Why No Pot?

Flashlight Modding and DIY Parts
1

No not that kind of pot. :bigsmile:

Why are pots not ever used in lights? Why is it necessary to have a driver with modes when direct drive with a pot is easily attainable.
Is there some drawback that I am missing aside from size? I have some ideas I have been mulling over some of which include a little pot thrown in the mix!

2

Wouldn’t it be a waste of the battery on low “modes” (not including digital pots)?

3

And I think it would take a huge pot to use as a dimmer in our use without any other electronics

4

It is possible think of a radio, this has a volume pot and big Power.
The controller senses the resistance and makes the PWM….
But then we can use a ramping driver without need of a pot

And it makes no sense to use it as voltagedivider direct connected between LED and BAttery because of the above mentioned posts

5

I’m currently using a pot to dim this. It’s only a 15,000 lumen/150 watt LED. 15,000 Lumen Bridgelux C9000 Light Engine

The pot controls the current sense feedback amp on the DC-DC converter. You can’t realistically use a pot to directly control the LED current (i.e. pot in series with the LED) of a medium-high power LED.

6

Some of my favorite lights all have VaraControllers. These are the Lambda Lights with 38 or so clicks. It’s hard to go back to using lights with several levels after using these. They can be turned on from any position if you are not familiar with the mechanism.

Going with the phychodelic theme of the thread, here with some UV in the background, lol!

7

I don’t know since a pot functions like a manual 7135. Just seems kinda low tech. Maybe do a mod with a thumb wheel pot. No rules here on modding.

8

The particular instance I am thinking is a camping lantern. I want to stuff an xml-2 into a table lamp and run it with a pot so it has the same feeling as the old thumb-wheel flame lanterns of yesteryear. Just a few D’s instead of kerosene :wink:
I think I may have to play with these.

I am wrong in thinking of a pot as a variable resistor? So on low it would be consuming the same power as high, thus the “waste” reefered(Pun Intended :bigsmile: ) to earlier. If you just need it to dim and be functional it seems ideal such as a camping light, just bring extra batteries. I am just trying to get around the PWM strobe effect while keeping a lantern minimalistic.

9

To use a pot to dim an LED would require a very low resistance pot (say 1-2 ohms) with a high power rating (like 10+ watts). Good luck finding one…

10

A pot is actually a completely viable option, albeit somewhat ancient.

A few misconceptions I've read above that need correction:

  1. A pot is NOT simply a varistor (variable resistor). Though it can be dumbed down to one, it's not.
  2. A pot is rarely ever used in 'the direct line of power' (if I could put it as simply as possible). In fact, this is poor circuit design that even a 6 year old can manage.
    Well, I'd like to think that when I have a 6 year old, he'd be able to design an effective circuit.

If I were to design a system with a level-control pot I would have a number of criteria:
  1. The pot is above 10K ohms.
  2. The pot is logarithmic. (though our light sensitivity approximates a square root function, a log-pot is the easiest to get, that is not linear)
  3. Digital is the way to go. It's just so easy to pick up a CC chip from TI (Texas Instruments) and design a circuit around it. THEY EVEN DO IT FOR YOU!
    Their WEBENCH Design Tool is on the front page of their site. (I started with Vmin - 3.0V Vmax - 8.4V Vout - 3.3V Iout - 3.0A and Amb Temp - 30C)
  4. Haven't thought of any other (need to go to big-kid school in like 10 mins.)
I know this might not be true in all electronics, but in high-end audio, the most expensive stuff is definitely pure analogue. (Think hundreds of thousands of dollars for 1U of rack space.)
It's entirely possible (and not all that hard) to design a great circuit with a pot and <1mA quiescent current. Do it and post pics of entire design and construction process please. Kay, thanks, bye.

EDIT: Additionally you could use a pot on the base side of a nice MOSFET (JFET not recommeded). Design around that. Unless you have a solid fundamental grasp of electronics, this'll be a fun learning experience for you. Enjoy the journey, don't just try to get to the destination.
11

This is a video I did using one of the VPT lights. This video is the XPG2 version. I started the video with it turned down and cranked it up to max. The other VPTs have videos too, but this was was the only one that isn’t high the whole video.

12

Yep, there’s a sucker who thinks he has golden ears born every minute… I have some nice oxygen free copper polymer power cords available for only $10,000 each.

13

Yes I was one of those “suckers”, but had to sell my system a few years back when I hit hard times…nowadays a glass or two of beer/wine improves the sound quality of my current system! :wink:

As to why there are very few pots used in flashlights, I think that with budget lights its because of the cost of the extra parts- its cheaper to write a bit of code for a linear driver and with more expensive lights it maybe a water/dust proofing issue?

Woody

14

I had played a bit with a 12V LED driver from Fasttech, the chip on it can be dimmed by either PWM or pot. It worked quite good, but you now dimming is for looser, I want the full power.

15

I’ve got oxygen free unidirectional copper polymer power cords for only $12,000 each. The difference is night and day.

PPtk

16

Oh boy, geek wars! Better make some popcorn.

17

Meh, tin eared hack stuff. I’ve got oxy free, uni silver, with quantum spins aligned. $100K, but that includes the geodetic grade location and magnetic field surveys of the equipment location. If you move the equipment as much as an inch, it’s another $20K for a re-survey and atomic spin re-alignment. One year warranty against continental drift induced misalignment.

18

Haha… I just don’t have time to type anything more outrageous than that :slight_smile:

19

My real favorites though are the suckers who get talked into the $300 DIGITAL audio cables. I just want to smack them in the head with a pan.

20

Anybody old enough to remember Y2k-ready? EVERYTHING had to be Y2k ready back then. Even pots. (See, I didn’t derail this thread at all).