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#6 screw as heatsink

M

mkr5000

Jan 1, 1970
0
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.

Stays in place well and doesn't shift either like the press on types
at a sub-penny price. Of course, you need to have the room for the
screw to protrude.

Anyone else do this?
 
J

John Popelish

Jan 1, 1970
0
mkr5000 said:
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.
(snip)

You should have a quantitative idea of how much additional
power this bolt gets rid of, by doing some testing. I guess
the 1/2 inch long one adds a quarter watt of capability and
the 1 inch one adds a little more than a half watt, at
maximum allowable temperature. Not much help for that much
ugly. And not better than the watt or so capability of
small clip on heat sinks.

A TO-220 on no heat sink, at right angles to the board gets
rid of about 2 watts if it is 100C above ambient, but
something like 40 watts if it is mounted om a huge heat
sink. So, I think your bolt idea is incrementally helpful.

http://www.linear.com/designtools/packaging/therresist.pdf

My favorite trick, like this, for axial lead diodes, is to
solder a small loop in the lead, before soldering it into a
board, giving it Mickey Mouse ears. Also incremental, but
there is no real good alternative for heat sinking axial
leaded parts, except for soldering them between copper planes.
 
E

Eeyore

Jan 1, 1970
0
mkr5000 said:
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.

It does nothing of the sort.

Graham
 
M

mkr5000

Jan 1, 1970
0
Well...not that much being spent in the LM317 anyway but rather than
hot to the touch in 3 seconds it's at least continually "touchable".

I know the 317 can run damn hot, but every "little bit" helps I
suppose....I've seen these used with no heat sink in professional
designs and they're hot as toasters.

Can't bring myself to do that.
 
J

John Larkin

Jan 1, 1970
0
Well...not that much being spent in the LM317 anyway but rather than
hot to the touch in 3 seconds it's at least continually "touchable".

I know the 317 can run damn hot, but every "little bit" helps I
suppose....I've seen these used with no heat sink in professional
designs and they're hot as toasters.

Can't bring myself to do that.


My "continuous touch" threshold for a metallic surface is about 52C.

The bolt helps some. Bolting a fender washer to the can helps more;
may as well use a long bolt for max effect. The added mass is a bad
idea in a vibration environment.

Incidentally, a 6-32 ss machine screw has a thermal resistance of
roughly 100K/W per inch. So if you use a long one, use two nuts and
jam the screw so that it pokes out equal distances from the TO-220 on
both sides. Or use brass, about 1/5 the theta.

John
 
S

sycochkn

Jan 1, 1970
0
mkr5000 said:
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.

Stays in place well and doesn't shift either like the press on types
at a sub-penny price. Of course, you need to have the room for the
screw to protrude.

Anyone else do this?

I used to use the transistor as a mounting point for the board and use a
spacer and place the heat sink side of the transistor touching the chassis
with and insulator if needed.

Bob
 
M

mkr5000

Jan 1, 1970
0
I like the fender washer idea.

There available in a zillion sizes and CHEAP.
 
M

MooseFET

Jan 1, 1970
0
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.

Stays in place well and doesn't shift either like the press on types
at a sub-penny price. Of course, you need to have the room for the
screw to protrude.

Anyone else do this?


I use threaded spacers as heatsinks fairly often. It is the same idea
but lighter for how much heat it can carry way. If you put the screw
in from below the PCB, it will works as the holding nut and the
heatsink too.
 
M

MooseFET

Jan 1, 1970
0
My favorite trick, like this, for axial lead diodes, is to
solder a small loop in the lead, before soldering it into a
board, giving it Mickey Mouse ears. Also incremental, but
there is no real good alternative for heat sinking axial
leaded parts, except for soldering them between copper planes.

You can solder brass washers onto their legs.

You can stand them up and solder them to a brass object of some kind.

You can put them on the back of the PCB and press them down onto
Gappad
 
M

MooseFET

Jan 1, 1970
0
My "continuous touch" threshold for a metallic surface is about 52C.

The bolt helps some. Bolting a fender washer to the can helps more;
may as well use a long bolt for max effect. The added mass is a bad
idea in a vibration environment.

Incidentally, a 6-32 ss machine screw has a thermal resistance of
roughly 100K/W per inch. So if you use a long one, use two nuts and
jam the screw so that it pokes out equal distances from the TO-220 on
both sides. Or use brass, about 1/5 the theta.

Aluminum is a lot lighter and thus less of a vibration problem.
 
E

Eeyore

Jan 1, 1970
0
mkr5000 said:
Well...not that much being spent in the LM317 anyway but rather than
hot to the touch in 3 seconds it's at least continually "touchable".

I know the 317 can run damn hot, but every "little bit" helps I
suppose....I've seen these used with no heat sink in professional
designs and they're hot as toasters.

Can't bring myself to do that.

I suggest you learn some stuff about thermal mangement.

'Damn hot' is a pretty flaky way to spec anything. You'll find that
Tj(max) is speciifed on the data sheet.

Graham
 
J

John Popelish

Jan 1, 1970
0
MooseFET said:
You can solder brass washers onto their legs.

You can stand them up and solder them to a brass object of some kind.

You can put them on the back of the PCB and press them down onto
Gappad

Somewhere I saw a board that had long slots routed for the
diodes (generous air space on each side of the cylinder),
with the rather long leads soldered onto large copper pours
(maybe a square inch, each).

I guess you can get something like 6 amps average from a
large axial silicon diode that way, without mounting a heat
sink. Cheap, but it eats board area.
 
T

Tim Williams

Jan 1, 1970
0
John Larkin said:
My "continuous touch" threshold for a metallic surface is about 52C.

Yeah, somewhere around 50-60C is where the "ten second rule" passes/fails.
If you can't hold your finger on it for more than ten seconds, it's too
hot.

The disappointing thing about fingers is, they take a lot of energy to heat
up, being mostly water, and "measuring" the temperature of a lone TO-220 --
or even TO-92 -- is just about impossible to get an accurate value on.
When you touch it, it's hot, but you can't feel it. By the time you can
feel it, it's already near body temperature.

How much can fingers dissipate, anyway?: I've held my 30W soldering iron in
the palm of my hand for a minute (obviously from a cold start!), keeping it
hot but not burning. Let go of it for ten seconds and it gets too hot to
touch.

Tim
 
M

mpm

Jan 1, 1970
0
It does nothing of the sort.

Graham

I agree. A 6-32 screw and nut on the other hand will get you
marginally more.
However, for the price of an Avid Thermalloy 7136D, you can't go
wrong...

-mpm
 
J

JosephKK

Jan 1, 1970
0
Aluminum is a lot lighter and thus less of a vibration problem.

Yes and no. Brass and bronze are a lot stronger against thread pull
out. And not that big of cost in Theta.
 
M

MooseFET

Jan 1, 1970
0
Yes and no. Brass and bronze are a lot stronger against thread pull
out. And not that big of cost in Theta.


I think it breaks in favor of aluminum when you do like this:

Attempted ASCII art:


-----
! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

I have used this basic design quite a few times. The lower weight of
the aluminum, in this case, I think dominates the vibration question.

Using the power of copy and paste, I will now show case with the big
washer:

( ) <- Second bolt
! ! <- Split lock not shown
====================== <- big washer (www.bokers.com)
-----

! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

In this case, it is likely that brass wins.
 
J

JosephKK

Jan 1, 1970
0
I think it breaks in favor of aluminum when you do like this:

Attempted ASCII art:


-----
! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

I have used this basic design quite a few times. The lower weight of
the aluminum, in this case, I think dominates the vibration question.

Using the power of copy and paste, I will now show case with the big
washer:

( ) <- Second bolt
! ! <- Split lock not shown
====================== <- big washer (www.bokers.com)
-----

! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

In this case, it is likely that brass wins.

If something is working for you go for it. I just wanted to keep it
clear that there are choices and alternatives and tradeoffs.
 
G

GregS

Jan 1, 1970
0
Just sharing....

You know the little hole in a TO220 tab?

Just a 1/2" to 1" machine screw with nut tightened to it does a very
respectable job of sinking heat.

Stays in place well and doesn't shift either like the press on types
at a sub-penny price. Of course, you need to have the room for the
screw to protrude.

Anyone else do this?

I would also attach a thin piece of aluminum I cut to whatever heat
dissipation is needed. If its flat on a board, I would try a brass screw.

greg
 
M

MooseFET

Jan 1, 1970
0
If something is working for you go for it. I just wanted to keep it
clear that there are choices and alternatives and tradeoffs.

Agreed. There are people reading along who are just starting out. I
hope this conversation has helped some of them to see the options and
issues.
 
J

John Larkin

Jan 1, 1970
0
I think it breaks in favor of aluminum when you do like this:

Attempted ASCII art:


-----
! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

I have used this basic design quite a few times. The lower weight of
the aluminum, in this case, I think dominates the vibration question.

Using the power of copy and paste, I will now show case with the big
washer:

( ) <- Second bolt
! ! <- Split lock not shown
====================== <- big washer (www.bokers.com)
-----

! !
! ! <- Threaded spacer
------ ! !
---! ! ! !
! =================== <- TO220 tab
--- ! -----------------------
--- ! ----------------------- <- PCB
! ! <- Split lock not shown
(___) <- Bolt head

In this case, it is likely that brass wins.

Don't skimp on the lockwasher. The FR-4 will cold-flow in these
situations.

John
 
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