What cause burned FET driver and FETS on 9920 - RC-Monster Forums

tom255 · 04:26 AM

first specs:
Motor-9XL
Controller-9920
Gearing 44/14
Battery-TrueRC 5S2P 8000mAh (one brick)
UBEC- dont remember but some new generaition with radio noise shield up to 5S (5V/6V)
Lipo Saver: Dimesionengineering LipoShiel
Capacitor: 1000uF 16V

One day i assembled my HB LSP and made some free runs (Wheels on air) tried brakes and etc But this day i tested about 10 mins all seems ok And decide next day assemble it fully.
Next Day i went to Electronics shop, bought some switches wires and Capacitor. I asked 6V cap but they dont have it and i decide to take 16V cap
I am connected all and cap to spectrum RS3000 AUX + and -
Assembled it and tried to make final free run and all seems ok a pressed the triger tried couple high runs and brake and one longer run (5-6sek) not on full throttle (prevent balooning and suddenly heard like cogging sound then controller stoped and smoke escaped from ESC i tried disconect battery fast as possible ( but you know tight DEANS) it takes couple secs do disconect. And after that nothing works
BEC disabled by removing middle wire
I checked all wires, wires OK no mistakes all is made like on BrianG homepage.
Now i am think what caused it. Can it be Capacitor its only thing that i connected after first run becouse first test OK and i ran motor much longer than second time next day. Can 16V cap do it?

I disassebled ESC and found fried FET DRIVER (IR2102S) and 3 FETS (IRF7413) on other side. I am want to buy new fets and fet driver and assemble ESC again. Realy hope to fix it.

I finished technical highscool (studied HIGH voltage) but know how basic low voltage components works and pretty handy with welding tool. Made before some simple amplifiers for subs and filters. I know basics. So i am not so newbie in that. But in other side not proffesional

But question again what you think can 16V cap fry it?

05.10.2007, 03:41 AM

sounds like your esc fried not a capacitor caused it.
so if you check all wire all right, i think just only ESC problem.

BrianG · 10:16 AM

Andy is right, the cap would not have caused it. Using a cap with a higher voltage rating than needed is actually good since it won't be running close to the max rating. And those electrolytic caps usually come in v ratings of 6.3v, 10v, 16v, 25v, 35v and so on.

At most, a bad cap could maybe fry the BEC chip if it somehow internally shorted. But most BECs have a thermal and short-circuit cutoff.

After looking at the datasheets for the part numbers you posted, one is a FET driver IC, the other is indeed an output FET. Driver ICs don't usually go bad since they are low current devices. I would think that whatever caused that one to go bad, might have fried others as well.

Here are the datasheets if you're interested.

IR2102S datasheet
IRF7413 datasheet

tom255 · 05.10.2007, 10:57 AM

I thougth same...
When i come home i will check cap on short circuit. hmm but on other side if in cap short circuit i supose that first thing what will burn its UBEC.
Anyway next week i will get parts so i try to resolder

GriffinRU · 05.13.2007, 05:51 PM

Driver can blow output FET's if it is overloaded and wasn't able top close FET fast enough, or didn't have built-in delay for protection... you can get the idea

CAP can course failing in driver if it doesn't have ESR low enough, Higher voltage caps have higher ESR then lower voltage ones.

It is always about balance, and drivers, FETS and CAP's are very sensitive to temperature you can finish the rest...

BrianG · 05.13.2007, 05:58 PM

Quote:

Originally Posted by GriffinRU

CAP can course failing in driver if it doesn't have ESR low enough, Higher voltage caps have higher ESR then lower voltage ones

I was assuming the cap he was talking about was on a receiver plug, not part of the ESC. But maybe I read the post wrong...

zeropointbug · 05.13.2007, 06:34 PM

Quote:

Originally Posted by GriffinRU

Driver can blow output FET's if it is overloaded and wasn't able top close FET fast enough, or didn't have built-in delay for protection... you can get the idea

CAP can course failing in driver if it doesn't have ESR low enough, Higher voltage caps have higher ESR then lower voltage ones.

It is always about balance, and drivers, FETS and CAP's are very sensitive to temperature you can finish the rest...

Hence all these problems could be from the caps in these controllers... the more the merrier!

tom255 · 05.14.2007, 04:35 AM

I put cap to receiver, not to the ESC.
For now i took ESC completly apart. Removed top heatsink from fets and cleaned bottom fets. So total found 12 damaged fets. 2 fets damaged when i removed heatsink. 10 fets burned on the side of +wire and 5 fets on bottom plate and 5 on top plate. 3 fets from 10 had visible burning damage and others had short circuit between Gate and Drain, also found burned resistors, For now i resoldered 7 damaged fets on top plate and seems now OK. on bottom plate is 2 small "GATE" resistors what have 4 resistors in one case, i dont have any idea how i can resold so small things and replace that 2 resistor packs.
Can anyone recommend what to check more? Caps on controller?
Maybe some circuits? Maybe some circuits on driver side?
Lets tel if ESC will work what i can improove? Buy better caps to controller? which ones? Maybe special brand?
Ofcource i will redesign the ESC case for better cooling

GriffinRU · 05.18.2007, 02:31 PM

Quote:

Originally Posted by BrianG

I was assuming the cap he was talking about was on a receiver plug, not part of the ESC. But maybe I read the post wrong...

My fault,

to tom255:
If you have bad cap in receiver it is very bad and there is no need to discuss what can happen to ESC, garbage in - garbage (smoke) out. Noise on input can kill any controller.

tom255 · 05.18.2007, 06:23 PM

OK
Seems i fixed it, i programmed it and made couple short runs without tires on my truggy. If i find a time i will putt bigger heatsinks on it and weld all thing to one piece. Now i have question. What you think change or not stock caps to bigger one ofcourse using quality caps
What you think about "ELNA" http://www.elfa.se/pdf/67/06718035.pdf is it ok?

BrianG · 05.18.2007, 09:18 PM

Where are you putting that cap? Is it for the receiver or the ESC itself?

If for the receiver, you don't necessarily need top quality caps. There isn't much current drawn so low-ESR types are a little overkill. They won't hurt, but they won't much, if at all. I've used RadioShack ones on two vehicles for quite a while without any negative effects.

If it's for the ESC, you'll need part# 6718480 or higher since you need at least 35v.

tom255 · 05:06 PM

I mean CAPS on ESC itself. On BK 9920 are 4 (samwha RD-series) 220uF 50V caps http://www.samwha.co.kr/upload/CAT_E/list_pdf1/RD.pdf Looks like they are more like Standard caps
i tought maybe change them to LOW-impendance bigger one like 330uF or 470uF or its unnecessary?

Edit: What a long read on "Quark fried, blown capacitor" thread learned lot and understood that LOW impendance is my friend it helps keep my ESC cooler and probably solve problems with weak brakes on 9920. I think i will buy 470uF caps and solder it to board.