Customized vent fan assemblies condensation issue?

[Mountainhwy4]

Hi all,
Just came back from our second ever outing with the teardrop in Point Reyes, CA (it was a blast!), but one issue in particular kept popping back up. I built some custom vent fan assemblies (shown in the picture) on the side of the teardrop since a fantastic fan on the roof would be too tall for our garage, and they consist of 2x 80mm computer case fans mounted to a hinged board just inside of a vent cover on the side.

I chose this route because the case fans would be able to deliver the appropriate airflow to keep the trailer comfortable, all while being quiet and not drawing too much power (0.16A each!) I've tested out the fans several times during the build process, and they have given no issues. However, on both mornings when we would turn on the fans to help clear out the condensation, the dedicated fuse would pop. It's a 7.5A fuse, so well below the total power draw of the 4 fans together and I'm guessing there's a condensation issue shorting it out. Any suggestions? Are there any computer case fans designed for high humidity environments?

[pchast]

Do you have enough air flow with them running? Or are the vents too restrictive, the plenums too small? Do they blow the fuse if you leave the outside door open?

[Graniterich]

I really am struggling to believe that humidity is causing blowing fuses.

[Mountainhwy4]

I've run them with the doors open, doors closed (with windows cracked), and even with the vent covers closed! The only other variable I could see doing this is that it was cold, but I've run them in relatively cold temperatures as well!

I'll ask my electrical engineer buddy to see what he thinks...

[working on it]

from the thread Re: Side Vent or Roof Vent Fan? http://www.tnttt.com/viewtopic.php?f=2&t=73034&hilit=+vent#p1267736

• I also didn't want to put a fan on my roof, even though it already had a dozen 1/4" holes in it. I used stainless carriage bolts with acorn nuts/fender washers, for metal brackets securing the roof to the walls, in lieu of spars, sealed with PL adhesive, and painted-over with clear acrylic for further protection. But, I had no desire to cut a 14"x 14" hole for a rooftop fan/vent, inviting eventual leaks, so I decided on sidewall vents (with attached fans) for flow-thru venting, and a large under-shelf fan for maximum air circulation.
  
  
• Having run a shipping/receiving department for many years, I was familiar with vents used on the enclosed trailers of the trucks I loaded/unloaded at work, and that never leaked, as far as I could tell. I liked the look of a particular vent, designed for trailer roofs, but usually mounted on the leading wall of most trailers I saw. I found it at E-trailer, for about $20. It was galvanized (grey-ish color), which was ideal to match my grey color scheme, and the overall rough/industrial theme. They've been extremely durable, totally leak-proof during all sorts of thunderstorms (including horizontal rain), and have been perfect for bug-free operation, during the past 8 years.
  
  
• It was an easy install, and I put plastic screening between the butterfly closure and the wall, to keep out insects. But, I was not finished with them, yet. I added a swing-away bracket (piano hinge) to mount 120 mm hi-flow computer case fans for added circulation (if I wasn't using the 10-inch 120vac main fan). They are 12vdc, and use .18 amp-hour each, so I can use them for many hours, without much impact on the battery life, if off-grid.

vent & fans.jpg (88.03 KiB) Viewed 1570 times

interior fans;120 mm hi-static pressure versions

side view, rain-proof vents with full-time fans behind.jpg (152.81 KiB) Viewed 1570 times

* I leave one or both cabin vents open (at least partially) year-round, to aid fresh air flow and alleviate condensation. Running the not-quite-silent fans full-time probably will solve your condensation problems, too. And keep the fuse from blowing?

[Socal Tom]

What was the battery voltage when you tried the fans? We’re you plugged in when you tested at home? Low voltage would increase the amps potentially popping the circuit breaker. Also what size wire dud you use, and how long is the wire to the battery?

[TimC]

That's some beautiful design work on the enclosures! I went with case fans on my TD as well for many reasons... fantastic fan price, low noise, didn't need that kind of airflow, price, roof leaks, price. Did I mention price? Yeah, I'm too cheap for a F fan. Lots of folks love them though.

I don't see a fan spec label in the photos. Are you sure they are 12v fans? Are all four fans running (actually turning) when you pop the fuse? I agree with a couple of the others in that I don't think humidity is a cause. See if you can unplug one fan at a time and see if the fuse pops. Go through all four with one off and three others running. You might discover a bad fan. Doubtful but easy to check.

Questions not related to fuses blowing... You don't run these fans during the night? Are the fans all exhausting out of the cabin? The reason I ask is I have two 120mm fans exhausting air out of my teardrop. Rough calculations tell me that I am changing the air in the cabin about every four minutes with "makeup air" being my door's windows cracked open. I have camped down to 40 degrees and have never had problems keeping warm under covers or humidity build up with both fans running all night.

If you figure out the fuse problem please share it with the forum. That is a head scratcher for sure.

Tim

[Shadow Catcher]

These are Antec three speed case fans and 180mm if I remember correctly. I replaced one pair after 10 years. They are on a 10A fuse. As I understand it the fuse is to protect the wire which is 14 ga.

[MickinOz]

I really am struggling to believe that humidity is causing blowing fuses.

Well, condensation could blow a fuse, but I'm leaning toward the "possible but not probable" position too.
It could depend on whether these things are 12V or 110V, and I'm not sure from the preceding posts which it is.

Here's how I look at it:
You'd think condensation would be relatively pure water.
Even if it had 35g per litre salt, roughly sea water, it would have a resistivity of around 30 ohm-centimetres.
So if it was bridging a 1mm gap to cause a short on a circuit board (I believe computer fans do have little circuit boards in them), the resistance would be 3 ohms.
V=IR
So V/R =I.
12V / 3 OHMS = 4 AMPS.

i.e. even sea water bridging a 1mm/40 thousands of an inch gap shouldn't blow a 7.5A fuse on 12V.
These are apparently relatively new fans, so there shouldn't be a buildup of corrosion products increasing the conductivity of the water/condensate.

Of course, if the fans are running on 110V, then even relatively pure water could flow enough current across a small gap to blow the fuse.

I would probably disconnect the fans and test the wiring for shorts, and see if I can measure the impedance of the fans.
Pretty easy to put a screw or nail through a wire, pinch it somehow, etc.
In any case, I'd at least dry 'em out for a few days and see if they still blow the fuse.

[MickinOz]

I've now found the specs for the F8 Arctic
0.16A, 12V for 2000 rpm
0.1A, 7V for 1200 rpm.
0.08A 5V for 800 rpm.

Stick a metre across one and see if you can measure about 70 ohms.

[tony.latham]

I've been scratching my head over this, wondering how a brushless motor could short from moisture.

But I think Mick has enlightened me with his comment about the electronic board.

You might consider replacing the fans with a different brand. I was looking on Youtube and they are all over the place with their board designs.



Tony

[Socal Tom]

I've been scratching my head over this, wondering how a brushless motor could short from moisture.

But I think Mick has enlightened me with his comment about the electronic board.

You might consider replacing the fans with a different brand. I was looking on Youtube and they are all over the place with their board designs.



Tony

So in order of probability as determined by me

1) The wiring was damaged during install, and moved enough on the trip to cause a short.
2) There is a combination of low battery voltage and small guage wiring leading to excessive amperage accross the fuse causing it to blow
3) something else is on the curcuit and you forgot about it
4)poor grounding, leading to something like #2 above
5) Faulty fan
6) poor connections somewhere in the curcuit leading to something like #2 above
7) Its the wife's fault, ( I don't know how, but its her fault)
Its the dogs fault ( see above)
9) Bad switch ( see #2 above)
10) condensation causing a short

[MickinOz]

I've been scratching my head over this, wondering how a brushless motor could short from moisture.

But I think Mick has enlightened me with his comment about the electronic board.

You might consider replacing the fans with a different brand. I was looking on Youtube and they are all over the place with their board designs.



Tony

So in order of probability as determined by me

1) The wiring was damaged during install, and moved enough on the trip to cause a short.
2) There is a combination of low battery voltage and small guage wiring leading to excessive amperage accross the fuse causing it to blow
3) something else is on the curcuit and you forgot about it
4)poor grounding, leading to something like #2 above
5) Faulty fan
6) poor connections somewhere in the curcuit leading to something like #2 above
7) Its the wife's fault, ( I don't know how, but its her fault)
Its the dogs fault ( see above)
9) Bad switch ( see #2 above)
10) condensation causing a short

Trouble is, motors don't always draw more current as the voltage goes down. Even when they are the type of motor that does, the increase in current is proportional to the decrease in voltage. In this case the specs say the motor draws less current as the voltage drops.
Also excessively thin wire causes less current, not more.
I'm going with #7. I dunno how, but its her fault.

[Mountainhwy4]

Hi all,

Wow thanks for all the responses! I'll try to answer as many questions as I can on this! So after we got home, I opened up the windows and the vent covers and switched on the fans (with a new fuse of course) and the fans ran fine for a few hours so I switched them off. Came back a few days later when it was raining outside (the trailer is stored in the garage) and switched on the fans, they ran fine. The mystery continues...

The battery voltage was around 12.1-12.2 when the fuses popped, I believe the lowest I should let the battery run to is around 11.7 or 11.8V.
The fans are definitely 12V, and each pull an airflow of 31cfm which gives a total for all 4 of 124cfm. With an estimated internal volume of ~115 ft3, that's a little over one air change per minute!
The fans have 22ga wires leading off of them for about 5-6" to the main wiring from the switch which is all 16ga, runs less than 10' from switch to each fan assembly.
The fans are the Arctic F8 80mm case fans (5 pack), each draw 0.16A for a total of 0.64A for the 4 of them.

We did try to run the fans the second evening out (starting around 4 when the sun was still up), and when I checked back in around 6 the fuse had blown again!

I am thinking I may have to replace the fans, but if this is only a wintertime occurrence perhaps we can get away with just opening the top vents and cracking the windows. The trailer was still pretty comfy in the morning with that arrangement, albeit with excess moisture!

I'll try to do some additional testing next week to see what I can come up with, perhaps it is a grounding issue

[Tom&Shelly]

I'd bet on the damaged wire theory, possibly in combination with condensation (water shorting frayed wires), or perhaps the wife or dog, or more likely, just small temperature changes, causing the wires to move enough to cause them to short where frayed.

Can you run temporary wires (un-hidden to check for damage) from the fuse box to the fans? (Take the suspect wires out of the circuit.) If the fuses don't blow after several uses, it would tend to rule out bad fans, and other issues.

Tom