Does anything go right !! 3x TYOL D2DIM

Got everything together tonight to try out my new D2DIM powering 3x TYOL Stars (parallel wired). "L" Bin has a VF of 3.75-3.99. I wired up 2 LG2400 18650 cells in parallel for a 4.2v(fully charged) 4800mah pack. I connected the amp meter at full power and measured 1.7amps at just over 4 volts. I figured at this voltage and a pack this size I should have been feeding 1+ amps to each TYOL.....................why am I only seeing 566ma to each star??

Other power source results

2 x 18650 Parallel 1.7amps
4x 2500Mah NiMH 2.6amps
3xCR123 Surefire 4amps
2xCR123 Surefire 2.1amps
2x18650 series 7.2v!! 5amps (shut her right down after I took the reading)


Any pointers?

Mac

Re: Does anything go right !! 3x TYOJ D2DIM

In parallel, voltage is the same, but the current DIVIDES.

In series, voltage divides and current is the same.

Think of it like a water pipe. If you install a T, some will go one way and some the other.

With your LEDs in parallel, you will get about half the current to each one. If you want the full battery current to go through both LEDs, you will have to wire them in series.

If you have 1.7 Amps (no load) available, it is impossible to get 1+ amp in either leg (assuming that that the Vf is roughly the same).

...unless I am reading your question wrong.

My cells are good for 10amps. Why are my emitters which are driven at spec + only drawing 566ma each was the question. 3xTYOL drawing 1.7 total amps so 3 \ 1.7amps + 566ma each.

Mac

Ah...got ya. I thought you were measuring 1.7 amps with no load. Have to ponder this one some more!

Mac,

When I tested "L" voltage bin 3W LED's with 4.2V LiIon cells, I got between 800-900mA (don't remember exactly at this moment) - but that was for only a single LED. If you have several of these LED's in parallel, the LG cells will have the capacity to give more current total, but this current will be "fairly" equally divided between each LED depending on the individial vf's for each LED.

Withouth doing some measurements on my own, I can't tell you from here in Texas what is going on in your bench in Boston . My guess at the moment is that the point you are measuring is simply the equibilibrium point for these LED's and these cells, and possibly taking into account your current measuring equipment & techniques (measuring current accurately is tricky!).

Do you have access to an adjustable bench supply? Based on the fact that two CR123 cells (6.0 volts, no load) gives you 2Amps tells me something. I would love to record the total current when the voltage is slightly higher than 4.0 volts (assuming the supply can deliver 3-5Amps at this voltage), to see if these LED's simply need a higher voltage to "sing".

Will

Did you measure the 4 volts at the battery or the LED terminals?

If it was at the battery, which I am guessing it was, go measure the voltage on the LED leads.

I'd venture to guess, you are not getting 4V on the LED leads.

I measured the voltage and current directly at the battery. I have 6 new LG2400 cells with no real application to put them in I purchased 2 set for hotwire mods which failed as I didn't realize the startup current would be somewhere around 15amps on a 3.5 amp bulb. Then I just picked up 2 more cells to run in parallel for this application to which has failed also.


Mac

Ah, go check the voltage across the LED pins. I assume you have the D2DIM PWM driver you mentioned, between your cells and the LEDs?

I connected the unit to my lab supply that maxes out at 2.85 amps and needed 5 volts to draw the 2.85 amps. Looks like I need a 5.5-6volt pack to drive them at slightly over 1amp each


Mac

Well, I hate that my guess was right on the money, but at least you know for sure.

Have you considered running the 3 LED's in series, the two 18650 cells in parallel, and using a fatman regulator?

Will

I have an order going in to George probably today. I like the fatman but don't want to add a potentiometer to adjust brightness levels, though I'm looking into it and have interest in a slide poteniometer setup. I could just run a 4aa -1d holder which I already have and pull 866ma out of each LED but I really want to provide at least 1amp to each LED ideally 1.2amps.


Mac

Mac,

Technically you don't need the pot. You can leave it adjusted for max. brightness - george will show you how

The other thing to remember is that once you get to the 850mA per LED range, you will not get HUGE increases in light output when you get the 950mA or 1.2Amps since the current vs. light output is not linear. The other thing is that once they run for a few seconds at max. current, the LED's will get warm and then hot, which will lower their efficiency and output anyway - they will literally dimm!. At this point you are simply wasting battery power since you will have a larger percentage of your stored power being dissipated as heat instead of "light".

I would strongly recommend to stay in the 900-950mA as your max current, and even shoot for 850-900mA as your target/goal. Just my humble opinion

Will

cmacclel said:

I connected the unit to my lab supply that maxes out at 2.85 amps and needed 5 volts to draw the 2.85 amps. Looks like I need a 5.5-6volt pack to drive them at slightly over 1amp each


Mac

Click to expand...

Swell, so the D2DIM driver doesn't deliver enough voltage to the LEDs with the input voltage you had.

So, is there a handy-dandy chart, somewhere, showing minimum input voltage and current to achieve X amount of current to the LEDs at various LED Vf?

That would be pretty handy, so a fella would know ahead of time what they'd need.

Keep in mind, if you have a 6V battery pack, the battery voltage sags under load, which means you'll shortly reach your 5V minimum you found you needed, well before the cells are discharged.

Also, consider, the cell voltage drops alot as you discharge the cell, in some chemistries it is worse than others.

So if you want it to stay in regulation, you may need a tad bit more battery voltage.