Motor AMP draw depending on impeller HP ??

May 29, 2013
13
#1
Hi folks,

I have a pentair 0.5HP Pump and motor p/n 340036
The motor is currently drawing ~6A @230V

I purchased a variable speed motor centurion 1.65HP to replace existing motor - hoping to save some energy. However this motor can take 10A when running full speed.

I am wondering how many amps will the Centurion motor 1.65HP draw when running full speed but with an impeller rated for 1/2HP.

I am unsure if I can really achieve significant savings by replacing the motor

Thanks for hints.
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,296
Pleasanton, CA
#2
Are you going by the label amp rating? That is a rating for the maximum allowed current and not the actual amp draw. If you were measure the amp draw, the VS should be about 10% less current than your current motor at full speed. If you lower the RPM, the amp draw lowers as well so yes, it will save considerably on energy costs.
 
OP
OP
A
May 29, 2013
13
#3
Are you going by the label amp rating? That is a rating for the maximum allowed current and not the actual amp draw. If you were measure the amp draw, the VS should be about 10% less current than your current motor at full speed. If you lower the RPM, the amp draw lowers as well so yes, it will save considerably on energy costs.
Thanks for hint. I will let you know how it works once I swap the motors.
 

JamesW

TFP Expert
Mar 2, 2011
13,088
#4
You might want to upsize the impeller and diffuser to the ones for your pump model that uses a 1.65 total hp motor.

That way, you can run it at lower speed for the same flow but quieter operation.

By lowering the rpm and flow rate, you should be able to significantly reduce your total energy cost.

The big savings come from running at slower flow rates for longer times to get the same total amount of water going through the system.

355618 Diffuser, 1-1/2 HP (Total hp = 1.65)
355074 Impeller 1-1/2 HP (Total hp = 1.65)

What size is your pool?

Do you need any specific flow rates, like for a heater?
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,296
Pleasanton, CA
#5
Running a higher HP impeller at the same flow rate as a lower HP impeller should not be any quieter. Nearly all the noise from a pump comes from the flow rate from within the pump so if the flow rates are the same, the noise will be about the same.

However, motor noise at lower rpm might be a little lower.
 

JamesW

TFP Expert
Mar 2, 2011
13,088
#6
Motor noise is a lot lower at lower rpm.

TEFC motors have a back mounted fan. At full speed, they can get annoyingly loud.

Also, I think that the noise of a faster spinning impeller is louder than a slower spinning impeller moving the same flow rate.

Maybe it's the frequency that makes it worse or more noticeable.

I would say that two pumps side by side moving the same flow rate would be significantly different in total sound output.
 
OP
OP
A
May 29, 2013
13
#7
So I have completed the project over this weekend.
The max AMP is about 5.2 (VS) vs 7.0 when running full speed 3450RPM the same pump

When I go to lowest speeds, it can draw close to 1AMP @230V and is very quitet

However I have a SWG and I am worried going lower than 2000RPM, as I am starting to get gases backing up in the SWG cell.
Shall I be worried about getting gas buildup in the cell? What is the rule of thumb in regard to SWG and water flow/ water level in the cell (I have no way to measure the water flow)


Cheers!
 

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
12,296
Pleasanton, CA
#12
Are the pipe connections to your cell on the bottom or the ends of the cell?

It has been reported by many on the forum, that certain types of cell design will collect hydrogen gas if the flow rate is too low (i.e. insufficient to clear out the gas). So you may need to run at a slightly higher RPM to keep the SWG from filling up with gas.

Also, in this thread, the OP talked with Circupool and they recommended installing the SWG upside down to enable running at lower RPM but it may have been a different cell type. You might call Circupool to see if there is another solution.

Chlorinator and VS Pump
 
OP
OP
A
May 29, 2013
13
#13
Thanks.
How much Hydrogen is too much? I think my cell gets probable 5% filled up with gas at ~1800rpm and it sits there, I was thinking too that mounting the cell with connections on the top (instead of on the bottom), will help clear up gas so then I can go even lower.

Another question: I have the SWG and VS Pump on the same timer - should I better separate them? The VS pump has it's own 24hr timer system. The other timer is is an electro mechanical timer. Both have freeze protection BTW.
Or if I scale down the CL production from SWG settings - that should be enough? I am currently running it at 100%, and my CYA is 60ppm. I am in progress of raising it to 80ppm as we speak.

thanks