greenhouse fan motors

I have pretty much the same thing in my house. i think the motors are

20 years ould now.

Very unlikely to have that many defective motors. I'd look to another problem in mounting or gearing. My first guess would be the motor is too small for the pulley gearing you have, check a new one with an amp meter and see if its pulling more than name plate. If so, change pulleys or go to larger motor.

Also possilbe that mounting is poor taking the bearings out.

I suppose you'de know it you have low voltage problems at your site. Even occasionally kills motors.

Karl

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I'm agreeing w/ Karl; Emerson isn't just some generic import Chinese no-name; generally while they're assembled in Mexico they're good stuff.

A couple of other thoughts -- it's "humid" environment--any chance it's actually condensing environment and you're drowning them in internal condensate? Or are they getting wet from watering system or outside?

On mounting, they're not designed for anything except horizontal so if even slightly off that'll be very bad on bearings.

Are they open-flow or is there air blockage via a damper system or discharge/intake louvers or the like? That could drastically raise the flow restriction and raise motor loading if designed/sized solely for open unrestricted flow...

What does the vendor say? Surely they can't be happy replacing them this frequently if is under warranty?

Do these motors still rotate freely when disconnected, without fan blades? If they're getting noisy, the sleeve bearings may be failing faster than if these motors were used in less severe indoor indoors. I've seen considerable damage from sleeve bearing failures where the rotors drag on the stator poles.

Enclosed motors would very likely last much longer.

TEFC totally enclosed motors are available, and typically have ball bearings, so they wouldn't be affected by shaft rust from humidity, or dust wicking the oil out of the bearings.

Careful with the assumption here - many fans draw _less_ current "restricted" since they move less air, so they are doing less work. Counter-intuitive, but often true. Toss on a meter and try it. I think it was Bruce who mentioned that many people kill furnace blowers by "unrestricting" ductwork to the point that the motors overload...

Depends on whether the restriction raises head pressure significantly...

Really on if the blades have stalled.

And if there's increased head resistance, that's a partial stall...or at least more work to keep going against it. :)

LRA is something else again.

Too little to really judge; more useful than pic of a similar used motor from and eBay auction would have been pictures of the installation and links to the vendor of the fans and specific model to see what the app looks like as opposed to what the vendor spec'ed and the like.

Just checked with a Kill-A-Watt. A muffin-sized centrifugal blower draws 24W open, 18W with either the intake or exhaust blocked. jsw

On 7/11/2013 12:22 PM, Jim Wilkins wrote: ...

OK, let's recast what I was driving at...you're saying there's no fan curve/as-shipped design point for which it's possible the OP has done something to his ducting or louvers or the like that can result in raising motor load above design so he shouldn't/needn't consider that as a possible root cause/factor?

You said that, not me. I posted only the free-flow and fully blocked readings for a small impedance-protected motor that doesn't represent the loading curve of a larger one. The shape of the blades strongly affects the pressure the fan can produce and the full-load power. You'd need a wattmeter and a gage like this:

to determine the conditions of that specific installation. I've done it for the cooling fan for vacuum tube and solid-state radio transmitters, not for HVAC. jsw

On 7/11/2013 4:54 PM, Jim Wilkins wrote: ...

So then why are you hounding me over suggesting a possible area for the OP who's looking into motor problems w/ sizable vent fans in a greenhouse?

I don't have his fan curve; we don't even have pictures of the installation; all I'm trying to do is give the guy some things to go investigate that could help him get to the bottom of his problem.

Certainly he needs far more data than has provided here to have any hope of learning anything specific unless it's truly obvious and then it would seem would already have known...

I'd say that sounds right. Short of physical restriction (drag) it is difficult to overload a fan. Restricted air flow COULD possibly cause a fan motor to everheat due to reduced cooling, but not due to increased load.

Hounding you??? jsw

That motor has Zero cooling. Notice..no internal or external fan on it?

While it SHOULD provide its own cooling with the external fan...often times they dont cool very well because of the design of the center hub of the fan. The motor often times runs in a "dead air space"

Id consider getting a different style motor with an external fan. As for the fan running slowly..that could be for several reasons.

1. Do you lubricate them properly and regularly?
2. Are the run caps going bad?
3. Is the start caps going bad?

1. Are the motors actually the right hp for the load? Would a 1/2hp motor be more appropriate?

Gunner

House voltage is running a little above 120V; low voltage does not seem to be the issue.

A meter suggests that the fans are drawing 5.5A to 7A; the latter number is right up toward the nameplate rating but not way over it.

Some more background, in case it suggests anything:

The salesman who sold us the greenhouse ordered fans with 220V motors for it, even though he had ordered a 120V controller system. He then tried to correct it by ordering new motors only, not complete new fan setups.

The motors were changed on-site by the local electrician who was putting the system together.

So it is certainly conceivable that the belts may be too loose or too tight. I have no sure-fire way to know what the right tension is; they are tight enough that the belt doesn't flap; the adjustment method is so awkward that having the belts too loose seems to be more likely than too tight.

It is also possible that the pulleys are not right in some way. My understanding is that they are the original pulleys from the original motors that were nominally the same HP rating...

Some other sort of problem that I haven't thought of is also possible.

Bob

I am not watering the fans from either side. The installation is a standard type of greenhouse setup; they should not be seeing any more water or condensation than usual.

The mounting is slanted. Again, this is the standard way of installing this fan setup, so I assume the vendor selected motors with this in mind.

The system has the standard louvers opened by air flow.

The vendor does not seem to be happy, but so far they have not offered any ideas...

Bob

You would have been WAY better off staying with 220 volt motors. This is likely the design problem. A 220 volt motor has exactly half the current and runs much cooler.

Surely, your control system just closes a relay (or motor starter relay) so you can run either voltage on the motor. You sound like you're not a EE type, most any competant electrician knows how to easily do this with hardly any rewiring.

If you want to stay with the 120 volt setup at this point, my best guess would be to slow the fans down 20 or 25% with a pulley change. Keep in mind your amp test was only at one point in time, there are likely periods where combinations of heat, humidity, and wind are overloading them.

Good luck,

Karl

Good advice Karl!

Not necessarily. The wattage is the same. 110 just needs heavier wiring to frrd the motor. The motor efficiency is generally pretty much a "wash"

better ratio would likely HELP the situation. It may not be the cure. Also, being BELT DRIVE fans, where is the motor mounted? Is it in the air stream???? Generally motors without venting or fans are used in direct drive fans.