On 8/23/2011 12:21 AM, Fuqua, Bill L wrote:
> here is a better link
> http://www.customthermoelectric.com/Water_blocks.html
Wayy too expensive for a decent size. You can make them with just a
drill press and a bit of care. Even multi channel are not that difficult
In a solid state system the heat sink can be at ground potential.
>
> ________________________________________
>
>
> Here you go. If you want really effecient heat transfer use one of these heat
> sinks.
> http://www.customthermoelectric.com/Accessories/images/Water_block_3x3x625_opn_400.jpg
The top is gasketed in place, but the baffles are not sealed to the top
allowing for cross leakage and erosion. That particular one looks like a
poor design compared to the others.
> 73
>
>
>> If you want to look at what would be extreme compared to most
>> electronic applications, just look at a car engine.
> Yes, I have been thinking a lot about car engines. But it's hard to
> translate that to my amplifier! In car engines the thermal power is far
> larger, but also the allowable thermal gradient is far larger, the flow
> rate is far larger, the contact area is far larger, and worst of all, I
> don't really know how much contact area a car engine has! I really would
> need to take apart one, cut open both the block and the cylinder head,
> and measure them!
Even if you could section one it would be very difficult to measure the
surface area for heat exchange.
Plus they are generally nodular iron and the system runs under
pressure.. You can Measure the volume in the
head and block but they are extremely crude compared to the precision of
a cooler for a power FET.
>
> I just looked up values for solders: Common 60/40 solder conducts heat
> about one fifth as well as copper,
This is the reason we use heat transfer compounds like Artic Silver
>
> In a catalog from an aluminium supplier I found some extrusion stock
> that looks much like an Omega sign, but closed. Like a round tube
I'd stick with solid copper with a machined water way and a cover silver
soldered on
rather than one with a removable cover.
> m here?
> That's no issue for me. It would go into a closed container under the
> desk, holding maybe 20 liters of water.
Find for casual operating, but what about contesting.
>
> By simply letting the water in the bucket stay at grid potential too, I
> can easily avoid tripping the ground fault interrupter, but the water
> will be exposed to the full drain-to-drain RF voltage, which will be
> like 140V RMS at full power. I measured the resistivity of my spring
> water, and found that the water in the short hose running from one
> MOSFET group to the other would have a resistance like 200 kiloohms, so
You are looking for ohms per CM^3 or were you just measuring the
resistance between two probes?
It's rare to find tap, well, or spring water with more than a few
hundred ohms per cubic CM.
73
Roger (K8RI)
> in principle that's a non-issue too. But if over time the water
> contaminates with metal ions, that could be bad news! Talk about a
> slowly growing dummy load built into the amp! ;-)
>
> Manfred.
>
>
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