Inverter solely to run a water pump...

nyarelathodep

As the title states, I'm looking at my next upgrade to install a high power inverter to be used strictly in running a submersible 2 wire, 120vac 1/3 hp pump.  This would eliminate the need for me to go out and start the generator every time I want to charge up the pressure tank (18 gal drawdown).  This pump would not be expected to run for more than 5 to 10 minutes a day at maximum usage days. 
 Though I can't nail down a precise surge, I believe it to be near the 6k mark, based on trial and error of various generators I've tried. My Briggs 5550w(8500) starts it with the slightest of dip in power (engine bogs almost imperceptibly and the upstairs led dimmable lights will dim a bit)  The running watts are about 900-1k.  My plan this far is to hook up the inverter with the breaker turned on only for the time it takes to run the pump, to avoid needless tare losses and the like.  This is a 24v off grid system, 225ah bank.

My question here is:

A: Considering that I already use a generator to run the pump, would it be a bad idea to buy a MSW inverter instead of true sine wave? I know inductive motors don't care for modified wave, but taking into account the very limited run times, would I be harming the pump with such an inverter?

B: any inverter recommendations that won't break the bank? I have a charger (Iota dls 27-25), so it just needs the inverter component.  I am trying to keep it in the $500-900... I'm pretty sure I don't want a Chinese headache on my hands, but I'm sure I don't need an outback either.  I heard good things about GoPower, and the 24v 3000/6000 unit can be had for about $950.  Any recommendations would certainly be appreciated.

Aguarancher

think this has already been addressed: http://forum.solar-electric.com/discussion/23126/water-pump-question
No way would I use a MSW.

Aguarancher

I personally would save up and get the Outback, but this should probably run it. You could ask the people at the store to be sure though. http://www.solar-electric.com/inverters-controllers-accessories/inverters/sasiwain1/samlex-pst-series-pure-sine-wave-inverters/samlex-pure-sine-wave-inverter-pst-2000-24.html

ps..sometimes around the holidays they run a discount.. you might ask.

nyarelathodep

To reiterate, an expensive outback inverter/charger is no longer needed/desired, or even an affordable option anyway.  

Aguarancher

i posted an alternative as you were posting

nyarelathodep

That samlex will not handle the surge, I'm confident.  I've heard from multiple sources that the high power samlex inverters can be problematic, though I do have a 600 watt model that has been flawless for over a year.  The 3000 watt sa series I'm sure would handle the pump, but it's a bit pricey, tbh.

Aguarancher

if you can't fire up that pump in a stand alone situation with a 4000 watt surge, you have other problems. good luck

BB.

Any chance you can change the motor to something with lower surge current? Possibly a VFD  (variable frequency drive) to limit starting surge?

Possibly put  a dump valve+check valve in? (let the pump start against no back pressure, and have the valve close after a few seconds).

1/3 hp motor and needing a 3kWatt+ inverter or genset to start it... That sounds way wrong.

-Bill

nyarelathodep

I'm uncertain of your meaning...

Aguarancher

If this is for a weekender place you could use the one above, if you live there it would be better to use this one. http://www.solar-electric.com/inverters-controllers-accessories/inverters/sasiwain1/samlex-sa-series-pure-sine-wave-inverters/sa2wa24vosiw.html

they both have 4000 watt surge, which should start and run your pump. maybe you should explain in detail how your pump and pressure tank are set-up. pictures are always the best if possible.

nyarelathodep

Bill, I'm really not interested in changing the pump or fiddling with it to any degree.  So far as to the starting requirements, not sure what to say other than it is what it is. A 3kw genset would not touch it but my 5550 does without a problem.  

nyarelathodep

Agua, the pump is located about 100' from the house, static water line approx 12' down. The connection is 1" water line direct to pressure tank.  Super simple and direct set up. This is a full time living situation. Can't take pics at this time.

Aguarancher

I assume you "T" at the tank for the house run. First off you need a check valve on the supply line (pump) before it goes into the tank and before your pressure switch, otherwise the pump is starting against one heck of a load. What is the rise between the pump and the tank? What is your wire size for that 100' run?

nyarelathodep

Yes, the tee is at the tank. There's no check valve there, but I was told it was in the pump itself. I'm not overly knowledgeable about plumbing and pumps in general. The wire run is standard Romex 12/3, I believe. Total water lift doesn't exceed 20'.

Aguarancher

you need another ck valve as i stated by the tank. i assume you're running poly pipe? just pick up a 1" brass ck valve, a couple of threaded barb fittings, clamps and you're set. you need to run the voltage drop on your wire. but it's probably ok if 12ga.

Aguarancher

I just ran the numbers and for a 20 amp draw you should be using 8ga for a 3% voltage drop. you might run the numbers yourself and see what you come up with. http://www.electrician2.com/calculators/vd_calculator.html

nyarelathodep

The wire is 10/3...Went out and took a look yesterday. So having two check valves in place, one right above the pump (where in fact it is...i wasn't sure so i went and pulled it to look) and one at the tee will reduce the starting current by a substantial amount? I'm curious as to how the surge is reduced if the line is already primed... What does a second check valve do?

I'm also wondering by how much roughly... Without any expensive equipment to catch the surge, its been a guessing game, which is why I wanted to oversize the inverter.

Appreciate the input so far.

Aguarancher

The pump and the pressure tank are 2 different systems. Both need their own isolation, which the separate ck valves provide. Besides being cheap insurance if one or the other fails. You have a starting problem which is evident by the fact you can’t power up the pump with a 3kw genny. Trying to determine what is causing that problem comes down to a process of elimination. A weak or leaking ck valve at the pump can be one of them. Your 10/3 specs out at industry standard of 3% voltage drop w/20amp surge at 72ft max run length.

Until you can get the system to run on a 3kw gen set you are chasing your tail in trying to size an inverter to do the job. Just my opinion.

this is a typ set-up at the tank. http://www.buypumpswholesale.com/files/1928173/uploaded/tanktee.jpg

mike95490

I know for a fact, that my 1/2hp pump consumes 1Kw - the  inverter logs it's loads.  Starting load (locked rotor) is going to be upwards of 8KW..  I researched all this out years ago as I was building up my system, and went with a 6Kw inverter (if a fridge is on and the pump starts.....)
Motors, as they get smaller, have lower efficiency,  Power Factor (PF) is around .65  all the losses ad up.
 A 3KW genset has a lot of rotating mass, and can power the surge needed to spin the pump up, but if it's a cheap one, marginal windings, fast acting breakers, it could fail to start the pump.  your 5.5KW is nearly 2x the size of your 3Kw.
With MSW, all the problems get worse, and the pump lifetime will plummet.
With battery and wire resistance, maybe 24V is not enough to handle the DC current, you may need 48V.
Say you need a 6Kw surge, at 24V that's 250 amps (for 1 second) wire resistance and internal battery resistance are all working against you here.  48V gear would only be 125A. 

 Me, I'd stick with the generator till I find a dealer willing to loan a couple inverters to see which will be reliable to start with.