Auto transformer on load side of deep well pressure switch?

Saggys · December 2020

Have any of you tried this? I have a T240 auto transformer supplying my panel board in our cabin which feeds our deep well pump. The well pump is our only 240 volt load, it seems this is not the most efficient setup as the transformer has a 12 watt hour consumption. I am thinking about removing the T240 and installing a more compact T220 transformer on the load side of the well pressure switch so it is only on when the pressure switch calls for it. The well pump is a Grundfos SQ series soft start so I am hoping the in rush current to the transformer and powering the well pump will not be so severe, as this configuration would burden the inverter more than the present set up. Is this worth the effort?

mike95490 · December 2020

Just try it and see. Sometimes, the inrush to the transformer & the pump, can be worse than the steady load. If it doesn't work, wire it back to the original way, and plan on a 240V inverter when that time comes. Note that a 240V inverter needs a little bit of load balancing.

mcgivor · December 2020

You could use a relay to power up the transformer when the pressure calls for water and a time delay relay to power the pump from the same pressure switch, but first try without the complexity, the soft start may make it redundant.

Saggys · December 2020

If I go through the work of the rewire, it might be time to do an inverter up grade. All of my wiring is code compliant with conduit raceways so it is a little more work than open wiring as I would have to make changes at 3 locations. The 240 volt inverter is probably the best way.

mike95490 · December 2020

how about trying to hook the transformer up to a 120V outlet, and see if that crashes the inverter. Good transformers work even with an eu2000, but lossy ones crash inverters.
This 3kva transformer works with eu2000, with the 240V side wired as an autotransformer, but it's 115lbs

Image: https://us.v-cdn.net/6024911/uploads/editor/zz/igc09krtkjbv.jpg

lbs

jtdiesel65 · December 2020

When i had that setup I used am ameritron icp-120 for the transformer inrush

Saggys · December 2020

Mike, I was just up there yesterday and looked at it and came to the same conclusion, temp. wire it off an outlet and see if it works. If it does I will run it like that for a couple of weeks, monitor current and voltage measurements before I change wiring in 3 locations. This costs no money, just time.
Jtdiesel65 I have never heard of what you used for inrush current, is that a type of transformer?

jtdiesel65 · December 2020

It's a current limiter mostly used in front of music amplifiers so when you turn them on, they don't fry everything else as power dips. It the same scenario when you have inrush when you power on a transformer.

Good description here:

https://www.dxengineering.com/parts/ame-icp-120

BB. · December 2020

Inrush current limiters are (usually) basically just a Negative Temperature Coefficient Resistor... At room temperature, they have relativley high resistance. After they "warm up", the resistance drops:

https://en.wikipedia.org/wiki/Inrush_current_limiter

They were even used in older power supplies (non-power factor corrected) that have a Diode/Capacitor bridge on their input. the diode+bridge have very low input resistance (impedance) and the high surge of startup (get turned near the peak AC Sine Wave voltage), can damage the diode/capacitor circuit.

The major weakness--The surge suppression only functions as designed from a "cold start"... If you have a circuit that cycles frequently, the NTC Resistor does not get a chance to cool down and go "high resistance".

In this case, if there is a pressure tank in the water line from the pump--Then it takes a few minutes (guess) for the pump to recycle back on. If there was no water pressure tank, could cycle on/off in a few seconds and reduce the surge current limiter effects.

-Bill

jtdiesel65 · December 2020

I used it for years with no problem with a Trace 4024(I still have this on a shelf and should be in working order. I should get rid of it). It was just two people using water. I finally ditched it and the transformer and went 240v. That change was mostly so I could put in AC and have 240v for tools in the garage not so much for the well pump situation. I'm sure there are losses using the transformer.

Saggys · December 2020

Jtdiesel65 that is really a neat device, I have never seen one of those, it gives me one more option. Thanks BB for the explanation, kind of the opposite of a degaussing circuit on old CRT televisions and monitors.

BB. · December 2020

PTC. Positive temperature coefficient resistor used on degaussing coil etc.

Bill

Ralph Day · December 2020

On my initial off-grid setup I had a 240v water pump. It was set up like described, the pressure switch would close causing power to run to the autotransformer and then to the pump. The Xantrex sw4048 (120vac) would have a mighty surge on startup, the saturation/powering up of the transformer plus the locked rotor start load of the submersible pump.

I once saw the sw's meter register 45 amps (as high as it would go), so who knows how high it actually went. If the tv was on (old crt colour Hitachi) the picture would go black and white and shrink from the sides of the screen by 30% at least. It was quite a draw. Not to mention dimming the house lights etc.

The problem was rectified by getting a Grundfos soft starting 120vac submersible pump. The pressure switch clicks, the draw starts from 0 amps and goes up to 10amps for the cycle run. Much easier on the inverter. That's my recommendation...install the soft start pump and save the cost of early replacement on your inverter. Been there, done that.

Saggys · December 2020

It may be a month or more but I will follow up with the results of this little experiment.

Saggys · January 2021

Finally got around to trying the temp wiring of the Trace T220 wired to the load side of the well pump controller pressure switch. It worked easily, inrush on the auto transformer primary, low volt side was only 3.6 amps, and the high voltage was 242vac, then the low voltage current rose to 6.8 amps and the high voltage dropped to about 230 vac and stayed there till the pressure tank was full. This pretty much confirms that Grundfos soft start works. The transformer that I have in circuit continously is the slightly bigger and better rated Trace T240. The inverter powering the load is a Trace PS2512.

Saggys · January 2021

Just out of curiosity, The T220 does not give an idle power rating like the T240 does. It only lists an insertion loss of .53 ohms at 117 vac, not having any luck yet trying to convert that to power loss.

Saggys · December 2021

Just a follow up on this, I finally permanently wired this into our system and everything works fine. Confirmed above measurements and they seem consistent. For anyone looking to maximize system efficiency this will help, can even use search mode on inverter now as Trace T240 auto transformer on output would not allow this due to loading.

Auto transformer on load side of deep well pressure switch?

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