Using a 110 to 220 step up converter

MainelyTom

Hi, have an off-grid 110 volt solar system. Need to add a well pump to the system (previously gravity fed surface water). Problem is that the well head is 120 feet from the house (septic system set back requirements) and about 230 feet deep (with about 40 feet to the top of the water). Plan is to place the pump at about 210 feet. But that gives a run of at least 330 feet and the pump installer is figuring a 3/4 hp pump. Likely a Grundfos 5SQ07-270. Because it has built in soft-start, we are hoping to avoid the usual motor start up surge. But still, that's 600 watts. At 330 feet I'm not sure what wiring to run. I've done the calculations and it should be able to handle 12/3wg the whole distance. Just don't want to get caught having to move up to 10/3 for the higher amps over that distance. Luckily the pump has a wide voltage range so It should be able to handle even a 20 volt drop at 220. Any thoughts? Go with the 110 volt without a step up converter? or go with the 220 with a step up converter. And do the step up converters use power when not in use? couldn't find an answer to that.
Thanks.

Estragon

FWIW, I had a similar issue with a submersible (lake) pump.  I ended up going 240v (my only 240v load) with an autotransformer.  The autoformer doesn't use much just being on (a few watts).  If power is tight, I turn it off at night, as water in the pressure tanks is usually enough.  The inverter search probe makes the autoformer a bit noisy, but it's almost silent just being on.   

I also found if the autoformer is turned on with the pump pressure switch closed, the gfi opens, but if the autoformer is powered first, no problem.  A well pump likely wouldn't have gfi though, so likely not an issue.

mike95490

Your 3/4 hp pump will consume more than 600w    My inverter logs my 1/2 hp at 1,000 watts, because of losses and power factor.

A DC or integral inverter pump may be less and if you starve the pump for power with small 12ga wire, your pump rate will decrease. for that distance, I'd suggest the 10ga if you can swing it.