Request for fan re-wiring advice

[merrill77]

So I have this fan that I liberated from my old heat pump when it was replaced. I'm planning to try spraying finish soon and need a decent fan to ventilate the garage when working inside. I have a little box fan, but this will move a lot more air...and it's got MORE POWER!!! . I'm getting ready to wire it up for testing before building a box to put it in. I think I've got a handle on the wiring, but though I'd post it here before melting anything.

Here is the wiring label from the motor. The colors listed match the wires in the harness, so only one surprise here - this implies a two-speed motor, though only one speed is listed on the other half of the label (800 RPM, IIRC). That isn't the way I expect to see a switch drawn...hmmm...I should try the black/red separately to confirm?

I got a surprise, however, when looking at the capacitor. I'm accustomed to capacitors having two terminals, not three.

They are labeled FAN, C and HERM. FAN and C (common) are obvious enough...but HERM left me scratching my head??? A little googling revealed that would go to the compressor. Ok, so the capacitor has 3 terminals because it serves two purposes? Well, I don't have to worry about the compressor, so I feel like I can ignore that one.

So this now seems pretty straight-forward: Coming from my 240 power cable, ground will go to the fan housing while the two power leads will go to (1) the purple wire and (2) either red or black wire (try each to pick a speed?). The capacitor goes between purple (C) and brown (FAN).

Anyone want to chime in before I set something on fire?

TIA!
Chris

 

[NC_Horn]

A dual run capacitor has 3 terminals. The condensor mortor will have a wire on the fan terminal (usually the lower uf/mfd value and is labeled on the capacitor as "fan") and the compressor "start" wire is connected on the "herm" terminal (usually on the higher uf/mfd value herm stands for hermatic compressor). The third terminal is labeled as "common" or "c". ....... Thanks google lol.

 

[scsmith42]

Chris, I think that you correctly identified how to wire the fan (at least that's how I would wire it).

Scott

 

[Touchwood]

So I have this fan that I liberated from my old heat pump when it was replaced. I'm planning to try spraying finish soon and need a decent fan to ventilate the garage when working inside. I have a little box fan, but this will move a lot more air...and it's got MORE POWER!!! . I'm getting ready to wire it up for testing before building a box to put it in. I think I've got a handle on the wiring, but though I'd post it here before melting anything.

Here is the wiring label from the motor. The colors listed match the wires in the harness, so only one surprise here - this implies a two-speed motor, though only one speed is listed on the other half of the label (800 RPM, IIRC). That isn't the way I expect to see a switch drawn...hmmm...I should try the black/red separately to confirm?

I got a surprise, however, when looking at the capacitor. I'm accustomed to capacitors having two terminals, not three.

They are labeled FAN, C and HERM. FAN and C (common) are obvious enough...but HERM left me scratching my head??? A little googling revealed that would go to the compressor. Ok, so the capacitor has 3 terminals because it serves two purposes? Well, I don't have to worry about the compressor, so I feel like I can ignore that one.

So this now seems pretty straight-forward: Coming from my 240 power cable, ground will go to the fan housing while the two power leads will go to (1) the purple wire and (2) either red or black wire (try each to pick a speed?). The capacitor goes between purple (C) and brown (FAN).

Anyone want to chime in before I set something on fire?

TIA!
Chris

Chris..are you talking about the motor driving the outside unit fan??..that's the compressor fan (big 30" diam fan). The air handler has the squirrel cage blower...usually two speed and 1000 CFM to 1500 CFM

Don

 

[ehpoole]

After you finish wiring your new fan, DO NOT forget to restrict the exhaust port before you power it up. These fans are meant to run with the restriction normally imposed by your home's HVAC ductwork and air handler... which will likely be missing in your new configuration. You can remedy this by choking off about ~1/3rd of the exhaust port.

Without this restriction you can overload and burn out the motor in short order -- even if the motor should prove sufficiently robust that it does not burn up, it will nonetheless very much appreciate the gesture and last a good deal longer with some restriction.

It can seem a bit counter-intuitive that restricting the exhaust would reduce the work load, but if you think of the work load as being defined by the amount of air being moved, it's not hard to understand how an unrestricted motor can overload while a 100% restricted fan (which is effectively spinning within its own vacuum) does very little work by comparison.

Best of luck with your new toy and be careful with the electrical.

 

[merrill77]

Chris..are you talking about the motor driving the outside unit fan??..that's the compressor fan (big 30" diam fan).

Yes - the big compressor fan. I have the squirrel-cage fan from the air handler as well, but I am thinking the bigger fan is going to move a lot more air in this configuration (basically an overgrown box fan).

 

[merrill77]

After you finish wiring your new fan, DO NOT forget to restrict the exhaust port before you power it up. These fans are meant to run with the restriction normally imposed by your home's HVAC ductwork and air handler... which will likely be missing in your new configuration. You can remedy this by choking off about ~1/3rd of the exhaust port.

Thanks for the warning, but I should have been more specific - I'm not using the squirrel cage fan from the air handler. I'm using the big fan from the compressor/condenser unit. I would think this expects some level of resistance as well, but I'm using the original top/vent from the unit - hoping that will approximate the resistance well enough (in addition to it being inside a boxy frame and having some sort of safety grid on the intake side.

 

[DaveD]

Couple of cautions on exhausting the garage....

Put a furnace air filter ( or two)in the box to try and capture spray mist. Put the filter before the air flow hits the motor, not after, to help protect the motor. You don't want to end up with a haze of spray mist all over the outside of your house. Nothing like all of a sudden noticing the front of your house has a 5 o'clock shadow. It's amazing how far overspray mist can travel.

Limit you spray material to water based products. That is not a explosion proof fan. You don't need the fan to mal function, find the air volatility is just right, and have a explosion. I know its highly unlikely and very low possibility it could ever happen but better safe than sorry.

Park your vehicles as far away as possible. Don't need any mist on them. Just because you can't see the mist doesn't mean it's not there. My neighbor found out the hard way that spraying outside ( i know this isnt your case) can have mist travel at least 20+ feet and land where its not supposed to (my truck)!

That mist will settle on everything in sight in the garage even if you can't see it initially. Be particularly aware of a garage door that is in the up position. I learned (the hard way) to cover the front face of the garage door with plastic even if it was open only one or two feet. If its open all the way cover it for sure.

 

[Mike Davis]

Couple of cautions on exhausting the garage....

Limit you spray material to water based products. That is not a explosion proof fan. You don't need the fan to mal function, find the air volatility is just right, and have a explosion. I know its highly unlikely and very low possibility it could ever happen but better safe than sorry.

This is not a rare occurrence, Modern spray booths are built with one weak wall designed to blow out and release the explosion outside the main building because so many entire manufacturing plants were destroyed by paint explosions.

 

[merrill77]

I'll be spraying laquer via an HVLP gun...it dries so fast I'm not too concerned about the overspray.

Thanks for the additional safety advice...my options are
(1) spray in the garage with this fan or a generic box fan (remote chance of explosion)
(2) spray in the garage with no fan (and breath more fumes)
(3) spray outside (still have to deal with fumes on breezeless days...and deal with stuff falling off the trees onto my work)

None of them optimal

But...that isn't what this thread is about, so I'll get back on topic: No words of imminent danger about my wiring question, so I'll give it a go tonight and see if I smoke anything

 

[FredP]

OK. couple of things come to mind. [and I spray a LOT of lacquer] You will need a respirator. [this will quickly become clear to you] You can blow yourself and your home to kingdom come with that type of fan motor. [it happens] It doesn't matter that the lacquer dries almost instantly. the overspray [yes there will be some] is highly combustible even though it is dry. [it is not cured] If you're garage workshop is attached to the house be prepared to hear what for from loyl. The smell can linger for days. You're house and you're lungs though so do as you will. I have a couple of extra computer fans that are explosion proof that I will let go cheap if you are interested. I mount them on a piece of scrap with a on off switch and put it in a window blowing out. I turn em on before I start and turn em off long after I am done. this is not the best solution but it is much better than what you have in mind IMO.

 

[junquecol]

Chris, the little box (see the part # right below it) where speed changes occur is a thermal sensing relay. When the temp (air temp, not motor temp) rises above a certain point, fan speeds up. You could replace it with a single pole, double throw (SPDT) switch. You can use a three way light switch for this.

 

[merrill77]

Thanks, Bruce and everyone else.

I wired up the fan last night and it worked It is definitely a two-speed motor...I'm surprised the motor plate listed only a single RPM (820). The fast speed is slower than I expected / remembered. It doesn't move as much air as I would have liked. I might be better off buying a pair of household box fans...but what fun would that be? So I build a box from some scrap construction plywood and have it mounted for use. I still need to put sort of safety cover on the open side (the other uses the grill from the condenser unit).

As an aside, I think I'll simply have the fan blowing into the garage, rather than out. That way the air on the motor is always fresh...alleviating any flammability concerns. I'll put this in one doorway (covering the remainder) so air will be exiting the other door. Also, I already have a respirator. The garage where I'll be spraying is only loosely attached to the house (shares only a brick wall and sealable doorway) and is not where my shop is located. So I think I can keep the household impact minimal. My first project (besides scraps) is very small - a mirror frame. We'll see how that goes.

 

[ehpoole]

Sorry for any confusion, I had assumed we were discussing the centrifugal (a.k.a. squirrel cage) fan, which is what most woodworkers recycle since it is the easiest to design around.

Axial fans (what you have) have a different issue altogether, namely that they do not function efficiently without a good shroud. Ideally the shroud should be equidistant from the blades over its full diameter and should come as close as practical to the blades without making actual contact. The greater the distance between the fan tips and the shroud the lower the efficiency of the fan.

Without a shroud the fan wants to throw air in all directions (rather than in a laminar column) and there is enormous turbulence at the fan tips with air looping from exhaust back to intake, to exhaust and then again back to the intake, which does not add anything to the useful output of the fan -- the shroud serves to positively seperate intake and exhaust and helps to channel the intake and exhaust into a laminar column.

 

[aplpickr]

BIG BOOM IN RALEIGH!!! Your drying lacquer is from evaporation of solvents. It is the solvent that goes BOOM. When the solvent/oxygen mixture gets just right you don't have a shop anymore. Please go explosion proof. This forum does not need any dead members. It ain''t cheap, but the only safe way to do it. Please check local codes before you spray.

 

[merrill77]

Sorry for any confusion, I had assumed we were discussing the centrifugal (a.k.a. squirrel cage) fan, which is what most woodworkers recycle since it is the easiest to design around.

Axial fans (what you have) have a different issue altogether, namely that they do not function efficiently without a good shroud. Ideally the shroud should be equidistant from the blades over its full diameter and should come as close as practical to the blades without making actual contact. The greater the distance between the fan tips and the shroud the lower the efficiency of the fan.

Without a shroud the fan wants to throw air in all directions (rather than in a laminar column) and there is enormous turbulence at the fan tips with air looping from exhaust back to intake, to exhaust and then again back to the intake, which does not add anything to the useful output of the fan -- the shroud serves to positively seperate intake and exhaust and helps to channel the intake and exhaust into a laminar column.

My shroud is pretty close to the original housing that it was installed in. If I had some scrap bending plywood, I could do a little better than the OEM setup.