Power air venting

[mmcl26554]

I am preparing a location for my 722K in my motor home. I am placing it in a small cabinet which is close to the ceiling. The cabinet has no air vents so I will install two 3" vents one will have a 2" muffin fan (off an old computer CPU) which operates on 5 volts I will get from the rear USB port on the 722K. I also am constructing a "Window comparator" which will energize the fan based on the the temperature settings I program into it. Now I have 2 questions:
1. Should I position the fan to push air out or suck air in or doesn't it really matter.
2. What would be the best on and off temperature settings?

Anybody have any experience with these two issues?
Michael

 

[boba]

I am preparing a location for my 722K in my motor home. I am placing it in a small cabinet which is close to the ceiling. The cabinet has no air vents so I will install two 3" vents one will have a 2" muffin fan (off an old computer CPU) which operates on 5 volts I will get from the rear USB port on the 722K. I also am constructing a "Window comparator" which will energize the fan based on the the temperature settings I program into it. Now I have 2 questions:
1. Should I position the fan to push air out or suck air in or doesn't it really matter.
2. What would be the best on and off temperature settings?

Anybody have any experience with these two issues?
Michael

Does the CFM change if its pushing or sucking?

 

[mmcl26554]

No, because it has to do with which way I mount the fan. From the viewpoint of the fan it always moving air the same direction.
Michael

 

[boba]

No, because it has to do with which way I mount the fan. From the viewpoint of the fan it always moving air the same direction.
Michael

Stop and think if the CUBIC FEET per MINUTE dosen't change does it make a difference?

 

[mmcl26554]

I would think it wouldn't make any difference but since I have the option I just wanted to confirm I am correct.
Michael

 

[Jim5506]

I would run that fan all the time the 722 is running and arrange it to pull air out of the left side of the 722, simply swapping out the ambient air around the receiver may not be adequate.

 

[mmcl26554]

My goal is not to provide increased cooling for the 722 but to make sure the environment inside the cabinet is the same as outside. So that the 722 does not run hotter just because it is inside a cabinet. I suppose I could use an additional thermistor on the outside of the cabinet to adjust the window of the comparator up or down so if it is warmer inside the cabinet it will turn the fan on and off if it isn't.
Michael

 

[upsss]

I am preparing a location for my 722K in my motor home. I am placing it in a small cabinet which is close to the ceiling. The cabinet has no air vents so I will install two 3" vents one will have a 2" muffin fan (off an old computer CPU) which operates on 5 volts I will get from the rear USB port on the 722K. I also am constructing a "Window comparator" which will energize the fan based on the the temperature settings I program into it. Now I have 2 questions:
1. Should I position the fan to push air out or suck air in or doesn't it really matter.
2. What would be the best on and off temperature settings?

Anybody have any experience with these two issues?
Michael

The air intake on the 722 is at the front right side and it exhaust hot air on the left rear side. You definitely want to suck the air out of your cabinet on the left side and have an intake vent on the right side of the cabinet. I would not bother with any comparators and fan temperature settings. A 2" fan running continuously will provide you with marginally safe air flow in an enclosed cabinet. Your mission is to keep the receiver HD "High" temperature below 136°. Keep in mind, the receiver consumes almost the same power whether it is On or Off and any changes in the receiver temperature would take up to 2 weeks to register correctly.

 

[mmcl26554]

What might be interesting is to incorporate a Peltier Junction in the in air flow and refrigerate the incoming air. I will also include a switch in the electrical supply because I want to shut it down when on the road or any other time when not in use for a while. No electricity, no heat!
Michael

 

[upsss]

As an EE I am very familiar with Peltier coolers and their applications. I don't think that would be very practical in your situation. Peltier coolers are typically used for spot or limited surface cooling. Remember, to cool one side of the junction you have to heat the opposite side. Since their efficiency is not that good, you would end up generating and have to deal even with more heat.

As far as turning the power to the receiver, that is a good idea if you don't mind waiting a few minutes every time you want to watch TV. You will be saving heat and electricity and all you need is a switched power strip.

 

[mmcl26554]

Since Day one (12 years ago) of my time with dish, there receivers have all crashed and needed to be disconnected from power to reboot, I have made switched outlets so it is easy to disconnect the power. Dish forgot to install a "hard on/off" switch in the mains line. Now, every piece of electronic equipment I have suffer this same disease (program crash) and must be rebooted but none have a "hard on/off" mains switch. So my population of switched outlets has grown. I once built a switch system which used 5 volt relays to control a bank of outlets, the switches were all located on a panel one for each pair of outlets. It also had a circuit which monitored 2 phone lines and would switch on the system when a call came in. The computer would boot to DOS and receive the fax. Today's operating systems take to long to boot so that doesn't work any more, but I still use the switch panel to control the individual outlets. I've been thinking about building a low power switch panel for my entertainment center to easily shut off power to any device to reboot it. Dish did put a "restart" button on the front panel of my 722k, but why didn't they just put an of/off switch?
Michael

 

[upsss]

Dish and most other consumer electronics manufacturers didn't "forget" to include a real power on/off switch. They simply don't want to add 50¢ extra to their cost if they can get away with it. Hell, if they can save 2¢ on every piece of equipment they manufacture, they will do it!

 

[mmcl26554]

Remember the old slogan from an electronics manufacturer: "we put the quality in before the name goes on". Now it could read: "we put our name on any old piece of junk and hope the consumer won't notice". Quality is but a memory for those of us who are old enough to remember.
Michael

 

[Centex]

You might also consider making it an exhaust fan and putting in some way to draw air in. For our home cabinet, we put an exhaust fan to pull air through, and them put small rubber stoppers to hold the doors slightly open (maybe 1/4 to 3/8 of an inch) that way new air gets pulled into the enclosure.

 

[Jim5506]

Actually having an "OFF" switch would cause these units to take up to 5 minutes before they display a signal - not many consumers would put up with that - DirecTV, TiVo and Dish DVR's all have similar behavior.
The Unit MUST remain in stand by for it to be able to conduct some of the operations that it does while not in use, like softwareupdates, guide updates and execution of timers.

 

[mmcl26554]

Jim,
I understand what you say about the long on time, but often you must disconnect the power to get the receiver to work properly again. Getting to the cord plugged into an outlet is often difficult, or at least not as easy as throwing a switch. I would have them mount the switch on the back or inside a compartment with an easily accessible lid. Also should you want to you could also the thing off such as during an electrical storm or when on vacation or just to save power.
Michael