Detecting counterfeit 4110 mosfets

[d8veh]

My Ebay Chinese Fets arrived today. One of the 15 was very different (on the right) and the rest look like poor copies. I only want them to switch my battery, so hopefully they'll be OK.

[methods]

Dude those are so fake

From now on nobody is allowed to buy that crap. $1.50 each in quantity 1. That is as cheap as I was selling them WAY back when I was trying to change the world by bankrupting myself.

-methods

[Kin]

Uh, so, I apologize for what is certainly a stupid question...but...

Methods, with respect to replacing fets, a page back you said,

"12 fets, 2pcs"
"18 fets, 3pcs"

You also say, paraphrasing, "don't be stupid, replace the whole bank."

As there are three phases, doesn't a 12fet have 4 fets on each phase? And a 18 fet, 6 fets?

[John in CR]

Uh, so, I apologize for what is certainly a stupid question...but...

Methods, with respect to replacing fets, a page back you said,

"12 fets, 2pcs"
"18 fets, 3pcs"

You also say, paraphrasing, "don't be stupid, replace the whole bank."

As there are three phases, doesn't a 12fet have 4 fets on each phase? And a 18 fet, 6 fets?

There's a high side bank, and a low side bank for each phase.

[Kin]

Righto. >.<.


Thanks!


I suspected something like that, but http://endless-sphere.com/forums/viewto ... =2&t=41159, shares my sentiments <<but then how the bloody hell does a 9FET work?>> I'll keep reading, it seems I should have searched that earlier. [General point summary: in the 9fet, 2 fets are on one side and 1 on the other, and the switching all happens on the two fets.]

[flez1966]

My controller just blew after <5 mins of use....

Fets have a lovely IR logo, date stamps, very very well printed, and the part number is FB4410 .....





The case moulding is very like real ones....

Guess i need to find some 4110's and upgrade while i repair..

[amberwolf]

What conditions was it being run under?

Also, does the rest of your controller look like the one here:
viewtopic.php?f=4&t=44226
because that one has some definite QC (lack thereof) problems, including the way the heatsink bar mounts to the case which prevents heat from being able to escape properly, and that would also blow up even genuine FETs. (and it has an SMD resistor just sitting on the PCB, not soldered to anything; probably other issues I haven't found yet, and it has not even been powered on yet).


Another potential problem I see with yours is that it appears to have wrinkles in the kapton tape. If thsoe also exist behind the FETs, they will not sit flat and they cannot get their heat out of the FETs and into the heatsink bar.

Similarly, there appears to be gobs of white paste on there, too, which will do the same thing, as while it is better than air it is not nearly as good as a direct physical connection, and often large gobs also have large air pockets, blockign heat transfer.

There may be other issues, too, but that's what I can see in that single pic.

[flez1966]

yeah I never thought of the tape, I have had it apart before use, I always expect QC to be non existent and so i strip everything i buy and bench test before use.

I was 'happy' with the build on this, I just read about the bar issues and must say mine was sat nice to the case and had transfer goo to the case etc.

what I dont like is the fact that pcb is not supported by the case at all, it had no support on one side, and is hanging by the fets on the other, I'm old school, heatsinks have screws and are screwed to the pcb, the fet then has no weight on its legs and its legs should have a S bend for thermal expansion, and thats how it will be modded when it goes into real service...

It would run fine on the bench, would trip out after 10-15 seconds and get worse like it was heating up or losing volts, i just just kept going to destructively get to the bottom of the problem, as poking about with a meter was getting me nowhere

so, eventually it got very weak, and then would not go and the motor started 'cogging' badly so i knew a bank had shorted a phase out. blue phase to +pack, I think thats the more common failure mode but not sure why.

as i never had more than a 15 second 'burn' and never got above 20mph, eventually seeing it fail at about 10mph, in my mind it was weak fet that failed, stressing the remaining two so they failed, no part of the case was hot, but the bar was warm near the middle where the fets went pfft

there always a chance that the original fault still exists, maybe in the bank that switches the phase to ground... that could have caused excessive current to flow (and maybe the tripping) through the high side set taking them out...

all good fun these things...

so, now trying to source genuine ones preferably in the uk so if they do turn out to be fakes i can send them back...

[CamLight]

Fets have a lovely IR logo, date stamps, very very well printed, and the part number is FB4410 .....
<snip>
Guess i need to find some 4110's and upgrade while i repair..

Something to consider if replacing your FETs is that, if genuine, they are IRFB4410Z FETs and not IRFB4410. They are close in spec but the 4410Z version has a very reduced safe-operating-area at higher voltages compared to the 4410. Most of the other specs seem pretty close.

And be sure to add a thin film of thermal compound to both sides of the tape! To me, it appears that the FETs do not have any compound underneath them in your photo. There only seems to be compound underneath the tape.