Variable Voltage question

[Bahnzo]

I completed my first VV mod last night. Everything works, but the voltage control is a bit weird.

I used one of these: Digi-Key - 3352T-201LF-ND (Manufacturer - 3352T-1-201LF)

What happens, is it controls the voltage just fine up to about 3 volts or so, then the adjustment becomes *very* fine. Like I can turn the wheel from 1.2v to 3v and it has a reasonable amount of turn in it. But from 3v up, just a minute turn jumps it to 5v...like there's no play in the thumb wheel past 3v. (am I making sense?).

Any idea why, or is it just that I shouldn't use the 1 turn thumb wheels and go for the 25 turn pots instead?

 

[asdaq]

I think Mamu said that most of the adjustment on a single or double turn pot is usually bunched up on one end only, so a 12 turn (or more) gives a more gradual trim. A bit like a screw with only one thread loop for the whole screw. To bad yours isn't the other way around that 0-3 is that slight turn, and 3-5 the comfortable range.

 

[Bahnzo]

I used Mamu's schematic (I think, linked below). I wonder if I reversed the two outside pins on the pot if it would reverse the "bunched" range?

 

[asdaq]

I'd strongly suspect it's internal physical limitations giving the resistance and reversing it wouldn't help, but if you are willing to replace with a multiturn anyway, might be worth a try. The regulator has protection circuitry.

 

[t9c]

Ah, the pot you used is 200 ohm, the one shown here is 200k ohm.

I used Mamu's schematic (I think, linked below). I wonder if I reversed the two outside pins on the pot if it would reverse the "bunched" range?

 

[asdaq]

Details, Schmeetails

 

[Bahnzo]

Well that would certainly do it then. I bought 200 ohm pots because I was planning on building BigBlue's Evercool mod, but wanted to hone my skills first with one of the regular adj chips first. Seems like BigBlue's mod uses 200 ohm, and these need 200k then.

Arrgh....well at least I have some for the other...but yeah...details.

 

[bigblue30]

Yep...200 ohms for the evercool. 200k ohms for the TI 383 or 283 everhot.