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Old 27-04-2018, 22:11   #1
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Compressor fan - how big?

Posted in the wrong forum and there seems no way to move it here?

I have two BD50 compressor units and the fan on one has gone feeble due to a bad bearing - or at least the bearing has flat spots and the fan seems to run slower than the other unit

Removed fan is 120 x 120 x 25mm
12V x .5A labelled but seems to draw .33 running
95 CFM at 44.5 dB

There are lots of fans, at various flow and current draw ratings
More air flow = more current draw and usually more noise

Has anyone fitted a 38mm thick fan?

How many CFM does one need for a holding plate system freezer in the tropics?
It was 42C yesterday, and in "winter" will still hit 30 in the day
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Old 27-04-2018, 22:55   #2
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Re: Compressor fan - how big?

A little more info:

The locker that houses these 2 compressors has 2 exhaust fans.

The reefer fans are controlled by individual relays

The CU100 compressors use the fan in sucking mode. Could one not use a larger fan on the other side of the condenser in blowing mode?

Found some great spec Noctua fans:
NF-F12 PPC 3000
110 CFM
43.5 dB
0.3 A
120 x 120 x 25mm so a bolt in replacement. Not clear if it will work as a puller, or better as a pusher?

https://noctua.at/en/products/produc.../specification
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Old 28-04-2018, 04:06   #3
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Re: Compressor fan - how big?

The function of the fan is to cool down your condenser. In most designs, it blows air towards the condenser and it is in-line with your compressor.

The Capacity of the fan decides how much air will be moved towards the condenser.... Better ventilation = better cooling performance..... I would install something within the -/+ 10% of the original CFM capacity (If the original part is not available)

Most commonly neglected issue is the ventilation of the compartment where the compressors located. If the compartment is not ventilated well, your fans will be pushing warm air to your condensers.. Since you are running two compressors in one small space, I would check (and improve) the ventilation of the compartment as well.

Good luck with your project.
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Old 28-04-2018, 13:04   #4
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Re: Compressor fan - how big?

We suck the air through the condenser with twin noctua fans . This makes maintenance easer . Much simpler to remove dust from a condenser it is not covered by a fan

Regards John
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Old 28-04-2018, 13:24   #5
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Re: Compressor fan - how big?

If the fan is connected to the actual compressor controller (terminals F and C, or + and F), then you need to observe the max current on that circuit. I believe the BD50 is a max current of 0.5A with a peak of 1A (no more than 2 seconds). If you leave it connected that way, then you should not exceed the max current rating.

Personally I matched my fan to what I took out. I trusted that the manufacturer put the best balanced (CFM vs power use) fan for the job. It worked for 12 years, so I'm hoping to get 12 more.
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Old 28-04-2018, 16:46   #6
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Re: Compressor fan - how big?

You might look into PC (computer) fans. I switched to standard 12V brushless fan which appears to have a more efficient blade design and is noiseless compared to the original fan, at a fraction of the cost. It is a drop-in replacement in my Frigomatic AV35F.
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Old 28-04-2018, 17:56   #7
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Re: Compressor fan - how big?

The Noctua fans are hard to beat, not the cheapest, but worth the money.
Going bigger on a fan will hurt nothing but power draw, and that is insignificant, and maybe even could save power by cooling the condenser better, lowering pressure and making the compressor not work as hard.

However make sure you donít overamp the controller, or fit a relay if you have to.

Too small a fan is bad, real bad, excess pressure and heat in the compressor will make it work harder and shorten its life. In fact in mounting the fan, it may not be a bad idea to make sure the air is blown over the compressor as well as the evaporator. Suck through the condenser and exhaust on the compressor maybe?
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Old 28-04-2018, 18:25   #8
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Re: Compressor fan - how big?

Quote:
Originally Posted by a64pilot View Post
The Noctua fans are hard to beat, not the cheapest, but worth the money.
Going bigger on a fan will hurt nothing but power draw, and that is insignificant, and maybe even could save power by cooling the condenser better, lowering pressure and making the compressor not work as hard.

However make sure you donít overamp the controller, or fit a relay if you have to.

Too small a fan is bad, real bad, excess pressure and heat in the compressor will make it work harder and shorten its life. In fact in mounting the fan, it may not be a bad idea to make sure the air is blown over the compressor as well as the evaporator. Suck through the condenser and exhaust on the compressor maybe?
Noctua fans are the best fans out there for CFM power consumption and lifespan . They use a very special bearing that makes them very efficient . These fans are not cheap and they require very clean dc power for them to start . We use the ip67 ingress rated ones . They will last the life of the compressor. The airflow from these fans is directed over the compressor as Danfoss recommends .

Regards John
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Old 28-04-2018, 20:36   #9
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Re: Compressor fan - how big?

I already tick all the boxes:
Two exhaust fans in the locker housing the compressors.
Fan sucking through the condenser and blowing on the compressor.
Relay on the fan circuit so that I can handle a large fan if deemed necessary.
I have stumbled upon the best fan - Noctura and cheap in here in Thailand at 33.00 USD ea.

No idea if the 95 CFM Delta unit that died is OEM Dometic, and in any case I am trying to optomise performance in the tropics.

The Noctua NF12-F12 PPC 3000 model I have in mind is is 110 CFM.
Few if any 120 x 120 x 25 fans offer significantly greater flow, and none that I can find at this current draw.

To achieve 199 CFM there is a Delta fan at 32mm wide fan x 1.85A startup with perhaps half that to run. Significantly more flow but rated at 6-12.6V which will pose a problem
I also do not know if this will fit the Dometic fan shroud as I am not on the boat now.

Seems to me that this is a case where bigger is better
How big is needed in the tropics?
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Old 28-04-2018, 20:40   #10
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Re: Compressor fan - how big?

Quote:
Originally Posted by ColdEh Marine View Post
These fans are not cheap and they require very clean dc power for them to start .

Regards John
Noctua spec states 12V

Given that battery voltage fluctuates with the state of charge, should I design in a regulator or is this already present on the Dometic board?
IIRC the Dometic cuts operation around 11.5V ??
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