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G90 front fan airflow measurements

 
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Apfelmousse




Joined: 26 Apr 2014
Posts: 74
Location: Germany


PostLink    Posted: Fri Mar 30, 2018 10:33 am    Post subject: G90 front fan airflow measurements Reply with quote


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Hi all,

before lifting my G90 to the ceiling I decided to examine the front fan. Its the noisiest part of the G90.

Today I unmounted the fan and tested in on my bench. First thing I noticed was quite some dirt around the fan and on the fan itself, although the boards are very clean. I recall the beamer had 1200 hours on total, but only 70 hours on the tubes. Perhaps there has been a swap of parts at 1100 hours.

Concerning the front fan itself, I got the specifications from another thread and noticed it was an "S" type. So the signal line (the 3rd wire) does not carry a speed signal, but a "fan locked" signal. Thats why some people reported problems with the SilenX fans as these do only carry a speed signal. The stock fan has a low signal only when the fan is running. Other fans have high/low signals depending on fan position, so when they get locked theres a 50% chance the projector will continue to operate.

I also noticed the fan is mounted in the metal enclosure without any cushioning. There seems to be room for improvement.

I made some airflow and temperature measurements, see this thread:
http://www.curtpalme.com/forum/viewtopic.php?t=40833
The speed of the airflow is very low, even with the grille and metal cover off. You can barely feel anything with your hand. Nevertheless the temperatures on the board are very reasonable, maxing around 50°C for 25° room temperature.

I want to find out what happens with the airflow if I just omit the front fan and rely on the suction from the main fans.

QUESTION to the experts: can I let the G90 run with the front board and the front fan removed, so I can take airflow measurements? Will the projector immediately go in error mode and remain in standby? I could connect the front fan and leave it outside the projector for measuring purposes. Otherwise I would try to run the main fans off an external power supply...

Thanks!
Martin



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Apfelmousse




Joined: 26 Apr 2014
Posts: 74
Location: Germany


PostLink    Posted: Fri Mar 30, 2018 3:08 pm    Post subject: Reply with quote

Here are some pics of the front fan.

- still mounted in the cabinet (you can see the dirt below the fan)
- unmounted (with modell number ...S)
- the remaining (small!!) hole

What I found out so far:

- the fan, mounted in a cardboard funnel of 15x15cm and 50cm long produced 0,3-0,4 m/s at the end, running with 12V.

- the hole the fan is pushing the air through is RIDICULOUS! Some 40% of the fan is working against a surface! And behind the hole are cables in all directions. Not good for the airflow, neither for the acoustics.

- when holding the running fan between fingers it has a distinct whining noise and it vibrates a lot!

cheers
Martin



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Apfelmousse




Joined: 26 Apr 2014
Posts: 74
Location: Germany


PostLink    Posted: Fri Mar 30, 2018 7:05 pm    Post subject: Reply with quote

Meanwhile I made my experiments with the main fans running off a regulated power supply. The G90 was totally disconnected from the mains.

The measurements from the other thread mentioned above gave the following readings:

At startup:
Front: 0,2-0,3 m/s @ 24°C
Back: 1,5-2,0 m/s @ 24°C

After 90 minutes watching a movie:
Front: 0,2-0,3 m/s @ 26°C
Back: 1,8-2,3 m/s @ 35-40°C

I adjusted the power supply to geht the same airflow at the back as in the above measure. That gave me:
10,4 Volt corresponding to startup
11,0 Volt corresponding to warmed up state

The stunning result is the airflow at front, with the front fan totally removed, the boards put back in and the metal cover put back:
with 10,4 Volt: 0,3-0,4 m/s
with 11,0 Volt: around 0,5 m/s

So the front fan not only adds a lot of noise, it also seems to hinder the airflow more than it helps!!

Sounds crazy. What do you think?

cheers
Martin
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winny




Joined: 09 Oct 2013
Posts: 403
Location: Sweden

TV/Projector: BD808s, BG1209/2


PostLink    Posted: Sat Mar 31, 2018 8:16 pm    Post subject: Reply with quote

Cooling work done/time unit is equal to flow rate * pressure, but assuming the geometry stayed the same for the airflow, your pressure should stay linear with airflow before and after modification. If you want to go into deeper details, you need an differential pressure guage or meter.
_________________
Melifluonze wrote:
Digital is easy. This is torture, but far more interesting...
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Apfelmousse




Joined: 26 Apr 2014
Posts: 74
Location: Germany


PostLink    Posted: Sun Apr 01, 2018 7:06 am    Post subject: Reply with quote

winny wrote:
Cooling work done/time unit is equal to flow rate * pressure...


You mean when there is more pressure with the same flow rate, there is more (denser) air for cooling, thus having a better cooling effect.

I see.

When looking at the the G90: the measure I took was in front of the fan, on the suction side. Without being able to do the calculations nor measurements, I guess a 0,5m/s airflow does not require a significant difference in pressure (significant in terms of increase or decrease of cooling capacity of a given quantitiy of air).

If this is the case, and if I measure the same intake velocity of the airflow on the front side of the beamer, with and without the front fan, doesn't that mean that the cooling capacity of that airflow should be roughly identical?

I had a closer look at the fan opening. There's another obstacle on the top side (see the pictures) just behind the enclosure, giving roughly 60% of the surface of the fan that is working directly against a surface!! When I leave the fan out the surface for the airflow through the hole increases since the fan itself can only passes air around its motor, and this motor sits right in the middle of the remaining opening. I estimate the surface available for airflow being at least 100% larger once the fan is out! BTW, there are openings for cables that can be seen on the upper right and left of the enclosure, where air could be sucked back in (back to the fan), further diminishing the fans efficiency.

I might be tempted to run the beamer without the fan and monitor the components with my IR-camera. The board looks quite fierce, power dissipation wise, with its large radiator. On the other hand, 50°C with such a low airflow does not look like theres really that much power to dissipate. Perhaps it depends on the settings (line frequency)? I had it running with 1080p@60Hz, piece of cake for the G90.

cheers
Martin
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winny




Joined: 09 Oct 2013
Posts: 403
Location: Sweden

TV/Projector: BD808s, BG1209/2


PostLink    Posted: Sun Apr 01, 2018 5:14 pm    Post subject: Reply with quote

Sorry, I have had one beer too many when I wrote that. Cooling power is air flow rate * temperature difference * k (a constant for air). Fan output power is air flow rate * pressure.

If you take a look at a desktop PC or big server, you will find that the designers try to maximize this by increasing the counterpresssure and choosing the pitch of the fan blades accordingly. In a very open design as a CRT projector, this might not be an option but they where designed in the 90’s and early 2000 when computer simulation of air movement wasn’t possible or economically feasible.

If you do manage to get IR imaging and really want to walk the mile here, you will most likley benefit from trying to increase the counter pressure using air guides to force the air to only go over the hot components and close off open areas with low pressure zones.

_________________
Melifluonze wrote:
Digital is easy. This is torture, but far more interesting...


Last edited by winny on Mon Apr 02, 2018 9:35 am; edited 1 time in total
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Apfelmousse




Joined: 26 Apr 2014
Posts: 74
Location: Germany


PostLink    Posted: Sun Apr 01, 2018 8:25 pm    Post subject: Reply with quote

winny wrote:
Sorry, I have had one beer to many when I wrote that...

Happy Easter! And thanks for the infos.

cheers
Martin
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