EE's and Electricians - I need help w/ a duct fan project for heat distr.

[DSinOR]

Hello! 

I found an old McLean Engineering cooling fan.  I removed the squirrel cage fan assy from the chassis. 

The motor is marked "115v, 2A, 3100rpm, Capacitor 4mfd @ 400V, Class F, thermal protection", etc. 

A wiring sticker on the chassis: "Air Flow Switch: White=common, Black=N.O., Green=N.C."

It moves a LOT of air, like a leaf blower.  It's smooth but a bit loud, and it's a hog.  Startup peak is 2.4A, 250w.  Running = 1.15A, 140w.

The fan assy is small enough to fit in a short wood-joist "ductway" in my house that allows heat from the woodstove to distribute into an adjacent area.

My project is to modify the fan assy so that it runs much slower (quieter and uses less power), and then install it into the ductway to pull heated air into the other rooms.  Conveniently, I have romex passing thru the ductway, so I can install a junction and switched receptacle.





Questions:
1 - what is the purpose of the Nytronics 4mfd 40vDC capacitor on the N.O leg?  The cap was mounted to the exterior steel surface of the chassis.  Is this an oil cap, or dry?  Is it a filter of some kind, or related to startup draw, or what?  (these questions are just for my education, thanks  )

The existing motor is strong and smooth and quiet by itself; no slop in the bearings/bushings; turns real easy. 

2 - What's the best approach?  Is there a reasonably efficient way to slow down the existing motor?  Or do I need to replace the motor with a smaller one? 

The fans come off easily.  They are on 1/4" shafts on either end of the motor, held in place with set screws.   

3 - Is there a chart somewhere that lists rpm/fan diameter/cfm lookups? 

Possibly, I could get a motor with one output shaft and use with one fan instead of two.

4 - What about DC motor running off a wall wart or other transformer?

5 - lastly - where does one buy small and medium size electric motors?  Are surplus items okay or is it better to buy new?  Links to favorite suppliers? 

THANKS!   

[rossw]

Questions:
1 - what is the purpose of the Nytronics 4mfd 40vDC capacitor on the N.O leg?  The cap was mounted to the exterior steel surface of the chassis.  Is this an oil cap, or dry?  Is it a filter of some kind, or related to startup draw, or what?  (these questions are just for my education, thanks  )

2 - What's the best approach?  Is there a reasonably efficient way to slow down the existing motor?  Or do I need to replace the motor with a smaller one? 

Hopefully you'll get some more informed responses, but here's my take on it.

1. The capacitor is likely to give the motor some starting torque by synthesising a "split-phase" supply (phase shift with the cap) onto a "start winding" in the motor.
Commonly, motors have a centrifugal switch in them to disconnect the start winding once the motor gets up to speed. It's possible they're using the airflow switch for this purpose.

2. A "reasonably efficient" way to slow these things down and reduce their power consumption - without throwing away half your power - is to add a capacitor in series with the whole lot. Capacitors are good voltage dropping elements in AC circuits, because they have low *resistance* but reasonably high *reactance*. This lets them not actually consume *POWER* (like a resistor would). The value cap you need will depend on the power being drawn, the frequency of the supply, and how much voltage you want to drop. I could give you the formulae, but I doubt it'd help you a lot. Easiest is to do it by "trial and error". Get some old motor run caps of various sizes and just try them. I'm not terribly familiar with 60Hz/110V stuff, but I'd start with about 20uF (roughly) and see how it goes. If thats too fast, go smaller. If the motor doesn't start at all, or is too slow, increase. (Parallel caps to increase their value if you don't have a larger one. 20+10 in parallel = 30uF)

[wpowokal]

What Ross said but I say the capacitor is a start/run capacitor ie it is not switched out of the circuit. While there are possible leanings in your proposed project, for a practical approach buy a similar fan of correct air flow capacity. Guessing but it looks like an oil filled capacitor.

allan

[bob g]

one thing interesting about a squirrel cage fan is you can choke down the intake and not load the motor
this will reduce airflow and usually quiet the fan too.

i am betting for a start run cap too, most of these little motors don't seem to have a centrifugal switch in them.

try blocking partially the intakes of the fans, and see how many amps it draws, you might sense the motor speed up
a bit, but it can't go faster than its syncronous speed anyway, so unless the amps increase there should be no harm done.

bob g

[Opera House]

These small motors have a lot of slip and you can increase that slip by dropping the voltage to thr motor to a point.  My furnace blower was too fast because it was a retrofit with very large diameter ducts.  I dropped the voltage about 20V with a buck transformer and restricted the input size.  Overall, this is a bad idea.  The motor will run hotter and may not start at times.   If the fan has an even number of blades you could remove every other one or use just one side.

[ghurd]

DC fans tend to use less power.
Changing the motor to DC could be expensive.

How much air do you really need to move?
Neither of these will be "like a leaf blower", but cheap and low power DC.
http://www.surpluscenter.com/item.asp?item=16-1390&catname=electric
http://www.surpluscenter.com/item.asp?item=16-1256&catname=electric

G-

[12AX7]

Questions:
1 - what is the purpose of the Nytronics 4mfd 40vDC capacitor on the N.O leg?  The cap was mounted to the exterior steel surface of the chassis.  Is this an oil cap, or dry?  Is it a filter of some kind, or related to startup draw, or what?  (these questions are just for my education, thanks  )

2 - What's the best approach?  Is there a reasonably efficient way to slow down the existing motor?  Or do I need to replace the motor with a smaller one? 

Hopefully you'll get some more informed responses, but here's my take on it.

1. The capacitor is likely to give the motor some starting torque by synthesising a "split-phase" supply (phase shift with the cap) onto a "start winding" in the motor.
Commonly, motors have a centrifugal switch in them to disconnect the start winding once the motor gets up to speed. It's possible they're using the airflow switch for this purpose.

2. A "reasonably efficient" way to slow these things down and reduce their power consumption - without throwing away half your power - is to add a capacitor in series with the whole lot. Capacitors are good voltage dropping elements in AC circuits, because they have low *resistance* but reasonably high *reactance*. This lets them not actually consume *POWER* (like a resistor would). The value cap you need will depend on the power being drawn, the frequency of the supply, and how much voltage you want to drop. I could give you the formulae, but I doubt it'd help you a lot. Easiest is to do it by "trial and error". Get some old motor run caps of various sizes and just try them. I'm not terribly familiar with 60Hz/110V stuff, but I'd start with about 20uF (roughly) and see how it goes. If thats too fast, go smaller. If the motor doesn't start at all, or is too slow, increase. (Parallel caps to increase their value if you don't have a larger one. 20+10 in parallel = 30uF)

Hello..

My ad/dc motor theory is weak at best.  So I'm not making any sort of comment addressing the use of caps with motors.
With that in mind I do have a question with this statement.

"Capacitors are good voltage dropping elements in AC circuits, because they have low *resistance* but reasonably high *reactance*."

I've always thought that capacitors are "high" resistance devices.  Checking a cap with an ohm meter should always indicate a very high or "open" resistance,  and it's reactance value is a (inverse)  function of frequency. 
Maybe I'm getting hung up on terms here but since I'm confused and this is the place to ask questions.. Help!

[DSinOR]

Thanks for the great replies!

If voltage drop = hotter motor and shorter life, that's not my goal.  

How does a rheostat switch work?  Is it basically a variable resistor (ie inefficient)?

In rossw's capacitor proposal, would the motor still get hot because of reduced voltage?  

I'll test the air-restrictions idea.  

Clipping vanes is also a good idea, but I probably won't do it.  This thing is 40+ years old & well made.  Hate to cut it up.  

It sounds like a motor change and perhaps using only one of the fans may be the way to go.  

My goal is a 75% reduction of airflow (and sound and wattage) - always-on, slow, quiet flow of air.

ghurd's links are sensible alternatives, but I want to give it a whirl with my present fans before I resort to buying a ready-made one.  

[DSinOR]

Also in the interest of learning...

I had a list of additional questions about rossw's cap proposal, but thought I'd put them in a seperate post.   I may not use this approach, but I wouldn't mind learning more about the concept if anyone feels like typing... .

1 - The cap in the photos is 4uf 400VDC.  Why is it DC?  Also, it's in series in the black "supply" wire from the extension cord.  How is it not already performing the "voltage reduction" function? 
2 - If I use an additional series cap as suggested by rossw, how would it differ from the existing cap.  Where would I put it?...in series on the white "return" wire of the cord, or
3 - In the OEM configuration, the original cap was fixed to the common chassis, ie it shared the common ground.  Is it necessary that this start/run cap share the same ground in the installed configuration? 
4 - If I search for motor run caps to use as described by rossw, what voltage spec should I be looking for?  Would "anything above 120v" be okay, or what?  Also - does it matter whether I find an "AC" or "DC" cap? 
5 - Does it have to be a "motor run" cap?  In my radial electrolytic grab bag, I see a 100uf 250v and a 22uf 400v and a 33uf 160v.  Are these suitable for testing or extended use?  Or would the moon implode?  I'd hate to do that to the moon. 

BTW - I wouldn't mind having that formula you mentioned.  Link?

[ghurd]

Well... Not exactly 100% correct, but may help you understand it a bit better.

Sort of think about a cap in an AC circuit like a diaphram?
The AC amps sort of go back and forth.  Left and Right?
The AC amps can go Left until the cap (diaphram) is full.  When it is full. no more amps get through.  
Diaphram looks like (
Then the AC wave switches direction, going to the right.  The amps can flow until the earlier amps get out of the cap, and it gets full the other direction.  
Diaphram looks like )

The ohm meter sends out DC to measure resistance.  When the diaphram is full, no more amps go through, and the meter interprets that as being near infinite ohms.

Excede the max voltage, and the diaphram pops.

The DC rating is the peak voltage.  You need more than 200VDC rating on a motor run cap.  Most are rated mid-300V or higher.

The AC amps sort of go back and forth.  In a way, that means there is no Positive and Negative.
That means you can not use a polarized cap.
That means you can not use an electrolytic cap.

There are ways to get around about anything, but not sure I'd want to sleep with some of them operating in the house!

You need a motor run cap.
G-

[Opera House]

Actually, one more thing comes into play.  While the dielectric may be able to withstand the peak AC voltage, that DC cap may still fail due to corona effects.  Corona may occur due to microscopic bubbles left in the foil wraps taht light up like a CFL each time the field changes.  Over time this eats away the dielectric and eventually causes a failure.  Some typs of construction can take it some can't.  As an example X2 capacitors are wound with a metal foil spacer in between, actually forming two capacitors in series.

Another thing.  When a capacitor and inductor are in series the voltage on either component can be much higher than the line voltage.  I use this trick to run 220V fans off 120V line power.  This happens anywhere near resonance.   So randomly putting a cap in series with a motor can have some unexpected results.

[rossw]

I've always thought that capacitors are "high" resistance devices.  Checking a cap with an ohm meter should always indicate a very high or "open" resistance,  and it's reactance value is a (inverse)  function of frequency. 
Maybe I'm getting hung up on terms here but since I'm confused and this is the place to ask questions.. Help!

This is where the AC theory varies a lot from the DC theory.

Capacitors and Inductors behave completely differently under AC than they do at DC.
"Reactance" is a term that describes basically "AC resistance".

The formulae for capacitive reactance is:

Xc =  1 / ( 2 * pi * F * C )       where F=Hz  and C = Farads

So a 20uF capacitor in a 60Hz circuit will have a "capacitive reactance" of  1 / ( 2 * 3.14159 * 60 * 20/1000000 ) = 132 ohms.

At DC, the capacitor won't pass anything (apart from leakage, and the initial charging current itself). You can *see* this with an ohm-meter. Put it on a lowish range and connect to a 1000uF electrolytic cap - observe the meter kick, then drop back to zero. Turn the cap around and repeat.

So, our 132 ohms of *capacitive* reactance, will behave to the circuit basically ilke a resistor in terms of dropping voltage, however the important difference is that a capacitive load will have the current 90 degrees out of phase with the voltage. Since power in an AC circuit is volts * amps * cos(powerfactor angle), a 90 degree phase shift means cos(90) = 0, so volts * amps * 0 will always be zero.

In real circuits there are some stray resistances, so it will never actually be 90 degrees, but it's very close - and for this reason, caps as AC dropping elements are highly effective.

[rossw]

Also in the interest of learning...

I had a list of additional questions about rossw's cap proposal, but thought I'd put them in a seperate post.   I may not use this approach, but I wouldn't mind learning more about the concept if anyone feels like typing... .

1 - The cap in the photos is 4uf 400VDC.  Why is it DC?  Also, it's in series in the black "supply" wire from the extension cord.  How is it not already performing the "voltage reduction" function? 

If the cap is already in series with the supply I don't fully understand what you have. It would be dropping voltage already. Without a circuit, it's hard to guess, but I thought in your original post you said it went to the (airflow detector) switch?

2 - If I use an additional series cap as suggested by rossw, how would it differ from the existing cap.  Where would I put it?...in series on the white "return" wire of the cord, or

Capacitors in series reduce their capacitance - and like any series circuit, they could go anywhere "in series". It makes most sense from an "understanding what you have after the event" point of view, to lump them all together.

3 - In the OEM configuration, the original cap was fixed to the common chassis, ie it shared the common ground.  Is it necessary that this start/run cap share the same ground in the installed configuration? 

OK, now I'm confused. If it's "in series with" the supply, and "shares the common ground" - that makes it sound to me like it's in parallel directly across the motor.

*IF* that's indeed the case, can you confirm if it's really in SERIES with, or PARALLEL ACROSS the line? If the latter, it is probably as a power-factor correction capacitor to reduce the effect of the motors inductance on the rest of your household wiring.

4 - If I search for motor run caps to use as described by rossw, what voltage spec should I be looking for?  Would "anything above 120v" be okay, or what?  Also - does it matter whether I find an "AC" or "DC" cap? 

The voltage should be "comfortably" above your line voltage - an order of two is "comfortable"
As another poster has pointed out - in some circumstances (particularly near resonance) you can get dangerously high voltages. Best to be safe.

5 - Does it have to be a "motor run" cap?  In my radial electrolytic grab bag, I see a 100uf 250v and a 22uf 400v and a 33uf 160v.  Are these suitable for testing or extended use?  Or would the moon implode?  I'd hate to do that to the moon. 

Motor RUN caps are rated for continuous operation on AC.
Motor START caps are rated for intermittent operation only.
Electrolytic capacitors, except for a few very specific non-polar ones, are absolutely unsuitable for use in this application.

BTW - I wouldn't mind having that formula you mentioned.  Link?

Provided in previous post -    Xc = 1 / (2 * pi * F * C)

[12AX7]

Yes,  I've had the xc=1/2pixfxc pounded into me years ago, as well has hundreds of others (many forgotten).

My hang up was simply the "low resistance" comment. 
I've a good grasp of what the difference is between reactance/impedance/inductance  and their relationship to frequency. 

ELI the ICE man..   and Bad Boys Red Our Young Girls But Violet Gives Willingly..   gsn 
those were the days!

[rossw]

Yes,  I've had the xc=1/2pixfxc pounded into me years ago, as well has hundreds of others (many forgotten).

My hang up was simply the "low resistance" comment. 
I've a good grasp of what the difference is between reactance/impedance/inductance  and their relationship to frequency. 

Ahh, well in that case perhaps I need to make a more technical comment that I'd been trying to avoid lest I be accused of overcomplicating it

My comment about "low resistance" was that I was specifically breaking up the "resistive" component from the "reactive" component.

Taking the example I did above, with a capacitive reactance of about 300 ohms,
The "total resistance" (resistance + reactance) is the sum of the reactance and the DC resistance. (Impeadance). Capacitors of this sort (motor run caps) have quite low *resistance* (the leads, plates etc). One can make a reasonable measurement of their resistance if one is curious enough - by measuring the impeadance at a high frequency where their reactance is very low (eg, that 20uF cap at 100KHz should have a reactive component of .08 ohms). The measured impeadance less the calculated value should show the caps internal resistance, close enough. (keep leads short so as to not add their inductance into the equation!)

[joestue]

that cap is a metalized plastic cap. at 400 vdc it will be good for a million hours or so. how big is it?
i've got a 1 uf 200vdc metalized polystyrene cap from the 70's, made by sprague. it looks the same as yours, about 2 inches square and one inch thick

you won't be able to measure its loss, unless you infer it from temperature rise with several amps flowing thought it.

generally the ac rating is the same as the dc rating divided by 2 to 3
there is a generous safety rating though for both dc and the ac ratings.

[DSinOR]

Thanks again!  More info...



Extension cord:
Green ground wire connects to White/Black
White neutral wire connects to Red
Black "hot" connects to Green
Black "hot" also connects to Blue cap wire, to "series cap", to motor.

The cap is 2" square by 1" height.  I instantly love anything with a million hour potential, just on general priniciples.  

In my comment about shared ground, I meant to say that the cap was bolted to the same steel chassis as the fan assy; therefore must be sharing the same ground??; and I wondered if preserving the same ground is essential to proper function, because my primary mounting surface is going to be wood, so I need to know that.

A sticker on the chassis described how to wire the "McLean Air Flow Switch":
White - Common
Black - N.O.
Green - N.C.
I believe this suggests there is a relay present?  Apparently, the cap is in series on the N.O. leg?  I'm using question marks intentionally, because I'm a student.  

These photos are my attempt to confirm that the cap is in series.  

FWIW - I notice the blue wire is slightly heavier gauge "in front" of the cap, compared to the blue wire continuing "downstream" of the cap.  

Yesterday, I purchased motor run caps online as follows:  one each 2, 4, 8, 12.5, 20, 30uF; all 370vAC or higher. They are all similar in appearance: cylindrical with two terminals atop each.  I should have them by the end of the week, and will attempt to further my education in the described manner.  

Joes comments suggests that my 4uF 400VDC cap is a different sort than the motor run caps I just bought, supporting Ross's suggestion that this cap is serving a different purpose?  

I have learned much from this thread already, but remain highly interested in further commentary.  

In particular, I want to be sure that if I attempt to reduce voltage with my motor run caps, I know exactly where to put them in relation to the existing cap, or whether I should first remove the existing cap, etc, etc.  

Thanks!

[ghurd]

The existing cap is for a lower power set of coils.

Go half way down to "Permanent-split capacitor motor"
http://en.wikipedia.org/wiki/AC_motor

G-

[Rover]

I've been reading this for a while, and not going to even try to comment on the re-use of the motor at a lower rpm , beyond my technical experience.

Also beyond my technical experience (yet curious), I'm no HVAC guy, is the other part of the question, which is basically distributing the heat. Based on the motor description, I'm thinking this is somewhere between a 1/5 to 1/3 hp motor. Not unusual to see this size in an air handler pushing air to multiple rooms.

I guess some basic questions, how much duct work are we talking about ? multiple ? length?

By lowering the design RPMs of the motor , isn't it also reducing the ability to push air?

Maybe I missed it it someone else's post, I'm just hoping that this all adds up to the intended goal 

[joestue]

well I just looked up nytronics, they existed around the same time my polystyrene cap was made.
who knows, yours might be a different plastic, like polypropylene instead of polystyrene.

million hour lifetimes are standard for metalized foil, as they are self healing.
lifetime decreases by over voltage ratio to the 15th power btw, but most will survive 3 x rated voltage without immediate failure.

There is no electrical connection to the chassis.

do you have a varac or other means to reduce the line voltage feeding that motor?
induction motors are a rather pain in the ass to make more efficient/spin slower when it comes to fans.

i'd look into reducing the line voltage some, blocking off the air and messing with the capacitor value.
you will need a watt meter, not just an amp meter to make these measurements.

[rossw]

Thanks for the extra info, and the closeup of the motor label. That confirms it's a "capacitor run" (split-phase) motor.
The 4uF cap that's there now has only *2* electrical connections - the two terminals the blue wires are on. Neither of those is (or should be) connected to the metal case, so mounting it on "the same ground" is immaterial.

Generally speaking, mounting electrical components on "timber" is a bad idea because it can catch fire. What you're proposing is probably considered "low risk".

The capacitor is not "in series with" the motor, becasuse you can clearly see *TWO* wires from the supply - one to the cap, one to "something else" inside the motor.
Internally, if you pull it apart, I'd bet good money that there are TWO coil windings. One end of each will be common and connected together inside the motor. That's probably the red wire (to the neutral).

One end of the main winding (green) will go to the "hot". The second winding will be fed via the capacitor to produce a phase-shift. This helps to get the motor turning. (To understand this, it's probably better you go google single-phase induction motors).

The remaining wire that goes to green (earth) is there purely as a safety measure. If, for any reason the windings fail and short to the metalwork of the motor, then the motor (and potentially any metal ductwork connected to it, and any metal it's bolted to) could be "hot" and a shock and/or fire hazard. The Earth SHOULD provide a path for the current and blow the circuits protection fuse or breaker.

If you choose to add motor run caps in series to slow it all down a bit, you would either add it in series with the red wire (neutral) - NOT my personal choice by the way, or in series with the green and blue wires (the "hot" supply line).

As has been suggested already, reducing the voltage MAY cause the motor to run hot because of lower cooling air flow and possibly higher coil currents (caused in part by higher slip in the motor). Monitor it - if it becomes excessive, you'll need to re-consider the plan. I doubt it'll be a problem though.

[DSinOR]

In ghurd's wiki link to "permanent split capacitor motor", it says the start and running windings are identical, and the motor can be made to run at different speeds by changing taps on the running winding.  What are taps?  Are they a selection of different connections for running winding, or something else?  BTW - thanks ghurd, that paragraph improved my understanding quite a bit.

Rover - very short duct.  Lower airflow / quieter / less power are all objectives.

I don't have a variac.  Rossw's suggestion for series capacitors to regulate AC is the general direction I was taking, but I want to consider the "tap" option 1st to see if this motor has built-in capability for reduced speed. 

Thanks again to all.

[joestue]

your motor does not have any taps, just a run winding across the mains and a starting winding in series with a cap.

will it run after starting up, without the capacitor?

[ghurd]

Never believe 10% of what you read, and only half of what you see.

Can not be completely sure what is in the motor without opening it.
Sometimes the start and runs are the same,
sometimes they are wound with the same gauge wire, but very different turns count,
sometimes the gauge and turns count are both very different.
In your case, there is no reason to open the motor.

I expect it is like this-

[rossw]

What are taps?  Are they a selection of different connections for running winding, or something else? 

"taps" are merely an alternative connection point along the coil. Suppose the coil was wound with 1000 turns of wire, they might "tap" it at 900, 800 and 700.
Taps of this kind are quite common in transformers - both on the primary (transformers might have 130, 120 and 110V "taps"), and on the secondary (6V, 9V, 12V, 15V). It a convenient way of making an investment in hardware "more useful" in a variety of applications, for a very modest increase in manufacturing cost.

Your motor doesn't indicate the presence of any taps. Retro-fitting them is fraught with danger. Just don't do it, ok? As Ghurd says - there's no reason to open the motor, so just don't.

Rossw's suggestion for series capacitors to regulate AC is the general direction I was taking

Point of clarification: the series cap won't *REGULATE*. It'll *REDUCE* the speed. It will also almost certainly REDUCE the speed regulation of the motor. With less torque, and a lower voltage, changes in back-pressure, bearing friction and line voltage will all make the speed vary - and most likely by more than it would have without the caps.

[DSinOR]

Some results:

I've been running the motor in the original photos with one fan as a temporary "air mover".  Itr draws .66A, 79w, with 120v across the green and red wires.  I assume it's turning 3100rpm, give or take. 

My motor run caps arrived.  I experimented with various caps in series on the green supply wire.  Results:

4uF - motor would not operate.
8uF - motor would start only with help, turning less than 60rpm, .61A, 9w, erratic voltage readings.
15uF - self-starts without help, turns ~250rpm,  1A, 29w, 32v.  Too slow for my needs.
20uF - self-starts, turns ~500rpm, 1.3A, 49w, 44v.  Perfect speed.  Quiet, slow air mover. 
30uF - self-starts, hiccups as it reaches top speed, 1.8A, 106w, 82v.  Too fast.  Also using more power for less rpm. 

I didn't notice any rapid heat buildup, but I only ran each combination for a minute or less. 

Pretty cool.  Thanks rossw!

I have a few other questions:

I bought some smaller motors, $4 each.  They fit the fan housing perfectly.   



Label:
117v 60hz 1140rpm Cont
65v 50hz 950rpm CONT
Type: KPT,  HP 1/40, PH 1

The paperwork that came with the motor calls for a 25uF 370vac run capacitor.

I don't have a 25uF.  I tested the motor with my 8, 15, 20, and 30uF caps. 

8 - .13A & 16w slow.
15 - .34A & 32w perfect speed.
20 - .56A & 51w faster.
30 - 1A & 105w faster still.

This motor is perfect for my air moving job with the 15uF cap, but it calls for a 25uF cap. 

Will I be shortening the life of the motor if I elect to use it with a 15uF run cap? 

Also - the motor has oil holes.  What type of oil?  Coupla drops enough? 

Lastly, the wire diagram says:
L1 to white
L2 to blue
L2 also to cap in series to paired green and black. 

It works in this configuration, but I guess there's no ground?

Thanks!

[DSinOR]

anyone?...

Can I safely use a 15uF motor run cap instead of the called-for 25uF for an always-on fan motor, or will it eventually damage the motor? 

FWIW - this is not an added series cap as described above.  It's a single motor-run cap performing it's normal function.

Thanks. 

[joestue]

as long as the motor stays within rated temperature rise you're good.

[kenl]

 Have you considered a VFD unit? TB Woods controllers are pretty common on Ebay and can be had for cheap if you keep an eye out. This would also let you fine tune the rpm of the motor for air flow and heating of the motor is no longer an issue. TB has a good web site for sizing the VFD and getting the right catalog number to search for. Just a thought.

kenny

seemed like a good idea at the time

[DSinOR]

Thanks Joe.

Thanks for the tip Ken.  It's amazing how much I didn't know about electric motors.  I read all about ac drives (vfd's) on Vacon's website.  Apparently, TB Woods sold their AC Drive division to Vacon.