Interesting. I bet TA just uses trial and error. 
His hand built units held up to torture testing so it might be safe assume that is not the cause of the failure.
It’s possible the FET that they used has too much internal resistance and that is what caused it to overheat. Or maybe the factory drivers used a thinner copper layer on the pcb which reduced it’s heat transfer ability.
I did some basic calculations but without a major change in design that would be basically impossible it was not possible to significantly increase the amount of copper cooling for the FET so I did indeed focus more on testing then calculations.
A thinner copper layer is possible but I used a 1oz for my test drivers and I doubt they went thinner then this.
A cheaper FET like the one lexel posted is the most likely cause. It was only rated for like 30A so it would make sense it would blow under bypassed springs conditions and that should be around 30A of current.
For those in the US, it looks like Richard at MTN Electronics carries the better FET for $1.35. Is this the right one?
Yep, that one will work fine.
There are some nicer once that Lexel found recently that I did not know about when I first built these drivers as well for those that order from mouser / Arrow.
I just keep sitting on my coupon codes for these lights until I know they are good from the factory. What a rollercoaster ride. Lol
I have 10 of those. If I use two fet it will spread the load and iz is more safe think.
Removed the fet with regular soldering iron heated the top and the package turned in to dust. With a lottle help of pliers removed the top and insoldered the big pad.the pcb survived without any damage.
My good fets and hot air station are at work so I will put on the good tomorrow.
The only problem with using 2 FET’s is that the resistors are setup for a single FET and using 2 will cause them to switch more slowly and increase the losses (aka, they will get hotter) and cause the ramp to change some in the low modes.
You can try it and see what happens though but a single SIR800DP should work fine. That is how the lights I built are setup.
Ok then I will use one.
Thank you for all your help!
interested …any reviews
I’m at work now. Covered the surrounding area of fet with kapton tape. Added solder paste. And reflowed the fet.
Now it is blasting again Now I’m at day shift so when I get hom remeasure output and finally do an intensity measurement.
I hope swapping the FET is all it takes to make it bulletproof.
So you got about 18k lumen stock. Was that the NW or CW version?
18270 lumens NW version.
I’m glad there’s a happy end to this story.
Hmmm, I guess that means the CW that I prefer is what, 3k lumen less?
Still, 15k lumen is nothing to sneeze at.
No. CW is usually has higher lumens output.
Glad it is an easy fix. Has anyone replied you on the spare FET pad question?
Really? I vaguely remember the lower forward voltage on the NW giving it a higher output.
I’ll have to check TA’s driver thread. Wait, I’m not sure what exact CW emitter the factory is using. I may have to wait for a comparison.
Yes! TA answered it. It is designed for one fet only. Two fet will switching slower.
If you use the same bin then the output should be roughly the same between tines minus the lux meter bias towards CW tints.
In the case of the MT09R, I am not sure what CW LED’s they are using now but in the last batch the CW LED’s were a lower bin then the NW and were a fair amount lower output. Around 20% lower IIRC (so around 3 bins lower).
It is possible that they upgraded to P2 bin CW LED’s like I suggested for this batch though.
Oh, I also heard that they will be discontinuing the MT03 after this batch is sold out. I really like that light, the best flooder I own. Tempted to get another one if I could justify it.
^ That’s odd. Seems to me that the MT03 is a winner, and a Haikelite flagship as well…