How is this Possible

[New2Electronics]

Hello. I have a DC power supply that takes 120vac into the transformer, steps it down to 8vac then puts that into the circuit using an LM 3 38 voltage reg.

Other than a bridge rectifier, a few strange looking diodes and the usual cap and resistor there are no other components. How is it then I'm able to get over 18vdc from this supply?

Thank you

 

[Alec_t]

Have you actually measured 8VAC from the transformer secondary when the supply has no output load?

 

[New2Electronics]

Have you actually measured 8VAC from the transformer secondary when the supply has no output load?

Yes.

The first thing I did was looked up the datasheet. According to the datasheet, at 115VAC into the transformer, with the current configuration, it should give 6VAC on the secondary side.

I've got 120v going from my wall into the transformer so I guessed I'd get a little more on the secondary side.

I measured it twice and it measures 8.4v on the secondary side.

 

[Bluejets]

Maybe the strange looking diodes and cap is a voltage doubler but crystal ball is cloudy today

 

[New2Electronics]

Maybe the strange looking diodes and cap is a voltage doubler but crystal ball is cloudy today

The cap is a cap. The diode looking component has a TS2 in print next to it. Does that help clear any cloudiness?

 

[davenn]

The cap is a cap. The diode looking component has a TS2 in print next to it. Does that help clear any cloudiness?

no

its time you showed us some photos of this PSU
both sides of the PCB and indicate input and output cabling


PLEASE, no-one else respond till the OP gives more info on his particular circuit


Dave

 

[New2Electronics]

no

its time you showed us some photos of this PSU
both sides of the PCB and indicate input and output cabling
Dave

Unfortunately I don't have the capability to upload pictures at the moment.

PLEASE, no-one else respond till the OP gives more info on his particular circuit

What particular info do you need? No-one has asked me any questions I haven't answered.

Obviously there a more ways than one for this to happen. I'm looking for possibilities to explore and/or trying to understand electronics a little better.

 

[AnalogKid]

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ak

 

[hevans1944]

Unfortunately I don't have the capability to upload pictures at the moment. ...

That is a serious limitation. Is it because you don't have a cell phone with a digital camera? Or a digital camera of any kind? Or is there a bandwidth limitation that would require an inordinately long period of time to upload an image of any kind? Perhaps you are blind? Will you attempt to resolve the problem so you can upload images, schematics, and the like sometime in the near future? Is there anything someone here can do to help you upload images?

 

[davenn]

+

What particular info do you need? No-one has asked me any questions I haven't answered.

I asked you for photos !!

if you cant do that as a minimum then there's not a lot we can do to help you and I mite as well close the thread

 

[New2Electronics]

ak

I don't have a
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CCCCCCCCC

 

[New2Electronics]

That is a serious limitation. Is it because you don't have a cell phone with a digital camera? Or a digital camera of any kind? Or is there a bandwidth limitation that would require an inordinately long period of time to upload an image of any kind? Perhaps you are blind? Will you attempt to resolve the problem so you can upload images, schematics, and the like sometime in the near future? Is there anything someone here can do to help you upload images?

I have resolved the problem thanks.

 

[New2Electronics]

+


I asked you for photos !!

if you cant do that as a minimum then there's not a lot we can do to help you and I mite as well close the thread

Wow! I can see you take your moderator position as a license to be rude. When you asked for photos I did not have the ability at that time to post them. Why would that cause you to threaten to close this thread?

Also pleading to others not to answer until I've complied with your demands. Is that how it is around here, your way or the highway?

please let me know so I can show myself out.

Thanks

 

[(*steve*)]

The point is that without information which could be supplies either with a schematic or some pictures (and even then they may be insufficient) we can't do any more than guess.

My guess is that there are other windings, or your readings are suspect, or you have the wrong voltage selected at the input, our that there is a voltage doubler, or that there is a boost converter, or that the output voltage is not 18 volts, or that the output voltage is incorrectly marked, or that the output voltage was incorrectly measured, or something else is going on that pictures might help us with.

I don't want to have to go through all of those possibilities when some pictures could lead I'd to the answer faster. I suspect Dave sees things this way too.

However, if you want to go up blind alleys, dead ends, and chase red herrings, feel free. Just expect people going in multiple directions and many of us not bothering.

If you would like to be shown the door, all you need do is ask, and a friendly moderator will ban you (although banning you for not understanding that we're trying to help you as efficiently as possible is not an option we would prefer).

 

[New2Electronics]

The point is that without information which could be supplies either with a schematic or some pictures (and even then they may be insufficient) we can't do any more than guess.

I understand the point. Please understand, I'm am learning so I won't have all the readily available info needed and I'm gathering as people request it.

However, if you want to go up blind alleys, dead ends, and chase red herrings, feel free. Just expect people going in multiple directions and many of us not bothering.

I understand.

If you would like to be shown the door, all you need do is ask, and a friendly moderator will ban you (although banning you for not understanding that we're trying to help you as efficiently as possible is not an option we would prefer).

Thanks. I do NOT want to be shown the door. Unless of course Dave's words and approach are the norm around here for when a moderator is dealing with someone trying to learn. I wasn't breaking any rules so I'm not sure why he's even bothering with my post.

 

[donkey]

hey new2,
the major issue is that as we try to help people label things weirdly. some of the items you think are Diodes could be another piece.
try to understand that as you are learning and as some of the people here are more experienced they tend to try helping out but need things like pictures. a picture could show us not only the components but the value so then we can draw the schematic ourselves. from there we can determine what is happening
if you are absolutely sure your components are correct then try to recreate it in a electronic cad program.
ultimately asking how something works is like trying to figure out how matter is made up, but without looking at the atoms.
grab a camera if you want to learn about circuits and take pics for us to view.

 

[hevans1944]

I am not a moderator, but I do post here and try (to the limits of my patience) to help newcomers. A picture (photo or schematic) really is worth thousands of words, unless you happen to be a particularly good wordsmith. And even if you are good at expressing ideas, concepts, and problems using the written word, a picture (or two or three or a dozen, depending on the information to be conveyed) can help others to understand what is going on. Let's go back and examine your original post:

Hello. I have a DC power supply that takes 120vac into the transformer, steps it down to 8vac then puts that into the circuit using an LM 3 38 voltage reg. ...

There is no mention of what goes on between the "8vac" secondary and the "LM 3 38 voltage reg". Since the peak-to-peak voltage of an 8 V (rms) AC voltage source is about 22 V, it is conceivable that the "missing circuit details" could be providing about 22 V DC to the input of the regulator, and that the voltage-setting divider on the output is commanding an 18 V DC output voltage. Or it could be the regulator is not regulating at all because it is defective and is simply passing through to the output whatever voltage is applied to its input. Without more information about what voltages and currents are present and an actual schematic of the circuit all of this is just conjecture.

... Other than a bridge rectifier, a few strange looking diodes and the usual cap and resistor there are no other components. ...

Oh, really? What are the "usual cap and resistor" components? Do these have values, voltage ratings or power ratings? Do they appear to be leaking or burned or in any way different from a new component? What circuit do the "usual cap and resistor" components appear in? Do you realize that the LM338 (if that is indeed the part you are calling "LM 3 38") requires at least two resistors to set its output voltage? And often, there are a couple of diodes and capacitors associated with the LM338. See circuit schematic below.

... How is it then I'm able to get over 18vdc from this supply?

Thank you

I have no idea how you are able to do this. Maybe it is by design, or maybe it is defective. How much current can you draw from the supply when your are "able to get over 18vdc"? Does the supply voltage drop when you apply a resistive load? What is the voltage and current from the supply with various loads applied? What is the maximum current rating of the power supply? What voltage is the power supply supposed to provide? Who is the manufacturer of this power supply? What is it's model number? What are the specifications for this power supply? From the little information you have supplied, it might as well be operating with magic. We don't do magic here.

 

[davenn]

Thanks. I do NOT want to be shown the door. Unless of course Dave's words and approach are the norm around here for when a moderator is dealing with someone trying to learn. I wasn't breaking any rules so I'm not sure why he's even bothering with my post.

we are ALL trying to help you but you are VERY reluctant to help us help you !!
I was just showing the frustration with you that ALL of us were feeling with your lack of helpful info

I have lots of patience with those learning and make an effort to help themselves,
you so far have not been one of those people

 

[73's de Edd]

Sir New2Electronics . . . . . . .


" I have a DC power supply"

On subsequent posts you were querying on component specifications for info for MAKING yourself a supply.

Repetetive . . . . .

BUT this must be an ALREADY manufactured supply, of ? Brand, so are there any of its specifications labeled on its proper that will be giving the units voltage and its amperage output capabilities or even its AC line side power consumption ?

New . . . . .
OR . . .can you have a photo "savvy" acquaintance take care of its photo documentation aspect for you ?


73's de Edd

 

[hevans1944]

I don't have a
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If you are really trying to learn, then learn how to "reverse engineer" your power supply and produce your own schematic. Then tale a picture of that schematic you have created from scratch and post it here for our comments.