FAQ
General
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How can I get a BLF GT?
Post in the main GT thread saying that you want one (or more). Then wait for a private message with further instructions. It may take a few weeks before you can make the purchase, because production is slow.The group buy closed on 5 Jan 2018. Lights continue to ship as they are produced, for those already in the group buy. We expect the GT to be available for retail sale at some point in the future.
Emitter and output
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What LED is used in the GT?
Cree XHP35 HI, D4 flux bin, 4000 K CCT.
Texas Ace did a detail review here:
GT LED review
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Can I get more throw if I drive the emitter harder?
No, not really. It’s already driven at 2.5 A, which is just shy of the peak for the GT’s emitter. There’s very little to be gained from giving it more power; it’ll mostly just produce more heat.
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Why is my lux meter showing me less than 1.2 Mcd for the GT?
Could be caused by several things…- Lux meters usually read higher for cool white lights, so the GT’s warmer tint could be tricking the meter. This doesn’t mean it won’t throw as well as intended, just that the meter isn’t very good as measuring it.
- The beam doesn’t fully collimate until ~20+ meters, so it may be necessary to increase the distance between the light and the meter for a good measurement.
- The light might be running at 2.0 A instead of 2.5 A. Be sure to take measurements on turbo (which is above the normal output modes; double-click to access turbo).
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How can I mod it to increase throw?
Try an Oslon Black Flat for maximum throw. The hotspot will be tiny though, and the driver may need to be replaced or modified (TBD).
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How can I mod it to increase lumens?
Try a 12 V XHP50, XHP50.2, XHP70, or XHP70.2. It will decrease throw though, and the driver’s sense resistor should be changed to increase power to ~5 A. (We are also looking at cooler running options for the FET and inductor.) Bigger hot-spot, more lumens, less lux. Texas_Ace tried it and says the result is nice. Using 8 cells is strongly recommended for this.
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How do I get a different tint LED?
The stock tint is a great tint for real qorld performance but it is not for everyone. If you want to change your tint you can swap in any XHP35 you desire. A good source for XHP35 LED’s is RMM here on BLF. If you send him your stock mcpcb, he will even reflow the new LED on it for you.
Driver and firmware
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Do I have the firmware bug?
The firmware bug is just a wrong ‘fuse’ setting on the micro controller. The low fuse was left at the default value of 62, instead of E2. This sets the MCU to run at 1 MHz, instead of the intended 8 MHz. There are no reported cases out in the wild yet. Normally when the battery tube is tightened down the light will flash twice to confirm power. If these two flashes take more than 3 s to complete, you have the bug.
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Where can I find information on the driver / get a driver PCB?
Please see the OSHPark page for the driver here:
OSH Park ~
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How does the driver work in layman’s terms?
From a post here :
Its a proper ‘buck’ driver.
The FET is pulsing the inductor and the inductor, by nature, outputs a DC current proportional to the duty cycle of the FET. (Not to be confused by the PWM output of the tiny85.) The inductor is the big black cube on the board, and is basically copper wire coiled around a ferrite core.
The brains of the buck operation is that small chip sitting next to the sense resistor. The tiny85 simply generates a 0-1.24 V ‘set-point’ for the buck chip. The buck chip compares this set-point with what it measures across the sense resistor and then does its thing to put out the requested amps.
Some things to note:- There is some PWM happening in the driver, but for most output levels the LED current is almost pure DC
- To get to the very low modes, it does output PWM to LED (modes below 10%, or 0.25 A). This is under the control of the tiny85 when we go PWM and when we go DC, so there is flexibility here for people doing their own firmware.
- Battery current is not same as LED current. Like for a transformer, the ratio depends on input vs. output voltage: Iled = Ibat * (Vbat/Vled) * Driver efficiency
- Driver efficiency is around 92%, depending again on voltages
- The FET is a p-type, not our typical n-type. It is being pulsed at up to ~600 kHz, so it also needs to be much faster than our typical ‘direct-drive’ FETs.
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What is the maximum input voltage that the driver can take?
Officially 20 V, as per the silk on the back of the driver. It should survive up to 24 V, limit being the MIC5235 LDO used for the MCU. Main power capacitors are 50 V rated, but C1 was specified for only 25 V. Going above 25 V calls for a 40 V FET, whereas the stock FET is 30 V rated.
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Where is the sense resistor and what is the formula for output current?
That would be R11, the big (2512 package) resistor. Stock value is 0.091 ohm. Maximum output current is approximately:
Imax = 0.248/R11 - Ir/2
where Ir = 0.3 on the stock driver
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What output current is used for the strobes?
2.5 A
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I set my GT for the mode-set UI, set 7, but I get two modes instead of the expected 100%-only mode?
From the user manual, page 6:
Note that MOON mode is enabled by default, adding
one extra mode (mode 0) to the above.Disable MOON mode and you will be good to go.
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The GT has low voltage warning and shut-off. At what battery voltages does this happen?
- At 12.0 V (3.0 V per cell) the GT will blink the main LED and step down in power. It will do this repeatedly until the battery voltage recovers above 12 V.
- At 11.2 V (2.8 V per cell) the GT will blink rapidly and shut down the main LED.
Note that these voltages can be ~0.05 V per cell off in either direction, depending on the component tolerances and temperature. These voltages are monitored under load and cells will read higher when removed and measured outside the light.
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What is the run-time of the GT on a set of fresh cells?
Using four Samsung 30Q cells (3000 mAh) gives about 45 minutes of regulated 2 A output, followed by another ~30 minutes of drooping output. Using eight cells doubles this time.
MRsDNF’s run-time tests with four cells
Body / host
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Why is the rubber boot for the button not transparent?
It is translucent black, the green back light is visible in a dark location only. If you received a light with an opaque black button we will work with LT to correct it.
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What is the size of the rubber boot for the button?
12 mm. These are available online, but less common than the standard sizes.
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Why do the front and back lanyard attachment holes not line up?
The tail-end attachment point can rotate inside the tail cap.
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My tailcap ring doesn’t want to spin. Help?
There may be a pinched or insufficiently-lubed O-ring inside. If you remove the Lumintop sticker inside the tail-cap, the parts should unscrew (reverse-threaded), and then you should be able to check and lube the O-rings.
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Why do the font lanyard attachment hole not line up with the button?
The driver compartment and the reflector housing are two separate pieces that screw together. It is difficult to have this align and it was never intended to align.
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Are any parts of the host glued together?
No. But they are tightened down well and especially the bezel can be a tough one to unscrew due to its size.
[Edit 2018-01-11: Driver and run-time details added]