Pump peculiarities with the electrics

[Kes]

I have upgraded my pump, filter and pipework to a design that requires a low flow rate (don't ask, I will explain but that's not the question). I need 5 cu mtrs (1,315 US gall an hour, 22 USG a min) across the filter. I have installed a Certikin HPS031M 1/3 HP pump which gives 6.3 cu mtrs/hr at 8 mtrs head. The head on my system is probably below 8 mtrs. However I have questions about the pump, specifically its motor (I'm UK but the basics are the same)

The pump has two labels on it, a sticky with 1/3 HP, P1 480 watts, P2 300 watts, as expected. It also had a riveted label saying 1/2 HP, P1 610 watts, P2 400 watts, not as expected. Certikin say that they may be labelling 1/2 HP pumps as 1/3 HP, as sales are minimal. But that wouldn't explain the differing P1 and P2 figures.

The pump connections had two very thin wires connected to them on the input side, terminated (just cut off) at the cable in gland. I discarded these. What could they have been used, or intended, for?

The pump is running, and a meter shows 650 watts being used. This, to me, is a 1/2 HP motor running at its max limit. The motor is very hot, too hot to keep a finger on. The pressure on the filter is 7.5 psi, which is nothing. The pipework is short and simple and the flow back to the pool feels strong. I believe that this wattage is excessive, and will be expensive and will eventually damage the motor. My not very deep understanding of electrics is that a motor under a low load will use less power, and power equals watts.

I am perplexed by this. Is this normal? Why is the motor running flat out? What were the thin wires used for? Any help would be appreciated. The pic shows the two wires from the power in terminals to the cable gland, where they are cut.

 

[mas985]

The pipework is short and simple and the flow back to the pool feels strong.

The power required to drive a centrifugal pump increases with decreasing head loss. The power required is proportional to the flow rate times the head loss. So even though head loss goes down, flow rate increases faster due to the shape of the head curve. So you are probably nearing run out of the pump where the pump will draw maximum power.

 

[Kes]

Thanks for the reply. Your answer is a revelation, even if it takes a little understanding. The 0.5 HP pump has a flow rate of 5 cu mtr hr at 10 mtr head, and 12 cu mtr hr at 6 mtr head. So the relative power required between the two head values is 72/50, which is 44% higher at the lower head?

As I believe I have a 0.5 HP pump instead of the 0.33 HP I wanted, would a move to a genuine 0.33 HP be better? Would I still have the same problem, as the flow rates for the smaller motor give an even wider spread of relative power?

Or is there any other way to alleviate this? A restriction on the return to the pool, to increase resistance?

Everything I read says reduce elbows and fittings, reduce pipe length, reduce the head loss. That's what I have done, and my pump is now suicidal.

 

[cfherrman]

My guess is that they use a 1/2 hp motor for both 1/2 hp and 1/3 hp impellers, and you got a 1/3 hp labeled motor with a 1/2 hp impeller

Probably wrong

 

[JamesW]

Do you have a picture of the motor label?

What are the measurements for voltage, amps and watts?

Are you using a watt-meter to measure the power?

Note that volts x amps are not always going to equal the actual watts used.

The true power is the apparent power (volts x amps) x the power factor.

Do you have a link to the motor installation manual?

What is the pump make and model number?

 

[RMcGirr83]

What is the pump make and model number?

It's in the very first post I believe. "Certikin HPS031M"

 

[Kes]

I have turned the return eyeball to its most restrictive position: the filter pressure has increased from 7.5 to around 9 psi and the watts from 650 to 620, so a small step in the right direction.

I agree that the pump manufacturers might fit a 0.5 hp pump with a different impeller, but the two labels (pics attached I hope) show different wattages. Is that possible?

Voltage is standard European 230. Amps are around 2.9 to 3.

There's a motor installation manual?

Sorry, can't attach or insert pics - will try later. Can't even save this edit..........

 

[mas985]

Thanks for the reply. Your answer is a revelation, even if it takes a little understanding. The 0.5 HP pump has a flow rate of 5 cu mtr hr at 10 mtr head, and 12 cu mtr hr at 6 mtr head. So the relative power required between the two head values is 72/50, which is 44% higher at the lower head?

Correct

As I believe I have a 0.5 HP pump instead of the 0.33 HP I wanted, would a move to a genuine 0.33 HP be better? Would I still have the same problem, as the flow rates for the smaller motor give an even wider spread of relative power?

It really sounds like that is the case. Power draw would have been less if a smaller impeller was actually used. In this case, they may not have installed the correct impeller. You can verify by removing the wet end from the motor and looking for an impeller part number.

Or is there any other way to alleviate this? A restriction on the return to the pool, to increase resistance?

Throttling will reduce flow rates and energy use but not as efficiently as using a pump will a smaller impeller. One option is to replace the current impeller with a smaller impeller if you can find one.

Everything I read says reduce elbows and fittings, reduce pipe length, reduce the head loss. That's what I have done, and my pump is now suicidal.

Reducing head loss does increase efficiency. However, it also increases flow rate which will increase the pressure loss across the filter which is opposite of your objective.

 

[JamesW]

There should be a manual that comes with the pump. Did you not get one?

The power rating of a pump is anything but straightforward.

Pumps are usually listed by the delivered power, not the supply power.

For example, a pump listed as a 1 hp pump isn't going to use 746 watts.

You have the listed power (in hp or watts), the service factor and the total power.

The total power is the listed power x the service factor.

So, a 1 hp pump with a 1.65 service factor will have a total hp of 1.65.

Then, you have the input power, which is going to be higher than the delivered (load) power based on the efficiency.

For input power, you have real power and apparent power. Apparent power is the voltage x the amperage. Real power is the apparent power x the power factor.

Typically, input apparent power (volt-amps) is about 1000 x the total hp.

The actual power used by the pump is determined by where the pump is operating on the pump curve.

If the pump is operating high and left on the curve, the power will be lower.

If the pump is operating low and right on the curve, the power will be higher.

So, you have to distinguish between real and apparent power on the input and the delivered power on the output.

Probably the most important thing is to make sure that the supply voltage matches the voltage on the label and the amperage does not exceed the amperage on the label.

The voltage and amperage listed on the label are usually apparent power.

Do you have a picture of the motor label?

 

[Kes]

This is a great help, I'm beginning to see some sort of light. I can't dismantle the pump as it is only a few weeks old and under guarantee. I'll try to get some info from the suppiers but I fear that all their '0.33' hp HPS pumps may be the same spec. I may have to return it and try to source a genuine 0.33 hp pump.

Certikin have said that they will contact the manufacturers in Spain, I'll post what they say but I doubt if it will be an immediate reply.

 

[JamesW]

The Certikin Swimflo swimming pool circulation pump is available in 0.3HP (0.24kW), 0.5HP (0.37kW), 0.75HP (0.55kW), 1HP (0.74kW) and 1.5HP (1.1kW) sizes.

The listed power is the delivered power.

The 1/3 hp pump should measure about 333 volt-amps and the 1/2 hp pump should measure about 500 volt-amps assuming a service factor of 1.0.

If the service factor is higher than 1.0, you have to multiply the volt-amps above by the service factor.

For example, if the 1/3 hp pump has a service factor of 1.5, the expected volt-amps will be about 0.333 x 1,000 x 1.5 = 500 volt-amps.

The main thing is to make sure that the amps are not going above the label amps.

If the measured amperage is above the label amperage, the motor is being overloaded.

 

[Kes]

Hi James,

Sorry, yes, I have a manual buit it is quite basic. What were you looking for?

The voltage is 230 on both the pump and supply..

I'll have to read your post in deatail, most of it is over my head.

Yes, I have pics but all attempts to attach or include fail for some reason. I'll try later.

 

[JamesW]

What is the amps listed on the motor label?

 

[Kes]

If volt-amps are amps times voltage, then I am seeing about 2.9 amps, times 230 comes to 667.

Label amps are 2.5 on the 0.33 hp, 2.9 on the 0.5 hp. The pump is on the limit.

 

[Kes]

At last. Pics show the two labels and the watts used before the minor reduction of closing the return eyeball.

 

[JamesW]

Is the 651 the watts or volt-amps?

It looks like the power factor is listed as 0.91 and measured as 0.87.

If the meter is displaying watts, the volt-amps would be 748 (651 ÷ 0.87) and the amps would be 3.2 (748 ÷ 230).

The motor label says 2.9. So, you're at or above the limit.

It looks like you have the 1/2 hp pump.

Can you measure the current and voltage separately?

 

[Kes]

Voltage 239, current 2.97 amps.

 

[cfherrman]

Might want to see if they sell a 1/2 hp pump as if they don't the chances messing up impellers is lower

Typically those watts meters are inaccurate and only good for comparing.

 

[JamesW]

The amperage is exceeding the label.

So, the motor is being overloaded.

Maybe the wrong impeller or maybe the impeller is binding for some reason.

Make sure that the impeller/shaft are moving freely and not binding.

You should just do a warranty claim and get a new pump.

 

[Kes]

If I had a genuine 0.33 hp pump it would deliver about 2 cu mtrs hr less at the same head. That would reduce the flow rate by 33 litres a minute which is a little better (don't blame me for using metric, you guys are still on the Queen Anne Wine Gallon of 1707, which is really confusing).

The previous pump had P1 450 watts, P2 250 watts, Amps 2.3, and chuntered along for around twenty years with no problem. I am trying to replace like for like, which is why I've gone for 0.33 HP.

The impeller is too far recessed to reach through the basket. I think a warranty claim is in the offing.