Irrigation Pump for Small Farm - Inverter Problems

[inetdog]

Actually, that was a bit of a joke about the difficulties of discussing technical topics with someone who has little knowledge in the topic, using two entirely different languages.

You're talking about what this is talking about:

"Single-Phase Problem
A motor's coils driven by a single AC phase all alternate at the same time, reversing north and south poles in unison. This creates a problem called zero starting torque. While it can run a motor already spinning, it has no "kick" to get a motor to turn from a dead stop. You can start it by spinning it by hand, but who wants to hand-start a vacuum cleaner?

Starting Capacitor and Switch
A capacitor, connected to a separate coil on the motor, creates an alternating electric current ahead of the main phase by 90 degrees. This happens because the current through a capacitor leads the voltage by 90 degrees. During a motor's start-up, a switch connects a capacitor and a special starting coil to the motor. After the motor reaches its operating speed, the switch disconnects the capacitor. If the capacitor remains connected to the motor, it puts a drag on the motor's efficiency."

That helps. I think of capacitors as being used to store energy for rapid release (like a flash bulb capacitor) or for filtering. I've never heard of them being used for phase shifting like that.

So, why *wouldn't* a soft start "provide the phase shift between the start winding and the run winding." Shouldn't there be a switch in the motor that is doing that?

Unless you are generating the voltage electronically inside the soft start box, the only way you can get a phase shift is with a combinations of inductors and/or capacitors.
If you want a soft start box to provide a phase shift between start and run winding, you must connect both windings directly to the soft start box, and have the necessary capacitor(s) inside the box. A switch cannot provide a phase shift, it can just turn on and off.

[kjmclark]

Sorry, let me rephrase the question. The softstart is completely outside the electronics of the pump. From the pump's perspective, the softstart is the electrical cord coming into the pump. But the pump must already have an internal mechanism to switch between the start and run windings.

So the question is, what about the soft start, or the power it's supplying to the pump, could cause the pump's mechanism to fail to provide the switch from start to run windings? Is the problem that the pump's very simple electronics might fail to work with the lower voltage/current ramping up to normal? What can I break by trying it?

Also, the soft start manual says:
"The ATS01N1 soft start is compatible with most single-phase motor designs, including split phase induction, capacitor start, and shaded pole."

So it doesn't sound like I'm risking the soft start.

[kjmclark]

Soft start works great

OK, so I finally figured out the wiring diagram for the soft start. (I'm sure the rest of you would look at the diagram and say "duh", but I though it was a little unclear.)

So I wired it up as a test. I need to get a proper switch for it, but I also need to test it with relays, since I'm going to control the current to the pump with an Arduino. For the first test, though, I just plugged it into a socket at home.

Before the soft start, this smaller, 1/2hp pump was drawing somewhere around 8-9 amps of inrush current. I couldn't tell because the needle jumped quickly and dropped quickly back down to its run current of ~3amps. Could have been much higher and my meter couldn't move the needle fast enough. Actually, I'd have to assume it went up around 15-20amps for a very short period.

After the soft start, the same pump goes no higher than 6 amps. You can hear that the soft start is slowly ramping up the motor. It's still pretty fast - the pump settles down (no load right now) to its 3amps within 2 seconds. The soft start doesn't signal that it's reached full voltage for about 5 seconds though.

If I remember, I'll come back next year (or someday) when I've switched things to 240v to run the big pump, and report back on how well the soft start works with that.

Just wanted to close the loop in case someone else looks for this thread in the future and wanted to know if it worked out.

Thanks to everyone who replied for all the great advice!