Modification to reduce fan noise for the WFCO 1000 W Inverter

[alano]

The stock Airstream 1000 W inverter that comes with the 2015 Classic is extremely noisy when enabled due to two internal fans that keep the inverter cool. Upon inspection these fans are simply the two-wire DC brushless fan variety with no speed control inputs. The following modification replaces these fans with four-wire DC brushless fans and a temperature speed controller to keep the fan speed reduced when the inverter is not dissipating lots of heat – which is almost all the time.

This modification surely voids the warranty, but for me is it worth the less than $50 worth of components and 1-2 hours to remove, modify and reinstall the inverter.

Equipment needed:

1. 2” length, ¼” heat shrink tubing, cut as needed
2. Nylon washer for 6-32 screw
3. 1/8”, 3/16” drill bits
4. 1/8” aluminum rivets
5. (2) 12 V DC Fans from Digikey, part number, 603-1755-ND
6. DC 12V PWM PC CPU Fan Temperature Control Speed Controller, purchase from ebay Store, AIX81. Confirm photo of the controller is the same as shown in Fig 2.

Procedure:

1. In the 2015 Airstream Classic, remove the front and back covers of the bench opposite the sink.
2. Disconnect the connections the inverter, being especially careful not to short the battery red and black terminals as they are always live.
3. Remove the four screws holding up the inverter on the wall of the Airstream and remove the inverter from the trailer.
4. Using a 1/8” drill, drill out (13) rivets. Careful not to let the drill-bit enter the case by more than 1/4”. Drilling into the enclosure more than ¼” may hit components and cause damage.
5. Remove the existing fans and replace them with the new four-wire version. Careful to note the direction of airflow of the existing fans and make sure the replacement fans are configured in the same direction. Both the original fans and the new fans indicate the direction of airflow. If you forget the air flow for both fans is configured such that air enters the front panel and exits the rear panel.
6. Mount the controller board as shown in Fig 1. Use or create a nylon washer to further isolate the circuit board from the heatsink.
7. Configure the controller switches such TFL is OFF, TP1 is ON, TP2 is OFF, BF1 is OFF and BF2 is OFF. This configure causes the fan speed to idle at 20% for temperatures below 40°C and full speed for temperatures above 50°C. I didn’t use the alarm feature since the inverter already has a built-in over-temperature circuit and alarm.
8. Drill a 3/16” hole in the heatsink for the temperature sensor (thermistor) and use superglue to affix the sensor to the heatsink as shown in Fig 2.
9. Wire both fans according to Fig 2. Use heat-shrink tubing to insulate the wires as shown. Leave the blue wire unconnected from one of the fans. It doesn’t matter which one. This wire is the fan rotation sense line and the controller only expects one connection.
10. Unsolder the cable assembly from the front fan that was removed and use this cable assembly to provide 12 VDC to the controller board. This cable is shown in Fig 3 as it comes from the speed controller to the inverter motherboard.
11. Carefully inspect the enclosure for any metal particles that may be remaining after drilling out the rivets and creating the hole in the heatsink.
12. If you have a power supply capable of supplying 12 V at 3 A, connect the power supply to the inverter while leaving all other connections unconnected. Press the power switch on the front-panel in and make sure the inverter comes to life. Both fans should come to life running about 10%. If you have a heat-gun or hair dryer, direct heat to the thermistor and verify that the fan increases in speed proportionally with temperature.
13. Reattach the top cover with 1/8” aluminum rivets and reinstall!

You might try other means to mount the controller board, such as drilling holes in the top cover. I certainly won’t win any awards for my method but I felt confident that the mass of the board was low and the screw was secure.

I found that the fan noise was inaudible when powering both TVs and the Blueray player after a couple of hours. As a test I ran the inverter with a 1000 W hairdryer for 10 minutes continuously and only managed to generate sufficient heat in the inverter to run the fans at perhaps 50% of its maximum speed. All in all I’m pretty happy with the modification and will continue to test drive it and see how it performs.

[NWRVR]

Wow! Thank you Alano for the post and detailed instruction. My inverter is under the bed and though our solar keeps the batteries up we have had the inverter fan come on during the night when it is cold and the heater runs a high percentage of the time. Your solution goes on my project list!

[NWRVR]

BTW, did you mean converter instead of inverter? My converter fan comes on if it is charging the batteries on shore power and my heater is running frequently.

[alano]

This modification is only for the WFCO 1000 W inverter. The inverter converts 12 VDC to 120 VAC when you are not connected to shore power and want to turn on the televisions or use the recliner. The stock inverter fan runs continuously and loud!.

[NWRVR]

Ok, thanks. I have not used the inverter yet but my converter fan is one speed and noisy. Would your variable speed fan noise fix be applicable to the converter?

[alano]

The controller board is usable, but you would need to research and verify that the dimensions, voltage, and airflow requirements for the replacement fan are compatible with the existing fan. The fan that I specified for the inverter mod meets or exceeds the existing inverter fan's specifications.

[BAB]

Like Alano, I was amazed at how loud the stock inverter was. Since I removed the entire unit and installed a Magnum MSH, I eliminated the problem completely. Had I not done that, I would have changed out the cheap WFCO for a Xantrex SW2000 ($347.50). This is a much higher quality unit and would be an easy swap out. I think it would fit behind the drawer. Mounting the inverter directly on the wall directly in front of the recliner without so much as a rubber insulator attenuates the already too noisy fan. I know that I would not have been able to tolerate the noise.

[beetlebob]

Babs Is this the unit you bought and did not use that you want to sell? Also do you leave your Wifi antenna up all the time. I am thinking of attaching ours to the cover I am putting on the vent(with a little reinforcement ). With my little truck I don't even know it is back there. I would not even feel a tire separation like you said in the other page. The Airsafe hitch is GREAR and no sway bars or anything.

[BAB]

Bob, I PM'd Page on the inverter. RE: the WiFi Ranger antenna: yes, it is a permanent mount. I'd guess that it is probably 4-5 inches higher than the forward A/C unit. Mine came with a three point mount, and seems pretty sturdy. Height is a consideration. It clears the roof of the Airstream shed by just under 2". Whew!