A puzzle for you electrictians...

[My Name]

OK, I have a power supply that is putting out 39V DC. I need it to put out 21V DC.

What's the easiest way of achieving this? Is it that simple, or is there more to it than that?

It would be best if the voltage was variable by 5V or so.

Any ideas?

 

[dementedchord]

get a fairly heavy controll pot... the outer 2 contacts go to the power supply... the wiper and which ever of the other 2 is grnd go to the unit the wiper then is variable.... the hard part is figureing out what controll to use you dont want it low enough to load the supply by its sef and you dont want it so high that the unit doesnt get enough current....

 

[demto]

My advice would be not to fiddle with it unless you know what you are doing.

If its a well made supply it will probably have 'voltage regulators' in it which are
sometimes adjustable. These set the DC output volts.

You may be able to adjust what you have already, otherwise the voltage regulators
will have to be changed for ones that will output the volts you need. This is a more
complicated subject than it seems. Unless you know what you are doing leave it alone or get somebody that understands these things to have a look for you.

good luck

 

[My Name]

Any idea how you work this out?


I would post a schema of the power supply but my scanner is shagged

 

[Wil816]

If you tell us the make and model of the power supply, there's a small chance the needed info can be found online. Depending on the load current and the output regulation you need, it may or may not be practical at all to get there with the particular supply you have. I've designed a lot of power supplies for our products; but if I just needed one and not a thousand, I would just buy the appropriate one.

 

[My Name]

Well it's actually the PSU that's in an ITAM 806. It's a pain in the arse actually as I can't seem to get the bloody thing working right. I've checked all the components and they all seen to be working right but the output is way too high. I can't work it out, I'm not an electrician. I just work of logic... if all the components are working then it should do as it should. But no!

Are you an expert with PSUs?
Is it possible to tell which component is not working as it should just by the symptoms, ie. the wrong output voltage?

I'll try and post the schema somehow

 

[ofajen]

OK, I have a power supply that is putting out 39V DC. I need it to put out 21V DC.

What's the easiest way of achieving this? Is it that simple, or is there more to it than that?

It would be best if the voltage was variable by 5V or so.

Any ideas?

Is it supposed to put out 39V or 21V? Or some other value?

Cheers,

Otto

 

[My Name]

It's supposed to put out 21V. I must be missing something... It's driving me nuts!!!

 

[demto]

Probably a stupid question but does the supply have an mains input voltage selector.

If so check its set for the mains voltage you are using the supply on.

 

[MCI2424]

It's supposed to put out 21V. I must be missing something... It's driving me nuts!!!

If it has voltage regulation, I would look there for trouble.

Some use voltage regulators and cheap supplies use zener diodes. You have to know what it is before you repair it.

 

[ofajen]

It's supposed to put out 21V. I must be missing something... It's driving me nuts!!!

Don't shoot at me... is this a bipolar supply? Any chance you're measuring the difference of +V and -V? That would nominally be 42V?

Cheers,

Otto

 

[Dr ZEE]

Well it's actually the PSU that's in an ITAM 806. It's a pain in the arse actually ...

the real pain in the arse is to search the net for itam 806 trying to find any info about PSU in it. and who do you think is going to do it anyway?

I can't work it out, I'm not an electrician. I just work of logic... if all the components are working then it should do as it should. But no!

Let's try the logic then.
First of all, componets don't "work", componets just are - they are either "good" or "bad". You can apply word "working" or "not working" on a circuit, that is built of components that are either good or bad. Then you can say that the circuit under the test "working right", "working wrong" or does not work at all which is a form of "working wrong", assumingly you are conducting a "right test" and you are conducting it correctly and you are 100% sure about what the "correct" result is to be expected.

Are you an expert with PSUs?

Is he or is he not - it does not matter. No circuit - no subject!.
The best you can expect is a bunch of generic blah blah about "PCU trouble-shooting", comming from all sorts of experts, of course.
If you provide schematics of a troubling circuit and information about how exactly you conduct your disappointing test, then you may get a useful answer or a thought,
...logically speaking.

 

[Wil816]

Originally Posted by My Name
Are you an expert with PSUs?

Is he or is he not - it does not matter. No circuit - no subject!.

That's about it. He had said, "I'll try and post the schema somehow," so that's what I was waiting for. Then I could make up a list of things to check (mostly voltages at different points) and see if what comes back makes sense. That would mean he'd have to be able to find and probe these points on the board. It also pretty much assumes a linear supply, not a switching supply. Otto had a good point though:

Don't shoot at me... is this a bipolar supply? Any chance you're measuring the difference of +V and -V? That would nominally be 42V?

If you just measured across labeled outputs say "+" and "-", the "-" may actually be another supply, a negative one, and you're measuring across two supplies instead of just from ground to the output of the positive one. What led you to this? What were the symptoms that prompted you to even measure the output?

 

[dementedchord]

i originally assumed we were talking about adapting a wall wart or something so rethinking the problem.... regulators have a pin tied to grnd this becomes in essence the reference it regulates from.... some times a manufacturer will use say a 18V reg to produce say 21 V by raising that pin above grnd by(in this case)3V... i'm betting this is the case here... and if that is opened the reference is shot to hell as the pin is now floating....