This is really a fascinating idea. I have noticed that there are water
cooling kits made for computer CPU's. Some of the bigger CPU's run over
225 watts of power. I wonder how applicable one those CPU kits might
be. They include a heat sink, pump and radiator.
73, Doug -- K0DXV
On 12/16/2014 11:10 AM, David Cutter wrote:
Hi Dick
Start from the LDMOS data sheet and work out the temperature you wish
to keep within at the junction. Because water cooling is so good, you
can choose either to run the device cooler than you would with air
cooling to improve reliability, or stick to the same temperature and
get more power / use a smaller cooling plate / use less water. There's
a direct relationship between reliability and temperature, but it's
not linear. Then use the temperature rise per W rating of the device
to get to the surface temperature.
In work I did >10 years ago all devices were directly bolted to the
liquid-cooled plate without an intermediate spreader, however, these
LDMOS devices are so small (ie very high heat density) there is a good
reason to spread the heat out first before cooling proper takes place,
I'm somewhat hazy what thickness, but you must achieve good flatness
of contact against the plate. Some very large devices eg IGBTs and
rectifiers the size of your open hand are supplied curved and the
bolting-down process achieves the flatness with the correct torque
setting on the bolts.
Then you do the same sums as you do with air cooling ie temperature
rise v watts dissipated from the heat sink data.
Say you want to dissipate 1kW of heat continuously (eg in a data
contest) then a small 2 pass model would give you around 90 to 100K
rise at the surface of the plate with 1 US gallon per minute, whereas
a 4 pass model would give you around 20K rise on a 152mm length plate.
This of course assumes that the heat is being delivered into the plate
evenly over the whole surface, ie using a spreader. Heat sink paste
adds a little to the thermal gradient and is needed in very small
amounts, evenly spread.
Do the sums several times with different criteria until you get to the
one you feel comfortable with. If you live in a cold climate you can
dump the heat into a small central heating radiator to keep the shack
warm and no fans required just an aquarian pump to run it; if you live
in a hot place, then put the radiator on the shade side of the house
or even bury it. If water is abundant, eg river water or a pond, you
can re-cycle it back to the source.
You can make your own water cooling plate, see here a small example
cooling a dozen TO-220 devices:
https://www.youtube.com/watch?v=WGpau-raMho
Somebody here will check my sums I'm sure.
73
David
G3UNA
----- Original Message ----- From: "Richard Solomon"
<w1...@earthlink.net>
To: <elecraft@mailman.qth.net>
Sent: Tuesday, December 16, 2014 4:44 PM
Subject: Re: [Elecraft] LDMOS for QRO [OT]
If one wanted to use one of these to cool an LDMOS VHF KW, where would
one find the design info to calculate which cold plate would provide
sufficient
cooling ?
I envision a stack something like this:
LDMOS PC Board
Copper Heatsink (thickness need be determined)
Cold Plate
Aluminum Heat Sink (is this really necessary ?).
73 es HH, Dick, W1KSZ
On 12/14/2014 4:32 PM, David Cutter wrote:
I'm a little surprised that folks in this group haven't suggested
liquid cooling for this modest application. Semiconductor cold
plates have been around for a long time, are economical to use and
in my view a much better solution than forced air cooling. They are
compact, quiet, require far less cabinet space, keep junctions
cooler and more stable than air could ever and enable higher
reliability.
Look at Aavid for instance, whose devices I used on many occasions:
http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf
If you play your cards right, you can cool the amplifier and the
power supply on a short 4-pass plate. Put the heat somewhere
convenient, not in your shack.
73
David
G3UNA
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to k0...@aol.com
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:Elecraft@mailman.qth.net
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to arch...@mail-archive.com
