# I Think I'm over my head....

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#### Louser

##### New Member
Ok I got a 24vdc 8.4A power supply out of a computer/pos system. And I want to make a variable voltage power supply out of it.

Datasheet:
https://www.electro-tech-online.com/custompdfs/2009/11/sp-200-spec.pdf

This thing has a voltage adjustment on it the pot will add or subtract about seven volts either way. shoukld i try and changet the pot resistance or build a seperate control circuit? If it is the latter does anyone know where to find a good schematic on how to get a variable voltage out of it? I plan on putting panel meters on it, and many I have found are pretty much plug and play.

Now I am a newbie and Batteries are getting old. I'm currently testing small circuits on an atx supply that I modified.

Any help would be appreciated. The learning curve is overwhelming but I'm determined to get this.

#### Boncuk

##### New Member
Hi Louser,

since you don't seem to have a schematic of the design I suggest to add a linear circuit for variable output voltage.

Boncuk

#### Louser

##### New Member
Thank you. i have a few from several books. know of any good resources?

##### Banned
Boncuk a linear regulator wouldn't be that great of an idea, even if you only wasnted a 12-24volt range at the 12V setting the regulator would have to be dissipating 100 watts of power at 8.4 amps.
Using the onboard adjusting POT would be a good idea as it's a switch mode supply so you're not dissipating any heat just adjusting it's internal voltage reference, but you're limited to it's maximum swing. You'd have to have more knowledge of the circuit to modify it to allow a greater voltage swing.

#### Boncuk

##### New Member
Of course a linear regulator circuit would dissipate a lot of power - converted to heat.

I read from the message the OP wants a full swing from close to zero to maximum voltage output.

He could also investigate the circuit around the present pot and try modifying the circuit for a larger swing.

Boncuk

#### Louser

##### New Member
Thanks Guys, The linear route wow it gets hot...Still working on it though, Heh I got a baaad voltage drop with any load...

#### Boncuk

##### Banned
Hot to the human hand is not hot to a semi conductor. Thermal considerations are complex for that simple fact. What is hot and cold to us is hardly a consideration to them. We simply have no real concept of the things outside our spectrum of experience.

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#### Louser

##### New Member
Wow...I'll post a diagram as soon as I can, Been real busy. Don't laugh when I do cause I'm just learning...

As for hot/Cold I see your point. I've been kind of sloppy, not working out my values and analyzing as I go along... I'm still fooling with the damn thing, When I have some Time I plan on working some of this out.

I was using an LM317 VR trying to get a 388 it may be more robust.

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