The BLF GT70 "Giggle Monster" is here! 7,500lumens, 1,500m throw! Group buy Closed!

Could be a bad connection by cells / carriers. Or a bad driver. Or a bad LED depending on exactly how bright it is, this is the most likely issue based on what you said.

Texas_Ace maybe the one to ask to test it if he has the time

Battery check with the cells in is 4 blinks then 2 blinks. So 4.2?

To rule out the carriers and batteries, clean all the springs, and connection points on battery tube and driver

For it to drop in output suddenly while using sounds like the LED or driver.

You still might be able to get a replacement over at nealsgadgets. This would require you learning to solder but the hardest thing is opening the head. You’d need two rubber strap wrench and a maybe vice

So I’m guessing this thing eats batteries for breakfast ? Own the original GT XHP35 but have never ran it to exhaustion. How long would this new 1 run at say half power ?

Edit: Didn’t realize it was lower voltage, nevermind.

Where did you see it is lower voltage? Both the GT and GT70 run at 12v?

The new GT90 runs at 3V but that is because the LED is a 3V LED. It pulls almost 30A to make up for it.

Sending the light to Texas ace for diagnostics. I just don’t have the time to tinker. To many other hobbies going on. Appreciate the recommendations and help!

My bad, saw 3V and misinterpreted. Kinda skimmed over it. So I guess it really does eat batteries.

It shouldn’t draw any more power than the GT70 does. These are rough numbers as the voltage and amount of voltage sag will vary based on the batteries used.
4v x 30A = 120 Watts
15v x 8A = 120 Watts

Shame I got the 1st one, although I am still happy with it, and the price was spectacular. This thing is really powerful as far as throw, I’m still amazed, but 7,500 lumens vs my 1,800. No doubt, I would be giggling.

You can buy a kit with new led, centering ring and driver from Neal’s gadgets if you want to convert it. I think its $50.

Yeah, I saw that. May possibly do that but not sure about trying to get that head apart. Would hate to scratch my baby. Maybe with a strap wrench.

You definitely need two rubber strap wrenches. They are cheap, though. $5 to $10 for a pair.

I needed only one strap wrench and wrap the bottom part in a towel in a vice. Would of been harder without a vice

Get two wrenches as Jason suggests. It’s very much worth it

Hello again gents. I am once again asking for your support. I’m trying to get my gt70 to run on 12v … spotlighting from the car.
Would flashing a custom firmware take care of that job or is the hardware never going to allow it to run off 12 /13v? It just thinks anything under 14v is too low and starts stepping down, then over 14v it seems to not want to rampto mid power.

Any advice is appreciated.

The LED itself needs ~15-16v to reach full power, nothing you can do about that really.

Far as running it from a car, you can get boost converters on ebay that could boost the voltage to what you need, although finding one that can support 15A input could be difficult. Sometimes you can use multiple converters in parallel to increase the current though but that will require research to see which ones would work.

One way or the other you would have to get the voltage up to ~15v or so to reach full power.

Thanks for the quick reply tex, did you see the video i linked? With a 4s lipo it doesn’t ramp, but will happily go full power till heat cut off. I’ll be able to sort out a step up dc dc converter of adequate wattage but if like for it to still have the ramping ui. Any thoughts as to what might be the issue here?

I didn’t watch the video the first time.

What cells are you using? They don’t appear to be high drain cells? Have you tried using some high drain cells?

The driver could be hurt, I have run into odd issues like this during prototyping when a driver was hurt due to excess voltage spikes etc.

The voltage reading the driver sees will also be a momentary reading on that driver IIRC, later we updated the firmware with a crude low pass filter to help mitigate this by spreading out the voltage readings over time. Basically if the voltage drops during the time the PWM is on, the driver can see this and think the voltage is low. Using high drain cells that don’t drop as much can take care of that.

The updated firmware might also be able to help, this should be the GT4 firmware which should work on the GT70 driver as well and has the low pass filter: GT4 firmware

The no ramping issue with the lipo is a reverse issue if I had to guess, the ultra high current capability of that battery combined with the wires that act like inductors can cause big voltage spikes that freak out the driver and can even damage it (did that when testing with a bench power supply a few times). For this better filtering could possibly help but the driver was not designed for this use case as it is hard to mitigate.

A simple option would be to add another 10uf cap to the empty C3 or C4 pad on the driver IIRC (it is at the top above the wire pads). Could even double up those caps if you wanted, they help control the voltage ringing but are not perfect.

The GT4 driver was updated to help with this issue due to the higher currents it deals with but not sure it would be enough for your use case.

Without a scope to see what is going on, it is all just guessing. It is possible that a large electrolytic cap added to the battery carrier just before it goes to the driver could help control the voltage ringing the driver sees but it is a bandaid fix at best. It is cheap though and would not hurt anything if you wanted to try it. I would get the largest cap(s) you could fit in the space rated for 20v+ (25-30v is better) if you tried this.

Yeah I have always been suspicious of the cells. Supposed to be 3500mah ncr18650ga but ebay can be very unreliable.

I have not been kind to this light or the driver i would not be shocked if it was hurt.

Ill try the updated firmware, add some caps and locate a good dc dc converter.

Thanks again for your help

Edit:
Can I get a second opinion on this dc dc converter? They’re saying 720w, but I’m not sure it looks beefy enough …
https://www.fasttech.com/product/9664388-dkp6012-720w-programmable-digital-constant

That converter appears to be a buck converter, it can only lower the voltage, so it won’t help you.

The important thing you want to look for with boost converters is the input current limit. if you feed it 12V and output 15V @ 8.5A, this means you will need:

15v * 8.5a = 127W of power

127w / 12v = 10.6A of input current before efficiency losses in the converter itself. These can range from 10–30 or more in lower quality converters.

So actual input current would be between: 11.6A - 13.8A

Basically, you would want a boost converter with a 15A input current limit to handle the GT70 at full power. This is hard to find as most cheap units top out around 10A. You can beef up the cooling on the converter in some cases to get more output though, sometimes just attaching a fan will do it, others it needs a larger heatsink. Might be worth trying a$5-10 converter with a 10A limit and beefing up the cooling vs spending $50 to get a 15A converter.