High Frequency noise coming from Maxxfan

[screamineagle]

I have a 2020 Momentum 395. I have had a High Frequency scream coming from Kitchen area when I turn my ceiling fan on. The is a Maxx fan unit. Air excel has been very gracious to help me through this issue. I will state what has been done.
2 motors have been replaced in unit
#1 replaced due to them thinking the motor or bearings were bad ( problem did not go away)
#2 Replaced after they sent another unit tested in fan at the factory ( problem did not go away)

Circuit board in fan unit replaced, suspicious to bad component. Problem still there.

• Fan makes this noise on speed 1 & 2 not 3 & 4
• Same thing with lights off
• Same thing with only shore power
• Same thing with only battery power

Contacted Grand design for some phone support and was rudely told to take the trailer in for service. Easy to say when it could be a simple fix. Its camping season and don't want to let it sit at dealer.
Has anyone else had this issue, I see other posting of people who gave up and not operated the Fan motor. I honestly believe the problem is hookup/electrical/interference not fan.

[howson]

I honestly believe the problem is hookup/electrical/interference not fan.

Easy enough to validate if you're OK with handling minor troubleshooting. If any of the below gives you pause or something is not clear--don't do it--call for help from an RV mechanic or "hire a friend".

Note I am assuming your Power Distribution Center (PDC) is similar to the one in my 315RLTS. If it's not--disregard this post. (Example of my PDC is in the pic.)



Turn off all a/c components in the trailer.
Turn off power at the pedestal and disconnect the power cord.
Turn the battery disconnect so 12v power is removed from the trailer. (None of the interior lights should work at this point. Neither should the fan.)
Carefully remove all of the blue fuses in the PDC except for fan (kitchen) and the large metallic looking fuses for the slides--leave them alone.
Turn the battery disconnect back on to apply 12v power to the trailer.

Test the fan--does it still make the noise?

After testing...
Turn off the battery disconnect.
Carefully reinstall the fuses.
Turn the battery disconnect back on (applying 12v power back to the camper).
Plug in the power cable and reapply AC power to the camper from the pedestal.

Howard

[howson]

screamineagle -- if you do the troubleshooting in post 2, note there may be a 20A fuse in the Furnace slot. Make note of the fuse ratings and ensure they are put back in the exact location they were removed from!

[Jkwilson]

It is acoustic noise caused by the PWM speed control. If Maxxair won’t straighten it out, change brands.

[howson]

It is acoustic noise caused by the PWM speed control. If Maxxair won’t straighten it out, change brands.

Out of curiosity, where is that control and what led you to that conclusion? (Personal experience with the issue?)

[Jkwilson]

Out of curiosity, where is that control and what led you to that conclusion? (Personal experience with the issue?)

Personal (professional) experience. PWM speed controls are known for creating acoustic noise in motors, especially fan motors, if the rise time of the pulse isn’t filtered some to smooth it out and particularly if manufacturing tolerances aren’t good. In effect, you are turning the motor on and off which can setup a mechanical vibration within the motor.

For more info from the technical side, check out https://ww1.microchip.com/downloads/...tes/00771b.pdf

[gbkims]

I remember I had a 600hp motor/compressor that I thought of it "singing" because of the variable speed drive.

[howson]

Personal (professional) experience. PWM speed controls are known for creating acoustic noise in motors, especially fan motors, if the rise time of the pulse isn’t filtered some to smooth it out and particularly if manufacturing tolerances aren’t good. In effect, you are turning the motor on and off which can setup a mechanical vibration within the motor.

For more info from the technical side, check out https://ww1.microchip.com/downloads/...tes/00771b.pdf

So that's why MaxxAir sent two motors to try and fix the problem!

What's interesting is the OP states MaxxAir tested the second motor before sending it, but the test was likely under ideal conditions (clean, stable DC voltage). Are there any conditions that can amplify the problem (make it worse or apparent in one unit when it works fine in another)?

[Jkwilson]

So that's why MaxxAir sent two motors to try and fix the problem!

What's interesting is the OP states MaxxAir tested the second motor before sending it, but the test was likely under ideal conditions (clean, stable DC voltage). Are there any conditions that can amplify the problem (make it worse or apparent in one unit when it works fine in another)?

Maybe opening or closing doors or windows could ameliorate it or worsen the sound, but generally the motor is as it is and the same for the drive circuit.

[screamineagle]

I have a 2020 Momentum 395. I have had a High Frequency scream coming from Kitchen area when I turn my ceiling fan on. The is a Maxx fan unit. Air excel has been very gracious to help me through this issue. I will state what has been done.
2 motors have been replaced in unit
#1 replaced due to them thinking the motor or bearings were bad ( problem did not go away)
#2 Replaced after they sent another unit tested in fan at the factory ( problem did not go away)

Circuit board in fan unit replaced, suspicious to bad component. Problem still there.

• Fan makes this noise on speed 1 & 2 not 3 & 4
• Same thing with lights off
• Same thing with only shore power
• Same thing with only battery power

Contacted Grand design for some phone support and was rudely told to take the trailer in for service. Easy to say when it could be a simple fix. Its camping season and don't want to let it sit at dealer.
Has anyone else had this issue, I see other posting of people who gave up and not operated the Fan motor. I honestly believe the problem is hookup/electrical/interference not fan.

Did some more testing
I hooked up a variable 12volt power supply
Set the output voltage at each setting for each speed and turned the motor on. Absolutely no noise!!!!! coming from motor. Plugged the motor back into RV noise came back

[gbkims]

Did some more testing
I hooked up a variable 12volt power supply
Set the output voltage at each setting for each speed and turned the motor on. Absolutely no noise!!!!! coming from motor. Plugged the motor back into RV noise came back

Huh, more gremlins with vent fans..
I guess you matched RV's 12V level on the DC supply.
I'd snap on a ferrite core with a couple of loops of the DC in to the motor and see if anything changes.
There are quite a bit of signals on the DC inside the RV.

[howson]

Did some more testing
I hooked up a variable 12volt power supply
Set the output voltage at each setting for each speed and turned the motor on. Absolutely no noise!!!!! coming from motor. Plugged the motor back into RV noise came back

Turn off the converter and run the fan (the fan will be running on battery power). The converter should have a circuit breaker controlling it in the Power Distribution Panel.

[screamineagle]

Easy enough to validate if you're OK with handling minor troubleshooting. If any of the below gives you pause or something is not clear--don't do it--call for help from an RV mechanic or "hire a friend".

Note I am assuming your Power Distribution Center (PDC) is similar to the one in my 315RLTS. If it's not--disregard this post. (Example of my PDC is in the pic.)



Turn off all a/c components in the trailer.
Turn off power at the pedestal and disconnect the power cord.
Turn the battery disconnect so 12v power is removed from the trailer. (None of the interior lights should work at this point. Neither should the fan.)
Carefully remove all of the blue fuses in the PDC except for fan (kitchen) and the large metallic looking fuses for the slides--leave them alone.
Turn the battery disconnect back on to apply 12v power to the trailer.

Test the fan--does it still make the noise?

After testing...
Turn off the battery disconnect.
Carefully reinstall the fuses.
Turn the battery disconnect back on (applying 12v power back to the camper).
Plug in the power cable and reapply AC power to the camper from the pedestal.

Howard

Tried it all, nothing.
I think where I go next is to see if the power is supplied to the fans with other items on the same line.

[howson]

Tried it all, nothing.
I think where I go next is to see if the power is supplied to the fans with other items on the same line.

By "nothing" you mean the noise is still there with only the kitchen fuse installed? And shore power was removed? If so, that rules out the converter and components not on that circuit.

It may not even be another 12v component on the kitchen circuit causing the problem! It could be noise injected through "EMI", or electro-magnetic induction. Another wire (or even coax) that is physically close to the 12v wire that feeds the fan may be injecting the EMI into the 12v wire. Jkwilson 's input about a poor filtering circuit in the fan motor explains why the noise is heard. gbkims note about the ferrite cores is, I believe, an attempt to block the EMI.

Hopefully I got all those terms correct--if not there are some very knowledgeable individuals that will chime in to help me out.

With an oscilloscope you'd be able to see the noise on the 12v line. It may even be possible to measure the noise with a multimeter set on AC in AUTO. It should be an exceptionally low voltage, but anything is evidence of noise injection on that wire.

Finding the source and separating the wires, or finding the right filter to eliminate the noise on the wire, can be a chore. I'm not experienced enough with configuring filters to advise on that process, but I *think* it's similar to noise reduction on a car stereo wiring. Again--someone will chime in here and correct or amplify on this soon.

I hope you'll continue to post and update the forum on your progress--very curious to what ultimately fixes the problem.

Howard

[screamineagle]

Latest, I replaced the wire coming from the wall switch to the fan, let it hang in the rv (not running through the roof) same thing noise still there.

I recieved a replacement wall switch and a cable yesterday,
Today i will replace wall switch and wire sent to my by Maxxair
I will also try disconnecting conver
I will also disconnect any wire that are on the same line as the fan power.

When thats all done I will drink a beer.
^ beers if it does not work. LOL