I have just bought my first newbie flashlight. Its a SAIK sa9, with a Cree XPE Q5 emitter.
It has an option of 3 x AAA's or 1x 18650. When I measured the current on the AAA's at the tailcap, I measured 570mA and with the 18650 some 1.5A. The driver is an S-20S.
My question is it safe? Running on a18650 seems to give an awesome light output but I fear it could be short lived. I understand the Cree Q5 should only be driven at 1A max. It does get warm after a while but there is no heatsinking to the case, only where it touches, which isn't very good.
If it was 1.5A direct drive yeah, you should be a little concerned. However, drivers aren't 100% efficient. The actually current to the LED is likely much less. Something like 1.2A should be fine.
I have the same light, unbranded, from eBay and have been running it pretty hard on a bike. No problems so far. I use it with 18650. It is actually a very bright zoomie. I like it.
I wouldn't be so sure there's a "driver" (ie regulator) in there. Even if there were, they're generally designed to bypass (ie. essentially DD) on higher voltage, in which case there might well be voltage loss/drop across some diode, but not exactly the same thing.
----
added:
I probably should've just looked at the photo. The supposition just above is accurate.
I'm assuming there are no parts on the other side of the board. If there are then disregard the following:
I see two 1R0 (one ohm) resistors in parallel, the red wire connects to one side of them. (It is marked with an "L".) The other side of the resistors has a "L+" marking on the board. I wonder if the resistors are even being used? Would moving the red wire to the other side of the resistors ("L+" side) put the resistors in series with the LED and thereby drop the maximum current a bit? Maybe remove one of the resistors to lower the current a bit further?
This is just speculation of what I see in the photo, I could be way off base...
By the way, if the light is either direct drive or resistor drive, the tail cap current (on high) probably represents 99% of the LED current. So if this light is drawing 1.5A, the LED is probably seeing almost all of that and will overheat without good heatsinking.
Well spotted Crux. There are no components on the other side. The resistors are not connected in this application and I don't think there is any regulation. It looks a basic circuit, processor, and output transistor. I do have a scope so I will have a look at the driver waveform soon. I have run it for over an hour on hi setting and the case does warm up to about 40 deg C, comfortably warm. The LED sits on an aluminum pil that has lots of clearance as it zooms up and down, so heat transfer is not optimized at all. I only have the dreaded *****fire 18650 at the moment, but it did run for over an hour gradually dimming during this time. The current seems to drop in proportion to the voltage so pretty basic, but it is a bright light for most of the time and is probably being overdriven for maybe 15 - 20 mins before the current comes down to 1amp.
I think a decent 18650 may be a problem (got some on order) as the overcurrent would be delivered for longer, so I might just run it on NIMH, to be on the safe side. I just have no experience of these emitters and how robust they are. Cree state 1amp max and this is being well exceeded, I think. That's where I hope you guys come in.......
Edit:
I scoped the output of the driver and it is, as suspected, just a basic circuit that is direct driven on high power, pwm on low power and flash. Still a good basic light for not much money.
just got the same one- my first I've been running the heck out of it even using on flood as a room light in a new apartment- never overheats- runs 2 hours plus on high then dims gradually.
I'd like to get one modded with same emitter as Deft EDC or some small high current emitter that throws better than an XM-L.
Ordered a slightly different one to see if I get a higher current model and to get modded, possibly.
It is clearly overdriven as much as mine. Never used it for long. The real problem is not that excess in current. The led can take it for quite some time (nowhere near the claimed 50.000h a few thousand max). It will die from overheating since the host is very poor in conducting heat. I made some improvements in mine hoping to make it last more but eventually will go away as a 3AAA light. Mine drew 800mA on ni-mh LSD AAA's.
