1-phase motor frequency control

[WattsThat]

Four wires to the motor should be run-common-start and ground.

Mains should be line to run and cap1. Cap2 to start. Neutral to common.

There is either a centrifugal switch or a current based switch in series with the cap that removes it from the circuit.

If that’s what you have, I would remove the capacitor and wire those three wires to the three phase output of the vfd. The reason is that you don’t need the capacitor to create the phase shift required to create a rotational vector in the motor, the vfd provides that. This scheme is shown in your links to the ato.com website detail the connection.

Vfd rating depends upon input type (1 or 3 phase) and the motor rating. I did not see a motor rating anywhere in the thread other than 800W. I assume it’s 230v 50Hz but what current does it require?

[jmaja]

The motor is rated 50 Hz 230 V 900 W. I haven't seen more than 860 W, but I have only used a small amount of the rated pressure head.

Isn't the connection shown in my earlier link different? In the link both capacitors are removed and one of the phases is connected  directly to the motor secondary coil. So the secondary coil is always active.

In my case there is a switch that will disconnect one of the phases at some stage. There also might be a run capacitor, which I can't remove.

Is this a problem?

[jmaja]

I bought Danfoss VLT5002 with 3-phase input. Output 2.8 A and 2.1 kVA. Hopefully it's big enough and works. It was cheap (50 €).

[beanflying]

Worth it for the experiment for the small cost. It will be interesting to see what the power consumed is overall and what sort of efficiency the inverter gives if you can have a measure 

[jmaja]

It should show the power and kWh taken by the motor. The efficiency of VLT should be 95%.

[jmaja]

No luck with 1-phase connection (leaving W unconnected). This one has too old firmware and doesn't have parameter 234, which can be used to disable missing phase alarm. Now it just tries for a few second and then trips with this alarm.

Need a bit of cabling for trying 3-phase connection.

[WattsThat]

2.2kW and 2.8 amps? That sounds like a 400V drive, not 230V.

Assuming it is a 230V drive, the 2.8 amp output rating appears undersized to me, perhaps 1/4 of what the motor requires once the drive is derated.

Just a back of the napkin guess here but the 900W motor would be somewhere around 3.5-4 amps at 230v single phase. Is there any nameplate data you can share?

A 3-phase input drive good for 2.8 amps output should be capable of perhaps 50% of that rating with a single phase input.

So you’ve got perhaps 1.5 amp available and need 3.5-4.0 at full pump output. You might be able to get enough current, long enough to at least prove the concept but I would expect the drive to trip at higher loads with a phase loss or bus ripple fault.

If those assumptions are correct, the chances of success appear small, regardless of the motor configuration of the starting cap present or not. I would expect better luck without the cap and wiring the main and start windings across the three output phases as shown on that linked web site earlier in the post. It appears that’s the direction you’re headed so I’m very interested to learn of the results.

[jmaja]

I haven't even tried the actual motor yet. I tried a hairdryer (just the blower) and a much smaller pump. Hairdryer caused the VFD to trip reporting short circuit and the small pump only started to make some noise and then missing phase was alarm caused a trip.

I don't have electricity near the borehole. I need to run the cable from the VFD to the borehole for testing. Need to buy the cable first.

Here's the name plate. I measured only a bit under 3 A. Note that I plan to run at much lower load due to reduced rpm. Maybe 200-300 W, if efficiency is not ruined.

[WattsThat]

A rating nameplate photo of the Danfoss drive would be helpful as well, or at a minimum, the full part number.

[jmaja]

VLT5002PT5B20STR3DLF00A00

T5 is a 380-500 V input, 5002 1.1 kW "powersize". The firmware is 3.12. I couldn't find any manuals for older than 3.7x versions, which already had parameter 234.

You can find all the specs e.g. here: https://files.danfoss.com/download/Drives/doc_MG52B202.pdf

I did some measurements with my LCR-meter on the three wires going to the motor with the capacitor removed. Very small capacitance, thus there is no capacitor on the motor. 100-170 mH and ESR 100-200 ohm depending on which pair of wires was measured. DC resistance was smaller, around 20 ohm. This includes the 20 m cable from control box to the pump.

[WattsThat]

A 400V 1.1KW drive will not function with a single phase 230v input supply. The input voltage range of the drive is listed as +/-10%.

If the drive appears to wake up at 230V, it will most likely trip on under voltage or similar fault when asked to run.

In the unlikely event that it would power up and run with 230V single phase input, you will not have sufficient output current to run the motor at more than perhaps 1/4 to 1/3 load.

The appropriate specs for a vfd with a 3 phase input would be 230V with an output rating of 2.2KW or approximately 8 amps. This derate is required due to the three phase to single phase input as explained in an earlier post.

If you could find a 230V drive with a single phase input, and they do exist, a 1.1KW rated drive would suffice.

[jmaja]

I'm not quite familiar with the terms regarding VFD as I have never installed one before. Maybe there is a misunderstanding here.

I have connected L1, L2 and L3 to three different phases of mains. We have a 230 V system, thus there is 230 V from neutral to each phase and 400 V between the phases. I have understood this is the correct way to connect this and it is within the 380-500 V range. I think I saw 542 V at parameter 614 "DC link voltage". According to manual this should be 1.35 * mains voltage, which is very close.

So I'm quite certain I have the mains (I would say input) correctly connected. But please correct me, if not.

Then I plan to connect all the three phases to the one phase 230 V borehole pump motor. I will remove the start (and run?) capacitor and connect the VFD output phases U, V and W to the three wires going from the pump control box to the motor in the borehole. Of course I will also connect PE to the earth wire going to the motor.

I hope this will work, but it may not. If the start capacitor is unconnected by a centrifugal or other switch, I will get a phase missing alarm and VFD will trip.

This is a 230 V motor and I have set that in the VFD parameter 103. I have understood that VFD will not supply more than 230 V. And that seems to be the case. At least what I see on the display of the VFD when tested without a motor connected.

So far I have only tested one phase motors with only U and V connected to the two wires. That test failed due to W phase missing alarm and trip. Unfortunately my unit doesn't have parameter 234, which could be used to disable that alarm.

I called Danfoss support. They said they do not support using their VFD's to drive one phase motors. It might work, but they don't support and give advices about it.

Mitshubishi support gave three parameters to set for usage with one phase motor. One of them was phase missing alarm disabling. But the VFD I planned to buy was already sold.

[WattsThat]

Yes, a misunderstanding. I assumed you had only single phase power. I guess it’s all those electric saunas in Finland needing three phase

Okay, you’re inputting 400vac 3 phase into the drive with the expected 540 volts on the dc bus. The drive can output 400 volts by design. It is only the motor parameters that is limiting the output voltage.

So, two issues as I see things but neither should be cause to stop your effort, at least short term.

1) You will not have sufficient drive output current to run the motor at full load, you should have 50-60% of the motor rating. Drives are current rated devices, not power rated. That means the output rating of 1.1KW is based on a 400v output, not 230v.

2) The motor may fail prematurely, long term. Single phase motors are generally speaking, not designed for PWM supplies. Failure could be days, weeks, months, absolutely no way to predict this.

The failure is in the insulation system of the stator windings, almost always happening in the exposed end turn loops of the stator windings. With the 400v mains and the resulting ~550 v dc bus, the motor can experience very short duration voltage spikes that are 2 times the bus voltage. This is know as standing wave. Motors that are “vfd ready” or similar marketing terms have higher voltage withstand insulation of the stator wire. If you had a single phase input vfd, this voltage stress would be only 650v rather than the 1100v that will happen with the higher drive input voltage. A filter can be used to limit the voltage, Danfoss lists these on pages 24/25 of the guide you linked. A dU/dt filter will limit the voltage peaks, a sine filter will remove all dU/dt and all or most of the PWM waveform, reducing the running temperature of the motor. The problem will be the cost for these filters unless you can find something used or build something yourself.

With regard to the phase missing alarm. You may be able to fake the drive out with a resistor in the missing phase. The question will be how much current is required. You might be back to starting point with the overall effect being zero net energy savings.

Did you ask Danfoss if the firmware in the drive could be updated to a version that supports the disabling of the phase loss? That’s a long shot but if you don’t ask, the answer is no.

Sorry for the wall of text. VFD’s appear simple. They would be if the output was pure sinusoidal.

[jmaja]

I really appreciate the long and thorough reply!

Our house is electrically heated as well with 17 kW installed heating power. We have 3x50 A main fuses. The sauna stove is only 6-10 kW so on par with kitchen stove, which are almost always electrical and three phase connected here. Most houses have only 3x25 A main fuses. Also many apartments have 3x25A, even when not electrically heated.

This whole thing is related to going for ground water source heat pump. This is very unusual here. A typical way is to install a collector into the borehole and not use ground water directly. I most likely need to buy a better pump, but would like to do a feasibility test with cheap equipment. Also I would like to learn about VFD's.

It seems I would have been better off with a single phase input VFD. I guess the high spikes are a problem even for a three phase 230 V pump? At least one three phase pump I just checked is star connected and thus 400 V. That would work fine? Or are even three phase motors specially designed for VFD?

It's a bit strange you can find a cheap (200 € new branded, e.g. Grundfos) circulation pump with internal speed control, but no such thing for borehole pumps.

[jmaja]

I just talked with the support of a local borehole pump manufacturer. Their three phase pumps should work OK with VFD, BUT can't be run at low frequency and must be ramped up to high frequency rapidly. This is due to motor seals, which need water in between. At low frequency seals rub against each other and will fail letting water in and destroying the motor. He couldn't really say a limit, but mentioned 30 Hz for a 50 Hz motor.

That is probably enough. A pump typically have third power curve for power (P ~ rpm^3). (30/50)^3 would mean just 120 W for their smallest 550 W three phase pump. That is 700 €.

Grundfos SQE-55 has curves all the way to 30%. It's more powerfull (700 W) than the local one. 0.4 l/s and 12 m is at 54% speed. 0.2 l/s 12 m is 45% speed. It must have a different kind of seal or maybe the local one is also OK down to 15 Hz?

[jmaja]

I got some sort of success. I removed the capacitor and connected the three phases. First I got a lot of alarms about asymmetrical reactans, over current and warning about torque limit.

Just adapting for resistance removed the first one. The last two were removed by using lower Hz.

I also think I had the motor running in wrong direction, so I swapped two output phases.

Now I can run without warnings at 25 Hz and with getting some torque limit warnings at 27 Hz. I get 0.3 l/s at 25 Hz and 0.4 l/s at 27 Hz. I tried 30 Hz, but got more often torgue limit warnings and much less flow. No or very little flow at 22 Hz.

At 25 Hz the VFD reports 110 V and 2.8 A, but kW reading varies a lot 0.2-0.4 kW up and down all the time. At 27 Hz 120 V and 2.9 A. Again kW goes up and down 0.25-0.42 kW.

I tried to measure the power taken by the VFD. I just have the kWh meter for the whole house. I removed all the fuses and got no pulses. Then only the VFD powered I got one pulse every 10.5 s at 25 Hz and 9.3 s at 27 Hz. Thus 340 and 380 W. Those were when the fan was not blowing. It does maybe 10% of the time and it's quite loud.

Now I just got a new warning 9 "inverter time". Have to see what that means.

[jmaja]

That was about overloading for a too long time. Can't run at 27 Hz for longer times.

[jmaja]

How is power defined for these pumps? Mine says in the label 900 W, 230 V and 3.9 A. 230*3.9=897 W and I measured 800 W, thus it seems to be input power, not output.

The more expensive pumps use Franklin motors. There is a local pump manufacturer which has even 370 W model. But for it 230 V and 3.9 A or for the 3-phase model 400 V and 1.0 A is given. Thus 370 W must be shaft power.

More detailed at Franklin: https://franklinwater.eu/media/319141/4inch-3-Phase-Standard-Motors-Product-Catalog_Engl.pdf
0.37 kW 400 V 3-phase model at full load 400 V, 1.1 A, cosphi 0.74 and efficiency 0.66. That means 560 W electrical power.

That pump should deliver 0.4 l/s at 40 m head. I got 380 W with just 11 m head, thus much worse efficiency.

Why did I get so poor efficiency? Is it due to motor run with three phases, when designed for one? Or is it due to the VFD I have?

It would have been nice to see what happens at 50 Hz. I guess the electrical power would have been much more than with normal one phase operation.

I guess that 370 kW (560 W electric) would work fine with this VFD. Well within current limits. If it can pump 0.4 l/s 40 m with 560 W, how much would it take at 0.4 l/s 12 m? With same efficiency it should be just 170 W, but maybe it will not be as efficient (both the pump and the motor).

[beanflying]

Just to be confusing pumps can have three power points. The motor can be rated at power in (from the mains), nominal maximum power out at the shaft and most importantly the power absorbed 'at the duty point'. Given what you are trying to do Motor power figures should be considered questionable.

Providing one and two are more than three everything is happy. Going back to the earlier pump curve and what I wrote about using a gate valve to choke the flow to reduce power is maybe important. If you are running the pump at open flow with near zero head to pump against it will be running way off the right side of the curve and may in fact be needing more power than the motor can deliver. The 'pump efficiency' also drops way off at the far right side of the curve. So by choking the pump with a valve you will improve efficiency and reduce the power absorbed.

Re Motors Franklin, Hitachi and a few others are the better options but way to expensive at the size you are sealing with.

EDIT Not that is will be an exact match for your pump but I added a 'similar' Grundfos alternate to yours of similar capacity and power (also a 0.37kW) below. Look at the '11 meter' point and see where you are on the curve. You are off the end and way down on efficiency.

[jmaja]

I know I was at the very right end of the curve and will be with all the 230 or 400 V borehole pumps I have seen. That's the reason why I'm trying to reduce rpm with VFD. Just not getting the much reduced input power I was hoping.

Grundfos SQE-55 has curves for reduced rpm. Unfortunately only for P2, which must be the shaft power required, since it is up to 700 W and input power is up to 1 kW.

At 0.4 l/s and 12 m SQE curves show 54% speed, 99 W P2 and 47% eta (must be just for pump). If rpm is not lowered and only more head produced by restricting, 0.4 l/s would be 60 m, which gives 100% speed, 568 W P2 and 41% eta.

My pump (the 900 W input one) gave just a bit over 800 W input power at 1.1 l/s and maybe 15 m (the water level in the borehole dropped a bit + more pressure loss in the pipe). Thus it had about 20% eta from pumping to input power.

The last point on SQE-55 curve is 0.94 l/s and 18 m. It shows 100%, 534 W P2 and 31% eta. Thus from input to pumping eta is actually about the same as for my pump at this high flow point.

So reducing from 1.1 l/s to 0.4 l/s by reducing rpm and at the same time reducing the head a bit should give better efficiency and much lower shaft power. Only about 1/6 should be needed.

I'm running now a 50 Hz pump at 27 Hz, which is exactly the same 54% speed given by SQE-55 curve. Thus P2 should be in the order of 100 W. But my pump still takes 380 W. The motor efficiency must be about 25% while it could be 50-70%. Also it most likely was about 70% at 1.1 l/s running normally from 230 V one phase.

So it seems my pump performs very badly with my VFD. It should take much lower current at 27 Hz with low head.

It is still better than restricting the flow, which would probably end being closer to 900 W. Eta would be better, if I needed the extra head, but I don't.

[jmaja]

I can buy here a borehole pump with 370 W three phase 400 V Franklin motor for 600 €. Thus not that expensive, especially compared to SQE-55 + control box, which is about double the price.

But I would like to know in advance, how that would work with VFD.

[jmaja]

Here are the curves for SQE2-55 with the three operating points I wrote about.

[beanflying]

If you are looking at a new pump and you have 3 phase fairly nearby then get one that is close to best efficiency at the duty required rather than one that is way over and needs a large turndown. Also providing you can fit a 100mm pump down the bore then go that way the pumps run back at 2900 RPM instead of the 10k of the smaller diameter ones.

In your case the SP2A-6 would seem closer to your duty point https://product-selection.grundfos.com/products/sp-sp-g/sp/sp-2a-6-09051K06?productnumber=09051K06&custid=GMA&tab=variant-curves&pumpsystemid=1243702574

[jmaja]

I have now had the pump running for 18.3 hours at 26 Hz and the kWh counter of the VFD shows 6.1 kWh. That makes about 330 W. It probably counts kWh output so the kWh input is maybe 350 W, thus very close to what I counted from the meter pulses.

[WattsThat]

Industrial motor nameplates provide output power in kw or horsepower and amps consumed. I don’t know what the standard is for residential application and appliances, I know some may omit output power and list amps only. If it’s not defined on the nameplate, asking the manufacturer would be the only way to know for certain.

The poor efficiency at lower speeds is usually due to poor power factor (cosine) of the motor. Best case at full speed is perhaps 0.8, that can go down below 0.5 at low speeds. It’s probably worse with a single phase motor but I have zero experience with that configuration.

Another factor could be the harmonic distortion caused by the non-linear nature of the diode rectifier front end of the drive. This would depend upon your metering, I do not know if you’re using electromechanical meters or electronic and how you pay for service.

Here in the US, we typically do not pay a penalty for poor power factor with residential service.

It would appear that the Franklin Electric pumps are not rated for vfd operation. Asking them would be the safest approach as I would not assume anything with non-industrial motors. DOL (direct on line) operation is all that they mention in the documentation.