3D printed Lamb 7.2" -> 8.4" adapter.

[Hatsuwr]

My central vacuum's rotor burned out, and considering the cost of just a replacement rotor or a similar motor, it made sense to upgrade the motor for a bit more performance (moving from an estimated 384 air watts to to 700). I saw that the 8.4" generally have the same mounting pattern as the 7.2", but they have a sloped bottom instead of the flat bottom of the 7.2". This makes sealing against an existing housing a bit more complicated. You can see the difference below:



I figured an adapter would be pretty easy to make. It would need to have a flat bottom to sit against the vacuum housing, a groove around the bottom outer circumference for an o-ring to assist in sealing against the housing, a flat ring on the top to interface with the flat outer circumference of the bottom of the motor for primary weight bearing, and a slope that closely follows the slope of the motor for secondary weight bearing and sealing. I also added some walls that go up the sides of the motor for better sealing there.

Here is the cross section of what I ended up with:



And the whole part, with some softened corners:



I only have undyed filament, so it's a bit hard to see much detail of the actual part with a picture. I also need to tune my printer a bit more to give a nice finish. I printed in ABS with 20% infill. Total filament used, including supports, was about 180 grams, so a material cost of ~$4.

The part turned out quite close to what I wanted, with a couple exceptions:

1. The inner diameter of the thin walls going up the side of the motor is right around 1 mm too large. Better too large than too small for the first print though, and it's easy enough to seal that gap up.
2. The sloped part that interfaces with motor wasn't sloped quite enough. This made it so that weight bearing was happening around the hole in the motor for air intake instead of around the rim. I'm again glad the error was in that direction though, since some careful heating with a heat gun allowed me to sort of mold it against the motor. Still a bit of pressure being applied around the air inlet, but much less. Plus, ABS is flexible and will creep a bit over time. On a reprint I might lower the inner part of that slope very slightly - less than a millimeter to start with.

I tried attaching the file for the model, but I don't think its format is allowed on the site. If it doesn't work and if anyone wants it, just send me a message and I can email it.

 

[Vacuum Facts]

Why did the rotor burn out? I noticed the electrical power consumed by the motors weren’t mentioned. How many Watts do they both burn through? I ask, of course, since in earlier discussions we’ve established the best cleaning performance can be achieved with just a few hundred Watts with the most superior designs, and I was interested.

Given that, if you use a more powerful motor, how do you know it isn’t going to get too hot either to be harmful to its own lifetime (following Arrhenius) or a danger to its surroundings if its temperature gets too high with your modifications? Or is it suck it and see?

 

[Hatsuwr]

Why did the rotor burn out? I noticed the electrical power consumed by the motors weren’t mentioned. How many Watts do they both burn through? I ask, of course, since in earlier discussions we’ve established the best cleaning performance can be achieved with just a few hundred Watts with the most superior designs, and I was interested.

Given that, if you use a more powerful motor, how do you know it isn’t going to get too hot either to be harmful to its own lifetime (following Arrhenius) or a danger to its surroundings if its temperature gets too high with your modifications? Or is it suck it and see?

Guessing it was an internal short that caused it. The motor had a few thousand hours on it, so a good life for a motor of its type and implementation.

Full power consumption and performance details are given in the spec sheets of both of the motors. The new one uses more power at any given system restriction, but is more efficient and has a better cooling system.

I wouldn't necessarily agree with the statement about best cleaning performance. It will definitely depend on tool size and geometry, and the surface being cleaned. The low hundreds of watts definitely isn't at the point where gains in performance stop though.

All that said, cooling of the motor definitely isn't a concern. As long as you don't obstruct the motor's air intake/exhaust and have a separation between the two to prevent hot air recirculation, then it's operating within intended parameters.

 

[Vacuum Facts]

Can't easily find the spec sheets. Could you state what their motor powers are?

Edit, I found them. The electrical power consumed is always hidden and rarely volunteered...and it's clear why: ~1.4 and 1.8 kW respectively! Comparable to a winter room heater, but less than some of the most wasteful mains machines.

Earlier, I meant performanced measured reputably and independently to formal industry test standards.

Incidentally, motor airwatts listed (~384/700) are not the same as airwatts present at the cleaner head (the only location relevant for cleaning) in a given situation (varies in use), since air resistance in different parts of the air circuit varies. They'll be relatively greater under identical use conditions for the second motor though, and therefore suction pressure will be greater (equations). Hopefully there's no head clamping.

Interesting project though. I can't see the typical user doing this kind of thing though.