Direct Drive

[tabetha]

NO not the car, but my torches.
I have just recieved my first few led's for some modding.
The lights I use are 18650 x 1, or 2 or 1 x RCR123 powered.
So long as I keep the voltage to below what the led maker says it can take, would I be able to just have a switch to switch direct, without a "pill" thingy ?
The led is up to 4.2V, the battery is 3.6Volt, I'm thinking of my Romisen RC-F4, as it just went dimmer a while back for no reason, and I really love it.
Please help as I'm a bit stupid, as I missing something, other than a brain that is, thanks
tabetha

 

[^Gurthang]

If your batteries are protected you're set w/ DD. Otherwise you could over-discharge the battery which is BAD [dangerous to re-charge]

^G

 

[Oznog]

The performance could be poor.
Mfgs don't specify limits by voltage really, the current matters. Current is not well controlled by voltage. One LED could be drawing 250mA @3.7v, another 350mA @3.7v. Actually as a given LED warms up, the current drawn under any specific voltage increases.

The thing I don't like most is that single-cell li-ion direct-drive lights, or linear stepdown-only regs, fade a lot once the battery drops to 50% capacity or so. This sucks, I don't find the light level acceptable so I just pretty much have to say the light has half the useful runtime.

 

[old4570]

If you have a light that already uses a driver , then swapping in a better LED will improve its performance ..

If you want constant output then a Buck Boost driver might be the way to go , Direct Drive can be a little hit or mis depending on the application .

Both DX and KD sell a 1A buck boost driver that seems to be rather good in 17mm form . Hooked up to Q5 or R2 may very well offer you many battery options and decent power output .

 

[lctorana]

NO not the car, but my torches.
I have just recieved my first few led's for some modding.
The lights I use are 18650 x 1, or 2 or 1 x RCR123 powered.
So long as I keep the voltage to below what the led maker says it can take, would I be able to just have a switch to switch direct, without a "pill" thingy ?
The led is up to 4.2V, the battery is 3.6Volt, I'm thinking of my Romisen RC-F4, as it just went dimmer a while back for no reason, and I really love it.
Please help as I'm a bit stupid, as I missing something, other than a brain that is, thanks
tabetha

No, your logic is OK. It really will work OK. The only thing to watch with full direct drive without even a resistor, is the current draw can be very high when the battery is fresh. A Cree XR-E will draw over an amp off a fresh 18650 - the driver may have put out somewhat less. So proper and thorough heatsinking of the LED is required, which may be much more than the original torch provided.

 

[Greg G]

I do it sometimes on a single 18650 light, but I'm careful to handpick an emitter for it. I don't have my notes handy, but my selected Cree R2 LED's will usually start off around ~1600ma on a fresh battery and gradually drop from there. And once you've built the light you can't swap out a cheesy high resistance switch with a McClicky for example because that will raise the current a LOT, so you need to have anything that effects resistance set before you pick out the LED that has the right resistance for the light.

I've got a Tiablo A9 and a Raidfire Spear set up in DD using Cree R2 emitters. No driver to fail, so they are likely the most reliable lights I have, and boy they are bright.

 

[tabetha]

Thanks for all the excellent comments guy, it really is appreciated.
All the mod ones I do are to existing led lights, I understand now about the current being correct.
I have a cycle light to mod as well, it is a CAT EYE front led light, that frankly would have a job being seen in a totally dark room, I'm not really bothered about it as it's rubbish so just going to swap in a LED, a P4, and see what happens.
The original led is on a star, but no heat sink compound on it or anything, guess it's that weedy doesn't need it ?
This is powered by 4 X AA cells, so must use a driver to limit current/voltage.
I'm even eventually wanting to do some day lights like audi's have on them, using led's, to fit on my cossie, would look nice and show up well, otherwise I will copy the US system of main beam on 1/2 brightness as this works brilliantly as well during the day.
Thanks again for the input, anything else would be appreciated.
tabetha