240vac 6amp pump

moorsbmoorsb Solar Expert Posts: 38
I am running my water well pump off of solar pv and battery bank.
I have 28 GE 66watt panels charging a 12v bank of 10 T105s
I am using 2 Wellsee 60a MMPT charge controllers
I am using a modifed sine wave 12vdc 8000watt invertor 120vac out.
It back feeds a 5 kva 480-240/240-120 transformer.
I have been running a day now with minor issues dealing with the pump.

The transformer put out 220v, how should I connect the neutral to feed 120vac loads?

Comments

  • RCinFLARCinFLA Solar Expert Posts: 1,327 ✭✭✭
    Re: 240vac 6amp pump

    A 12 vdc 8000 watt inverter is beyond absurd. Requires about 800 amps at 12 vdc.

    Pumping a modified sinewave through a transformer to run a pump is not good either.

    You don't need a neutral for a 240 vac pump (assuming U.S.). If transformer is true isolation then you can connect a secondary centertap to neutral if there is a center tap.

    If transformer is an autotransformer don't connect anything to ground or neutral on transformer as inverter may not allow a groundable neutral. Make sure case of pump is grounded so if motor winding shorts to case it will not become live.

    Did you check pump motor to see if it can be wired for 120vac?
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: 240vac 6amp pump

    Is the transformer "isolated" or "auto-wound"?

    If isolated (separate input and output windings), the center tap of the output winding would normally be grounded (like North American split phase 120/240 VAC home wiring) and the other two legs would provide 120 to neutral (A-Neutral; B-Neutral) and the A-B connection would be 240 VAC.

    If the transformer is auto-wound (one common winding with different taps for different input and output voltages)--Grounding a center tap could be an issue.

    Many (most?) MSW inverters have no isolation transformer internally. So, if the DC battery bank negative (or positive) terminal is grounded (common practice) by you. And the you ground reference the AC output of the inverter (via a "center tap" directly or indirectly through the auto-transformer--You can get a dead short through the inverter and destroy the internal switching transistors.

    If the MSW inverter is already a 120 VAC output--Why are you wanting to create a split phase 120-240 VAC output (is this for out at the pump building?).

    One other question... An 8kW 12 volt input inverter? That would require from a 12 volt battery bank:
    • 8,000 Watts * 1/10.5 volt cutoff * 1/0.80 inverter eff * 1.25 NEC safety factor = 1,190 Amp 12 volt circuit
    Basically a 1,200 amp circuit to run it at the 8kW rated output (excluding surges).

    That is a lot of copper/battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 240vac 6amp pump
    moorsb wrote: »
    I am using a modifed sine wave 12vdc 8000watt invertor 120vac out.

    Let me guess; another AIMS inverter rears its ugly head?
    Throw this piece of junk out and get a good inverter. Problem solved.

    What inverter you actually need depends on what the pump motor actually draws. You may need to rewire the system for higher Voltage, as you can't safely get more than about 2kW from 12 VDC - the current gets too high.

    Some inverters to muse on: http://store.solar-electric.com/maensiwainac.html
    Two of those already provide 240 VAC output so there's no transformer issue. The MS4024 should be able to handle up to 1 HP pump under most circumstances, and it shouldn't be too difficult to reconfigure your existing equipment for 24 VDC.

    I want it carved in stone somewhere that water pumps are one of if not the most difficult things to run from solar. Try to do it on the cheap and you get a system that either doesn't work, doesn't work well, or doesn't work for long.
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    I am back feeding the transformer the coils are independant. Normally it would be fed 240 v and it would output 120 v I am feeding it 120 and getting 240volt I do not see a center tap.

    I do not see the point of calling stuff junk.

    I do not intend to feed the invertor full load, I want the surge cability which it proves it can do. I have a 600amp fuse on the inverter. For $375.00 it works.
    The pump does not run that long, only 30 minutes a day.
    I want to run other things in the pump house at 120v. I want to fed a panel in the house which is 120/240 so I need a neutral. I am not sure if I should ground the invertor to the battery bank or try to figure out if I have a center tap on the transformer.
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    FYI I took 1" copper plumbing pipe and flattened it I use that as a copper bus to feed the inverter. The T105's bolt to the bus and then I use a short piece of copper wire to the inverter with 600amp rectifier fuses limiting the current to the inverter.
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: 240vac 6amp pump

    If it is an isolated transformer--then it is perfectly OK to ground reference one of the output leads.

    Have you tried looking up the transformer on the internet and see if you can find a wiring diagram? Here is a PDF document from one transformer manufacturer that you may be able to match your terminal identification too (if standard).

    The problem with a generic non-isolated MSW inverter--You can ground the battery side or the output side, but not both at the same time--Or you will get a dead short through the inverter.

    You need to look at the manual (or see if there are any plaques on the side of the inverter) for there supported grounding. You have three questions to answer:
    1. grounding the battery bank (usually grounded)
    2. grounding the metal chassis of the inverter (usually grounded)
    3. grounding the output (usually not grounded for MSW inverters)
    Some inverters may ground their output (can be done on isolated type TSW inverters) to the chassis internally. So #2 and #3 are already done by the vendor.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: 240vac 6amp pump

    You are trying to run a fairly sizable AC induction motor from a Modified Square Wave inverter. The motor is not going to run well. It will run slightly slower, draw more current, and produce more heat. Ultimately it will burn out before its time.

    AIMS inverters take the bad qualities of MSW and add to them unsafe multiple DC pathways to supply their ridiculously high output Wattage. Quoting RC: "A 12 vdc 8000 watt inverter is beyond absurd." They making even bigger ones which are even more absurd. Properly fused, this monstrosity should have one single 800 Amp fuse to handle its current potential. There should never, ever be multiple fuses in parallel on one circuit. When something goes wrong power must be interrupted quickly and wholly all at once. Pop! And it's off. Not: Pop! Pop! Pop! until eventually all power to the unit is stopped. That's how fires start.

    Right now you are searching for the neutral connection and have come up against one of the big problems with MSW inverters: if you bond neutral to ground as is standard AC wiring practice, and the inverter (-) is grounded as well, you will fry the inverter. Normally the output is "floating" on one of these: no neutral-ground bond. If you step it up through a transformer to get 240 VAC you can only get 120 VAC if there's a center tap; you can't "reference" back to the inverter output against the transformer output.

    Best-case scenario for what you've got: isolated 120-240 step-up transformer with a center-tapped secondary.

    But this set-up has "future failure" in its make-up. Possibly catastrophic failure. Sorry, but that's how I see it.
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    The Transformer is like Diagram 1 on pg 16 of that manual. Both windings are on primary and secondary are in parallel.
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: 240vac 6amp pump

    Is that Diagram #8 on page 16?

    If the High Voltage windings are in parallel for 240 VAC--then there is no accessible center tap for your 240 VAC?

    What are your 120 VAC loads in the pump house? In the end, you may be forced to just use a small 240/120 step down transformer. If your 120 VAC loads need a ground referenced neutral--then you would need an isolated step down transformer.

    By the way, do you turn the inverter DC input on/off when you need the power? It would be normal for a transformer to have ~5% or so of rated power as standby losses (24 hours x 7 days a week--and that adds up)--As well as the standby losses from very large inverters (may be 50-100 watts +/-)... Those standby losses can really hurt if you have limited power available from your system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    Diagram 1 pg 10 of the above ref pdf file
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: 240vac 6amp pump

    Yea--If the low voltage winding are connected in parallel, and the high voltage windings are connected in parallel, then you cannot get split phase 120 (grounded neutral) from that transformer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Lefty WrightLefty Wright Solar Expert Posts: 111 ✭✭
    Re: 240vac 6amp pump

    Why are you not running 120VAC to the pump house and mounting the transformer near the pump motor controller in the pump house?
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    Everything is located in the pump house. I am thinking about trying to run my pool pump off it too. I noticed that the system is pulling 50amps from the battery with the sun out. I am thinking my pool pump runs during the day, It might be nice to have it run off solar if the sun is out or switch it to ac power if a photo cell does not see daylight.
  • BB.BB. Super Moderators, Administrators Posts: 31,061 admin
    Re: 240vac 6amp pump

    Is it time to look at Grid Tied or at least a Hybrid Inverter (like the Xantrex/Schneider XW) which can do both Grid Tied and battery backed off-grid?

    Usually, you will have better results with a Hybrid Inverter instead of trying to switch between Grid and Off-Grid system (batteries will be cycled and probably not last as long in the Grid/Off Grid setup).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • moorsbmoorsb Solar Expert Posts: 38
    Re: 240vac 6amp pump

    I decided to try my swimming pool pump 12A @230vac
    No Luck. I do not blow the 600a fuse feeding the inverter, but the inverter just goes off line. If I toggle the power switch on it it comes back on line. Yes this is what lookes like the AIMS inverter I got it diretly from china on ebay for 1/2 the cost.
  • mike95490mike95490 Solar Expert Posts: 9,020 ✭✭✭✭✭
    Re: 240vac 6amp pump
    moorsb wrote: »
    I decided to try my swimming pool pump 12A @230vac
    No Luck. I do not blow the 600a fuse feeding the inverter, but the inverter just goes off line. If I toggle the power switch on it it comes back on line. Yes this is what lookes like the AIMS inverter I got it diretly from china on ebay for 1/2 the cost.

    Maybe a soft start kit for it, will let it spin up.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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