1-phase motor frequency control

[jmaja]

I would need to control the rpm of a 230 V 900 W 1-phase motor. I thought it would be straight forward, but it seems to be much more difficult than with a 3-phase motor.

What I have learned so far, it would be necessary to remove the starting and running capacitors. I haven't yet checked is that possible. It's a submerged water pump in a well. There is a separate control box, which may have the capacitors.

So can this motor be controlled at any 3-phase VFD? Or are there some special requirements for 1-phase motor capable VFD's?

I would need to control the water flow to 1/6-1/3 of the maximum with good efficiency. This most like means reducing the rpm by much less than that. Maybe just 50% reduction is enough?

[beanflying]

Far better you run a flow control valve with a centrifugal pump than have a poorly speed regulating abomination. Depending on your 'actual flow rate and system' there will be little to be saved with speed control over flow control. Depending on this system (head, pipe run etc) you may only need a small reduction in speed (possibly only 20-30%).

Three phase control is another concept and you can get decent turndown with an inverter.

The Curve below is just a generic 250W Submersible Drainage pump you will notice that as the flowrate drops (valve modulated option) so does the absorbed power.

The second curve is another generic showing a centrifugal pump curve with variable speed. Generally most submersible pumps don't run VFD drives so this is not based on anything other than to give an indication of how performance is changed by speed reduction.

[Berni]

Yeah if its a submersible pump you probably will not easily get at the starting capacitor. And even so single phase induction motors on VFDs made to run them are a bit iffy. They are still loud and inefficient and success partially depends on what motor it is.

But if its a centrifugal pump type then you could reduce the flow by mechanically restricting the output pipe. For centrifugal pumps the torque required to spin it is mostly dependent on the flow trough the pump, so the more you restrict the output the less flow you get and the easier the pump is to spin. Its the positive displacement pump types that can't handle this (like rotary vane, gear, piston pumps...) since restricting there output makes them harder to turn.

[jmaja]

Far better you run a flow control valve with a centrifugal pump than have a poorly speed regulating abomination.

I would only need 0.2-0.4 l/s and 11 m head. The pump delivers now 16 m and 1.1 l/s at 800 W. I don't have curves for this pump, but a much more expensive pump shows 0.95 l/s 17 m takes 528 W. 0.2 l/s 11 m would take only  49 W and 0.4 l/s 11 m 92 W.
https://product-selection.grundfos.com/fi/products/sqe/sqec-2/sqe-2-55-96510151?tab=variant-curves&pumpsystemid=1230921145

The efficiency of my pump is now about 21% at 1.1 l/s. The much more expensive Grundfos pump has 30% at 0.95 l/s, 47% at 0.4 l/s and 44% 0.2 l/s.

If I would just have a control valve on that Grundfos pump, it would take about 480 W at 0.2 l/s and 580 W at 0.4 l/s producing about 50 m extra pressure head.

This cheap pump will not likely be as efficient, but I had hoped I could get about 100 W at 0.2 l/s and 200 W at 0.4 l/s. Would this be possible with VFD.

[beanflying]

Explain what you are doing with the pump (rough vertical lift, pipe diameter and length or run)? I spent a large chunk of my 'real job' time playing with industrial pumps so maybe a better pump selection might be in order.

Also is the flow rate desired 'fixed' or do you need to vary it ? Generally a simple gate valve or even an 'oriface plate' is used so nothing electrical at all.

[jmaja]

This would pump to a heat exchanger, which is used for a ground source heat pump. This heat pump takes 2-10 kW energy from the pumped ground water depending on outdoor temperature. The water level is 10 m below surface, thus only a submerged pump (or an ejector pump) can be used. The well is 11 cm in diameter, thus only pumps designed for this purpose can fit.

The water temperature is 7 C and can be safely cooled 5 or maybe 6 C to 1-2 C. The flow control is needed to reduce the amount of water used and power needed. If the 800 W pump runs all year round, it is quite expensive. If it would run at 100-200 W, it would be OK.

Piping has 26 mm inner diameter and is about 30 m. Thus not a big deal at 0.2-0.4 l/s.

I haven't seen any pumps that would produce these numbers. Usually they produce 50+ m pressure head and take at least 400 W. I called Grundfos and the pump I linked was their best option, but it costs about 1500 € with their own controller, which is not very suitable for this purpose.

I would add a control system, which starts the pump when the heat pump starts and the controls the flow so that the return from the heat exchanger is safely above freezing. 0.2 l/s could be the minimum, although even less would be OK at minimum power.

[Berni]

The pump A won't magically get all the characteristics of pump B by simply running pump A at the speed of pump B.

The shape and dimensions of all the components in the pump are optimized for certain operating conditions. You obviously have a pump that is designed to run at fairly high powers. So even if you reduce its power by slowing it down or just restricting the flow rate it will still likely consume considerably more power than the other small pump that it optimized to run at those flow rates.

Also with centrifugal pump the speed mostly determines the head pressure, not the flow rate, the flowrate simply becomes whatever is possible with the given head pressure trough the restriction of the pipes and the pump itself. So getting a low flowrate out of it trough slowing it down might become a knife edge balancing act, one speed might not provide enough lift to get the water up there, slightly higher speed might make too much flow trough a very low restriction end.

Running a huge 5 liter V8 engine at 20hp output will also have crap efficiency compared to a little 1.2 liter economical inline 4 that is optimized for great efficiency there. But the V8 might also be able to produce 400hp when the little inline 4 simply can't.

[beanflying]

An offset Injector pump while an option is fairly inefficient and also noisy. For mechanical/cost reasons shaft drive is out at this small size. So back to 4" nominal Borehole Pumps as the best solution.

Ok quick calculations you need the 10M vertical and a bit over 1M more for pipe friction for 11 total. The 110mm bore being the main limiter.

So two options Mains single phase and throttle it (three phase will be prohibitive on cost) or likely a better option DC Motor and speed/power control it. Just after midnight here but I can have an ask around tomorrow locally but on a quick search there is plenty of options available in 24 or seems more likely 48V DC in 4" Borepumps. So have a search while I 

[jmaja]

The pump A won't magically get all the characteristics of pump B by simply running pump A at the speed of pump B.

Of course not, but these pumps are quite similar. The other one just has published curves also for reduced rpm. Now the pump is running at very low load, since it is designed to output up to 60 m head. All of these pumps have similar curves. Efficiency is very low at low high flowrate + low head and low flowrate + high head.

Changing rpm should move the optimum flowrate and head closer to my operating point. Flow control doesn't need to be that accurate. Main point is not to consume 800 W all the time. Also 1.1 l/s is much, since the water needs to be dumped somewhere. There seems to be enough water coming from the well. The water level didn't drop at all when I pumped one hour (4 m3).

[beanflying]

The pump A won't magically get all the characteristics of pump B by simply running pump A at the speed of pump B.

Of course not, but these pumps are quite similar. The other one just has published curves also for reduced rpm. Now the pump is running at very low load, since it is designed to output up to 60 m head. All of these pumps have similar curves. Efficiency is very low at low high flowrate + low head and low flowrate + high head.

Changing rpm should move the optimum flowrate and head closer to my operating point. Flow control doesn't need to be that accurate. Main point is not to consume 800 W all the time. Also 1.1 l/s is much, since the water needs to be dumped somewhere. There seems to be enough water coming from the well. The water level didn't drop at all when I pumped one hour (4 m3).

Just a minor thing so everyone is on the same page. Why I was suggesting a valve or plate you won't be pumping more volume than you require. You are effectively increasing the head the pump sees and as such decreasing the volume it passes. With this reduction in volume the power decreases. ** This applies to centrifugal pumps and NOT to Positive Displacement types (some of the DC pumps are Helical Screw types) so speed control is needed to modify flow or you could also return some back down the bore (inefficient).

[jmaja]

All the curves I have seen for 1-phase borehole pumps shows lower power input at low head + high flow rate compared to high head + middle flow rate.

I didn't realise there are 12 and 24 V borehole pumps. There aren't any available here, but easy to order abroad. Do they last as well? There seems to available about 200 W models with about correct head and flowrate. Some are not stainless steel.

[jmaja]

I have looked at some of the 24 V borehole pumps. They seem to all be targeted for solar usage. Nothing wrong with that, but I haven't found any details yet how they operate. Most seem to have a MPPT controller. This is mostly external. They seem to have brushless permanent magnet motors. But only two wires to the pump. Doesn't a brushless motor need to have several poles and thus more than two wires? And PWM with accurate phase control needs to be used.

Is the motor controller inside and only simple DC goes into the pump? How can the rpm be controlled then?

Not much curves for these 24 V pumps. This 200 W pump seems to be able to output 0.4 l/s and maybe 17 m, which means 33% efficiency. Maybe the controller can reduce the power as I want? Quite much more expensive than many other options, but OK price, if it works well and lasts.
https://www.ebay.com/itm/3-DC-Shallow-Well-Solar-Water-Pump-24V-200W-Submersible-Off-Grid-MPPT-BoreHole/233371349632?hash=item3656043280:g:IrQAAOSw4mNehZy2

It would be nice to see a manual or datasheet.

[beanflying]

Think of the motor more like a PC fan than say an R/C BLDC one so it has no brushes and only two wires.

Typical bore pump motors use a standard NEMA bolt pattern and shaft coupling but that was always a bit hit and miss even with larger companies deviating from this standard. The DC versions seem not to be following any standard so are likely custom made for the pumps. But if you can find a manufacturer of NEMA Flanged and shafted DC motors then this is an option (likely more expensive).

Three main types of pump are Helical Screw, Diaphragm and Centrifugal. The first two are positive displacement types and more suited for higher head lower flow applications so stick with centrifugal.

In the centrifugal ranges you will also find Plastic or Stainless impellers providing you don't have to much sand or fine grit in your bore either are fine the rotating parts and bearings are still metal in both cases.

Had a quick look locally and most of the DC pumps appear to be sole imported out of China rather than the larger manufacturers like Grundfos and Lowara.

Coffee time...

[beanflying]

Made a couple of phonecalls to some people I still know in the industry. Seems none of the main players really do DC in 4" diameter The exception to this has always been Mono (Helical Screw) and Shurflo (Diaphram) which as per earlier higher head lower flow.

This Chinese based seller 'seems' to be one of the sources of Pumps at least in Oz https://kairuijidian.en.alibaba.com/company_profile.html?spm=a2700.shop_index.88.51 so they might be worth contacting directly to try and find a curve and suitable model.

Apart from that I suspect you will be importing your own if you go down the DC path.

[jmaja]

So whatever type of motor they have in their 24 V DC pump I could just skip the possible MPPT-controller coming with the pump and control the rpm with plain 24 V DC PWM?

What method for rpm control does the Grundfos SQE use? What is special about the SQE vs. all the other Grundfos 230 V 1-phase borehole pumps? It can be used directly with 230 V or via Grundfos control box, which allows efficient rpm control. There seems to be only Danish datasheet. I can understand the most of it, since it's close the Swedish, which I can. https://api.grundfos.com/literature/Grundfosliterature-1401035.pdf

It uses MSE 3 motor and the MS 3 is the same, but without rpm control. Also for it the datasheet seems to be only in Danish. It says "MSE = Elektronisk regulerbar motor med mulighed for kommunikation via CU 300 og CU 301", which means electronically regulated motor with possibility for communication via CU 300 and CU 301. So are the rpm control electronics in the motor and some data transfer method via the normal three wires for 230 V?
https://api.grundfos.com/literature/Grundfosliterature-145908.pdf

Is using VFD with 230 V 1-phase ruled out? Even if the capacitors would be in the control box and not under water? Is there a problem with this type of usage: https://www.ato.com/using-vfd-for-single-phase-motor

[Berni]

If its a brushless pump then the 24V are powering the integrated BLDC driver electronics. So PWM might not make it very happy. But you can offten run these controllers at a much lower voltage and the motor spins at a slower speed as a result (it doesn't have the voltage to overcome the back emf of the motors windings at higher speed). So it will probably run just fine at half speed on 12V

[beanflying]

The Chinese 24V examples will be DUMB motors unless otherwise mentioned so yes simple PWM control should be ok.

The SQE MSE based pump on reading the manual is not a synchronous motor and has some form of powerline data to and from the motor to allow some additional functionality from their proprietary controller to some motor mounted electronics. Costs on these was always a large premium even when fitted to above ground Pumps for water supply. MSE spec here https://product-selection.grundfos.com/sg/products/ms-3/mse-3-96160539?tab=variant-specifications

The MS3 motor spec is here and is also 10k RPM+ https://product-selection.grundfos.com/sg/products/ms-3/ms-3-96160535?tab=variant-specifications Interestingly the motor is described

MS 3
The motor is a single-phase motor of the permanent magnet rotor type ensuring optimum efficiency within a wide load range. The motor is fitted with a replaceable end cover with socket.

As to VFD control of a synchronous 4" (your existing?) pump motor without factory information I wouldn't. As the heating issue with speed turndown is largely negated by the water cooling maybe but 

[jmaja]

The Chinese seem to be brushless. Doesn't that mean they can't be dumb motors and must have an internal controller?

1-phase VFD always has a heating problem? There is very little information about it. I understood that the worst problem would be with starting capasitor remaining applied when the centrifugal switch doesn't operate at lower rpm. But if I can remove (haven't checked that yet with the current pump), that can't be the problem.

It would be quite cheap and easy way to try it. I can get a good second hand VFD for 100 €. If I still need to buy a new borehole pump, I don't mind burning the one I just bought (139 €), if there is a chance for this to be a good option.

[richard.cs]

1-phase VFD always has a heating problem? There is very little information about it. I understood that the worst problem would be with starting capasitor remaining applied when the centrifugal switch doesn't operate at lower rpm. But if I can remove (haven't checked that yet with the current pump), that can't be the problem.

If you take the capacitor off you could run it with a 2-phase VFD, or possibly with 2 phases of a 3-phase VFD. I'm not really sure how now capacitor and 1-phase vfd would work - where's the rotating field for start-up.

[jmaja]

This guide connects all the three phases.
https://www.ato.com/using-vfd-for-single-phase-motor

I have seen other ones, which use only two phases. But then you do not remove the capasitors.
http://www.gohz.com/1-hp-single-phase-output-vfd

Both of these are with a 3-phase output VFD and two or three phases are used. I haven't even seen a one phase output VFD. There are plenty of one phase in three phase out VFD's.

[jmaja]

I called Mitsubishi VFD distributors technical support. They said it should be OK to use a 50 Hz 1-phase motor down to 15-20 Hz even with the capasitors. If you try lower Hz, it will supply current, but the motor won't run. You just need to turn the output phase loss protection off.

[jmaja]

I finally opened the control box, which had tri-wing screw and I didn't have these special screw bits with me previously.

There's one big capicitor and 3+1 wires to the pump. Thus I probably can use these 3 wires with 3-phase VFD. Likely there is still a small running capacitor inside the motor.

[sam_sam_sam]

As general rule if you are going to single phase VFD drive that does not have 3 phase input you have to double the amperage of the motor current but even doing this does not guarantee that you would not fry the drive doing this but there single phase VFD but most of them are a minimum of 240 volt input you might find a 120 volt version but will take a lot of researching and they are going to cost a lot more than a regular VFD 3 phase will cost

First of all you have to use a 3 phase motor to be able to use a 3 phase VFD drive

Now I have seen some where I can not remember what company has these VFD drive that are single phase VFD drive which would work but you would have to have the right motor for this purpose 
but like said earlier unless the drive is setup as single phase VDF drive it will not work correctly

Now depending on your current draw on the motor you have there might be a solution to your problem

[WattsThat]

As general rule if you are going to single phase VFD drive that does not have 3 phase input you have to double the amperage of the motor current but even doing this does not guarantee that you would not fry the drive doing this but there single phase VFD but most of them are a minimum of 240 volt input you might find a 120 volt version but will take a lot of researching and they are going to cost a lot more than a regular VFD 3 phase will cost

First of all you have to use a 3 phase motor to be able to use a 3 phase VFD drive

Now I have seen some where I can not remember what company has these VFD drive that are single phase VFD drive which would work but you would have to have the right motor for this purpose 
but like said earlier unless the drive is setup as single phase VDF drive it will not work correctly

Now depending on your current draw on the motor you have there might be a solution to your problem

Not sure you’re stating that correctly. I’ll take my whack at it.

If you use a standard three phase input VFD with a single phase input, the output amperage rating of the VFD should be (at least) two times the amperage required by the motor. It does not mater if it is a single phase or three phase motor, the same derate applies. Amps are amps.

The doubling of rating is an approximate rule of thumb and does not always work with all brands of drives.

The reason for the rating increase is due to the input current as seen by the input rectifiers goes up by the square root of three and the bus capacitors must increase in capacitance due the reduction of input frequency by way of losing two phases. Instead of a rectified 300 Hz pulse rate, the dc bus capacitors only see 100 Hz (with a 50 Hz system). Most drives measure the ac ripple on the dc bus and this causes a fault trip when a high value is seen by the VFD. Many times the fault shows up as an input phase loss. The drive doesn’t actually know anything about the incoming phases, it just knows what the dc bus ripple is high - so the fault doesn’t occur until a high load with a corresponding high bus ripple occurs. This fools many users into thinking the drive bad when it’s just undersized.

There are plenty of VFD’s out there up to about 2.2KW that are single phase in, three phase out. Those can typically made to work with a single phase motor so long as you can disable the output phase loss fault. Some of the really cheap drives don’t have output phase loss because they just measure DC bus current by way of a shunt and extrapolate the AC motor current.

The only manufacturer of a single phase in, single phase out VFD that I am aware of in the industry is Invertek out of the UK, known as the purple drive guys. Check their website for more info, their drive reliably runs a single phase motor without removing caps or other modifications (although I don’t think the drive could possibly work with a centrifugal switch on the starting cap).

One of the things never mentioned in these discussions is the risk for motor bearing failures caused by the eddy currents created in the stator by the PWM switching energy. It’s well known in the industrial world.

Another issue is that VFD’s will cause a rise in stator temperature, again due to PWM switching and the resulting harmonic distortion. I doubt it would matter on a submersible pump with a duty cycle. But the potential for stator heating is real.

If you have any VFD questions, ask away. No specific single phase motor experience but I know a few things about drives. It’s all 3 phase industrial but yeah, that’s the day job. Drives up to 700V and 5MW.

[jmaja]

I have no problems using three phase VFD, but the motor is one phase. We have 230 V system here in Finland. Thus I can use 230 V single phase or 380 V three phase as input to VFD.

There is just one capacitor (two wires to it, thus not a combined run/start) in the control box. Four wires going from the box to the motor.

There is no current to the capacitor when the motor is running  according to my true RMS clamp meter. About 3 A to the motor while plug power meter shows 800 W.

Should i remove the capasitor or not? I have a LCR-meter. Maybe I can use it to find out more about the motor and possible run capacitor. What to measure?

I'm looking for a second hand VFD. There are a few available here in the 50-100 € range. Should I go for three or single phase input? What would be the minimun power or current rating?

I almost bought a Mitsubishi FR-740 with 3.7 kW 8A rating for 100 €, but someone was faster than me.

There's also FR-S520S 1.5 kW (single phase input) and Danfoss VLT 5002 2.2 kW (three phase).

[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.

[jmaja]

We don't pay for poor power factor and the energy meters count only active power. I don't know which kWh my VFD shows, but likely active as well, since it is very close to some efficiency (90-95%) × energy meter.

I talked with Wilo technical support. They use Franklin motors in borehole pumps. They said it is OK to use a VFD, but not below 34-36 Hz for the 50 Hz three phase Franklin.

0.37 kW three phase 400 V Franklin has 66% efficiency and 0.74 PF at nominal power and 50 Hz. Do you have any guesses what they would be at 34-36 Hz?

I don't understand much about one phase motors. How does it work with the 16 uF capacitor vs. now with three phase input? Too much current to some windings now? The windings were clearly different while a real three phase motor would be symmetrical.

Could this work better with the capacitor in place and with just two phases, if I had a VFD, which didn't trip with one phase not connected?

[jmaja]

I found a Swede who is using this pump with VFD. He gets 50 l/min with only 90-105 W at 30 Hz. And it is even cheap. Hope it fits into my borehole (110 mm).
https://www.erdbohrer.de/Pumpen/fuer-Waermepumpen/Brunnenpumpe-fuer-Waermepumpe-4200l-370W-Franklin-mit-30m-Kabel::795.html

And now I know what to look for and there are a lot of options. E.g.
https://diepumpe.com/Tiefbrunnenpumpen/Speziell-fuer-Waermepumpen:::118_145.html

[cdipak]

Single phase motor frequency can be controlled by a single phase variable frequency drive.There are many companies who manufactures VFD such as Schneider, Mitsubishi, Denfoss and many more.
One can learn more on electrical equipments on https://favreadblogs.blogspot.com/2020/01/what--current-transformer-meaning.html?m=1

[jmaja]

Just to let you all know. I run the pump at 26 Hz for more than a week. Still pumped OK. Now I have ordered a new three phase pump. The one I linked earlier was no longer available with Franklin motor. I bought another one with SUB motor, which should be quite similar to Franklin. It's made in Italy and should work fine with VFD. 0.37 kW, 400 V and should have 63% efficiency (66% for Franklin). I hope I'll get it during next week. 446 € with 40 m cable.
https://duggmbh.de/pumpen-308/4-zoll-tiefbrunnenpumpen/orlando-tiefbrunnenpumpen/orlando-tiefbrunnenpumpen-sp-serie-edelstahllaufraeder/orlando-tiefbrunnenpumpen-sp-18-serie-4200l-h/4-zoll-tiefbrunnenpumpe-orlando-sp-1806-edelstahllaufraeder.html

I think the motor is one of these: https://www.subteck.it/motors/
I e-mailed them and asked what is the lowest recommended frequency. Let's see if they answer.

[Eugenijus]

Let me inform you about Franklin not so pleasant feature - minimum allowable frequency is 30Hz .
Running with lower frequency will cause problems with bearings lubrication and damage the motor

[jmaja]

Let me inform you about Franklin not so pleasant feature - minimum allowable frequency is 30Hz .
Running with lower frequency will cause problems with bearings lubrication and damage the motor

Yes I knew that. 30 Hz is likely low enough. The shaft power should depend on third power. Thus (30/50)^3= 0.22. 78% reduction in power. Let's see how that works out for electrical power and pumped flow rate at the head needed.

I still haven't got any answer from Subteck.

[jmaja]

Now I got an answer from Subteck. Just short "do not use frequency lower than 35 Hz". A bit of disappointment that it was not 30 Hz. Still should be 66% less than 50 Hz and hopefully not more than 200 W, but that will depend on many things.

[jmaja]

I got the new 3-phase pump today. It was not Subteck. It actually had nothing about the manufacturer in the manual and the "plate" that came with it. It said made in Italy. Maybe it is this one: https://conforto.it/images/pdf/en/Submotor.pdf

The "plate" (actually just a sticker not attached to the motor) said Submotor, but it also said 1.8 A (1.5 A in the link above). The manual that came with it said that 30 Hz is the minimum.

How does this actually work? I could get different powers at 30 Hz depending on the settings. If I set the motor voltage to 400 V (as per plate), I get higher power than when I allow VFD to adapt the motor. Then it drives only 365 V at nominal 50 Hz. I can get even lower power, if I set the voltage to 240 V (only 240, 380 and 400 V are available). Maybe I could get something else, if I changed the resistance and reactance settings.

What happens when the voltage is lower, but the frequency is still 30 Hz? Will the motor actually run at lower frequency? I would think it doesn't need much current, since the torque taken by the pump should reduce at rpm^3.

Now (using auto adapt) it takes 1.13 A/220 W at 30 Hz and 1.5 A/650 W at 50 Hz while pumping 45 and 75 l/min.

[jmaja]

Reading the VFD manual it appears I should try one of the variable torque settings. I now have constant torque. A pump has rpm^2 torque.

What do these settings actually do? They use a different voltage, which is actually lower PWM at the same frequency? What thus that actually change? If the motor is running at the desired RPM with lower voltage, what does the higher voltage do? Decrease slip and thus a bit higher RPM? Or just decrease efficiency? Too low voltage increases slip until motor stops?

All I can see is the water flow. If it doesn't drop much, it's fine to use a lower torque setting?

[WattsThat]

It’s the Volts per Hertz output relationship.

Constant torque applications use linear Volts per Hz, matching the torque requirement.

Variable torque uses Volts per Hertz squared. This will will result in lower flux levels in the motor, lowering the current and usually the audible noise. Savings should be proportionally better in smaller machines since flux current is a larger proportion of total motor current.

[jmaja]

There are a lot of options in my VFD for voltage Hz dependence. I could even give my own piecewise linear function.

Should I just lower the voltage as low as the flow rate is still about constant?

Does this effect the durability of the motor?

The pump is 15 m below water in the borehole. There is no noice I can hear.

[jmaja]

Found this: https://www.gsengr.com/uploaded_files/Variable%20Frequency%20Drive%20Recommendations%20For%20Centrifugal%20Pumps.pdf
"A voltage proportional to the square of the frequency is recommended for pump applications in order to maintain both motor efficiency and the correct magnetisation level."

Thus a 400 V pump motor should be run at 144 V @ 30 Hz. I have now 220 V and get 1.13 A and 220 W according to VFD. I tried to measure the effective power taken by the VFD using kWh-meter pulses and got just a bit over 300 W. VFD efficiency seems rather low ~70%. Is that expected at lower powers? Would it be better with lower power or newer VFD?

Let's see later today what happens when I change the torque setting to variable torque.

[jmaja]

I did some tests @30 Hz with variable voltage.

220 V gave 1.15 A, 220 W and 46 l/min
180 V 0.88 A 195 W
160 V 0.85 A 180 W
140 V 0.84 A 170 W
120 V 0.865 A 160 W
110 V 0.89 A 150 W and 33 l/min
100 V 0.92 A 150 W.
Variable torque low gave
146 V 0.84 A 170 W and 40 l/min

The last one seems to be about the best. 110 V has already higher current and much lower flow rate. Thus a lot of slip and probably too low rpm for min 30 Hz spec.

I got 240 W from the kWh meter so 70% VFD efficiency.

I'm quite happy with that, if the pump lasts with these values. Probably I'll buy another VFD, since the fan is very noisy and it turns on every now and then even with low power.

[WattsThat]

Changing VFD’s is not likely to change energy usage in any considerable way as simple 6 pulse drive topology is unchanged for thirty plus years.

Perhaps a marginal savings with the lower Vsat voltages with newer IGBT’s and rectifier diodes - but at the power levels you’re running - nah, not worth chasing, IMO. A 10-15 percent improvement would be as much as you could possibly hope for under the absolute best of conditions.

[jmaja]

This VFD should have 96% efficiency at full power. The new ones have the same. But this one is for 1.1 kW shaft power and I only have 0.37 kW shaft power motor. A new 0.37 kW VFD has 93% and 0.55 kW 95% efficiency. Shouldn't these have close to 90% at 170 W electrical power? Or is there something about VFD design that makes it impossible to have good efficiency at low power?

What about using 1-phase input 3-phase output VFD? I could only get 40 Hz due to 240 V max output, but the load would be closer to maximum. Better efficiency?

Saving 50 W is not such a big deal, but having a physically  smaller and less noisy VFD would be more important. Many of the 0.75 kW and smaller seem to be fanless, thus they must be quiet.

I could probably find one at the same price I could sell this one.

[jmaja]

I found this efficiency calculator for current Danfoss models.
http://ecosmart.danfoss.com

E.g. FC-202 0.55 kW should have 94% at 60% frequency and 25% current and 96% at 60% frequency and 50% current. There is one for sale at 140 €.

[WattsThat]

There are no easy answers to efficiency questions. It may appear easy but it’s not as measuring the overall combined efficiency of a vfd, motor and pump, known as watts to water, is problematic at best. Some incredibly pricy and fussy gear is needed to accurately measure the power in and out of a vfd. Measuring motor power is easy but it requires a dynometer, anything less is an estimate. Pumps appear easy as you can measure pressures and flows but still not have all the data since you’re missing the delta T of the water.

It’s not that a smaller drive will be more efficient, it’s just that the measurements with a drive that matches the motor rating will have better resolution, nothing more. If a smaller, quieter drive is a better fit for you, go for it. Just don’t expect any performance improvements.

[jmaja]

Well I already bought the FC-202 0.55 kW a few days ago for 100 €. It has arrived and I'll pick it up tomorrow. Hopefully it is not noisy and a bit more efficient. At least it should be much newer and have a nicer display. It's about the same size.

I have no idea how accurate are the kWh and kW readings of these VFD's show on their display. But it should be easy to see how much energy the new one takes once I have set it up for the same pumping setting (l/min and head).

I guess VLT 5000 series is quite old. From the 90's? I would think the standby current consumption has gotten much better since then, which could show better efficiency at low powers. The ecosmart tool says that FC-202 should have 14 W standby loss and up to 29 W drive loss. I measured about 30 W for VLT 5002 standby.

But let's see. I will report when I get it running.

[jmaja]

Now I have the "new" VFD running. It's much less noisy, but still has a fan. The settings are quite different and I had some dificulties getting the same Hz and flow rate at the same time as the old had. Not much of a difference in efficiency.

I could get the same 40 l/min at 40% variable torque curve at 30 Hz or at automatically optimized 28 Hz. Both took about 175 W according to the VFD and 230 W according to kWh meter of the house. So maybe 10 W less.

The automatically optimized takes about 200 W at 30 Hz (260 W at kWh meter), but then it pumps 44 l/min. 145/190 W at 25 Hz and 35 l/min.

[Envieq]

Hello,
from our huge experience, I can tell you that there is no efficient solution for single-phase motors except Grundfos SQE pumps and Grundfos CU301.
The other solution can be to use the frequency converter that has IN 220V single-phase and OUT 220V three-phase, but in this case, the motor of the pump should be also 220V three-phase. Franklin produces this kind of motor, and there are a few producers that supply this type of frequency converter, one of them is Elentek. The Elentek solution incorporates an ABB inverter which is very easy to set.
Anyway, we can supply all these solutions, but my suggestion remains the same, Grundfos SQE pump + CU301. The pump has built-in all types of motor protection including dry-running protection, what do you want more?
Visit our website, if you have questions, use the online chat also for technical questions
https://www.envieq.com/
Thank you!