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ub0211042
2007.10.05, 03:19 AM
Hi All,

It's me again with new question about FET's haha :D
I have had 2 problem with fets in the past month.

1. 3 x 2 4562's on an AWD running on PN Xeric motor.

The problem was, after running it for 2-3 hours (with not much resting time)
The car starts to shut down, meaning no forward but reverse works.

I held the car direct to the aircond and let it cool off, then it can run for few laps. Then the problem re-occur.

2. Single layer 4562 on MR-02 running on speedy AWD motor.

Same thing happen, no forward and got reverse.

Does this means that the FET's are overheated?

Hope can find good answers here again.

Thanks.

kja812
2007.10.05, 09:54 AM
Does the car run the next day or do you have to change the FETs to get it working again?


If it works the next day:

Remember reverse still uses 1 FET from each package (n-channel of 1 package and p-channel of the other). The 2 FETs in the 8pin package are bonded together (thru the four pins that you can solder together) and will be at the same temperature.

After 3 hrs of hard racing, the entire circuit will be warmed up - it may be another part of the board that needs to cool down.

If it doesn't work the next day:

You may have damaged the forward direction FETs by long term overheating them. FET on-resistance usually goes up after suffering thermal strain. This makes them heat up faster than before which may explain why you only get a few laps after cooling them down.

ub0211042
2007.10.05, 02:41 PM
Does the car run the next day or do you have to change the FETs to get it working again?


If it works the next day:

Remember reverse still uses 1 FET from each package (n-channel of 1 package and p-channel of the other). The 2 FETs in the 8pin package are bonded together (thru the four pins that you can solder together) and will be at the same temperature.

After 3 hrs of hard racing, the entire circuit will be warmed up - it may be another part of the board that needs to cool down.

If it doesn't work the next day:

You may have damaged the forward direction FETs by long term overheating them. FET on-resistance usually goes up after suffering thermal strain. This makes them heat up faster than before which may explain why you only get a few laps after cooling them down.

wow, nice explanation...the car does run well today, lucky i didn't have to waste money just to change the whole fets again.

on the first case i faced, i just swap the forward fet with the reverse ones.
then i put a heatsink on top of it. I use computer Ram heatsink but need to cut them to half to fit it nicely on top of the 3 layer fets.

no heat issues after that anymore. Oh btw, the AWD with 3 stack fets ran on NML when the problem occur.

kja812
2007.10.05, 03:42 PM
There are all kinds of thermally conductive glues and greases that would help transfer the heat to your chunk of RAM heatsink - especially if its just ontop of a 3 layer stack.

You swapped the 2 FET packages - does that mean you got forward and no reverse instead of reverse and no forward - or did you get to run in both directions?

ub0211042
2007.10.05, 04:50 PM
The forward FET is not 100% damaged, it can still run but only for 2 -3 laps maximum.
So i just swap the 2 towers and it works great until now.

So the forward side is the fet that is not having the thermal effect but the reverse site does...but we rarely use the reverse for long rite?

kja812
2007.10.05, 05:45 PM
So the forward side is the fet that is not having the thermal effect but the reverse site does...but we rarely use the reverse for long rite?

Sounds like a ok solution until you have time, desire and $ to replace the parts.

Toodeep
2007.10.05, 09:29 PM
I never run mine more then 30min at a time. Before cooling it down with a Fan box i made.

ub0211042
2007.10.05, 11:10 PM
so u guys have any idea of whats the time limit for playing mini-z before it needs to rest?

how about endurance race? how do those guys managed to stay from the heat problem?

dohc
2007.10.20, 03:56 PM
im not sure about those fets you guys are using. im old school so 7389 fets all the way baby! i've ran mines 5 hours straight on 6 cells. no over heating whatsoever. tower stack is 15x2 = 30 fets LOL. i've also replaced my awd with a 3x3 runnin 4 cells and a pattern wound motor. 5 hours straight runnin, no heat on fets/ less glitches at all. it may have to do with your soldering on the fets. make sure that you got a solid solder per legs. thats the cause of mines before. i'd lose reverse but will have forward.

arch2b
2007.10.20, 09:44 PM
so u guys have any idea of whats the time limit for playing mini-z before it needs to rest?

how about endurance race? how do those guys managed to stay from the heat problem?
the e.u. guys run an annual 12hr endurance :eek: i don't recall anyone mentioning fet heat issues.

ub0211042
2007.10.21, 02:49 AM
i'm using vishay 4562 fets, i don't know what might caused the problem other than the heat. IMO, I think any electronic component does have some limit for the temperature.

how about the new AWD, they do equipped with some capacitor to automatically shut down the power to the motor when it starts to heat up.

Aurora
2007.10.29, 09:07 PM
ub0211042,

IIRC, the auto shutdown for AWD usually attributed to the square piece that attached to the x-speed motor, which acts as a circuit breaker.

For the fet overheating, I am wondering whether it could be a drivetrain issue or just plain overheating. 3x2 4562 should be able to handle xeric just right, and for myself, I did have some motor overheating issue once, until I discover there are some drag created by the drivetrain.

ub0211042
2007.10.29, 11:39 PM
ub0211042,

IIRC, the auto shutdown for AWD usually attributed to the square piece that attached to the x-speed motor, which acts as a circuit breaker.

For the fet overheating, I am wondering whether it could be a drivetrain issue or just plain overheating. 3x2 4562 should be able to handle xeric just right, and for myself, I did have some motor overheating issue once, until I discover there are some drag created by the drivetrain.

i think maybe because of over gearing. but anyway we only have 5 min race here :) for now

herman
2007.10.30, 12:25 AM
kyosho warning... here it is...