Upgraded pool pump motor questions

[natokills]

My pool pump motor died, and without too much research, I found and purchased something on Craigslist, and am looking for advice as to how bad of an action I took.
My pool and equipment are 15 years old. Approx 11k gallons, spa spill over to pool. Sta-Rite System 3 cartridge filter, Dnya-Glass pump, and a heater. 1.5" piping. The pump had a 1HP A.O. Smith SQ1102 motor on it. I purchased a V-Green 2.7 HP Square Flange 48Y Variable Speed Motor - ECM27SQU. A little bit of reading after the fact, seems to point towards my reasoning not being sound that the motor would simply run at a lower speed and all would be as it was originally on my system.
The initial questions I have are, how bad of an idea is it to use this motor on my setup? Should I continue using the original 1HP impeller or change it to something more fitting of the new motor? Does anyone have any suggestions on the programming of setting a routine on the motor for my pool?

Thank you,
Dusty

 

[mknauss]

Welcome to the forum!
To fully understand, you are just replacing the motor. Correct?
If so, you will need to replace the impeller and diffuser I believe.

Let's ask @mas985 or @JamesW for some advice.
I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.

 

[mas985]

You probably could have gotten away with the 1.65 HP V-Green with the 1 HP impeller but the larger motor will still work fine and still save in energy costs when running on lower speeds. You could up-size the impeller and diffuser which would allow you to run on even lower speeds for the same flow rate and it would save a bit more in energy costs. Noise level would go down too with the larger impeller at the same flow rate. But the total cost of this pump with the extra parts is getting closer to what a new pump would have cost.

 

[natokills]

Yes, I am only replacing the motor and keeping the dyna-glass pump.
My old impeller was rated as 1HP / 1.5 Up Rated HP. I have ordered the 2.5HP impeller available for the pump, and already have the largest diffuser offered, a 1.5 HP model. Is there any math that can be done to help estimate the old water flow versus the new, or is that why people buy those sensors? Something like (new impeller) 2.5HP / (old impeller) 1.5HP = 0.6, (old RPM) 3450 * 0.6 = (new RPM) 2070 ? Or do things not work as simply as that?
I should have things running by tomorrow evening to see what it all looks like.
Thanks,
Dusty

 

[Hootz]

Since your replacement motor is variable speed you have the convenience of setting the speed and run time to your preference. If you have a salt water generator, the run time is dependent on chlorine requirements for your pool. If you do not have a swg, you can get by with around 4 hours at a low speed (approximately 1200 rpm) to mix chemicals daily; any additional run time/speed is your preference to keep the top water skimmed of debris. If you have a heater you will have to experiment to find the speed required to engage the pressure switch. No need to worry about the flow rate or turnover...this pump should serve you well.

 

[mas985]

My old impeller was rated as 1HP / 1.5 Up Rated HP. I have ordered the 2.5HP impeller available for the pump, and already have the largest diffuser offered, a 1.5 HP model. Is there any math that can be done to help estimate the old water flow versus the new, or is that why people buy those sensors? Something like (new impeller) 2.5HP / (old impeller) 1.5HP = 0.6, (old RPM) 3450 * 0.6 = (new RPM) 2070 ? Or do things not work as simply as that?

What is the impeller number for both the new and old impellers? You really can't estimate flow rates by HP. But you can with head curves. I just want to make sure I am comparing the correct impellers. Also, the 2.5 HP impeller is most likely full rated which means it needs a motor that is slight large than 2.5 HP. I believe the service factor for that impeller is 1.1 so you would need a 2.75 THP motor to run that. The V-Green is close and would still probably work but if you find that it shuts down on full speed, just limit the RPM to 3000 or so and it should be ok.