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Old 11th February 2012, 12:16 AM   #1
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Default 800W Load - Rackmount

I bolted everything to the underside of a slide out shelf...
When not in use, slides fully into the rack, dissapears, and
becomes a normal shelf. But havn't wired anything yet.

The front is organized for series & parallel bus wires to go
through the posts sideways. The hole in the side of each
binding post is the same size as the hole in front.

So, anyways: This is Qty8 of 4ohm 1% non-inductive 100W.
Lead times and prices on >100W were unreasonable, so we
settled for several 100W that can be reconfigured as needed.
These Dales came from Newark.

I used bolts that would normally be countersunk, such that
the top shelf surface is still reasonably flat and unobstructed.
Attached Images
File Type: jpg Load.jpg (232.3 KB, 125 views)

Last edited by kenpeter; 11th February 2012 at 12:26 AM.
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Old 11th February 2012, 12:32 AM   #2
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Nice work.
I think such resistors expect some surface heat transfer to make full wattage. Don't know if they will do full spec with just freeair dissipation. A bit of heat sink compound between resistor and chassis will definately help. Just a thought. Also, if you are going to opperate in flip up attitude, a small plastic or sheet metal tent over each resistor will help promote chimney effect free air cooling.
Doc
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Last edited by thaumaturge; 11th February 2012 at 12:35 AM.
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Old 11th February 2012, 01:06 AM   #3
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I'm surprised you didn't bolt them to an aluminum heat-sink with a fan on it.
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Old 11th February 2012, 02:02 AM   #4
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Indeed resistors like that can dissipate much more power on heats-inks.
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Old 11th February 2012, 02:17 AM   #5
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The shelf is plenty big enough for a box fan when deployed
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Old 11th February 2012, 02:31 AM   #6
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A resistor load is fine for testing.

I would always also test using speakers as they are a more inductive and capacitive load and can cause an amplifier to oscillate.
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Old 11th February 2012, 02:54 AM   #7
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Quote:
Originally Posted by kenpeter View Post
The shelf is plenty big enough for a box fan when deployed
As I said first in my comments: Nice work!
Doc
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Old 11th February 2012, 02:56 AM   #8
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Quote:
Originally Posted by nigelwright7557 View Post
A resistor load is fine for testing.

I would always also test using speakers as they are a more inductive and capacitive load and can cause an amplifier to oscillate.
When I have a procedure to follow that calls
specifically for measurements with resistors,
resistors have to be used.

I opted for non-inductive resistors at extra
cost, cause you can always add inductance.
But darn hard to make it go away.

We have speakers too.

Last edited by kenpeter; 11th February 2012 at 03:12 AM.
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Old 11th February 2012, 03:11 AM   #9
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I suppose it depends. I have some high power resistors like that bolted to a large heat-sink and on sustained high power tests the sink gets really hot. I am sure that you could easily increase the total sustained dissipation capability by using a better method for cooling, but whether or not this is needed is another matter entirely.
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Old 11th February 2012, 03:23 AM   #10
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If it needs more of anything, it will get more.
For now, this is probably slight overkill.

Don't go over-imagining that I would use this
at full power 24x7. Its for production testing,
not solid weeks of burn-in or characterization.
Our customers have their own labs for that.

If you are building a load for sustained use,
those considerations are probably relevant.

Last edited by kenpeter; 11th February 2012 at 03:40 AM.
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