When Mosfets Shoot THrough!

[knoxie]

Hi

I had another controller in for repair today, err em well yes!! smoke damage board damage my goodness!! 2 complete banks of fets had blown and shot through, the on board voltage regulator had blown off the board and the smoke had got so hot in the controller that it had melted the skin on the capacitors!!

I have never seen anything like it, its so important to stress just how important a fuse is in-line, I have a feeling this particular person didn't and only turned it off when he smelt something bad, this is a total fire hazard.

Mosfets when they fail always seem to fail short circuited, which is bad news as this normally (low and high side) results in the power rail being shorted out! also this particular controller had been getting wet as well as there was evidence of water inside and corrosion on the screws.

The potential fault currents with e-bike systems is so huge you can have 1 hell of a fire if you don't protect things well.

I don't think even the master fixer Fechter would have a go with this one, I would take some pictures but I cant even bring it in the house it smells so bad! (this controller came in for repair its not one of mine!!)

I think as a challenge I will try and fix it, I just cant understand what would blow the 5 volt voltage regulator clean off the board? unless it was a huge free wheeling ball of current from the motor flying back through the shorted mosfet? anyone?

Bottom line. keep them dry, use a suitably rated fuse and keep an eye on them!! ha ha crikey

Take care folks

Knoxie

 

[Ypedal]

Well.. then take your camera outside.. to the controller !!! ( would make a good contribution to the Woops thread ! )

 

[knoxie]

Yes I will tomorrow! ha ha stinky old thing it is, the fets have been destroyed

 

[fechter]

Oh yes, we must have pictures!
Too bad they don't have "smellivision" perfected yet, but I can almost smell it from here

If it blew the regulator off, then I would guess somebody connected it to the batteries backward. There's likely to be lots of dead parts there!
I've seen where the jet of superheated silicon vapor has shot out of a FET and melted the solder right off the buss (where it's really thick).

I love the smell of silicon in the morning - it smells like....technology!

 

[Toorbough ULL-Zeveigh]

When any semiconductor (diode, whatever) fails short, it's almost always due to overcurrent. Or more precisely overheating brought on by overcurrent. The silicon melts together into a blob so there is no more P-N junction & it goes from semi-conductor to conductor. An overvoltage condition on the other hand will result in failing open as the static charge will punch a hole thru the junction without heating.

 

[deecanio]

why is my controller making me nervous everytime i look at it now?

D

 

[knoxie]

Hi Guys

Thanks for the replies and explanations, I figured that he had connected this the wrong way around, there is no reason otherwise for that voltage regulator to have blown off the board the way it did, people are just not honest with you though, the controller had got wet regularly this was obvious and had only been run at 48V, however a combination of this and the reversal did the damage.

I think I will tell him the bad news, its beyond economical repair IMHO and yes Fechter the damaged fet has done just what you said, quite amazing it has punched a hole right through the thick mass of solder on the board, would make for quite a weapon dont you think!! ha ha a Fetgun! perhaps its another line for xlyte and their controllers! ha ha.

Interesting point on why they fail short circuit as well so thanks to the new poster for that and Deecanio don't get nervous just make sure you fit a fuse in-line to your battery, I would bet this guy had nothing in there, there must have been a real load of smoke off this and I am sure he wasn't moving at the time as he has connected this in reverse for sure.

One question Richard, do you think the fets would have blown if the guy had simply reversed the power supply? or do you think its more likely the fets blew whilst it was running maybe and then he reversed it to make sure he didn't get the controller back repaired and would get a brand new one? what do you think? I suppose I can try it on a fet.

I can beef these controllers up and put bigger fets in there and adjustable current limits, but its hard even with polarised connectors to stop people from connecting things the wrong way around, the damage done to the controller is so obvious when someone does this I would advise controller retailers to maybe highlight that they will only warranty std unit failures and not reverse connection as reverse connection is obvious and very destructive rendering the controller to the bin.

Its a miserable day today so I will pop out in to the garage with the camera and take some snaps.

Cheers

Knoxie

 

[fechter]

The body diodes in the FETs will conduct if the controller is connected to the battery reversed, even if the power switch is off. A fuse might not save it in this case, but it couldn't hurt.

 

[Mathurin]

Come on, please? With sugar on it...

 

[Toorbough ULL-Zeveigh]

:lol: There's an animation that should prove useful. I lovett!

And the 'slightly warped' is a sort of color blindness test!

 

[knoxie]

sorry guys yes I am toe rag! I haven't been near my computer for a couple of days, under strict orders from the boss, her indoors! ha ha

Will get out and snap some shots and get back in as will be fitting new fets in the other controller tonight, the one that is repairable!

Cheers

Knoxie

 

[knoxie]

Right

I had to fix the other controller tonight which is all fine and working ok now! which is good news this one however is dead, its not worth repairing you can see looking at the photos, multiple fets blown and that solder blown off the board effect Richard mentioned, you can also see the smoke damage on the skin of the capacitor and inside the can of the controller, note the voltage regulator also blown off the board.

This is what happens if you get the polarity reversed on a controller and have no fuse protection! I do worry sometimes about some of the people out there with these things!!

Here is you snaps!

Cheers

Knoxie

 

[fechter]

Holy Weapons of Mass Destruction, Batman!
Those FETs really blew. Seems like I could use them for mini welders or something. I'd say that controller is pretty much toast.

Thanks Knoxie....

 

[knoxie]

Hi Richard

Ha ha yes I reckon so as well it is too much to fix it, I may have a go if I get really bored! ha ha I don't think I have the steady hand required to replace all those SMD.

Its toast like you say!

Cheers

Knoxie

 

[Toorbough ULL-Zeveigh]

There's probably (almost defiantly) a whole bunch of other components blown that don't show any external damage. Even if you get it to sorta work & breathe some life into it, you'll be chasing down the last ones for quite some time & most likely not work quite right again anyway. For the hundred bucks or whatever it costs, the time is better off spent with your kids. If you can salvage a few components off it that still work you'll be ahead of the game.

Thanx 4 the pix, as they are a good illustration that there's a lot of power at play & not to get too complacent about safety. I'ts easy to be lulled into a false sense of security because 99+% of the time nothing this catastophic ever happens, but it's when things go wrong you have to prepare for. This is why I think it a bad idea to carry anything more than 4 double A's on your person. A backpack full of any type of battery, let alone Li-ion is just nuts.

As for the regulator blowing off. Assuming it was a conventional linear type, 7800 series or the like, then any time the input is grounded, any voltage present at the output such as from filter caps (let alone a motor-generator) is basically shorted to ground thru a large junction in the regulator. A 10uF output cap can produce a 20A spike that even tho the surge is momentary, that's enuf to damage the IC if the input is shorted to ground or below ground. Not sure if the same holds true for LDO's.

 

[Ypedal]

Woooo..ooooo man..... now that's one crispy critter !!!..

I can almost smell it from here ! yikes.

Thanks for the pics.

 

[knoxie]

to prepare for. This is why I think it a bad idea to carry anything more than 4 double A's on your person. A backpack full of any type of battery, let alone Li-ion is just nuts.

This damage was caused by reverse polarity on the unit, it had nothing to do with where the batteries were being carried? :? If I for one minute thought my lipo batteries were going to flame on me, I wouldn't have them in the garage let alone on my back, the reason I am happy to have them on my back when testing new rigs is that they are light and powerful and its the easiest way for me to use them?

In my opinion if you are worried about an accident you shouldn't be playing with any kind on vehicle and if you are worried about battery fires you need to ditch your laptop your mobile phones your mp3 players etc. etc, no matter how it is powered, our houses are full of dangers all around, there is 230V in the wall wherever I put my hand, I am probably in more danger in my house statistically than I am playing in the park on my e-bike ( I only do tests with the batteries on my back, daily they are on the bike )

I have had a couple of people bring this up unless I am missing something I don't see a danger in carrying 10lbs of lipo on my back anymore than I am happy to be sat on a gas tank whilst riding my motorbike, they are both possibly volatile and If I was to have to make a choice of which to be near if they took off I would go for the lipo as these packs just bloat and smoke when they go, with petrol its normally a little more violent.

If anyone reading this thread is worried about lipo dont buy them, well infact buy them and send them to me, I will test them for you :lol:

Anyway that's getting away from what this thread was intended for.

Knoxie

 

[Toorbough ULL-Zeveigh]

The particular chemistry is irrelevant. It's a lot of stored energy in a small space. If that energy gets released in an unintended manner in a small period of time, your pictures show what can happen.

There have been undercover police officers that have suffered serious burns while carrying a 'wire' with far smaller watt-hour & lower voltage battery packs. The problem is the close proximity to flesh. There needs to be some separation. Rather than my saying that its's 'just nuts', perhaps it would be more constructive to say that it is taking an unnecessary risk.

I believe Alfred Nobel said the same thing almost word for word as you, about how safe he felt nitro-glycerin is.

 

[TylerDurden]

Ever put a 9V battery in yer pocket and forget you also have coins there too?

 

[Toorbough ULL-Zeveigh]

Yep.
Just once.

In my early teens. Except it was keys.
It leaves an indelible stamp in your memory.

 

[xyster]

Back in my grade school days as a mini-terror in training, I used to connect two 9v batteries together backwards, then quickly bury them in the school playground, awaiting what I hoped was a dynamite blast.

Didn't work out that way, the batteries just got hot and ruptured a little. I was into digging tunnels under the playground during recess, and thought this might be a good method to speed up the tunneling process.

 

[TylerDurden]

Back in my grade school days as a mini-terror in training, I used to connect two 9v batteries together backwards, then quickly bury them in the school playground, awaiting what I hoped was a dynamite blast.

Ja... highshcool chem is where thing start to get interesting.




But is is worth noting you were trying to trying to blow-up batteries even at an early age...

 

[xyster]

But is is worth noting you were trying to trying to blow-up batteries even at an early age...

The more things change....

Perhaps I'm a distant relative of Fechter's!

 

[knoxie]

The particular chemistry is irrelevant. It's a lot of stored energy in a small space. If that energy gets released in an unintended manner in a small period of time, your pictures show what can happen.

There have been undercover police officers that have suffered serious burns while carrying a 'wire' with far smaller watt-hour & lower voltage battery packs. The problem is the close proximity to flesh. There needs to be some separation. Rather than my saying that its's 'just nuts', perhaps it would be more constructive to say that it is taking an unnecessary risk.

I believe Alfred Nobel said the same thing almost word for word as you, about how safe he felt nitro-glycerin is.

Hi

petrol is pretty much for its weight the most powerful fuel source in the world!! we all pump it in to our cars, we have it in our houses in our camping stoves, cigarette lighters etc etc, I dont see the difference? on the Bionx bikes the lithium pack is right between your legs!

I am not saying it is not safer to have them on the bike, of course it is I am just saying that I dont think it is dangerous to have them on your back thats all.

There are a lot of areas on these high power bikes we need to watch out for, a lot of people still dont wear helmets on 30mph bikes! Steve Head is a very naughty boy! ha ha and also many people dont run deadmans handles or break inhibits, or decent brakes and tires the list is endless I see so many people with lead acid batteries cable tied to the top tube and allsorts.

Oh I know how to make things go bang as well!! I think I spent most of my youth making bombs and explosives!!

knoxie

 

[Lowell]

Things that go bang are better off here:
http://roguesci.org/

Unless it involves suicide bombing with an e-bike of course. After seeing my initial bike build, where the batteries were wrapped in black plastic and hung on the tubes, someone commented it looked like some kind of IED.