Frig Fan Replacement and How to do Dual Fan

[TankerIP]

I just replaced my frig external fan with a new Silenx fan that seems to work very well, at least very quiet. Now I have several questions. Hopefully I can get some answers. From the forum posts I learned that the OEM Rodale fan moved the air at 105CFM. The Silenx has just 44CFM. Now I wonder if need to put in another fan to get enough exhaust, and will a dual fan installation still be quiet compared to the old OEM?

Looking at the posts in the forum I cannot get a clear picture of wiring the two fans for either series or parallel operation. Which is preferred? And, for instance, if the positive of one fan runs through the negative of the next; is that called series or parallel. I have not been able to see a wiring diagram.

One other issue I have is how best to eliminate the fumes when burning on propane. Sometimes the fumes are noticeable inside the trailer. I would assume a dual fan setup would help in this respect. Any other ideas?

[glcmranger]

Since the CFM was lower on the Silenx fan vs. the OEM fan, I wired 3 fans together in series. Then, I also put an on/off switch in-line in case you don't need the fans running if the refrigerator is off. I can't hear the fans running from the inside. If interested, I can send you a schematic later today (it's in the trailer).

[TankerIP]

Originally Posted by glcmranger

SIf interested, I can send you a schematic later today (it's in the trailer).

Sure, thanks. I guess you can PM to me, if that works.

[glcmranger]

You bet...

[Johnnyooo]

I replaced the original fan with three fans in parallel, and it's still much quieter than the original..I can turn them off with the existing on off switch when their not needed...Combined they move more air than the original fan...

[Boxite]

Wiring them in "parallel" is the same as wiring them individually.

Wiring them in "series" is what you described as connection one's "positive" to another's "negative".

If you wire them in series...you will INCREASE the total CFM of air moved commensurately with the number of fans installed, IE, if you put dual fans you will closely double the CFM. (OK, engineers... don't get into technical details of air resistance versus volume of space please...I'm only trying to make this description simple.)

If you wire them in series.... each fan's speed will be reduced almost in half... In other words, dual fans wired in series will only see about 6 volts instead of 12 volts...so the fans will run slower thereby each moving less air than if they received full voltage. Wiring them in parallel will provide full voltage to each fan.... but will use more current (after-all...you're running twice...or thrice...as many fans at full speed.)

I installed two 12V computer fans in series and therefore they run at half-speed...but more quietly than if running at full speed. The PURPOSE of the fans is to encourage the warm air (created by the absorption method) to LEAVE the compartment. It only takes a bit of encouragement because warm air rises on it's own and congregates at the top of the compartment. The fan is intended to discourage stagnation of that air. Blowing 44 Cubic Feet per Minute (cfm) of air out of the compartment makes room for more cool air to enter the bottom ...drift upwards...be warmed by the evaporation fins...and exit the compartment. If you drastically increase the cfm of air moving thru that compartment...you reduce the amount of time that air has to absorb the heat to be carried away. (It's why your auto has a thermostat in it's cooling system ..even in cold weather...because if you move the coolant too quickly it cannot aborb the heat and carry it away.)
One fan is sufficient probably... but adding more fans pulls the cool air across more fins. Speeding that increased air flow will not likely do much more than drain your batteries more quickly (when boondocking, for example.) That's why I added a second fan (to increase the number of fins being exposed to cooling air) but wired them in series (to pass the air by those fins ...s l o w l y... both to allow the air time to aborb/remove the heat...and to avoid increasing my electrical current use.

Hope this layman's explanation helps.

[rmkrum]

From the 'overkill engineering' department:

Wire the fans in parallel--they work better that way. Consider using a fan that includes a temperature sensor to control speed--that way when it's hot in the fridge compartment, they will run faster and cool the area better. To put icing on the cake, add a set of switches, one per fan, to allow customization of the noise level...

Mount them neatly on a baffle mounted and sealed to the inside of the top door, to make sure they are actually circulating air out of the compartment, instead of just stirring it.

Add more insulation on the sides and top of the frige box to improve cold retention in warm weather.

Consider a small circulating fan inside the fridge to even out temperature, either battery-powered or wired to 12 volt power.

Make sure the factory installed (hopefully) baffle across the middle of the compartment is in place. Mine was a simple 4" wide piece of sheet metal caulked in place on each end. I think it fell out and landed in the bottom of the compartment when the AS was delivered to the original owner in 2007!! The replacement will have appropriate metal tabs bent from the replacement sheet metal and properly screwed to the sides of the cabinet area to KEEP it in place, directing air flow over the fins and tubing on the back of the fridge to improve efficiency...

Keep in mind that the absorption cycle fridges are not super powerful, so improving efficiency and insulation is key to making them work better...

[greghoro]

I did almost exactly like glcmranger with three fans. But no switch. See this post for a picture of my installation.

The fans I purchased, Scythe Gentle Typhoon D1225C12B3AP-13 120mm came with 4 pin computer electrical adapters so I just daisy chained the fans using these adapters, essentially wiring them serially but electrically in parallel. I connected into the trailer wiring using a 4 pin computer power connector.


Greg

[GettinAway]

I’m not a EE, that will become very clear when I get this question asked. I’m finally putting in a can I bought a year ago. It’s a Silenx fan also, but it’s 76cfm vs the original at 105. Our refrigerator has never had a problem keeping anything cool.
My question is. Which wire is what and goes where? The fan im taking out has the two wires. The replacement fan has a stub with two wires and a harness with several and a couple of clips. Can someone tell me which ones go to which ones on my existing wiring?
Pics included.
Thx
These are the new wires.

New fan mounted.

[PaulnGina]

I'd like to post this for your reference. It is a link to our Avion owner's site, and I installed some fans along with a nice, cheap thermostat. If you'd like, I can certainly make a separate thread here, and/or I would be glad to answer any questions.
They work great!

http://www.aviontrailers.net/viewtopic.php?f=8&t=342

[CruizinDux]

Try this link to post #711 on the 20 footers thread.

http://www.airforums.com/forums/f542...ml#post1774433

When om doubt, strip the 3 wires (one is a speed controller...the shorter of the 3 in my photo) and open the TV's hood. It can only work one way and will not work in reverse.

Here is my link to the post install eval.

http://www.airforums.com/forums/f542...ml#post1785587

Note Silvergate's recommendation of simply opening the ext. door usually is sufficient to turn off the fan automatically via the thermostat within 5 minutes.

Good Luck

Bob

p.s. I have since replaced the failed rubber screws that were OEM with the silenix. Burrs on the fram bracket wore thru. I have since suspended it like a trampoline with 4 springs and tossed the mounting bracket.

Originally Posted by GettinAway

I’m not a EE, that will become very clear when I get this question asked. I’m finally putting in a can I bought a year ago. It’s a Silenx fan also, but it’s 76cfm vs the original at 105. Our refrigerator has never had a problem keeping anything cool.
My question is. Which wire is what and goes where? The fan im taking out has the two wires. The replacement fan has a stub with two wires and a harness with several and a couple of clips. Can someone tell me which ones go to which ones on my existing wiring?
Pics included.
Thx
These are the new wires.
Attachment 308650
New fan mounted.
Attachment 308651

[SeeMore]

There many ways to use Silenx fans to boost cooling. Air movement is best on the "outbound" side of the blades and when mounted close to the heat transfer fins. I use four 2" fans wired in series that produce almost no noise whatsoever and included both a temperature sensing switch and manual override switch in the circuitry:

http://www.airforums.com/forums/f425...ml#post1320168

[GettinAway]

Thanks! Checking out the links. I’ll see how this works. I may need add a second fan.

[Boxite]

Originally Posted by Boxite

Wiring them in "parallel" is the same as wiring them individually.

Wiring them in "series" is what you described as connection one's "positive" to another's "negative".

If you wire them in series...you will INCREASE the total CFM of air moved commensurately with the number of fans installed, IE, if you put dual fans you will closely double the CFM. ....

I make a "typo" when I posted the info in bold above... I meant to post:
If you wire them in parallel...you will INCREASE the total CFM of air moved commensurately with the number of fans installed, IE, if you put dual fans you will closely double the CFM.

Sorry for any confusion.

[PaulnGina]

Correct.... parallel keeps the voltage at each fan the same. So your 12V fans will still have 12V powering them. I have 4 fans in parallel and they move a good amount of air. That, along with the $5 thermostat and a $2 switch allow me to keep the back side of the fridge cooler than without, thus helping the efficiency of the fridge. I LOVE being able to walk by the vent on the side of the trailer and head the fans doing their job...... quietly. One of the best modifications I have installed!