I was wondering if anyone has seen this happen. I have one of these drivers piggy backed on a yezl stock driver used for an eswitch.
It’s been running good using some rigged software based on JonnyC Star code. It was running fine when I turned it off at the tail. When I turned it back on, it just sits at what looks like 50% pwm and no response to anything.
I took it apart and checked the Tiny13a with avrdude, everything checked out. I uploaded a fresh copy of the firmware, just in case something went crazy. Same result on the bench. I then flashed in the original star driver and it still runs at what looks like 50% when on, no modes.
I was wondering could this be the Mosfet needs replacing? Or is it the Tiny13a pwm that went (and still checks out good)? Or could this be something else that happens right when you need your light!
Thanks
EDIT Think I’m gonna replace one at a time to see… I hope it isn’t a resistor have to order those. I was just wondering if it was a common thing to happen. I’ve banged around the stock buck driver on the yezl and drove it way over spec, they still keep chuggin Oh well, I’ll fix it one way or another- or order another one from RMM. I just wish I knew what happened.
I have 4 or 5 SRKs that all use that same FET and four Samsung 25Rs, haven't fried one yet (and many single cell lights). If 25Rs won't kill it a dinky MNKE 26650 sure isn't going to.
What's the voltage at the gate? If you ground the gate, does the LED turn off? If you jump B+ to the gate, does it go to normal full output?
If it was being feed the correct gate voltage so it could turn on all the way I really doubt that the FET died due to overcurrent. I have pushed 20A+ through these and they never even get too hot to touch. What you could have been doing in that light isn't even close to enough to kill one of these. Something else happened.
Had to take care of some business on the farm. Man it’s nice out. Let me get the measurement. It’s definitely the fet imo though, on the other driver I linked with ic clips to test it out. It was stuck with a brand new driver at 50% out. That’s the only thing connected that’s new. I guess could put full power to the gate and see if she goes full out. Sometimes it’s good to have more brains- I was going about it all complicated. But it’s definitely the fet imo
Let me jumper and see what happens though. If it opens up I’d be very surprised.
EDIT Yep full power to the gate- same result. Oh well hey RMM I think saw those on your site for sale. I need to order one get this fixed. Maybe it was just a bad fet who knows.
So you get this result on the bench as I read your post.
This is just an idea.
Maybe try to test for continuity from various points on the driver to where there should be none. Sounds to me like you may have a leak current somewhere. Operative word: may
Obvious ones are:
from spring to negative ring
From negative led pad to negative ring
From gate to negative ring
But sooner or later someone has to get a dud. Sorry if it turns out it is you.
Thanks for the tips led… I put power direct to the gate though- it should have opened and didn’t. I’ve even tried with a brand new driver and ic clips to the fet. Same results. It’s just a dud They’re cheap though only a buck each on mountain- already ordered. Picked up some efest batteries too, fry me another chicken.
But really I haven’t had a problem with that buck on the yezl. I braid the diode to the pill wall and it handles 6 amps with 2 batteries in series without breaking a sweat. One’s being used nightly by my redneck kin. I’ll fix this but I’m not too confident it will hold up. Be nice to compare the efest to the mkne. I have a feeling it’ll be the same though. Oh well Live and learn.
Fellfromtree mentioned this thread & problem over in the BLF17DD Info Thread - Reference (post #142) and I thought I’d chime in. Fellfromtree mentioned a suspicion that the gate drive resistor might be incorrectly spec’ed, but I don’t think that should be the problem. AFAIK the gate drive resistor is simply there to protect the MCU from a potentially heavy drain on it’s little 20mA-per-pin sourcing ability - NOT to protect the FET from anything at all. Besides just getting a bad FET, I think the most likely thing sounds like a sudden open circuit during operation.
Offhand I’m not sure if turning off the tail clicky should be able to cause a voltage spike, but disconnecting the LED definitely should be able to do that. (Due to the inductance in the wires to the LED.) Here it sounds like the LED was already securely wired in, so I suppose that we can assume the LED was not suddenly disconnected it. In that case I guess the tail clicky did it? Hmm.
BTW fellfromtree… you have confirmed that the LED is OK, right? EG at some point after this incident occurred you wired this LED up such that you saw that it is capable of lighting up at the normal maximum which you are accustomed to?
Yeah it’s good. I even took it all apart and used another led.
So a disconnect from the LED could cause the FET to go? That’s interesting stuff. I dunno what happened- I’ll replace it though and hopefully doesn’t happen again It doesn’t light up to the normal through the FET, the gate is just stuck
Thanks Wight… I’ll double check all my connects to the LED next time. I didn’t know a disconnect could cause something like that
I’m pretty sure it’s possible, but I wouldn’t really expect it to happen under normal circumstances either. More of a hypothetical problem. Long heavy gauge wires would probably make it more likely to happen, maybe especially if they were looped around a certain way (like an inductor).
If the FET is running cool then current flow isn’t bothering it. So while the FET is running cool the only potential problem is voltage spikes, and voltage spikes come from the inductive stuff going on in your wiring as the FET switches on and off.
I feel like you’ve probably hit the nail on the head when you say that you might have gotten a bum FET.
In bench testing I've done all kinds of unapproved stuff like that - holding the emitter leads to the driver pads instead of soldering, just to get a quick reading on something, fingers slip, wires come loose, etc. If there's a wrong way to do it, I've done it, but no dead FETs.
Fair enough. My own behavior along those lines is what I was thinking of when I typed #11. I haven’t done a fraction of the fooling around with FET drivers that you have, but I’m sure that if suddenly disconnecting the LED normally killed FETs we’d know by now.
So, that said… what’s your theory on what did kill the FET? Fellfromtree has done the requested checks as far as I can see and the FET sounds like it is in fact dead…
I have a 12*7135 (I stacked 4 chips) on a Convoy S2+ build I did, it ran fine for a while but now it won’t come on but in moonlight (lowest) mode for some reason
I wonder if possibly the diode feeding voltage and for reverse polarity is bad…I will have to check
I had that happen and it turned out to be a flux corrosion issue on one of the inputs to the XM-L emitter. Same deal, just a low moonlight output. Driver was fine, and the emitter was fine once removed from the MCPCB.
It’s a 3x XP-G…ran great for about 5 min testing it out, shut it down…won’t come back on, I used a prototype ramping from turbo down to high (1 tick ever .25s) vs the large step down…I think it’s the firmware…but will re-flash just to make sure
But I will definitely check the inputs just to make sure…thanks!
Well, worth remembering that ESD adds up slowly over time, it’s not like being struck by lightning.
They used to call it “wounding” in the old days. A semiconductor has a narrow range within which it changes from being an insulator to a conductor — and ESD can change either side of that range by some small amount. Once enough components have wandered slightly off spec in various ways, the sum total performance of the circuit is, I believe the technical term used to be ‘cattywampus’
But maybe things like that don’t happen any more. I recall they never happened to young people, only to older people ….
Oh well, I’ll fix it one way or another- or order another one from RMM. I just wish I knew what happened.
