rear AC fan motor

Since I have removed the AC, I'd like to re-use the two nice looking squirrel cage fans as "vent fans" instead of the usual Fantastic fan. Power supply wires first go to a little black box, then to the the fan. Each of 2 fan assemblies has its own box. Box text: "Entstorfilter AMP 2x91 mH vergossene Ausfuhrung Art.-Nr. H11-002-531 S.Nr. 03/06 334


Anyone know what this box does or what input it needs? It would be nice to have speed control.

Closer in on the motor itself:

Konvekta 12V H11-001-274 MADE IN CANADA 0706

https://htac-bus.en.made-in-china.c...tor-Spal-006-A40-22-Konvekta-H11-001-274.html
This copy looks to have options for "with or without speed control resistor"

I'm not understanding how with just 2 wires any resistors would be involved with speed control.

The made-in-china.com illustration has a 4-pin plug, so that version likely has an internal resistor?
If you want speed control, you’ll need to put a resistor pack into the circuit somewhere.
I’m not familiar with the roof a/c units. There may be a resistor pack closer to the controls that drops the voltage reaching the fan motor? It’s an easy but inefficient way to drop motor speed... a lot of power is soaked up by the resistor. Tshe better roof fans use brushless motors and/or electronic controls like pulse width modulation to vary the fan speed and conserve your battery. If your fan is single speed you can probably pick up (or build?) a PWM module to control its speed, though I’d only bother if you want to run it without the engine or shore power.

-dave

I do intend on running without engine or shore power, extensively, so it's worth it to keep investigating.

Here are some measurements with 12V hooked up to the Box input leads:

Fan in open air, no restriction:
Battery V: 12.9
Voltage at box: 10.1 (was using small wires)
Voltage at fan: 9.7 (so the box is making a voltage drop of 0.4)
Amps 13.7 (measured with Victron battery monitor)

Fan outlet blocked by pressing against floor (not 100% blocked but very restricted):
Battery V: 12.9
Voltage at box: 11.42
Voltage at fan: 11.2 (voltage drop through box is 0.2)
Amps:7.5

All voltages were measured with the same multimeter.

I would have expected the fan to draw more power with the outlet blocked, but that's an aside- does any of this hint as to what the box is doing? It looks too big and nicely packaged to be a simple resistor, maybe it has PWM inside? But how would it know what voltage to target, maybe it's able to sense motor RPM through the power circuit?

It's way overpowered, and producing a decent amount of thrust when I hold it, and too much noise. I may try supplying only 5V by using really long wires, see if it quiets down. If that works, I will look into some PWM solutions. Any recommendations?

https://electronics.stackexchange.com/questions/20483/understanding-the-circuit-diagram-on-a-filter

Some hints here, looks like it's some kind of filter, probably not doing anything to the speed or power to the fan.

Found on another site: "It's hard to do PWM into an inductive load without introducing a lot of noise into nearby circuits such as a radio receiver or sound system. It requires a significant amount of additional circuitry to do it well." As the reason why automotive blowers use resistors instead of PWM. Maybe this filter exists because Mercedes was using PWM for the rear AC? If that's the case, all I need to do is locate and re-use those parts.

It looks like the Fantastic Fan uses resistors, didn't find info on Maxx fan. Maybe the losses there are too small to care about, but would be interesting to compare to the factory setup at the same airflow.

If you want a really quick solution, and are willing to only have two speeds, you can simply wire a switch/relay to operate the motors in series (so each sees 6v) or their normal parallel (so each sees 12v).

MB does use PWM throughout the Sprinter (such as the EGR), but usually not to heavy-load motors. Those get resistors.

As for your voltage/current readings, depending upon the design of the fan, blocking flow can lower the amount of work being performed (volume of air moved). Less work = less energy required. A vacuum cleaner is a good example of this: block the hose, and the motor speeds up since there's no air coming in to be pushed around.

--dick

The series parallel is a good idea, but I'm only planning to use one of the 2 motors, for now. Each motor has 2 fans for 4 fans total. I found the relevant part of the service manual

and wiring diagram


Can someone help interpret what's going on here? Are there 2 speeds? 3 relays?

the motor speeds up since there's no air coming in to be pushed around

Click to expand...

Thanks, totally makes sense when said like that

The more I dig into this, the more impressed I am with the fan engineer at Mercedes- each one appears to be balanced with little weights that clip onto the fan blades. Rubber isolation mounts. Nice fitment and sealing of the air ducts with good materials. These noise suppression filters... Lots of attention to detail. I wish this guy could have been involved with the paint/anti-corrosion planning.

Got it installed today, talk about overkill for a bathroom vent, this thing is like a miniature hurricane

Here's what I'm thinking for the controller:
https://www.amazon.com/RioRand-7-80...rd_wg=2ZDwT&psc=1&refRID=VRHCP0GP0254T0ZC16JJ

markxengineering said:

The series parallel is a good idea, but I'm only planning to use one of the 2 motors, for now. Each motor has 2 fans for 4 fans total.
...
and wiring diagram

Can someone help interpret what's going on here? Are there 2 speeds? 3 relays?

Click to expand...

ROFL.... ... they're doing series/parallel ... the left-most relay in the drawing (shown "at rest", which is the slower speed) is putting the left motor (which has a permanent ground connection) in series with the right motor.
If the left relay is pulled in, the right motor is then connected directly to ground, so it should speed up.

That drawing must be missing wires (and/or confused), since it would appear that the left and center relays coils are tied together... which means that you'd always be breaking the series connection when the center relay is powered??
And it appears that the right-most relay has nothing connected to its 87 and 87A contacts???
Likewise, when the right motor is getting full power, the left motor doesn't get anything???
It would appear that triangle E powers all three relay coils, whereas triangle K only powers the right-most relay coil, with the diode blocking current flow to the other two.

--dick

Thank you for looking into the wiring- I went the route of the Amazon pwm controller, and will report back about how it works. I did not go with a model that has "soft start" due to the cost difference. Does anything shown above indicate that Mercedes had some kind of soft starting function?

markxengineering said:

Thank you for looking into the wiring- I went the route of the Amazon pwm controller, and will report back about how it works. I did not go with a model that has "soft start" due to the cost difference. Does anything shown above indicate that Mercedes had some kind of soft starting function?

Click to expand...

No. The relays as shown in the schematic are simple make/break switches.

-dave

markxengineering said:

Thank you for looking into the wiring- I went the route of the Amazon pwm controller, and will report back about how it works. I did not go with a model that has "soft start" due to the cost difference. Does anything shown above indicate that Mercedes had some kind of soft starting function?

Click to expand...

Hey there, I was wondering how this worked for you? Did you end up giving it a shot? I am thinking about doing something similar.

Thanks!