Motor controllers

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Rangeball

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May 25, 2007
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I was wondering why a person couldn't buy and install a motor controller to dial in the rpm and subsequently GPM flow for their pump motor, in effect making a multi speed pump capable of manually matching what the intelli flow style pumps do, for a greatly reduced cost?

Talking to my union electrician brother last night, as long as the motor was compatible, he didn't see why it wouldn't work.

I can get a 2 speed 3/4 hp whisperflow for about $430, or a 1 speed 3/4 hp eliminator (both identical flow and electrical use rated) for $230 and a controller for about $60, giving me a dial in flow pump for about $290, or a savings of $140 with more control?
 
I am reasonably sure that pool pump motors are synchronous motors, which means the controller won't work. The fancy continuously variable speed pool motors are also synchronous but they vary the AC frequency, something I don't believe any $60 controller can do.
 
When I get ready to replace my pump (when it dies, or maybe next year :) ), I'll have him look up the specific details and spec it out. If it's possibly, I'll definitely consider it.

I'd add a controller now, but my 1 hp AG pump for my 21,200 IG pool wouldn't be up to the task. Or would it? Flow drops off pretty fast as dynamic head loss increases, but that may not have anything to do with how it would flow at a lower RPM, would it?

I currently have the 1 hp Pentair Dynamo AG pump.
 
One thing to consider is that most of these controllers are less than 100% efficient, even when running the motor at rated speed, so you will take a hit on the electric bill. They use a DC-DC converter, which usually has about 85% efficiency, which would mean you take a 15% hit on your electric use while on high, and running it at the slower speeds will use more electricity than your single speed does now.
 
JohnT said:
One thing to consider is that most of these controllers are less than 100% efficient, even when running the motor at rated speed, so you will take a hit on the electric bill. They use a DC-DC converter, which usually has about 85% efficiency, which would mean you take a 15% hit on your electric use while on high, and running it at the slower speeds will use more electricity than your single speed does now.
Click to expand...

Which would kind of defeat the whole intended purpose...

How are the variables like the intelliflow handling this?
 
Rangeball said:
JohnT said:
One thing to consider is that most of these controllers are less than 100% efficient, even when running the motor at rated speed, so you will take a hit on the electric bill. They use a DC-DC converter, which usually has about 85% efficiency, which would mean you take a 15% hit on your electric use while on high, and running it at the slower speeds will use more electricity than your single speed does now.
Click to expand...

Which would kind of defeat the whole intended purpose...

How are the variables like the intelliflow handling this?
Click to expand...

The Intelliflow is a permanent-magnet synchronous-motor with an integrated controller. $$$$$ is the basic reason, because the motor and controller are both designed to maximize efficiency. That's why they cost so much.
 
JasonLion,

Re: "I am reasonably sure that pool pump motors are synchronous motors, which means the controller won't work."

I think that most pool pumps are single-phase induction motors, not synchronous motors. Synchronous motors will run an synchronous speeds - 900 rpm, 1800 rpm, 3600 rpm, etc. - , whereas induction motors will slow slightly as load is applied to the motor. For example, my Magnetek 2 HP pump (circa 1996 from Leslie's Pool) shows an rpm of 3460 rpm, which is what the motor will slow down to (from 3600 rpm) at an applied load of 2 break horsepower.

Variable speed controllers should be able to vary the speed of these single-phase induction motors.

As a side note, if one is able to accurately measure the actual rpm of a running motor, this provides a hint of the applied load to that motor. For example, using my 3460 rpm, 2 HP motor from above, if I measured an actual speed of 3530 rpm, I could conclude that the motor is seeing a load of approximately 1 HP.

(3600 rpm -3530 rpm) / (3600 rpm - 3460 rpm) = 70 / 140 = 50%

This is not perfect, but it will get one in the ballpark.

Titanium
 

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Titanium said:
I think that most pool pumps are single-phase induction motors, not synchronous motors.
Click to expand...

Ah yes, right you are. There are some synchornous motors, notably the Intellifow and Ikeric, but most of them are induction. I guess that means the cheaper speed controllers will work; though energy efficency is a different question.
 
Titanium said:
As a side note, if one is able to accurately measure the actual rpm of a running motor, this provides a hint of the applied load to that motor...
Click to expand...

Or check the current to the motor (with a clamp-on ammeter). As the load increases, the rpm decreases (more slip), causing current to increase.

If you want to reduce gpm and save money you don't really need a motor controller. Just put a valve or other restriction on the discharge side of the pump and reduce the gpm. The current to the motor will decrease right along with it with little loss of efficiency. Like magic, a variable flow rate for the cost of one valve.
 
chatcher,

You have to be really careful using the motor amps as a gauge of how much horsepower load is on a motor. For kicks a long time ago I put an ammeter on a motor that was not hooked up to anything at all - the shaft was spinning in open air - and I got a reading around 50% of the motor nameplate full load amps. What the heck?!?

This website says it better than I can (look at the bottom right column on page 1 and the curves at the bottom of page 1):
http://www.loadcontrols.com/application ... ontrol.pdf

"We often get calls saying, “I put a clamp-on ammeter on
the motor and I’m getting 50% of full load amps. Your
device is only reading 10%. What gives?”
If you look at the curve, you can see that for a lightly loaded
motor, the current is high. Why? The power factor is low! As
you start to load the motor, the power factor increases, but
the current doesn’t change much. This is the advantage of
sensing power rather than amps. When the load is low, the
power is low. When the load is high, the power is high."


This effect and relationship (misleadingly high amps on motors loaded less than 50%) is best seen with the "Mr. MotorMouth Calculator" (really dumb name, but one of the best calculators I found to illustrate the concept).

http://www.loadcontrols.com/free_stuff/free_stuff.html

Titanium
 
Titanium said:
You have to be really careful using the motor amps as a gauge of how much horsepower load is on a motor. For kicks a long time ago I put an ammeter on a motor that was not hooked up to anything at all - the shaft was spinning in open air - and I got a reading around 50% of the motor nameplate full load amps. What the heck?!?
Click to expand...

It is not a linear relationship, but then neither is rpm. But either one works to find where you are on the curve.
 
As someone pointed out current generation pool pump motors are AC synchronous induction motors which means they do not have a magnet and they do not have brushes. The current excites the outer winding and induces a current in the inner winding without the need for brushes.

The speed of this type of motor can be adjusted by adding windings with taps called poles. Standard speed motors have 2 poles which dictates the RPM.

RPM = 2 * 60 Hz * 60 sec/min / # poles (2 is for AC)

So with field slip, full speed runs at about 3450 RPM which is slightly less than the 3600 RPM theoretical. With 4 poles, RPM is 1725.

For the Intelliflo, I haven't quite figured out how the work the multiple speeds but I have a theory. I don't think they use frequency adjustments since this would be very inefficient. So the only other thing they could do is use a large winding with multiple taps to create fractional poles. By exciting each set of taps in different combinations, I believe that they are able to get many different RPM settings so even though the display may allow you set an RPM, they probably just choose one that is close enough.

As for horsepower input vs output, the horsepower load on a motor is effectively the pumping horse power which is found from this:

Pumping Horse Power (PHP) = Head * GPM / 3960

This peaks at the best efficiency point and is usually where you get the best GPM / KW as well. The input power has a somewhat linear relationship with GPM but a fairly high intercept so the more flow you have, the more power the pump draws. So for either side the best efficiency point, the efficiency of the pump drops off and thermal losses go up. So a pump with full head or no head will generally run hot. A pump at dead head will still draw about 40% of the peak power but is doing no useful work, PHP = 0, so all of the energy is released as heat. A pump itself has head loss so even a open ended pump will run with a little bit of head loss.

A pump run without load at all (i.e. no water running through it) will be very inefficient so it is not surprising that you would only see 50% power draw. Probably most of the energy is going into heating of the windings and bearings. And the power factor would be very low due to the lack of load.
 
http://www1.eere.energy.gov/industry/be ... 097517.pdf

This document says that the amperage method should not be used for motor loadings under 50%, but how does one know when this is?

On the other hand, this document says that "while the voltage-compensated slip method is attractive for its simplicity, its precision should not be overestimated. The slip method is generally not recommended for determining motor loads in the field."

This document prefers direct readings with an fairly advanced electrical multimeter that can read power factor, in addition to current and voltage.

Example: Input Power Calculation

An existing motor is identified as a 40-hp, 1800 rpm unit with an open drip-proof enclosure. The motor is 12-years old and has not been rewound. The electrician makes the following measurements:
Measured Values:
V ab = 467V I a = 36 amps PF a = 0.75
V bc = 473V I b = 38 amps PF b = 0.78
V ca = 469V I a = 37 amps PF c = 0.76
V = (467+473+469)/3 = 469.7 volts
I = (36+38+37)/3 = 37 amps
PF = (0.75+0.78+0.76)/3 = 0.763
Equation 1 reveals:
469.7 x 37 x 0.763 x ?3
Pi = 1000 = 22.9 kW

Unfortunately, my multimeter is not quite this advanced. On the other hand, I would guess that 99% of the electricians out there do not have a multimeter advanced enough for this task either.

Titanium
 
mas985 said:
...So for either side the best efficiency point, the efficiency of the pump drops off and thermal losses go up. So a pump with full head or no head will generally run hot. A pump at dead head will still draw about 40% of the peak power but is doing no useful work, PHP = 0, so all of the energy is released as heat. A pump itself has head loss so even a open ended pump will run with a little bit of head loss.

A pump run without load at all (i.e. no water running through it) will be very inefficient so it is not surprising that you would only see 50% power draw. Probably most of the energy is going into heating of the windings and bearings. And the power factor would be very low due to the lack of load.
Click to expand...

For a centrifugal pump driven by an induction motor, operating at no head means maximum GPM flow, maximum motor current ($), and maximum input and output HP (but not maximum efficiency). The water flow keeps the pump cool, but the motor will run hot, and depending on the design (relative sizing of the motor and pump) may overheat and trip the thermal overload switch. Operating at dead head means zero GPM flow, minimum (not zero) motor current, minimum (not zero) input HP, zero output HP, and zero efficiency. The motor runs cool but the water in the pump housing is churning, building up heat, and with no flow to cool it will most likely vaporize, causing permanent pump damage.

Obviously neither case is where we want to run our pumps. Ideally we would select a pump that would provide the exact GPM we want at the exact head we have, while operating at its best efficiency. But typical pump curves show that efficiency on either side of that elusive point does not drop off rapidly. There is a pretty wide range of conditions above 90% of best efficiency. If you are operating at 100% of best efficiency and want less flow, increasing head (with a valve or restriction in the discharge line) will reduce the flow rate, the motor current ($), and yes, the efficiency, though not drastically if you don't make a huge change.
 
Summation so far: There is more than one kind of motor and more than one kind of speed controller. If you get the right kind of speed controller for your motor you will be able to vary the speed. The energy efficiency of the speed controller is not going to be perfect, so it is unclear how much electricity you will save.

The discussion then moved on to explore how the Intelliflow pump might work and how pump energy efficiency varies at different flow rates.
 
The Ikeric line of pumps is a 3 phase pump controlled by a small single phase to 3 phase converter with additional electronics controlling the settings. Single phase 220v goes into the box, 3 phase 220v comes out. You can set 4 different speed levels, which control the pump RPM, which obviously controls the flow, though I am pretty sure it is not linear. (As I understand it, the Ikerics are very similar to the Intelliflo line of pumps by Pentair).

Ikeric provides a set of charts that can show, within reason, the flow at a given RPM and the corresponding energy use of the pump. I am not an electrician so I don't know much about the converter, but it does work. And the pump motor is defintely 3 phase (says so right on the pump in big, bright letters).

My solar guy, who in real life is a power control specialist for government buildings (power distribution panels, HVAC power, backup generators etc), said the whole setup reminded him of lots of the stuff he does, just on a much smaller basis.

As for efficiency, the Ikeric pumps are approved under the California system for energy saving rebates, if that means anything.
 

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