Re: (ET) 12V winch - PWM controller from scooter

[David C Robie <mycroftxx1 juno com>]

YAH i know about the heat sinks.  Aluminus meltus.  I don't think that
the people out there designing in boom boom land know much about power
fets but it seems when a speaker gets suddenly disconnected by some idiot
owner who hangs a switch in em to run externals in a camping trailer or
such he fries the brain if he switches them hot.  And if there's an
impedence mismatch they fry themselves.  Which is excellent because if
there's one thing I detest, it's hearing those jerks out there on the
road makin themselves big men by running about 1000 advertised watts of
jungle noise on the road.  Especially when I'm stuck in traffic near
them.  Especially when they go by the house in the middle of the night. 
Especially.  Especially.   BTW - I sorta collect pipe organ music and
have one tape that's guaranteed to blow out most of those boomer systems.
 They cant take sustained low bass notes.  The front speakers always go
out first. with a nice scratchy sizzle.
    Yes have seen EV controller innards with a whole big mess of scrapped
silicon in serried ranks bigger  than a boomer PA.  Didn't realize about
the touchy layout.  But hope I never have to. (retired from the part time
hopeless battle of wits against throwaway consumer electronics a good
while ago. Kept enough stuff to fix my own when necessary and really hate
to do that, throw most of it away) (at present, am teaching a guy I've
known for years (a local hi school instructor) the finer points of fixing
tube type TV sets, he collects them).  

Dave
Weymouth MA 
  

On Sat, 02 Sep 2006 15:37:54 -0400 Robert Adsett
<subscriptions aeolusdevelopment com> writes:
> At 09:25 PM 9/1/06 -0400, David C Robie wrote:
> >FETS in parallel are an iffy thing. They gotta be matched 
> perfectly,
> >which is the only reason they work at all, rigorous laboratory 
> matching
> >before assembly.  Slight manufacturing differences, slight 
> differences in
> >heat sinking, slight overload, or a spike from load disconnect  
> will wipe
> >the whole bunch of em out in microseconds.  Most often noisily with
> >shrapnel, faster than a fuse can blow.  Seen a whole lot of those 
> 'boom
> >boom car'  audio power amps where this has happened. You don't fix 
> em,
> >you chuck em out.
> 
> FETs actually parallel quite nicely IF you know what you are doing 
> and set 
> up layout correctly.  Layout is critical.  Modern EV controllers 
> parallel 
> FETS extensively.  I've worked on one that used 28 in parallel (no 
> lab 
> matching needed).  Nicely enough if a FET overheats from higher 
> current 
> it's resistance rises pushing current off to it's lower resistance 
> brethren 
> so they tend to share.  You do have to make sure they all turn off 
> and on 
> simultaneously though (layout is critical) and the power paths have 
> to be 
> matched as well (I really should tell you layout is critical).
> 
> Yes and FETs often blow to protect the fuse, although I've seen them 
> blow 
> short and slag heat sinks too.  Although a lot of times the reason 
> they 
> blow due to inductive spikes on turn off rather than current (did I 
> mention 
> layout was critical?)
> 
> Robert
> 
> http://www.aeolusdevelopment.com/
> 
>  From the Divided by a Common Language File (Edited to protect the 
> guilty)
> ME - "I'd like to get Price and delivery for connector Part # XXXXX"
> Dist./Rep - "$X.XX Lead time 37 days"
> ME - "Anything we can do about lead time?  37 days seems a bit 
> high."
> Dist./Rep - "that is the lead time given because our stock is 
> live.... we 
> currently have stock."
> 
> 
> _______________________________________________
> Elec-trak mailing list
> Elec-trak cosmos phy tufts edu
> https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>