Maxxfan 7000K voltage regulator

[richm]

Originally Posted by tdf-texas

I just went out to check. AM/FM/over the air TV - no noise.

Below is attached the datasheet for it. The datasheet has some errors - it's made in China.

Analog Devices has data sheet for the LTC3780 chip itself. A sample complete circuit is here.

The data sheet suggest it operates in the 200-400Khz range.

[medora]

Originally Posted by rubicon327

Is there any chance you're mistakenly in AUTO mode and the fan is reacting to a cabin temperature that is lower than the set point? Is the green light on next to the auto button? This has been known to catch some MaxxFan owners by surprise.

I wish this was the case, but I don’t think it is. I’ve now spent over 3.5 hours on hold with them over 3 days. Furious. I’m going to email the guy someone suggested for help, as I have no idea what to do here and we really could use a freaking functioning fan on our upcoming trip.

I’ve been trying to also figure out a number for their corporate office - does anyone know what the parent company is? I can usually figure this out, and in this case it looks like they’re in Wichita, but I can’t find a working number.

[cpaharley2008]

Try this https://www.airxcel.com/rv/maxxair/p...s/fans/maxxfan

[medora]

Originally Posted by cpaharley2008

Try this https://www.airxcel.com/rv/maxxair/p...s/fans/maxxfan

I tried this last week - no go. But I did hear from
Perry, the guy who someone posted an email for. The funny thing is that Perry called me back by mistake thinking I was a vendor, so who knows if he would have called otherwise. Anyway, he had me check the voltage in the board itself, which is still almost precisely 12v. He then set up a motor replacement. But the more I think about this, the more dubious I am. The fan runs, it just doesn’t STAY running - the beeping and flashing green light signal shutdown. And I really don’t want to wait 6 weeks for a new motor if the issue is really the board. Any thoughts on this?

[Rossue]

This might help-

https://www.youtube.com/watch?v=5TmFnWKPoiY

He mentions with the motor disconnected you can feed 12V straight to it to test the motor. Also, he mentions the keypad could be an issue and he shows his has some mild corrosion.

[medora]

Originally Posted by Rossue

He mentions with the motor disconnected you can feed 12V straight to it to test the motor. Also, he mentions the keypad could be an issue and he shows his has some mild corrosion.

Thanks, this is helpful … tho we have confirmed the motor does work, because the fan blades spin. I just got a response from Perry about this: “ I am suspecting that the motor is back feeding voltage and kicking the PCB out.”. Hmmm. I didn’t even know that would be possible, let alone likely, but i am still concerned the motor isn’t really the issue. BTW, it’s a very new fan which we’ve only had out once or twice, no corrosion anywhere and I’m not even sure we’ve really run it in any damp weather.

[medora]

A final update on this - I did end up getting my hands on a new board, installed, and ... same problem. So rather than wait for the replacement warranty motor for 8 weeks (the current ETA) - I ended up just buying an entirely new fan, and am sorting it out with Maxxfan now as the one I'm replacing made it through ONE trip before frizzing out. I'll never know whether the motor was indeed back feeding voltage, as the MaxxFan tech thought, but it does seem that was likely.

Meanwhile, hours and hours later -- at least I have a nice breeze in my sweet little 17B.

Thanks for all your help.

[dstreight]

Exact same problem here. Brand new MaxxAir fan that doesn't work right out of the box. I have another brand new MaxxAir fan...just need to take the time to pull the board and swap into the presumably defective unit.

So frustrating they can't seem to get their design department and QC under wraps. I just wish, like so many companies, they would focus on making a product better...rather than cheaper.

[sameo416]

Originally Posted by tdf-texas

Per the manufacturer's recommendations:
Dometic 2554/2663 9.6-18 volts
Suburban SW6DE 10.5-13.5 volts
Maxxfan 7000K 10.6-13.7 volts
Atwood AFSAD12 10.5-13.5 volts
Dometic 9500 10.5 – 15.5 volts
2017-2018 LED light <=12 volts

The ones in red should be considered weak links.

Ken (wetzk) contacted Dometic to get the voltage range for the awning and asked about having other devices on the same power circuit as the 9500. Here is their response:

Dometic.com Support Form - US - productsupport - rv - b2c

Hello and good morning. No there should not be anything else connected to the wiring for the awning..

This is stated in the Dometic 9500 installation manual as well but the Dometic rep confirmed it. The Dometic 9500 must be on a dedicated power circuit. This could be a justification to void warranty if Dometic pushed it.

I bet if you check your trailer wiring, you will find multiple devices being powered by the awning circuit. My trailer has the range vent fan and half the lights on it. So the mission to clean up the wiring continues.

As a footnote to confirm this really useful discussion to May 2023:

Just checked this with Dometic. My 2021 has good lights and Maxxfan for 14.6 volts (although we just had the fan protection shut it down, lol). Dometic confirmed that its furnaces are still 10.5-13.5 volts.

[Lanark Camper]

We installed a regulator for our fan a couple of years ago. A couple of days ago with the fan running we heard two loud pops ! Then some smoke came out of the fan shroud. I pulled the fuse and opened the fan up.
Looks like two of the regulator electrolytics self destructed. It had been raining and there was some moisture in the fan shroud. The fan board is also toast. So I’ve ordered a new fan board, some fresh conformal coating for it. I’ll install the voltage regulator in the converter box so the whole circuit is regulated. I have a spare regulator waiting at home.

Bob

[Ron in BC]

Was the failed one conformal coated?

It's a tough environment, too bad the board has to live in it.

I've had two previous problems but a session with a hair dryer solved them.

Ron

[Lanark Camper]

No it was not coated, live and learn ! This is beyond the hairdryer fix 😉.

Fortunately no big deal. I’m at the point of using a resistor to drop the fan voltage to a medium speed and forget and boards at all. One way or the other this is my last Maxx board !

Bob

[Chamberman]

The fact that both output capacitors blew simultaneously is very telling. The output voltage greatly exceeded the max rating of the capacitors. This was almost certainly due to the failure of the regulator chip or pass transistor which allowed the full boosted voltage to show up on the output rails. This high voltage spike is also what killed the maxx fan control board.

While it could be moisture related its most likely due to a borderline design or components.

Typically one of the most expensive components on one of these boards will be the heatsink and capacitors and thats also where the designer will go with as inexpensive an option as they think that they can without affecting short term reliability. I say "Short Term" because they really do not care what happens to the unit 6 mos or more down the road. While the heatsink may be acceptable when its mounted in a certain orientation in an open environment with convective air movement, mounting it under a cover and with the fins facing horizontally and downwards likely reduces the Deg C/W rating by at least half. this means that the life of the regulator pass devices will be greatly reduced in high load conditions.

You may want to consider mounting the unit near the WFCO and orienting it in such a way as to allow for the heatsink fins to run vertically. In addition, adding a larger heatsink would help immensely too.

There's a lot of boards out there, of all types, available from oddly named Chinese sources. I do a lot of electronics work and I use these inexpensive boards for projects many times. The Chinese boards of unknown origin will use many borderline or outright fake parts. I'll usually try to buy them as a kit if available and then I'll source new capacitors from a reliable US supplier like Digikey or Mouser and I'll upgrade the heatsink when possible.



This is probably more info than you wanted, but I thought I'd give an opinion so possibly you can avoid killing another expensive Maxx fan control board.

[Lanark Camper]

I really appreciate your detailed analysis and advice, thanks !

What you said makes perfect sense. I will mount it near the wifco on a heat sink. I could shop for a regulator with a higher current rating I suppose.

Bob