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Last update 12/09/2010
* Unfortunately Maxxair recently crippled this unit with a 3 speed non-electronic control instead of the infinite speed one as I discuss on this page. 


It is MUCH less satisfactory.  I bought one for my mom's motor home and hate it. It's always either too slow or too fast.

Worse, instead of being a PWM control which minimizes power use, the new "controller" is a simple 3 step resistive controller, with large resistors mounted in the air stream.  So much for power economy.


MaxxAir TurboMax Fan Mods


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The MaxxAir Turbo/Maxx exhaust fan is a wonderful device.  It's rain-proof, quiet and low power consumption.  It can suck or blow and do so at variable speeds*

Unfortunately it had a couple of problems that were quite annoying.  The first problem is that the thermostat cycles too rapidly.  There is too little deadband in the electronic controls.  Under the right conditions it can cycle every 4 or 5 minutes. Quite annoying when you're trying to sleep.  Maxxair will provide a replacement control board if you ask but it's much more fun to solve the problem yourself.

The second problem is that the Pulse Width Modulation (PWM) speed control emits a lot of electrical interference (EMI).  In particular, it greatly affected my E-meter, making its readings erratic and pretty useless.

This page documents my solutions to both of the problems.

Breezes blown since -5/23/07


This photo shows the control board removed from its housing.  A pair of capacitors have been soldered across the incoming power terminals to knock down the EMI.  A 1000uF electrolytic to catch the gross stuff and a 0.1uF to catch the high frequency stuff that the electrolytic misses.

Note the long leads.  They are necessary, as becomes apparent in a moment.

Here is the control board with its protective cover re-fitted.  
The red arrow points to the thermister that senses the air temperature and signals the thermostat.  The thing is very small and of low mass which makes it respond to air currents.  The proper way to slow this response is to design in some delay in the electronics.  Since I didn't want to modify the controller itself, I added thermal mass to the thermister.  
Here we see yet another use of good old silicone RTV rubber - adding thermal mass.  The red arrow points to the glob of RTV squirted on the thermister.  No computer modeling was performed - I just squirted until it looked right.  
The controller back in its plastic housing.  The necessity of the long leads on the caps are now apparent.  They are secured against vibration with yet another glob of RTV.