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Old 03-28-2017, 04:39 AM   #1
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Continuous Use Fans for Frig Heat

What type of setup is best to use to draw the heat build up from refrigerators. The cabinet area that the frigs are mounted in builds heat during the summer months which cuts down on the effectiveness. I would like to mount some duct work and fan (12V or 120V) to draw this heat out of the cabin area. Most bilge fans I see are not for continuous use (short life cycles) and / or noise restrictive.

My setup: Mainship 40
2 - Isotherm Stainless (12V/120V) Units (130 Size Units)
1 - Isotherm Clear Ice Maker

Thoughts for a good solution. Thank You!
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Old 03-28-2017, 05:00 AM   #2
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A 12vdc computer power fan. Comes in all sorts of sizes. Big ones are now used in most PC power supplies.
You can power from a walwart or boat DC power. might setup so when compressor kicks on so do the fans.

The faster ones may be noisier, and the amp draw is listed on the fan.

I have collected quite a few, and tested them to select the quieter ones for my onboard PC.
Sound quality varies a lot.
I oil mine with full synth 0-20w engine oil, and it lasts a very long time. You will find old PC fans, the oil may dry up.
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Old 03-28-2017, 06:17 AM   #3
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Have used a 12v, 3" computer fan for years. Cheap, easy to install. Runs continuously.
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Old 03-28-2017, 06:26 AM   #4
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Computer fans, use two one to push one to pull.
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Old 03-28-2017, 07:34 AM   #5
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I am about to do the same ..... I'm thinking just to cut a lower and upper louver at the back and install just one fan for now in one of them ( maybe with T Stat maybe not .. ? ) to see how it will work. As was said, maybe even across the compressor and have it run all the time.
Computer fans are continuous duty, an 8" fan draws less than .25 A so I picked up a pair c/w grilles at an electronic surplus store 5.00 ea.
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Old 03-28-2017, 07:41 AM   #6
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So the fan isn't on contiusioly, you can add a relay that triggers a fan when the compressor goes on. Relays and computer fans are available in 110 VAC or 12 VDC. We added fans on our 12 volt system using Bosch style relays (less than $10). We took the trigger voltage from the compressor and used the power in source for the fan power/voltage. The fans we installed put us over the current draw limit to power them from the compressor it self. That's why we used relays. There's lots of info on the internet. Here's one example.
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Old 03-28-2017, 08:36 PM   #7
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Check your power supply, the SECOP/Danfoss control modules have a limit for condenser fan power (amperage). You can parallel a second, remote fan onto the fan connections provided it's within the limits of the controller. If it's out of range, the controller will sense it and error out on a fan fault, so don't just add one without doing some checking. As mentioned in a previous post, a relay allows you to add whatever load you want (within the relay capacity), since the relay coil is the only additional load the module sees, PROVIDED you power the dry contacts of the relay from the main 12V connection at the control module.

As far as additional ventilation, it's probably the single most beneficial change you can make to any refrigeration that has an air-cooled condenser, particularly if that condenser has a tendency to recirc its waste heat as most all marine refrigerators do. Jam the thing into a dead end space and just leave it to choke on its own waste heat.

The compressor head pressure runs consistently high, it uses more power, runs hot, can cause the motor to fry or can cause valve damage. All for the want of some ventilation.

If possible, add ventilation high and low, natural convection will assist with removal of waste heat. The whole objective is to provide a means to move cooler air over the condenser, thereby reducing the load, improving service life.
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Old 03-28-2017, 11:16 PM   #8
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I have used those muffin/computer fans for years to do what you are talking about, forcibly exhaust the heat tossed out by the fridge.

The Danfoss BD35 can handle up to about 500mA or 0.5A at 12 volts. I asked.

Most 4" muffin fans will draw maybe 100 to 200mA.

The Danfoss also has a fan drive outlet for this purpose turning the fan on at compressor start and shutting the fan off at compressor stop.

Get a fan with ball bearings, not sleeve bearings. Will cost a few bucks more but they are a lot quieter. I use the sleeve bearing units for other purposes where some noise is not so bothersome.

I do not recommend two fans. I tried this and the twins, 3", made an unholy racket Each individual 3" fan was nearly soundless but the two , not so much. I changed to a 4" single. Barely hear the 4". Your experience could be different.

Depending upon the fridge location all you need is an exhaust hole high up in the fridge cavity so the fan blows the heated air out. The less duct work the better so if it can be avoided then avoid it.

Just be sure air can enter low down also.

If you have a different compressor then ask the mfgr. about the fan drive and its output voltage and amp output.

Fuse the fan. It will be a tiny fuse but do not omit it.
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Old 03-29-2017, 01:59 AM   #9
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if a $5.00 part could really make the fridge work more efficiently and last longer, wouldn't the manufacturer have installed one ?
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Old 03-29-2017, 03:31 AM   #10
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Quote:
Originally Posted by Benthic2 View Post
if a $5.00 part could really make the fridge work more efficiently and last longer, wouldn't the manufacturer have installed one ?

The area being exhausted is not the refrigerator but the cabinet in which the refrigerator sits. Unlike a home situation these cabinets are usually closed and the heat builds up.

Many of the marine/rv refrigerators exhaust heat to the back so as to avoid heating the galley. Getting rid of that heat is the goal of these added on fans.
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Old 03-29-2017, 10:52 AM   #11
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Another way of controlling a fan would be a heat sensing switch mounted on the coil.


Just saying.


Now if the holes in the cabinet are big enough and properly located, a fan might not be necessary. While a fan might make the refrigerator more efficient, the increased efficiency might not balance out the power used by the fan.
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Old 03-29-2017, 01:17 PM   #12
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Does your fridge already have a fan mounted to its compressor? My new NovaKool did. I spoke with the engineer for NK and he explained to me how I could remove the fan from its mount and extend the wires. I then cut a 4 inch hole into the cabinet side and mounted the fan there. That cabinet fan dumps into an enclosed void behind the stove. I installed a alstic black grate through the countertop from that area so the fridge heat vents aft of the stove through the countertop grate.

The fan cycles on/off with the comressor and is so quiet I have to strain to hear it. Ample vent space is available below the fridge to allow cooling air to enter the cabinet as it`s purged out the top back.
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Old 03-29-2017, 09:00 PM   #13
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Originally Posted by Benthic2 View Post
if a $5.00 part could really make the fridge work more efficiently and last longer, wouldn't the manufacturer have installed one ?

Some boat builders do a good job of venting the cavity the fridge is mounted into, some do a lousy job. Often the trouble is where it is installed , on an exterior wall that the sun beats on in hot weather.

Danfoss provides a fan drive terminal for that reason. But the builder/installer must get and mount the fan.

The fridge mfgr. has no idea where these things are intended to go.

I learned this many years ago when my previous fridge ran & ran & ran in hot weather. It was on the sunny side, the sun was hot, the black cabin sides absorbed heat and the poor thing could not cool. I made some mods including adding a fan to a unit that was not intended to have one. The fan exhausted the hot air from the cavity and the fridge was able to do what it was intended to do - cool.
THe problem was not the fridge but the installation.

The same is true of your home fridge. Read the instructions and there are usually recommendations for clearance minimums above, to the sides and the back. Failure to follow those minimums can cause even a good fridge to perform poorly. It is often not noticed because electrical power use is seldom truly monitored. But on a boat it becomes important because a fridge that cannot cool is a power hog and that poor performance is often more readily noticed.
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Old 03-31-2017, 05:53 AM   #14
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Thank you for all the good ideas and advice. I have it in my head how I need to take care of it now. Adding it to the to do list for the next couple of weeks.
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Old 04-01-2017, 06:06 AM   #15
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Most times the added fan still dumps the heat into the cabin. So why not simply purchase a reefer with a front exhaust ? No extra wires or fans to install.kiss.
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Old 04-01-2017, 10:52 AM   #16
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Most times the added fan still dumps the heat into the cabin. So why not simply purchase a reefer with a front exhaust ? No extra wires or fans to install.kiss.
A new refrigerator will cost a lot more than a small fan.

Or, you may not have a choice to fit your opening.
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Old 04-01-2017, 11:39 AM   #17
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Improved refigerator performance
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Old 04-01-2017, 07:59 PM   #18
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What about this fan? It has a 12vdc power source and a built in temp controller that varies the speed from 300 to 1200 rpm depending on temp of the sensor... quiet as well.

https://www.amazon.com/ARCTIC-F12-TC...led%2Bfan&th=1
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Old 04-02-2017, 12:09 AM   #19
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Should work. Power use is 200mA at 12Vdc according to blurb.

The only thing I can think of that maybe in question is the temp sensor. It may not shut off when the fridge compressor shuts off so it then becomes an ongoing load parasitic to the batteries.

38oC is about 100oF so depending upon where you are and how the sun beats on stuff it may not shut off on its own.

Maybe can be hooked to the fridge fan outlet contact [BD35} so it can run only when the compressor is running and the sensor/speed control will then determine what speed is required to get rid of the heat.

Cheap enough that if it does not do what you want then it can be replaced. It's just how much trouble it is to get at it for replacement.

I just reread some of the comments about this fan. It does not shut off, there is a minimum speed that it will always run. When the compressor shuts off this fan will then become parasitic to the batteries unless you do as I suggested above,
connect it to the fan drive on the BD35 .
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Old 04-02-2017, 09:37 AM   #20
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..................... I just reread some of the comments about this fan. It does not shut off, there is a minimum speed that it will always run. When the compressor shuts off this fan will then become parasitic to the batteries unless you do as I suggested above,
connect it to the fan drive on the BD35 .
The point of installing a fan is to remove excess heat from the area around the refrigerator so it would seem that "heat" should be controlling the fan, not the fact that the compressor is running. There will still be excess heat in the cabinet when the compressor shuts off.

That said, it would be best if the fan shut off when the temperature inside the cabinet is equal to the temperature outside the cabinet.
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