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CMB-16 enclosure question


Tim Fischer
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Hi all,

I'm just about ready to start my CMB-16 enclosure. Looks like I'm back to a "storage container" for this one, since I wasn't able to locate a cheap 'real' enclosure that would fit a ATX power supply and the board (I didn't want to disassemble the ATX supply for safety reasons).

Anyway, my question: The supply is rated at 14A at 12V. My max load would be around 2A, and usually lower.

Will I be ok to seal the supply and the CMB-16 in an enclosure, or will it require outside ventillation? I'm pretty sure the CMB itself will be fine, but I'm more concerned about the power supply, which is used to having the fan pointing out the back of a PC. But it shouldn't get hot with my load levels, should it?

I'll want to allow for future expansion, but I'm sure I'd never approach 14A on this...

Thanks,
-Tim

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From the lack of responses after 25 views, I'm guessing the answer so far is "I have no idea"? :)

My gut feel tells me that making it fully enclosed shouldn't be a problem. Unless someone wants to jump in and tell me I definitely need ventilation, I think I'll build it enclosed, but in such a way that ventilation can be added. Then I'll monitor temps for awhile in controlled conditions to see if it's getting warm inside...

-Tim

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Richard Hamilton

Tim Fischer wrote:

Hi all,

I'm just about ready to start my CMB-16 enclosure. Looks like I'm back to a "storage container" for this one, since I wasn't able to locate a cheap 'real' enclosure that would fit a ATX power supply and the board (I didn't want to disassemble the ATX supply for safety reasons).

Anyway, my question: The supply is rated at 14A at 12V. My max load would be around 2A, and usually lower.

Will I be ok to seal the supply and the CMB-16 in an enclosure, or will it require outside ventillation? I'm pretty sure the CMB itself will be fine, but I'm more concerned about the power supply, which is used to having the fan pointing out the back of a PC. But it shouldn't get hot with my load levels, should it?

I'll want to allow for future expansion, but I'm sure I'd never approach 14A on this...

Thanks,
-Tim



Hi Tim,

It is probably just the weekend that has people busy.
Good idea not to diaassemble the ATX supply.
If it were my project, I would not seal the enclosure even if there were practically no load. One issue can be condensation. When you use the word "seal", I am probably falsely assuming you mean an air tight enclosure.

The potential issue I am thinking about is condensation. As it warms and cools through use, there could be some moisture build up. Even a small amount of ventilation will eliminate most buildups. You probably noticed that even though the LOR prebuilt units are nice tough covered metal, there is still the ability to have some small air circulation though the bottom hole and tiny cracks around the cover.

Aside from moisture, you mention your max load is 2Amps ar 12Volts. That is still 48 watts, and the heat can build up quickly unless there is a way to bleed off the heat through metal or air.

Bottom line, I would suggest finding some way to keep the heat from building up.
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Tim

Even at a small load the power supply will produce heat. You are going to want to vent the heat. (plug a wall wart in and do not connect a load - the transformer still heats up and power is consumed)

On a side note - have you tried your ATX power supply? As I recall the ATX required a MB to be connected to switch from a high power state, no power state and a sleep state. The AT supplies didnt care, they had the switch on the front to turn off the PS

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Thanks for the replies.

I didn't mean "airtight", just "as watertight as practical". Condensation is really not an issue here in Minnesota in December -- we rarely warm up above freezing, and are often much, much colder. If I understand correctly, the people who suffer most from condensation are places where it warms up above freezing for a few hours during the day, then dips down below it at night... (or maybe I should replace "freezing" with "the dew point...)

The box wouldn't be any more "sealed" than, say, a CTB-16PC enclosure... I was wondering if I should vent it even more (e.g. cut the whole bottom out of my enclosure). The problem with doing that is that if we get very dry, powdery snow, it likes to find it's way into the darndest places -- including into an otherwise raintight enclosure with significant bottom openings...

Anyway, I'll run some tests to see how hot things get. I appreciate your thoughts.

-Tim

P.S. Regarding the ATX power supply -- yes I've tried it and it works great. You need to jumper the green wire to any black wire to make the power supply turn on. Then yellow and black together will give you 12V (yellow being +). All other colors can be disregarded and capped...

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Tim,

How big is the enclosure and what material? (how much surface area is the real question).... The fan running on the power supply will allow air circulation and get the heat out to the surface of the enclosure. So even if it is not a great conductor of heat, you will still move heat through it.

You may even be better off because many switching power supplies are not rated below 32 degrees so it may be good for it to keep running and stay a little warm.

Dan

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LightORamaDan wrote:

You may even be better off because many switching power supplies are not rated below 32 degrees so it may be good for it to keep running and stay a little warm.




Interesting point. I'm now going to have to run a test -- stick the ATX power supply in the deep-freeze, then run cold and see what happens ;). Better to find out now vs. when I first bring stuff outside!

Not sure of the size of the enclosure yet -- I bought one yesterday and decided it was way too big. I bought a second one today, and to my chagrin, I found out the dimensions they listed were exterior and greatly inflated, so the power supply won't fit :D so it's too small. So the search continues... It will be made of plastic, unless I find something better in the meantime...

-Tim
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Richard Hamilton

Tim Fischer wrote:

Condensation is really not an issue here in Minnesota in December -- we rarely warm up above freezing, and are often much, much colder. If I understand correctly, the people who suffer most from condensation are places where it warms up above freezing for a few hours during the day, then dips down below it at night... (or maybe I should replace "freezing" with "the dew point...)

Uh well, I would think that condensation would be a problem there. It isn't just the fact that the outside air temperature stays constantly cold. It's the fact that the box internal temperature does change a lot in your location. It warms up during your equipment operation and then cools down again until you use it the next night.
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Richard Hamilton wrote:

Tim Fischer wrote:
Condensation is really not an issue here in Minnesota in December -- we rarely warm up above freezing, and are often much, much colder. If I understand correctly, the people who suffer most from condensation are places where it warms up above freezing for a few hours during the day, then dips down below it at night... (or maybe I should replace "freezing" with "the dew point...)

Uh well, I would think that condensation would be a problem there. It isn't just the fact that the outside air temperature stays constantly cold. It's the fact that the box internal temperature does change a lot in your location. It warms up during your equipment operation and then cools down again until you use it the next night.


In any case, I haven't noticed any issues. I don't load most of my channels up beyond a few strings of minis, though...

-Tim
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