Insulating hardware, esp.washers

[[email protected]]

I've got an electrically and thermally hot TO-220,
that needs mechanically securing to a grounded
heatsink.

Anodizing isolates the TO-220 from the heatsink, but
what do you guys use to isolate the mounting hardware
to prevent it from shorting the device to the sink?
Something that'll maintain the mechanical mating
force, despite long-term operation at >80c?
.----.
|////|
|////|
~ ~
TO-220 ~ ~
split | |////|
washer V |////|
| .-. |////| nut
V | | |////| /
.-. | | |////| .---./
_ | | | | |////| |___| bolt
/ || | | | /
_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./
_| |
.-vvvvvvvvvvvvvvvvvvvvvvvvv'
\_|| | |___|
| | | | |////| | |
'-' / | |////| '---'
/ | |////|
/ | |////|<--.
| | |////| \
| | |////| Heatsink


The split washer maintains compression.

Is there something better than fiber washers / bushings?
Somehow I don't trust nylon heated in compression, esp. over
time. ISTM it will cook, then crumble.

TIA,

James

 

[Lasse Langwadt Christensen]

Den lørdag den 21. december 2013 19.34.12 UTC+1 skrev [email protected]:

I've got an electrically and thermally hot TO-220,

that needs mechanically securing to a grounded

heatsink.



Anodizing isolates the TO-220 from the heatsink, but

what do you guys use to isolate the mounting hardware

to prevent it from shorting the device to the sink?

Something that'll maintain the mechanical mating

force, despite long-term operation at >80c?

.----.

|////|

|////|

~ ~

TO-220 ~ ~

split | |////|

washer V |////|

| .-. |////| nut

V | | |////| /

.-. | | |////| .---./

_ | | | | |////| |___| bolt

/ || | | | /

_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./

_| |

.-vvvvvvvvvvvvvvvvvvvvvvvvv'

\_|| | |___|

| | | | |////| | |

'-' / | |////| '---'

/ | |////|

/ | |////|<--.

| | |////| \

| | |////| Heatsink





The split washer maintains compression.



Is there something better than fiber washers / bushings?

Somehow I don't trust nylon heated in compression, esp. over

time. ISTM it will cook, then crumble.

use a spring clip instead?

either a heatsink that is meant for it or something like this:
http://www.tarapath.com.au/productRange_image/240/3120_3121.jpg


-Lasse

 

[[email protected]]

I've got an electrically and thermally hot TO-220,

that needs mechanically securing to a grounded

heatsink.



Anodizing isolates the TO-220 from the heatsink, but

what do you guys use to isolate the mounting hardware

to prevent it from shorting the device to the sink?

Something that'll maintain the mechanical mating

force, despite long-term operation at >80c?

.----.

|////|

|////|

~ ~

TO-220 ~ ~

split | |////|

washer V |////|

| .-. |////| nut

V | | |////| /

.-. | | |////| .---./

_ | | | | |////| |___| bolt

/ || | | | /

_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./

_| |

.-vvvvvvvvvvvvvvvvvvvvvvvvv'

\_|| | |___|

| | | | |////| | |

'-' / | |////| '---'

/ | |////|

/ | |////|<--.

| | |////| \

| | |////| Heatsink





The split washer maintains compression.



Is there something better than fiber washers / bushings?

Somehow I don't trust nylon heated in compression, esp. over

time. ISTM it will cook, then crumble.



TIA,



James

Nylon 6/6 GF30 (30% glass-fiber reinforced) is really durable.
http://www.plastic-products.com/nylon66.htm

PPS is a good/better alternative, this is more available:
http://www.aavid.com/product-group/accessories/washers

 

[Maynard A. Philbrook Jr.]

I've got an electrically and thermally hot TO-220,
that needs mechanically securing to a grounded
heatsink.

Anodizing isolates the TO-220 from the heatsink, but
what do you guys use to isolate the mounting hardware
to prevent it from shorting the device to the sink?
Something that'll maintain the mechanical mating
force, despite long-term operation at >80c?
.----.
|////|
|////|
~ ~
TO-220 ~ ~
split | |////|
washer V |////|
| .-. |////| nut
V | | |////| /
.-. | | |////| .---./
_ | | | | |////| |___| bolt
/ || | | | /
_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./
_| |
.-vvvvvvvvvvvvvvvvvvvvvvvvv'
\_|| | |___|
| | | | |////| | |
'-' / | |////| '---'
/ | |////|
/ | |////|<--.
| | |////| \
| | |////| Heatsink


The split washer maintains compression.

Is there something better than fiber washers / bushings?
Somehow I don't trust nylon heated in compression, esp. over
time. ISTM it will cook, then crumble.

TIA,

James

I like Mica with a full body clamp or the package sandwiched between
heat sink.
Jamie

 

[Martin Riddle]

I've got an electrically and thermally hot TO-220,
that needs mechanically securing to a grounded
heatsink.

Anodizing isolates the TO-220 from the heatsink, but
what do you guys use to isolate the mounting hardware
to prevent it from shorting the device to the sink?
Something that'll maintain the mechanical mating
force, despite long-term operation at >80c?
.----.
|////|
|////|
~ ~
TO-220 ~ ~
split | |////|
washer V |////|
| .-. |////| nut
V | | |////| /
.-. | | |////| .---./
_ | | | | |////| |___| bolt
/ || | | | /
_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./
_| |
.-vvvvvvvvvvvvvvvvvvvvvvvvv'
\_|| | |___|
| | | | |////| | |
'-' / | |////| '---'
/ | |////|
/ | |////|<--.
| | |////| \
| | |////| Heatsink


The split washer maintains compression.

Is there something better than fiber washers / bushings?
Somehow I don't trust nylon heated in compression, esp. over
time. ISTM it will cook, then crumble.

TIA,

James

Use mica insulators and a bar clamp. You can also get spring clamps
from mouser.

CHeers

 

[Martin Riddle]

What we used in automotive electrical connection applications (such as
mounting alternator regulators) were Belleville (aka Belville)
washers.

...Jim Thompson

Yep, constant spring pressure is the best.
As long as the spring can keep it's K.

Cheers

 

[Maynard A. Philbrook Jr.]

Yep, constant spring pressure is the best.
As long as the spring can keep it's K.

Cheers

Which they usually don't!

Jamie

 

[Martin Riddle]

As long as they don't get too hot... or they get over-torqued... as I
did to them on several occasions :-( (But the boss has to do
something to keep the technicians amused ;-)

...Jim Thompson

Beryllium Copper contacts have good spring tension. Run high current
thru them and they loose their K. In my Tahoe the dash lights used to
blink when it was hot, it turned out to be a bulkhead connector
contact, the main B+ for the instrument cluster. Re bent the one
terminal an all was good. There is some thing about those auto
designers that they never seem to get electrical stuff right.

Cheers

 

[[email protected]]

McMaster Carr sells ceramic shoulder washers for a nickel.

http://www.mcmaster.com/#shoulder-spacers/=pwnu8q

Thanks Phil. Those are nice to know about. Here I'm
chicken ceramic will crack.

The link redirects to a listing of parts. I didn't see
any for a nickel--if this link works, 5 pcs are ~$13.
http://www.mcmaster.com/#shoulder-spacers/=pwtqgg

Cheers,

James Arthur

 

[[email protected]]

Den lørdag den 21. december 2013 19.34.12 UTC+1 skrev [email protected]:




use a spring clip instead?

That's what I'm leaning towards. I'm working on it today, so I'd
hoped for something I could get locally.

Just for this prototype I'm considering using a clamp--I can make that
here, today:


.----.
|////|
clamp |////|
| ~ ~
V ~ ~
.----------.|////|
split | .--------'|////| lock
washer| | |////| washer nut
| | | |////| / /
V | | |////| .-. /
.-. | | |////| | | .---./
_ | | | | |////| | | |___| bolt
/ || | | | | | | | /
_ '-^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^./
_| |
.-vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv'
\_|| | | | .-. | | |___|
| | | | | | |////| | | | |
'-' | | | | |////| | | '---'
| | | | |////| '-'
| | | | |////|
| | __| | |////|
| | / | |////|<--.
| \ | | |////| \
\ \ | | |////| Heatsink
\_| | |

either a heatsink that is meant for it or something like this:

http://www.tarapath.com.au/productRange_image/240/3120_3121.jpg

Nice. Thanks.

Cheers,

James Arthur

 

[[email protected]]

Nylon and FR4 will both cold flow and loosen up the hardware.


A bigger package is better, TO-247 or some such.

This unit was designed to run cool, loaded, as operated by a
sophisticated user (it drives part of a process experiment).
But, the user is proving electronically inexperienced.

Normally it switches 50A (screamingly audible--hearing protection
required) and dissipates a few watts. Unloaded--i.e., under fault conditions--the FETs dissipate the entire input power. So instead
of 3W conduction loss I'll get 150W of avalanche, and probably all
in one device. That's the rub.

I included thermal shutdown, but I didn't expect to actually
need it--the design wasn't meant for this kind of abuse.

TO247s have the screw insulator built-in.

http://sigma.octopart.com/526578/image/International-Rectifier-IRFP4468PBF.jpg


All that needs is a screw and a lockwasher or Belleville to clamp it to an
anodized sink. The bigger footprint is a huge thermal advantage.

For un-repairable stuff, skip the hardware and use epoxy or krazy glue.

There are isolated-silicon TO247 types, which would save anodizing the heat
sink.

Or clamp them down:

https://dl.dropboxusercontent.com/u/53724080/PCBs/Amp.jpg

That looks like the way to go. Easy, and all sorts of advantages...

Cheers,

James Arthur

 

[[email protected]]

I like Mica with a full body clamp or the package sandwiched between
heat sink.

Jamie

Sounds good. A colleague told me woodworking outlets sell 24x24 inch
mica panels, cheap. They use it for decoration.

Cheers,

James Arthur

 

[[email protected]]

Use mica insulators and a bar clamp. You can also get spring clamps
from mouser.

I've seen that, but forgot. Sounds like a good combo.

Thanks,

James

 

[[email protected]]

No... HARD Anodizing creates an electrically insulative layer.
Used to be three levels in the mil spec days.

Yes, hard anodized.

A larger, flat washer to spread force on the bottom,
and *maybe* a thin teflon strip on that side of the sink in the hole
locations. NO lock washer on a surface you do NOT want to make
electrical contact with.

Teflon squeezes out in slow-mo. I like PTFE, but not compressed.

Thanks for the thoughts.

Cheers,

James Arthur

 

[[email protected]]

Nylon 6/6 GF30 (30% glass-fiber reinforced) is really durable.

http://www.plastic-products.com/nylon66.htm



PPS is a good/better alternative, this is more available:

http://www.aavid.com/product-group/accessories/washers

Nice parts. Those would make for an easy retrofit on this
project.

Thanks.

Cheers,

James Arthur

 

[Phil Hobbs]

Thanks Phil. Those are nice to know about. Here I'm
chicken ceramic will crack.

The link redirects to a listing of parts. I didn't see
any for a nickel--if this link works, 5 pcs are ~$13.
http://www.mcmaster.com/#shoulder-spacers/=pwtqgg

Cheers,

James Arthur

Roight, I was looking at the nylon ones. Silly me.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Paul E Bennett]

I've got an electrically and thermally hot TO-220,
that needs mechanically securing to a grounded
heatsink.

Anodizing isolates the TO-220 from the heatsink, but
what do you guys use to isolate the mounting hardware
to prevent it from shorting the device to the sink?
Something that'll maintain the mechanical mating
force, despite long-term operation at >80c?
.----.
|////|
|////|
~ ~
TO-220 ~ ~
split | |////|
washer V |////|
| .-. |////| nut
V | | |////| /
.-. | | |////| .---./
_ | | | | |////| |___| bolt
/ || | | | /
_ '-^^^^^^^^^^^^^^^^^^^^^^^^^./
_| |
.-vvvvvvvvvvvvvvvvvvvvvvvvv'
\_|| | |___|
| | | | |////| | |
'-' / | |////| '---'
/ | |////|
/ | |////|<--.
| | |////| \
| | |////| Heatsink


The split washer maintains compression.

Is there something better than fiber washers / bushings?
Somehow I don't trust nylon heated in compression, esp. over
time. ISTM it will cook, then crumble.

TIA,

James

There are application notes by many of the Semiconductor manufacturers where
they describe mounting arrangements that can be used with their devices.
These include the Mica and Silicone based Insulations washers and insulated
sleeves and collars for the mechanical fixings.

<http://www.onsemi.com/pub_link/Collateral/AN1040-D.PDF>

--
********************************************************************
Paul E. Bennett IEng MIET.....<email://[email protected]>
Forth based HIDECS Consultancy.............<http://www.hidecs.co.uk>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-510979
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************

 

[George Herold]

I've got an electrically and thermally hot TO-220,
that needs mechanically securing to a grounded
heatsink.

Anodizing isolates the TO-220 from the heatsink, but

Is there something better than fiber washers / bushings?
Somehow I don't trust nylon heated in compression, esp. over
time. ISTM it will cook, then crumble.

TIA,

James

Hi James, Nice art work! So are we talking about the washer between the back side nut and the heatsink? (not shown in drawing) How about an anodized aluminum washer? There's a washer company up in Idaho that has all sortsof options. (Do you do any prep to the to-220 surface so it doesn't scratch the anodization*? What about where the screw goes through the hole in the heat sink?)

Re: nylon and crumble at ~80C.. have you seen this? (Does your device run 24/7?) I've used teflon shoulder washers for ~120C heater operation.. and nylon at lower temps.

George H.
*I've had issues with burrs left on a threaded hole punching through sil pads and shorting the to-220. I don't know if the same thing can happen withhard anodization.

 

[[email protected]]

Nice ASCII!

Thanks Michael.

Cheers,

James

 

[[email protected]]

[email protected] wrote:




There are application notes by many of the Semiconductor manufacturers where
they describe mounting arrangements that can be used with their devices.
These include the Mica and Silicone based Insulations washers and insulated
sleeves and collars for the mechanical fixings.



<http://www.onsemi.com/pub_link/Collateral/AN1040-D.PDF>

It's been decades since I read that, and I needed the reminders.
(I hardly do anything that needs heatsinking any more; I'm always
trying to use all the energy and waste none. Heat = waste.)

It's the first published reference I've seen that recommends anodize
on Al (as I'm doing here) as electrical isolation for low-voltage
circuits.

I also had mistaken "wavy" washers for Bellville--that was good
to learn too.

Thanks.

James Arthur