HVAC Fractional HP Fan motors- Why are most of them junk, and how to get better ones?
Back when I was working in maintenance, I always wondered why every small (1/20 to 1/3 hp) blower motor/condenser fan was a complete pile of garbage. It seems like any machine we've purchased with one of these, it's ended up failing within about a year and a few months time - I guess they really have the warranty thing planned out right. And this goes form everything from test cabinets to small chillers, cabinet coolers, etc.
All of these motors have plain bronze/oilite bearings, with no provision whatsoever to oil (or the occasional small slot which directs oil kinda-sorta near)
Typically one of the bearings is a a hemispherical shaped one that wallows around in the housing and generally makes it unrepairable by the time it's pulled out.
Does anyone actually make a fractional hp ac motor with ball or needle bearings?
I wish they would...
Yes, and no... I've seen plenty of small AC electric motors that had replaceable ball bearings, but they were specific-purpose motors, made to fit a specific machine.
Originally Posted by Muffler Bearing
The problem with lots of HVAC stuff now, is that the motors are all made for specific purpose... not a generic mount, and oftentimes, not a standard single-speed setup... so if the manufacturer decides to go oillite instead of having the motor made to industrial durability, you're kinda screwed.
It's sad. We know how to make durable, long-lasting machines, but we don't... and then we choke on the price to replace it, and environmental friendlyness when it goes to the scrap bin. Seems to me that if it was built better from the git-go, it would last a whole lot longer, and waste less energy and resources over the long-term.
I don't know that oilite is automatically trash...... I have fans that work about 12 hours per day half teh year, and have been doing it for years, and they are oilite bearings.
The biggest issue with oilite is that in some apps (like direct-drive fans) there is a felt reservoir of oil, but that is supposedly a "lifettime supply".... well it ain't in a typical fan. The shaft is usually not protected from the airflow.
In fans the more exposed bearing normally collects dust, and that then wicks out the oil. That "lifetime supply" gets exhausted fast, and if you do NOT oil the "pre-oiled for life" bearing, it will have a mighty short life, may bind up, or may just waller out.
If you make a habit of oiling them, they last. Where oilite stinks is in a belt-drive application, seems like they will egg-out no matter what. The oil doesn't come out until after the start-up, and so it starts up rubbing every time, losing a tiny bit of bearing.
So the issue may be less the motor or the bearing, than it is an application-type issue, not thinking about the dust and wick-out issue.
I used to work for a company that as a side line, represented a mfr of muffin fans for enclosure cooling. They offered "maintenance free" fans and they offered ball bearing versions, which cost about 50% more. Nobody, and I mean NOBODY, bought the ball bearing fans. 5 years at that company, their sales of ball bearing fans was zero. The mfr was angry about it because they made more profit on the ball bearing fans and wanted our salesmen to push for the upgrade since they were made in the USA and the others were brand-labeled cheap imports from Asia. Didn't matter, nobody wanted to pay extra for them.
That company eventually sold out to an Asian competitor and the US production was shuttered. So what I am saying is, we (as consumers) get what we collectively ask for.
I specified a goodly number of "muffin style" fans for our products at the old employer.....
I NEVER specified a ball-bearing fan..... or more accurately, I only did it ONCE.
Our product was audio equipment, and ball bearing fans clicked and rattled way too much. We got so many complaints about fan noise that we almost recalled the products, but decided in the end to just change over.
Plain bearing fans were far quieter and lasted a long time. Our preferred vendor was Comair-Rotron, based on performance, so you already know we were not all about lowest possible cost only.
Things are not always what you assume they are......
JST's note about belt-drives is an excellent point- in belt drives, and also in chain and gear (which don't apply to HVAC blowers), the driving load is 'overhung'... that means there's side-thrust on the shaft, which isn't so great for a bronze bushing. With an end-mounted motor in a big squirrel-cage blower, the blower spool frequently SURROUNDS the motor, which helps keep it cool, and as noted, tends to dry the wick and suck dust, etc., into the bushing... neither good... but the load is centered on the motor's axis, so the greatest moment is torque... the only lateral loading is the weight of the blower spool and hub. If it's pulling a belt, the sheave-end bearing is taking a pretty good lateral load just for belt-tension's sake, and the bushing is perpetually loaded to one side.
I had one situation many years ago where a wallowed-out bushing caused a furnace blower to stop... it was Christmas day, and a friend called in distress. I found that it's bushings were wallowed out in the bottom (weight of the rotor), so I loosened the mounting nuts, spun it about 120 degrees (all I could make it rotate on account of the wiring), and locked it back down. That blower ran for the rest of the winter, and the whole furnace got changed the following summer. If it'd had good sealed ball bearings, I'm sure it wouldn't have failed, but as noted, we sleep in the bed we make.
I could write a whole service manual on just furnace draft inducer motors alone. Lubrication is everything with these motors, and what you say is true about the slot that kinda sorta directs the oil to the bearing. I have disassembled these motors by un-crimping the ends and drilling out the rivets holding the bronze bushing and felt oiler. I then polish the shaft where it runs in the bushing and install a new quality felt since the old ones turn to mush. Then I make my own oil tube to reach the felt and insure the oil gets there. Re-assembly consists of using small screws and nuts in place of the rivets and re-crimping the case. This is the only way to get a long reliable life out of these motors. This all takes time and patience,or you can just do what everyone else does, wait until the motor fails, then pay to have it replaced.
Interesting post showing a solid counterpoint that may shed some real insight.
Originally Posted by JST
A mechanical clink/whirr is typically associated with "a piece of junk", so maybe after enough customer complaints early on, the major players in HVAC just said hell with it and made the decision to stay with sleeve bearings.And the knock-offs.. well, they are going to go cheapest route no matter what, so it's not even a real design decision there.
For HVAC in an office or residential environment, I'm sure low noise is one of the absolute top design priorities, with the "cheap" units being distinguishable only by the fact they make more noise.