Direct driving a LED

[737mechanic]

About to build a custom flashlight from scratch. Was thinking of using MC-E or P7 emitter. Going to be made from 1.25 to 1.5 round aluminum bar with as much copper heatsink as I can get in it. I want to drive the LED as bright as I can and be able to run it for as long as possible before needing to turn it off due to heat. If using protected cells would these act as a form of regulator and would the 4.2 max volts be ok until it dropped to the nominal 3.6 or should I still consider a driver due to the possibily of damaging the emitter.

All I want is high and low so I was thinking I could use a simple resistor to get the low. I was thinking of using 3 18650 protected cells unless you guys have a better suggestion.

Also is there a D size rechargeable 3.6 LION battery or should I use the 3 18650's that I was thinking.

Any input and ideas would be great.

 

[Der Wichtel]

paralleling Li Ions is a little bit difficult. They need to be balanced before they are connected and forthermore they can discharge each other.

You should go for the D size Li Ion.

 

[jar3ds]

der wichtel is right that if you run in parallel you got'a be a little more anal and crazy due to the maintance...

for using just 1 mce/p7 w/ 1 LiON... i'd use the 8xAMC7135 method (search AMC7135)

 

[Drewfus2101]

The AMC board is a good simple way to regulate output, and you can get two modes out of it. If you go this route, find a emitter with a low Vf, because the board will pull down the output voltage slightly (~0.6V).

 

[737mechanic]

So where can I order a D size Lion and after looking for a 8xAMC7135 I came up empty. I did find a couple people putting 2 4xAMC7135 in parallel but I am trying to keep the size as compact as I can and stuffing it with 2 IC boards isnt what I would like to do.

If I did direct drive a mce is it going to be safe at 4.2 volts.

 

[Oznog]

You can put 3x Li-Ion in series and use a buck regulator. This will greatly reduce the average current from the cells. However, you need a high capacity/low ESR source capacitance there to avoid drawing high current spikes from the batt, which lowers their output and life. Tiny tantalums often have high resistance and low ripple ratings.

MLCC is much better, usually trivial ESR, and there are some high capacity SMD pkgs now. They can be expensive, like $0.20-$0.50 from Mouser, and you may need several depending on current and freq.

 

[Justin Case]

The AMC board is a good simple way to regulate output, and you can get two modes out of it. If you go this route, find a emitter with a low Vf, because the board will pull down the output voltage slightly (~0.6V).

Not sure what you mean by "will pull down the output voltage slightly". The AMC dropout voltage is only 120mV. Thus, all you need to do is supply Vf + 0.12V and the board will run in regulation.

The recommendation to find a low Vf emitter also doesn't make sense unless you also remove the diodes, which is the source of the "~0.6V" figure that you provided. To run in regulation, a second criteria is Vf > Vdd(min) + Vdiode ~ 2.7V + 0.6V = 3.3V. Thus, at a typical 1050mA max drive current for a single die LED like a Cree XR-E or Seoul P4, you will probably have Vf already greater than 3.3V and thus diode removal is irrelevant. If you are using a 1xAMC or 2xAMC board with drive current of 350mA or 700mA, then Vf could be less than 3.3V and diode removal becomes relevant.

 

[Justin Case]

So where can I order a D size Lion and after looking for a 8xAMC7135 I came up empty. I did find a couple people putting 2 4xAMC7135 in parallel but I am trying to keep the size as compact as I can and stuffing it with 2 IC boards isnt what I would like to do.

If I did direct drive a mce is it going to be safe at 4.2 volts.

A two board AMC sandwich is only ~17mm diam (same as a single board) and ~5.7mm high (less than a quarter of an inch, and shorter than many single driver boards that have a large inductor). If this is too large, you can just piggyback solder additional AMC7135 chips to the ones on an existing single board. That will save you the thickness of the PCB, reducing the overall height to around 4.7mm.

 

[Der Wichtel]

However removing the diode and selecting a low Vf LED will let the driver stay in regulation a little bit longer.

 

[Aircraft800]

Hey fellow 737 mechanic,

You can also use a hipCC Driver from TaskLED, or even a hipFlex (if you want multiple levels, programmable low voltage warning, and temperature monitoring) TaskLED drivers are some of the best made, and are ideal for a full custom build.

The Shark Buck is another alternative, three light levels with the remora, but will not give you low voltage warning, so protected cells are suggested.

Each of these drivers can be run with 3 18650 protected cells.

I suggest you don't run a P7 Direct Drive too long. Take a look at my P7 Mag some night. The emitter dome is starting to yellow from excessive heat after multiple long runs in the Texas heat!!

I believe the only place (as of today) to get a protected D Li-Ion is Kaidomain (he also had unprotected), but AW is rumored to be making some and also download.

 

[737mechanic]

Thanks for the help guys.

Aircraft800 Are you still working Hanger Ron, I have tried a couple times to track you down but couldn't find you.

How long do you run that P7 direct driven. I normally only need a light for a few min at a time. Do you think I could get away with doing that without building up to much heat.

 

[Aircraft800]

Thanks for the help guys.

Aircraft800 Are you still working Hanger Ron, I have tried a couple times to track you down but couldn't find you.

How long do you run that P7 direct driven. I normally only need a light for a few min at a time. Do you think I could get away with doing that without building up to much heat.

Bumped to Nite Line with M-T off! :shakehead

DD would be fine for short runs. I have a 1D Mag with a d2Flex for direct drive with dimming. The d2Flex bypasses the switch, so you don't have any resistance there. My tailcap spring is just one coil, so there isn't much resistance there either. On a fully charged KD Li-Ion I can see as much as 4.1A, so it's hella bright. I let a gate agent use it one night when the jetway lights were out to let the passengers deplane, when I got it back, it was the hottest I've ever felt. The P7 dome is yellowed a bit, but it still is wicked bright, I can't see a difference.

I only use it on high when I need it, to see the top static wick and tail, but level 3 is fine for everything else. I can probably run it that way continuous. I like to keep Hi level for "Burst".

I think I have accumulated well over 50 hr. on this light with never a hiccup!

Definitely my favorite setup thus far. When I build another, I think I'd do a 1C cutdown to fit a LiMnNi Rechargeable 26650 just to keep it smaller, and have the piece of mind in a Safe Chemistry cell, but I'd loose a little runtime.

Did you find a machinist at work? I've got some ideas.

 

[737mechanic]

Line Ron , that explains why I havent seen you. Sign up for Day structures OT and we will talk about modding flashlights.

I have a lathe I restored and have been playing with it and am now ready for my next project. I would like a fully custom homemade flashlight including the body but have been going through all kinds of idea's on what I want to do. I am not real concerned with battery life if it is powered by 18650's because I rob the batteries out of the laptop battery packs they throw away here at work, after opening them up I usually find 1 cell that is bad and the rest are just fine, the only drawback is they are not protected but they are free and I have a bucket full of them so i could always have plenty charged and ready to go if the light was a power hog. What I would like to do is put a chaging port on the bottom and be able to charge it without needing to take the batteries out but I might drop that idea for my first custom build until I see what I can do with just a basic design.

Depending on what kind of machining you need done I might be able to help out.