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Pool motor 1/2 hp AOSmith runs fine, 1/2 hp Marathon overheats

Pool motor 1/2 hp AOSmith runs fine, 1/2 hp Marathon overheats

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  #1  
Old 04-12-13, 12:04 PM
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Pool motor 1/2 hp AOSmith runs fine, 1/2 hp Marathon overheats

Have a bit of a puzzle. Do Marathon brand motors tend to run hotter than AOSmith?

Swimming pool setup worked for decades with a 40 year old pool pump and a reused 1/2 hp 115v AOSmith motor that met the pump specs.
Pump finally rusted beyond being patchable. Impeller was worn down.
Swapped in a 20 year old pool pump with new impeller, with a reused 1/2 hp Marathon motor.
AOS is model S48H2N103, Marathon is an O213 model 56C34D2099
Motors are basically identical in all specs hp, hz, rpm, SF etc.

Minor difference is the Marathon is set to run at 240v (tag says 5.2amps / 3.6amps.)
Pool is about 40' from the garage sub-panel, wiring is 14 gauge.


AOS basically ran 24/7 from mid May to mid September. Now, the AOSmith motor always ran warm, (amps on tag are 6.7/8.4) but the Marathon motor runs hot to the touch, trips the overheat protection after about 4 hours during a 90 degree day.

Used compressed air to blow out the dust and spiders; guess the next step is to disassemble the Marathon, clean off, reassemble and hope it runs cooler.


So, any suggestions on how why a motor runs hot and what to check?
 
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  #2  
Old 04-12-13, 12:26 PM
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[old pump]1/2 hp 115v ...Minor difference is the Marathon is set to run at 240v
Did you change the supply to 240 volts?
 
  #3  
Old 04-12-13, 12:47 PM
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Looking at both motor specs. That A.O. Smith motor was listed specifically for pool duty.

While that Marathon motor was listed for oil burner service.

Did you try putting an amprobe on the marathon motor to see what it is drawing ?
 
  #4  
Old 04-12-13, 01:13 PM
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Did you change the supply to 240 volts?
Grin - Yes, checked the obvious

that Marathon motor was listed for oil burner service.
Actually, this particular Marathon was OEM on a water well jet pump.

That's the odd thing, specs are basically identical

1/2 hp
60hz
3450 rpm
Amb 40c
cont. duty
AOS has SF 1.8 verus 1.6 for Marathon
rated draws at 115v are AOS 6.7/ 8.4 verus 7.4/9.8 for the Mara.

Did you try putting an amprobe on the marathon motor to see what it is drawing?
Haven't checked amps under load yet...

First part of troubleshooting was to disassemble the pump and check the impeller clearance,
next is checking whether the motor vents were blocked.
 
  #5  
Old 04-12-13, 02:26 PM
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Bump-

Just occurred to me that there is another difference between the AOS and the Mara motors-


The overheating motor is an old capacitor start motor.

What symptoms would a worn out capacitor or a stuck centrifugal switch cause?

Has anybody known either of those issues to cause a motor to run hot?
 
  #6  
Old 04-12-13, 04:22 PM
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A problem cap could. If the centrifugal was stuck you would get lots of heat.....quick.
 
  #7  
Old 04-12-13, 09:30 PM
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In a capacitor start motor the capacitor is removed from the circuit as soon as the centrifugal switch opens. A stuck centrifugal switch would draw excessive current and trip the overload in less than a minute normally.

Notice that the Smith motor has a "service factor" of 1.8 vs. the 1.6 of the Marathon motor. That difference in service factor could be all it takes.

New pump is also suspect as a centrifugal pump's power requirements increase significantly as the flow increases. You really need to put an ammeter on the pump and then try throttling the discharge valve to see if you can get the running amperage to not exceed the nameplate rating. I'll bet that the new pump is moving more water than the old pump and THAT is the real problem.
 
  #8  
Old 04-13-13, 05:49 AM
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A well jet pump would only run for a couple of minutes to build up pressure. It may not be designed for continuous usage like the pool pump that runs for hours.
 
  #9  
Old 04-13-13, 09:49 AM
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First, thanks for the suggestions,


It may not be designed for continuous usage like the pool pump that runs for hours.
Originally Posted by Furd
I'll bet that the new pump is moving more water than the old pump and THAT is the real problem.
Checked out the specs, seems that BOTH motors are standard well/pool/jacuzzi/HVAC standard (NEMA 56???). Both motors are rated for constant duty.


So, as a baseline, both old and new pump-heads fit the power specs of the motors.
Yes, the old pump impeller was worn down and the new pump's impeller is fresh,
but the new pump's gmp/hp requirements should by met by both the Marathon and AOS motors.


Got some Mara motor amp readings, no load, clamp on ammeter, with the Mara motor running no load.

{actual readings are 7.3 mA and 1.2 mA from clamp on ammeter, (reads 1mA per 2A),
this ought to be independent of whether ac voltage is 120v or 240v.}

So, momentary start = 14.6amps,
In a split second, running amps = 2.4 amps

In about 2 seconds, there's a definite "click" when the centrifugal switch opens.
Tried flipping the switch (2 pole) to try and get an amp reading with/without centrifugal switch engaged, but there's a split second delay before the multimeter display give an amp reading.

(While my multimeter has a PC interface, it's a RS232 serial port, and I no longer have a computer
with a serial port in the workshop. Arrgh, could use those RS232-to-usb adapters which I donated a couple years ago...)

While I'm waiting for the epoxy to cure on the new pump housing, I'll try and get amp readings on the AOS motor.
 
  #10  
Old 04-13-13, 03:52 PM
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And the answer is - rust, and surge.

So, we have an answer-
appears that overheating was due to blocked vents and/or dirty or stuck contacts or centrifugal switch.

After blowing the spider and dust out the casing, and cycling the motor several times, Marathon motor runs warm but steady within 3-5 amp range, no more overheating.

Still have a slight problem with an air leak is causing a "slurp and surge" feedback which builds up and occasionally stalls out the motor, but that should go away once the fittings are airtight, and once the filter tank is pressurized it should smooth out the surges.
 
  #11  
Old 04-27-13, 07:26 AM
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And, within hours of posting that the motor ran steady at 3-5 amps, went back
to unsteady 2 amps or 8 amps....




The fastest way to fix a problem is to order a replacement part.

Ordered a 1.5 HP replacement motor in the morning, overheating problem with 1/2 HP motor stopped that afternoon.

I had cleaned up some problems with the 1/2 HP:
- sticky centrifugal switch
- rusted contacts on capacitor
- poor cooling due to dust and cobwebs

But, cleaned up motor still overheated.


Originally Posted by Furd
a centrifugal pump's power requirements increase significantly as the flow increases.
... I'll bet that the new pump is moving more water than the old pump and THAT is the real problem.
Yep, new pump draws more water. New pump has a 2" inlet, old pump had a 1-1/2" inlet.
The actual impeller is larger on the new pump - and moves more water.

So, added a gate-valve so I could fine tune the flow to the motor,

Restricting flow - motor still overheated.


Originally Posted by Furd
You really need to put an ammeter on the pump and then try throttling the discharge valve to see if you can get the running amperage to not exceed the nameplate rating.
Tried that for a day, didn't work. System was unstable with light-switch tendency depending on the valve position. Below 1/4 open there's cavitation. At 1/4 open the motor idled around 2 amps without drawing water. Over 1/4 open and the motor surged to 8 amps and tripped overload.

Next day ordered a 1.5 HP motor that would drive pump at maximum flow.

Then, tried 1/2 HP motor one last time, BINGO, the 1/2 HP motor runs at a stable 4 amps,
And it stays at 4 amps with the valve anywhere between 1/4 open and full open.

My first guess is that sand in the filter settled and compacted enough to suppress the pressure swings.

My second guess: you've heard of "Toy Story" where a little boy's toys talk to each other;
this is the complementary version "Tool Story" where big boy's tools talk to each other....
 

Last edited by Hal_S; 04-27-13 at 07:51 AM.
  #12  
Old 04-27-13, 01:10 PM
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Gate valves are not for throttling service and one used in that manner will give very poor results. You did put the valve on the pump discharge and not the suction, didn't you? Try using a globe valve (not a ball valve) and tighten the packing gland securely to prevent the valve from moving from pump vibration. Adjust the valve for full-load amperage or a bit less.
 
  #13  
Old 04-27-13, 02:39 PM
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Why did you go to a 1-1/2 HP motor from a 1/2 HP? This could require changes in over-current protection, and larger wires. Another thought occurs to me- Is your voltage steady? Prolonged dips & surges could cause overheating issues.
Andy
 
  #14  
Old 05-08-13, 07:29 PM
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Originally Posted by Furd
Gate valves are not for throttling service and one used in that manner will give very poor results.
Eh, it worked well for what I wanted. Allowed me to fine-tune the flow to the pump, in order to keep the 1/2 HP motor within specs.


Originally Posted by Furd
You did put the valve on the pump discharge and not the suction, didn't you?
Nope, mounted on the intake, worked fine.
If closed too much, it did cavitate like USS Dallas in Hunt-For-Red-October, but otherwise worked fine on the intake.

My reasoning is that the valve was very basic RV style waste gate valve.
I trust it under a few PSI vacuum, but not under the higher PSI you'd see on the pressure side of the pump.

Anyway, the gate valve is a non-issue.
After running for a day, with the gate valve restricting the intake, the pump/motor/filter with 1/2 hp motor "settled down" and was stable (even with the gate valve fully open, or totally removed from the system.

Of course, this actually makes no sense, as the system WITH the 1/2 hp motor and gate valve was unstable initially.
Then, for some odd reason, (after buying a replacement motor) the system ran fine.
After running for a day it just worked - WITH or WITHOUT the gate valve to restrict the flow.
So, running the system on "recirculate" which overloaded the motor the day before, worked fine the day after.

But, since then, have upgraded to a 1-1/2 hp (aka 2 hp "upgraded") motor driving the same pump and the whole assembly is running nicely, system runs at a stable PSI and flow.

Ah, plumbing - go figure.

Originally Posted by Andrew
Why did you go to a 1-1/2 HP motor from a 1/2 HP? This could require changes in over-current protection, and larger wires.
The "new" pump housing is an odd ball - "Viking Hydro model 100"
can't find any online origional specs.
(viking hydro is now the trade name for Exmark lawnmowers)
Intake is 2" pipe, which means the pump is going to run around 80 GPM.

Did some calculations and figured out that at 80 GMP I needed about 1 HP.
1 HP motors on Amazon/Ebay were around $185.
Found a 2 hp for $85. (Actually 1.5 hp "uprated" to 2HP)

Anyway, 1.5 hp motor is running at 240v. It's rated at 10 amps, digital ammeter max draw is around 7 amps, stable at 5 amps.
The 14 gauge wire it's on is rated at 15 amps. Working fine.
 

Last edited by Hal_S; 05-08-13 at 07:59 PM.
  #15  
Old 05-08-13, 08:23 PM
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If you are such an "expert" when it comes to centrifugal pumps why did you even bother posting this problem?

Of course my 33 years of working with all manner of pumps and valves just makes me an idiot.
 
  #16  
Old 05-08-13, 08:43 PM
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Of course my 33 years of working with all manner of pumps and valves just makes me an idiot.
Nope, but I inherited this particular 1960's sylvan pool setup.
I grew up helping my dad with it, so I've been working with it for about 44 years.

If you are such an "expert" when it comes to centrifugal pumps why did you even bother posting this problem?
Simple.

Had two functionally identical motors, same HP rating, giving different responses.
Curious whether there was any brand difference, or whether I should look elsewhere to figure out
why motors with the same power rating behaved differently.

But, since then, system has 'decided' to work.
I can't say why. And I have learned to accept that.
 
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