Transformer options to run 240V 1P motor on 120V 1P

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fastline

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I will try to keep this simple for clarity. This particular project is personal, so I want to try a few things. We have a huge remote garden that will be watered off a water well, fed by a generator for now, but will end up moving this to solar. Inrush on these darn pumps has to be considered. They start hard. I am really looking for a better solution like a 3P pump motor and VFD, but those are nearly impossible to find, or very expensive.

Right now we will have to drive a 1P, 1HP, 2 wire pump. Already tested in the field at 9.6A/240V at load, and 40A inrush.

All this being said, I would like to employ an RV type generator and they are 120V only.

Some time back, we had a discussion here about slaving a buck/boost transformer rather than a true isolation transformer. ?? Basically feeding the 120V in the primary as a split phase config, then pull 240V off that primary?

By the math, it would seem you would need to double the size of the buck/boost to account for driving only one primary coil at 120V? I am not sure how inrush may play with these?
 
I have run all calculations for head loss, lift, and minimum system pressures to ensure valves function correctly. That number is about 180-200ft of lift, and the well can only sustain 11GPM so our target flow is 10-11.5. Obviously a VFD would allow the ultimate in dialing the system in!

However, finding a VFD is not an issue. Hell, I have a few I could use right now. We just derate for the 1P and turn off phase loss in settings. The bigger issue is finding a motor to drive. I think I found one a couple weeks ago and was around $1k just for the motor.

What further frustrates me is the very poor efficiency. I have confirmed 1900W to run the current 1HP pump. There is nothing wrong with it, I have seen this sort of thing from these Franklin motors and pumps in the past. It sure seems pretty wasteful when you calculate the actual power needed at 100% eff is only like 1/4HP.
 
You can try smaller transformers than recommended. Can't more than not work and it's not like the motor is sitting inside the living room.
I thought your entire issue was with the starting current of the motor. (Ignoring the inrush of the transformer). Yes, the VFD is the least expensive of the components required.

Get a bigger generator would be the less.
 
ptonsparky said:
You can try smaller transformers than recommended. Can't more than not work and it's not like the motor is sitting inside the living room.
I thought your entire issue was with the starting current of the motor. (Ignoring the inrush of the transformer). Yes, the VFD is the least expensive of the components required.

Get a bigger generator would be the less.
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Well it becomes a train of factors here. The inefficiency leads to the need for upsizing the pump, which leads to higher inrush, which leads to oversizing a generator/solar equipment. Technically a 1/2HP pump should do this with ease!

As well, since you also provided the Franklin chart, you can see that 2 wire pumps use an internal triac and start winding I believe, and just start 'harder' in my experience and do have higher inrush than a 3 wire with a start capacitor.

I guess beyond this little project, we are trying to do some learning because there are plans to install more of these in the field.
 
Hey, I was trying to look up the PN you provided, which appears to be a micro drive? Reason I ask is that might be an avenue we are currently looking at. Basically we REALLY want to try to stay with 120V because the supplemental generators are much easier to come by in that voltage. But it seems the pump size that is needed, it is nearly required that we stay with 230V class goods.

I was recently schooled that some of these micro drives actually accept 120V/1P input, and output 230V/3P? Do you happen to have a reference for any of decent quality? That could really be a game changer for us! What I might like to do is use our proposed 3kw hybrid solar inverter at 120V, and it can provide the 120V to the VFD. Our proposed solar inverter is capable of syncing its generator input to its own output so it can use both. I want to say some call it "AC coupling" but those lines start to get blurred IMO.
 
fastline said:
As well, since you also provided the Franklin chart, you can see that 2 wire pumps use an internal triac and start winding I believe, and just start 'harder' in my experience and do have higher inrush than a 3 wire with a start capacitor.
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Yes, the 2-wire motors are split-phase, with a starting winding consisting of fewer turns and finer gauge wire than in the run winding. This increases the resistance and decreases the inductance so that the resulting R/L ratio achieves about a 30° phase shift in the current vs. applied voltage. But the overall impedance of the winding at starting is quite low, leading to a high starting current. Also the relatively small 30°phase shift produces less torque than there would be with a 3-wire capacitor start configuration.

I don't have any experience with them, but Phase Technologies has a "Residential Single-Phase VFD" for 2 and 3-wire pumps. It has controls for a constant pressure system, but it appears like it can also be used "open loop."
https://www.phasetechnologies.com/products/vfd/es

The drive parameters can be tailored to the specific pump used such as the phase shift for a 3-wire pump, the pump manufacturer, etc. For example, the parameters below are listed on pg. 22 of the pdf file https://www.phasetechnologies.com/v2/downloads/manual/ES-Manual-current.pdf

ES_drive_parameters_pg22.png

I have no idea of the cost, but I'm sure it must be quite a bit more than a bare bones VFD. It seems to be thoroughly worked out with specific features for a pump application. Franklin (and likely others) have similar products, but at first glance they appear to be more turn-key with less flexibility on how they are set up.
 
Thanks for the links and info. What I REAAALLY want to know at the moment is what are these drives doing to speed control a 1P motor? I am just itching to see graphs of frequency, current, etc. Not really a big deal to slow a 1P motor that is running, but another to soft start one with good torque.

As for my consideration of the 3P motor in the hole, I still feel pretty good with that thought as I have had all sorts of 2 wire motor failures in the hole. In a Franklin, the Triac can fail, leaving a motor that has a good main winding, but will never start again. I have had some that have a built on capacitor on the motor in the hole. Capacitor failure so one would think "get a capacitor", except you can't get them and they are potted up so just not worth it. I will never touch another.

I like the old 3 wire systems because most start boxes have proper overloads that won't auto reset. I can usually save a motor with that setup.

But I figure a 3P motor in the hole with a more universal VFD would give me parameters that are prob not available on these proprietary VFDs. I used to think overspeeding a motor was a huge issue until I learned otherwise in CNC automation. It should give me some flexibility in the system, as well as protections.
 
What about a Hyper Engeneering Surestart soft starter for an AC condenser motor? It made my AC go from 105+ amps of inrush to like 5amps of inrush above its FLA(25a total inrush, 20a fla) There only a few hundred bucks. My 5 ton AC will now start on my 9kw portable generator. This with a transformer? Screenshot_20230216_222211_Firefox.jpg
 
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fastline said:
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I was recently schooled that some of these micro drives actually accept 120V/1P input, and output 230V/3P? Do you happen to have a reference for any of decent quality?
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Pretty much all of the major drive players offer this option. My advice is to stick to the known names from local suppliers that can help you if necessary, as opposed to the dirt cheap no-name Chinese junk being sold on Fleabay and Amazonk. Most of those are truly horrible quality and are giving the entire industry a bad name.

Keep in mind that although the VFD will prevent the inrush current issue, you are going to still need a minimum of a 20A circuit to feed 120V power to that drive if you are going to run a 1HP motor. The 230V 3 phase motor will have a much lower FLA value, but ALL of the power for it still have to come from the 120V 1P source.

Lastly, take extra care in mounting a VFD outdoors, they don't like heat and they don't like extreme cold. And like all electronics, they don't play well with water.
 
I have often wondered why not make a 4 wire VFD for split phase motors with a 90 deg phase difference?
fastline said:
but will end up moving this to solar.
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If your going to move to solar, and have not bought the generator yet, you might also look into 120VDC water pumps.

120 DC is a good voltage for off grid, unconventional water pumping, as there is there is lots of surplus equipment in that range.

 
tortuga said:
I have often wondered why not make a 4 wire VFD for split phase motors with a 90 deg phase difference?…
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That’s not the problem. The problem is that most single phase motors will have a centrifugal starting switch and if you slow them down below the activation speed of that switch, it puts the auxiliary start winding and capacitor (if any) back in the circuit. Start windings are not made to run continuously and with start caps there is a race to failure between the caps and the drive transistors.

There are VFDs available for single phase PSC and Shaded Pole motors but they are ridiculously expensive because the sales volume is really low. It’s usually cheaper to buy a 3 phase motor + single to 3 phase drive.
 
I have briefly shopped for the above mentioned VDC pump setups and I might be open to that as speed control would be easier, but I find those pieces to be quite proprietary and far from cheap. My concern is walking down the line with something like that and having a failure. Due to the commercial nature here, a fast repair, even temporary has to be considered.

I have been looking at new, old stock 3P motors as I know if we are in a pinch, we have many 1P motors around and could get something going quickly on 1P and a generator if we just had to. Problem I am finding is 230V class 3P motors are not nearly as common as 460V variants.

I guess I am trying to reduce complexity at this point, but I think most would agree that 3P motors are inherently more reliable as nearly all 1P pump motor failures I have dealt with (lots) are due to the start circuit. I really don't fully know how the Franklin motors work, but they don't use a start cap. However, I inspected one for something recently and found the motor to be pulling LRA amps without starting and was not locked, so that points to a start circuit failure.

I still want to know how those "soft start" modules work.

Still just weighing options I guess.
 
fastline said:
I have been looking at new, old stock 3P motors as I know if we are in a pinch, we have many 1P motors around and could get something going quickly on 1P and a generator if we just had to. Problem I am finding is 230V class 3P motors are not nearly as common as 460V variants.
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You might consider using a 120/480V transformer with a 480V VFD. The VFD current rating would need to be increased by a factor of 1.73 when providing only a single-phase input.

If the 120V RV generator is started with the transformer connected, then as it gets up to speed it should ramp up the voltage and thereby minimize the resulting peak transformer inrush current. For example, see this post: https://forums.mikeholt.com/threads/generators-with-step-up-down-transformers.89428/#post-1433583
If you had to power up the transformer when the generator was running and this caused tripping that could not be resolved, a soft starter before the transformer would be a possible option. One option: https://blackhawksupply.com/product...kw-single-phase-integrated-bypass-w-heat-sink


fastline said:
I really don't fully know how the Franklin motors work, but they don't use a start cap. However, I inspected one for something recently and found the motor to be pulling LRA amps without starting and was not locked, so that points to a start circuit failure.
Click to expand...

https://franklinwater.eu/media/320268/4inch-2wire-Motor-Function-Description.pdf
 
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