2HP AC Single Phase Motor very weak at start or hums 4

[Smyers75]

I have an A.O. Smith 2HP, 220Single-Phase pool pump motor that started giving me trouble.

It has been working for the past year or so, but just started having starting problems.

When I turn it on sometimes it starts, most of the time it just hums.

If I give the shaft end a spin, it will always start but I can always hold on to the shaft with two fingers and it will never start.


I did a search here and saw the answers about the cap possibly being bad, but I did the VOM test at 10K and it seems to pass.

After discharging it, it starts out at zero ohms then takes about 10 seconds to swing across the dial.

I read about looking at the centrifugal switch, but I think this one doesn't have one...or is it I just don't know where to look?

I attached a link to the manual for this motor.


Should I try replacing the cap, even though it seems to pass the test?

Shouldn't this motor have way more starting torque than two fingers of a weak, computer programmers hand?

 

[ScottyUK]

Post a photo of the nameplate or tell us which model of motor you've got.


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If we learn from our mistakes I'm getting a great education!

 

[Smyers75]

I wish I could, but a year or so ago, I had a pool guy work on it and he either rebuit the motor or put in a rebuilt one.
Either way, it was re-painted all black and the only thing
I can see a a message saying

A.O. Smith Centurian Switchless - No Switch / No Governor - Total HP=2.00

It has only two spade terminals, marked L1 and L2 (plus a ground screw)

It has one 25UF 370V Cap mounted on the side.
I put new bearings in it to see if that would help, but is was already spining very easily...it take about 15 seconds to stop spinning when I shut it off.

 

[Smyers75]

There are pictures of the motor in the photobucket link.

http://i856.photobucket.com/albums/ab129/smyers75/PoolMoter/DSC02073.jpg

http://i856.photobucket.com/albums/ab129/smyers75/PoolMoter/DSC02074.jpg

http://i856.photobucket.com/albums/ab129/smyers75/PoolMoter/DSC02072.jpg

 

[ScottyUK]

Ok, switchless so the #1 suspect - the centrifugal switch - is not fitted.

The two possibilities I would explore are a knackered starting cap or an open-circuit winding. Electrically there are two windings, one of which has the capacitor in series with it. The individual connections could be tricky to get to, but if you can find them you should find each winding has a resistance of a few ohms. If the windings are ok then I'd suspect the cap. Obviously you can't measure resistance through the cap, so you need to get at the connection to the winding itself.


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If we learn from our mistakes I'm getting a great education!

 

[ozmosis]

Agree with Scotty.
Do you know the tune it is humming...?

 

[edison123]

Since it starts once you turn by hand, I would try replacing the cap first before opening the up motor.

Are you sure you're applying 220 V and not 110 V ?

Muthu

http://www.edison.co.in

 

[waross]

This may have a two circuit overload device. If so check that both circuits are good. Check the continuity of the start winding.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zlatkodo]

Capacity-test that you have made, is insufficient.
Cheap capacitor very often lose a part of the nominal capacitance and the rest is not sufficient to start the motor.
The only thing you can do is try with a new capacitor.
If is same case again, it is necessary to rewind motor.
Zlatkodo

 

[Smyers75]

Thanks for all the ideas...much appreciated.

In answer to the replies, I verified that the motor is indeed seeing 220VAC by using the VOM accross L1 and L2.

I'm going to look around this weekend and see if I can find a cap to see if that helps.

I checked on MCMasters and didn't see the exact same rating (25UF - 370VAC about 1-5/8" diameter and 3" long), so I'm going to try a motor repair shop if I can locate one open this weekend.

Thanks again!

 

[Smyers75]

One more question.

I see on Digikey a cap that has the same rating, but it's marked as a Motor Run, not a Motor Start.

I don't suppose there's any difference, but since I know more about computers than motors, I figured I'd ask just in case I can't find one tomorrow...

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=338-1857-ND

 

[edison123]

Since yours doesn't have a centrifugal switch, it would be a motor run cap.

Muthu

http://www.edison.co.in

 

[waross]

What Muthu said.
The difference is that starting capacitors are adequate for starting duty but will generally fail if left in the circuit for an extended period of tie.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dArsonval]

Knowing the problem described here has likely been corrected or solved
by now, can I politely call attention to another possibility?
Was the motor actually being used for pumping water?

The comment(s), “…If I give the shaft end a spin, it will always start but I can always hold on to the shaft with two fingers and it will never start…” alludes or implies the impeller end is exposed.

And, “…I put new bearings in it to see if that would help, but is was already spining very easily...it take about 15 seconds to stop spinning when I shut it off…” would indicate the shaft seal is completely wore out or removed.

These two comments raise the question of “up-n-down” motor shaft play which is typically a trademark failure in pool pump motors.
If the motor is all electrically “O.K.”, the impeller end shaft journal, or bearing housing fit is suspect due to the corrosive environment of pool pump motors, and either fit could be wore out.

The motor will hum and not come up to speed if this is the case because the rotor is being pulled off electrical center when energized. A very wore out fit would not likely allow the motor
to start at all. Hence returning to the suggestion of an open circuit... either in the capacitor, or the start winding.

"Winding Down" on a Tuesday evening,

John

 

[jraef]

Just a reminder: discharge that cap before working on it!


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[Smyers75]

Well, it wasn't the CAP.
I put a brand new one in and it gave the same results.

I've been running the pump all day after starting it by hand because my pool started turning very green.
I hope running it won't make the problem worse, but at this point I think I'm going to have to buy a whole new motor anyways.

As for how I start it by hand, this model has a plastic cover on the opposite side from the main shaft.
It has two flats on it so you can hold the shaft while you unscrew the impeller.
I just remove the cover and give it a spin while it's humming and it starts right up and runs fine.

Before I give in and charge up an already maxxed out credit card for a new rebuild, is there anything else I can check?

Thanks again to everyone for all the help with this!

 

[edison123]

May be change the bearings ? But at this point, you might be better off with a new motor.

Sorry it didn't work out the new cap.

Muthu

http://www.edison.co.in

 

[ozsalty]

may also be an open circuit rotor bar.

 

[waross]

If you can start it be finger power, the bearings are not the problem. You may have some type of starting relay or device that has failed. The starting winding may have failed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[flandrax]

I would check and make sure that the starting winding is not open. It sound as if that may be your trouble. If the starting winding is not burn up, then investigate the thermal overload, as waross suggested April 23, or look for a broken wire in starting winding circuit. I never saw on the post that it was confirmed.