On Fri, 30 Aug 2002, Dale Botkin wrote:

>On Fri, 30 Aug 2002, Dave Dilatush wrote:
>
>> Dale wrote...
>>
>> >Yeah...  Dave like MOSFETs.  8-)  'Course he's right too.  My yard lights
>> >tell me so every night.
>>
>> Did you get those low on-resistance MOSFETs yet to cure the heat
>> problem?  IIRC, your original pair were getting hotter'n a
>> two-dollar pistol, and the replacements were expected to run
>> lukewarm.  Do they?
>
>More or less.  More than lukewarm, but not plastic-melting hot either.
>IRLZ34's are kinda toasty but manageable with about 8-9A of current.  The
>next rev board will have provisions for two pair and heat sinks (which I'm
>using now, but little bitty ones).  It's been running a couple of months
>now without any drama.

As I said in a previous posting, you can down the heating and use tiny
devices (even SMD) by putting many (not two) in parallel. For one offs
like yours, this is very easy. Order 10 fets and connect them 5+5 in
parallel. You can use TO220 cases with vertical mount (not laying down) so
they align. The dissipation goes way down very fast. P=I^2*R as you know,
25 times in the case of 5+5. For example there are RC power controllers
that can handle 300A at 7.5V with microminimal losses. They have 15 or
more SMD fets mounted w/o heatsink ... board and wire self heating are
more of a problem at these currents.

Peter

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