Thanks djozz. I wouldn't mind seeing your modded TC300 too. I think I remember seeing beam shots of your signature tree with it. I'm still using a MT-G2 that I purchased from dthrckt too, but in my case it has been in so many lights that I lost count. It's currently in my reflector focus tool.
Assembled the light last night and took it for a walk. It was cold out so heat was not an issue on high. Tint and CRI are so much nicer for my taste. The light works great, but has a terrible whine in the 5th and 6th modes (PWM 81 and 140). Guess I will be reflashing the MCU eventually.
Thank you garrybunk, dthrckt, and Ledsmoke. Also thank you ChibiM, siata94, MRsDNF, Nightfall for your earlier compliments that I haven't thanked you individually for yet.
I really need to get on the battery pack as I'm currently using the light with 3 cells taped together. This is by far my best headlamp. Mostly do the nice floody smooth beam pattern. I see why this light is so popular with the mountain and trail riders. Seems like a real good helmet light for those activities.
I have one of these lights and have been referred to this forum from MTBR. I have one of the “good” SSX2’s still with the aluminum pill and all. I recently changed my XM-L U2 (unknown tint) to XM-L2 T6 3B emitter/bases from FastTech.
While I got a much warmer tint and is fantastic in the snow, even by going to the XM-L2, I have definitely lost some lumens. I would like to get some of that back. To increase current, I have been referred to this post, which shows the current sense mod.
My driver has a single R010 resistor. So should I be installing a different resistor, or add one? And if so, by how much? Can you explain to me how adding extra resistance will increase current? It seems counter intuitive to me.
Interestingly here is another QX9920 based driver using an op-amp to work with a much lower sense voltage. Apparently the original “3 torroid” SRK drivers worked the same way. The SOT-23-6 chip marked 321 appears to be the op-amp.
Welcome to the forum neons97. I'll address your last question first because there are a couple issues going on at the same time in your light as it is is currently modded. When parallel resistors are added, resistance is actually reduced. This is because you provide additional pathways for electricity to flow. The equation for calculating the overall resistance of a group of parallel resistors is Req = 1/{(1/R1)+(1/R2)+(1/R3)..+(1/Rn)}. Your driver regulates current by maintaining a certain voltage drop ("Vdo") over the voltage resistor bank. When resistance is dropped, more current must be supplied to attain the Vdo. If you know what this voltage drop (Vdo) is, you can calculate the current based on the overall resistance of the voltage sensor bank.
I did not attempt to measure what the drop on this driver is for a couple reasons. First, there are other factors that will also impact the amount of current that will flow to the emitters. Second, experience gives me a ballpark idea of where to start with resistor mods. So my approach is generally to measure current stock, add a resistor that I think will get me where I want to be and then remeasure current. I can tell you from my measurements of current, the Vdo for the resistor bank is about .24 volts. The equation to calculate current from that is to divide Vdo by the Reg.
Regarding your conversion to XM-L2 and the loss of lumens. The higher Vf of the XM-L2 (verses the XM-L) takes your buck driver out of regulation because there is no longer adequate voltage overhead for the buck driver to buck. Check out my measurements after converting to XM-L2 (This is with an additional R33 and R50 resistor added):
PWM
Emitter Current
(Modded)
Modded 2S Cells
Modded 3S Cells
Stock
1
0.01
.02
3
0.02
.03
9
0.03
.08
27
0.12
.33
0.43
81
.56
1.01
1.05
Strong Whine Modded
140
1.22
1.84
2.08
Strong Whine Modded
255
2.43
3.14
Before swapping over to the XM-L2, the emitters were getting 3.10 amps with only one R33 resistor added to the voltage sense resistor bank.
EDIT: Added more info on resister modding in the 1st and 2nd paragraph.
Thanks for the quick response. I am very very new to this, so please pardon my stupid questions. I’ve tried to read up on buck drivers, Vf, resistors, etc…I’m a pretty handy and technical guy, but I’m going to need a bit more of a crash course before I actually understand all of what you’re saying.
I now understand why adding a resistor will increase current. This makes sense.
Regarding the buck driver being out of regulation…so what are you saying? Should I go back to my stock XM-L instead of the XM-L2?
Regarding your measurements, are you saying that you experienced the same problem as me? Going from 3.1A on the XM-L, and then dropping down to 2.43A with the XM-L2? Is the trick to use a 3S pack (assuming my driver is similar enough to yours that it can handle 3S?).
You're questions are not stupid. I added more details to my above response. They may help.
Yes, you are having the same problem I had after switching to XM-L2. You understand the situation in a big picture sense as you just laid out a couple good options. Here are the obvious ones that I can think of:
Switch back to XM-L's to bring down Vf. This option makes me sad and is not a real option for me.
Rewire your emitters to parallel (They are currently wired in series). You will have to add more resistors to your voltage sensor bank (at least double in order to half the resistance). This may overtax your driver. Also, you driver will likely have other components that won't cooperate with that much current (You will have to double current since the 2 emitters will be getting feed separately).
Upgrade to 3S cells. You are already at 2S with your existing pack. The same safety precautions will need to be followed, but you will be taxing the cells (and wiring to the light) less as they will not have to deliver as much current. My 3S pack only pulls 2 amps on high.
Thank you for you interest in my thread. It feels good to know someone is benefiting from it. Please feel free to ask away. There are much more knowledgeable folks than me around here. BLF member wight above, taught me much of what I know in this area. He is one of the most knowledgeable driver guys around here.
So adding resistors to bring up the current (I measured Vdo of 0.25, so very close to your 0.24) really isn’t going to achieve what I want to achieve without going to 3S.
I have to solve my voltage issue first, before increasing current. And by increasing my voltage, my current will come back up to stock of around 2.5A, which should make my light look as bright as before, and maybe slightly brighter with the XM-L2’s…and won’t require increasing current to get it back to a “satisfactory” level.
This may be a good opportunity for me to go to a 3S lipo pack. I also have a cheap chinese liion 2s2p pack that I only use as a backup to my backup. I could turn this into a 3S pack just to see if it improves my current situation.
So adding resistors to bring up the current (I measured Vdo of 0.25, so very close to your 0.24) really isn’t going to achieve what I want to achieve without going to 3S.
I have to solve my voltage issue first, before increasing current. And by increasing my voltage, my current will come back up to stock of around 2.5A, which should make my light look as bright as before, and maybe slightly brighter with the XM-L2’s…and won’t require increasing current to get it back to a “satisfactory” level.
This may be a good opportunity for me to go to a 3S lipo pack. I also have a cheap chinese liion 2s2p pack that I only use as a backup to my backup. I could turn this into a 3S pack just to see if it improves my current situation.
Before I forget again to say this. Please don't take anything I write here as gospel. I'm really a novice when it comes to electronics (and maybe everything else flashlight). I know enough to be dangerous and sometimes get lucky.
With that said, you may want to try a resister mod. There could be something, I'm not aware of in this matter. Thank you for reporting your Vdo measurement. That is dead on with the your stock set up of 2.5 amps and 2 R200 resistors (.25/.1). I measured 2.08 amps stock on my light but that could be due to the DMM consuming current (maybe?) or variation in performance of our drivers. used the data point of 3.1 amps and an additional R33 to get my estimate of .24 Vdo.
I hope you don't mind if I add your measurement to the OP with a reference to you as the source. That is good information, that measurement you took.
I like your idea about just going 3S though. 2S just doesn't seem like enough voltage for even the stock light, at least not for long regulated runs.
If you driver does not look identical to mine and if you have the time, would you please post pictures of the 2 sides of it?
EDIT: I'm sure you have thought of this, but just in case. The voltage indicator lights on the back of your light may no longer give accurate info after you switch to 3S.
err, is Vdo the correct notation for that? I would have assumed that it stood for Drop Out Voltage, not Voltage Drop. The voltage you are discussing is actually called the Sense Voltage, I guess Vsense or Vsns might be an appropriate notation. Glance at a random datasheet such as the one for the ST LED2001 or the Maxim MAX16820 if you aren’t familiar with the sense voltage term.
Also, I’m pretty sure that you guys have your measurements/figures quite wrong. There should be no way you see a 0.24v voltage across that R010, that would be 24amps! (check an Ohms Law calculator - the resistance of an R010 is 0.010 ohms). It’s more likely that you see 0.024v across that resistor indicating 2.4A.
On the subject of a resistor mod not doing much to a light that’s out of regulation… I think you had it right in the first place ImA4Wheelr. While doing a resistor mod might increase current slightly IMO it’s just as undesirable as doing a DD mod. With the driver out of regulation as pack voltage falls, so will output current. My advice is to skip that and go straight for a higher input voltage so that the driver can get back in regulation.
Finally - can you point out the indicator LEDs? I don’t see them.
I need to get caught up on that thread and maybe post some constructive criticism. I think it would be good to make it more clear that DD lights will get significantly dimmer as the battery discharges. For a point of reference, a DD light I recently built pulls around half the current once the battery is >3/4 discharged.
^ Nothing wrong with a resistor mod if you want to change the current fed to the emitters. I think wight meant my suggestion that you might still want to just try a resistance mod in case it works. I agree it will likely not work. I just wanted it clear that I am no authority in these matters.
wight wrote:
err, is Vdo the correct notation for that? I would have assumed that it stood for Drop Out Voltage, not Voltage Drop.. . .
Also, I’m pretty sure that you guys have your measurements/figures quite wrong. There should be no way you see a 0.24v voltage across that R010, that would be 24amps! (check an Ohms Law calculator – the resistance of an R010 is 0.010 ohms). It’s more likely that you see 0.024v across that resistor indicating 2.4A. . . .
Probably not. I think I may have unconsciously made the abbreviation up a long time ago. Way before joining BLF, I use to mod LED lighting into my vehicles. I generally made drivers using voltage regulators like the LM1084. They can be used to make a CC driver. The term for the voltage used to control current is Dropout Voltage. Of course, the LM317/338/350/1084's have significantly higher dropout voltage (something like 1.5 volts) than this driver, but the concept is the same. Enough current is pushed over the voltage sense resistor to get the targeted voltage drop. I guess I must have just made up the term Vdo. Sorry for the confusion guys.
.25 sounds right. The 2 R200's equals .1ohms of resistance.
It appears that two different drivers are in this thread. I see now that the driver in the OP is not the same as the driver in your reply #1.
The driver in reply #1 is HX-1289 (the PCB’s are labeled A6 and B5, eg rev 6 and 5 respectively of the two part driver). It features a single 0.01 ohm sense resistor and an op-amp to interface it with the QX9920 buck controller.
The driver in the OP is HG0802. It skips the op-amp and therefore requires a 0.1 ohm sense resistor array. It’s also using a very different inductor, maybe it has some other big differences as well.
I assume that the HX-1289 is from a legit Solarstorm light. The difference in sense resistors is a big deal because the clone will drop 0.3v at 3A while the HX-1289 drops only 0.03v! That should make a big difference in where the driver falls out of regulation as well wasting nearly a 1 whole watt less.
EDIT:
I still think that this is wrong, even in the context you described. I think you might be thinking of Vref but I’m not sure?
beam shots? Looks like bright sunlight to me. I want to ride behind you. Amazing job.
I’m a visual type, pics make sense, technical details not so much.
I had a mtb night ride planned for tonight but my buddy got ill.
I’d spent 3 hours last night trying to mount a flashlight to my helmet. All dressed up and nowhere to go. Sipping a Ballast Point Sculpin to ease the pain.
