 5A AC transformer which I want to use by adding some windings as it can be seen as a cathode filament heating 3,5V AC source. The idea comes from a thread on mosfetkiller.net, which I cannot locate anymore.
Two questions:
- The transformers original secondary, 22V, should it be open circuit or shorted in this application or doesnt it matter anyways?
- I have about 29 windings on the new secondary giving me 3,5V without load. Toroidal transformers are said not to break down on voltage under load so I hope thats enough (I would have a problem with more windings too). I calculated the windings by using the information on sveral websides and always came to about 28/29 windings needed. But on the pictures I saw on mosfetkiller the secondary had maximal 10 windings on a very similar looking toroidal transformer. This puzzles me a bit.


My other problem regards the naming of a circuit I need. The circuit is supposed to switch a SSR on and off. The on and off cycles should be to choose freely as multitudes of one second. The pattern is periodic but can be changed whilst in operation. No user interface is needed it would suffice if the on and off duration can be defined by microswitches or even jumpers. 20 seconds as longest interval is enough.

This is to replace the usual on/off regulation on a microwave which applies off-phases which are just to long to keep temperature as stable as needed. Whilst I am under the impression that pulsation in most cases is positiv, the way it is implemented now is just to crude.

I have done plenty of reading so I am aware of minimum times on "on" necessary, on having the cathode heated seperately (see above) when this gets to short and the whole shebang whatnotever.

How would such a circuit be called and maybe a link to one of the better circuit pages where I can start searching. Tried "timer" and NE555 for I thought this might be the right one, but it seems to complex for a 555. A usable circuit may contain one or more 555....
Anyways give me a name please!

thx
/ORG

toroidal.JPG - 149kB

IrC - 24-2-2013 at 12:34

Not quite clear to me what time durations you are looking for. Are you wanting a circuit where you can select on times in one second intervals. If so in what range, one to twenty? Also what off intervals. As to the 22 volt winding if you short circuit it, your primary will appear as a dead short to the 220 VAC input. Is something along the line of a 555 driving a 4020 or 4017 what you are looking for?

watson.fawkes - 24-2-2013 at 13:04

Quote: Originally posted by Organikum  

- The transformers original secondary, 22V, should it be open circuit or shorted in this application or doesnt it matter anyways?
- I have about 29 windings on the new secondary giving me 3,5V without load. Toroidal transformers are said not to break down on voltage under load so I hope thats enough (I would have a problem with more windings too). I calculated the windings by using the information on sveral websides and always came to about 28/29 windings needed. But on the pictures I saw on mosfetkiller the secondary had maximal 10 windings on a very similar looking toroidal transformer. This puzzles me a bit.
As @IrC said, leave the existing secondary open. When you put an AC voltage on the primary, it will induce an AC voltage on the secondary. Since you don't want to draw power from the secondary, don't hook it up to a load. A short is a very high-power load. If you short the secondary and plug it in, you'll have made an effective test of your mains protection equipment. You might also melt something in the transformer.

As to the second question, "very similar looking" is not a particularly relevant kind of similarity. What matters is the turns ratio between primary and secondary. If you need 28 windings to get 3.5 V and another transformer needed 10, all that really means is that the number of primary turns of the two transformers were different.

The circuit you are looking for is variously called an oscillator with variable duty cycle, a periodic pulse generator, or a pulse-width modulator. You can build one with a pair of 555's and adjust it with a potentiometer. I posted in a thread here in the last few months; @12AX7 replied with data sheet details.

Organikum - 24-2-2013 at 19:33

Thanks for the answer on the transformator I had not shortened the secondary as I thought that could not be right but then an article on the net confused me once again.

This is the post you were talking about I suppose and it is a very interesting one I guess, for somebody who knows about this stuff already. So the if I would understand the provided information I would not need it from the beginning.

And from what I understand its not what I need anyways as this provides a signal the frequency of which can be altered. But I want to cycle a microwave in a pattern where switched-on-duration and switched-off-duration for the magnetron is periodical but not necessarily equal. I have to be able to go from permanently on (what translates to 20 sec. on, 20sec. on...) to 19 seconds on to 18 seconds on step by step down to 0 sec. on. Additionally the off-cycle shall work in the same way. from 0 sec. off in one second steps to 20 sec off. I dont think thats so hard to understand in special knowing the purpose of it. Well it might be more complicated then making LEDs blink rythmically what seems to be the mainpurpose of microcontroller programming but I am sure it IS doable and not even a PIC is needed.
From a logical approach it sounds to me like something of an oscillator for the 1 second pulses and two counters alternating action through a flipflop or however a simple switch is called in elektrospeak. The counters are adjustable (a solution for adjusting the 20 steps is needed like a potentiometer but click for click more resistance by adding resitors, thus exists I have seen it times ago. A more sophisticated approach would be nice as long it does not include a display just a two knobs. Thats one look to know the setting.
A circuit for this including the ICs and the still always necessary byload on discret elements and the parts to set the values for the counters (or whatever fullfills this function then, of course there may be other ways to this, I dont mind as long as it works and is to solder together by me. No SMDs. ).

Hopefully I was able to express now more exactly what I need. If such a device should not exist - na that cannot be. I am sure under the heaps of millions and millions of blinking LED drivers there must be something useful hidden...

thx
/ORG

watson.fawkes - 25-2-2013 at 05:25

Quote: Originally posted by Organikum  
And from what I understand its not what I need anyways as this provides a signal the frequency of which can be altered.
No, there's one adjustment for each oscillator. One of them adjusts the frequency of the oscillator, as you already gathered. The other, however, adjusts the period of the one-shot. The ratio of the one-shot period to the oscillator period gives you your duty cycle. The device you've asked for would have a fixed oscillator period (20 s by your design) and a variable duty cycle.

The electronics here is pretty basic, but if you've never done electronics, it could be tens of hours to make it go. Personally (and I'll repeat my opinion yet again) the investment in learning basic electronics is definitely worthwhile for amateur scientists of all kinds. On the other hand, if you don't want to make that investment now (or ever), then it's an easy bit of software to make a microcontroller output the right waveform. I don't consider this "a waste of transistors", though. It's a substitution of personal skill, which takes time to develop, with transistors; it's a perfectly good tradeoff for many people.

Organikum - 25-2-2013 at 18:52

Well I suppose we have different definitions of "basic electronics", for by now my knowledge completely sufficed to solder some circuits if in need (solder not develop) and to ask where to find things. Strangely here this does not work at all. The repeated advice to learn electronics from somebody who does a lot if it reminds me so much on the Linux freaks and their MAN pages you should read in their opinion. There is no difference at all to VERY religious people who want you to read the bible. They want to make their interest to yours.

watson.fawkes do you realise that your answers dont't help me in any way to solve my problem? Do you throw somebody drowning a lifesaver or do you tell him that in your opinion (and that you told him before!) everybody visiting the beach should learn to swim? I have a strong guess about what you would do....
If you by any reason of social disapt don't have realised this, that you answer but don't answer and that you behave like a missionary and that this way to be left helpless is pretty annoying much more then getting no answer at all then I have told you this now and you might consider to ask people around you if they see a similar problem and regard you as jerk with an attitude?

I still don't have search terms which enable me to pick out a circuit from one of the 769 circuit pages. Developing such circuit or programming a microcontroller is just ridiculous what a nonsense,a this exists already, by any logic it must.

Now I go and ask the kids on one of the HV/electronics pages and I bet I will get a working solution in no time, no doubt. Makes me sad though that it is not possible anymore for me to get valid helpful answers at home (and for me SCM is home in certain ways). It is not that the knowledge is not out here.

Thats worse then spammers.

/ORG :(

IrC - 25-2-2013 at 20:39

Your request is not specific enough for design. Show a graph or something indicating exact on/off intervals, and under what conditions the timing needs to change*. You make vague mention of durations changing with microswitches being activated, and so on. To design a specific circuit the designer needs to know exactly what conditions. Just as a flow chart aids in writing a program.

* Are you saying you want some type of switch, say a rotary, to select different times? If so indicate with precision. Are you needing the off time to be varied as well? When, what, how much. Without this kind of specific parameters I do not see how anyone could design it.


[Edited on 2-26-2013 by IrC]

watson.fawkes - 25-2-2013 at 22:53

Quote: Originally posted by Organikum  
If you by any reason of social disapt don't have realised this, that you answer but don't answer and that you behave like a missionary and that this way to be left helpless is pretty annoying much more then getting no answer at all then I have told you this now and you might consider to ask people around you if they see a similar problem and regard you as jerk with an attitude?
I won't be designing your circuit for you. I never intended to. Perhaps you can bully someone else into doing your work for you. Good luck with that.

blue_vitriol - 26-2-2013 at 16:19

You should look into pulse width modulation. Arduinos can do that and they are sold at radio shack.

ElectroWin - 26-2-2013 at 19:38

unused windings should be left as open circuit.

how many ohms load do you expect to have on your new secondary? for tests, measure voltage with a resistor of that value as a dummy load.

froot - 26-2-2013 at 23:44

Quote:
But I want to cycle a microwave in a pattern where switched-on-duration and switched-off-duration for the magnetron is periodical but not necessarily equal. I have to be able to go from permanently on (what translates to 20 sec. on, 20sec. on...) to 19 seconds on to 18 seconds on step by step down to 0 sec. on.


I'd use a voltage modulated PWM circuit, the input of which is fed the output of a capacitor discharging slowly through a resistor. The values of C and R can be easily calculated to get the response you're looking for.

A elements of this circuit should be found on here.

Edit: If your open circuit voltage of 3,5V drops significantly when loaded then your VA rating of the transformer is too low for the load, ie, the coupled magnetic core volume is too low and is saturating. To remedy this use a transformer with a higher volume magnetic core (VA rating).

[Edited on 27-2-2013 by froot]

Organikum - 1-3-2013 at 00:23

Thanks for the link and information froot! Thats the right direction, have not found exactly what I am after - maybe I just dont recognize it - but looks good.
Will do some more searching there and maybe be back with a possible selection and questions.

The transformer gives 3,5V AC without load and 2,9V AC with magnetron filament heating as load (whats his destined task anyways). 2,9V is a bit on the low side but still in the specifications, the transformer hums a little, but not loudly and does not get hot, just warm. Will do, has to.

@watson.fawkes, hey! I never wanted anybody design a circuit for thats completely nonsense as this exists already. A custom designed prototype would be the very last I want, I am not eager on troubleshooting an advanced lightswitch. A already tested solution is what I am after, a working one.
You feel bullied? Poor you. Just stay out of my threads and dont reply to my posts and we both will be happier, I for getting answers I can use and you for - whatever I dont give a fuck.

@IRC Thanks! Your request for a flowchart for this enhanced on/off switch I need gave me the best laugh for quite some time. Thinking about what else you then will need to have a flowchart, detailed instruction and what not, gave me a even bigger laugh. But sorry I dont want to be mean, I really can see how difficult this is for you lets just imagine whats called reproduction and not the eating and drinking part but the - you all know what I mean and IRC will have it as flowchart. At least I hope for him he has.


rotfl
/ORG

IrC - 1-3-2013 at 11:49

One would assume it was clear I was making an analogy. In effect relating a flowchart to program writing as relating specific timing information to designing the required circuit. I think this was very clearly stated previously by me and nowhere did I suggest the need for a flowchart to design the circuit you were requesting.

What I stated was post the precise on/off information and under what conditions it needs to be varied by selection or microswitches being activated since this is exactly what you were describing initially.

"The on and off cycles should be to choose freely as multitudes of one second. The pattern is periodic but can be changed whilst in operation. No user interface is needed it would suffice if the on and off duration can be defined by microswitches or even jumpers. 20 seconds as longest interval is enough"

"But I want to cycle a microwave in a pattern where switched-on-duration and switched-off-duration for the magnetron is periodical but not necessarily equal"

This information is too vague and nonspecific for design. All I did was ask you to provide precise timing information as I stupidly considered actually helping you. Do you often receive help by insulting and berating those you ask? Or should I say those who are willing to try?

Exactly how does one design a circuit to switch something in a way which is "periodical but not necessarily equal"? Build a random number generator, remove the LED dice, and wire it to an SSR?



[Edited on 3-2-2013 by IrC]

watson.fawkes - 2-3-2013 at 06:23

Quote: Originally posted by IrC  
Do you often receive help by insulting and berating those you ask? Or should I say those who are willing to try?
Yes, he does. He's asking to be spoon-fed. He doesn't know enough electronics even to recognize useful answers to the question he posted, now posted by four different users in this thread. And when he finds a mark, someone who seems willing to help but isn't feeding him his favorite flavor of baby food, he spits it out, and insults them. Presumably the "proper" outcome of the play book goes something like this:

Organikum
Please help me.
The Mark
OK. Here you go.
Organikum
That's not what I wanted. You must be stupid.
The Mark
I'm not stupid, and I read minds, too! Here's exactly what you wanted.

He's a bully. The only way to win this game is not to play. For the record, I've appended his abusive remarks to the two of us below.
Quote: Originally posted by Organikum  
@IRC Thanks! Your request for a flowchart for this enhanced on/off switch I need gave me the best laugh for quite some time. Thinking about what else you then will need to have a flowchart, detailed instruction and what not, gave me a even bigger laugh. But sorry I dont want to be mean, I really can see how difficult this is for you lets just imagine whats called reproduction and not the eating and drinking part but the - you all know what I mean and IRC will have it as flowchart. At least I hope for him he has.
Quote: Originally posted by Organikum  
watson.fawkes do you realise that your answers dont't help me in any way to solve my problem? Do you throw somebody drowning a lifesaver or do you tell him that in your opinion (and that you told him before!) everybody visiting the beach should learn to swim? I have a strong guess about what you would do....
If you by any reason of social disapt don't have realised this, that you answer but don't answer and that you behave like a missionary and that this way to be left helpless is pretty annoying much more then getting no answer at all then I have told you this now and you might consider to ask people around you if they see a similar problem and regard you as jerk with an attitude?