Minimum Backup Sizing For AC Pump

soulersouler Registered Users Posts: 12
I'm looking for an easy solution, but new uncertainties arise. This said as a credit to your forum here. You are saving people from many problems down the road.

May i ask about this specific perspective:

1) I need to invest in a battery backup system able to handle a standard artesian well pump which ordinarily draws 4-5 amps at 230 volts. This emergency use may happen only rarely, but is our primary concern. My wife's flower business cannot risk power outages in wedding season, (especially for water). Plus having that capacity, on very short notice, alleviates many other needs.... So I'm thinking of a 2000w inverter to cover water need. I've got a big 120-240V transformer already.

I want to dabble with alternative battery charging sources.

2) I was hoping to use AC charging when needed: Do flooded cells require AC charging at substantial rates in case solar charging is very minimal? In case prolonged cloudy weather happens regularly? (Latitude= 44.4) Is battery life shortened for lack of high charge rating?

I was hoping to buy a minimal solar array which might refill batteries when power needs ease up. When we don't use any more backup power for the rest of a day or for some weeks. So....

3) Can an undersized pv array eventually charge batteries (fully) ? Say four Trojan 6v batteries?

4) Are there better equivalent batteries, better for longevity?

5) Can a 1000w Honda generator optionally recharge batteries, given enough time? (Advice on matching 1KW charger?)

Thanks so much for any advice, rants or insights.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,471 ✭✭✭✭✭
    Re: Minimum Backup Sizing For AC Pump

    The running amps of the motor are not the problem, it's the starting amps that kills inverters and chokes step up transformers. (Once a transformer reaches saturatuation, you cannot pump one more extra watt through it).

    What is a "standard artesian well pump " ? An artesian well is free flowing at the surface, all you need is a bucket.

    Look at the pump label (if it's not underground) and report back what it says about it's electrical specs.

    I can tell you that my 1/2 Hp well pump, consumes 1,000 w @ 240V, as reported by my inverter. It's starting current is guessed to be about 6x the run. It has a starting capacitor in an above ground control panel.

    With pumps, it's all about lift (pressure) and flow (volume), figure out your needs, and then we can narrow it down. Many pumps installed on the grid, are 2-3 x oversized.

    Mike
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Minimum Backup Sizing For AC Pump

    I'm following this thread with interest, not to hijack it but I have a similar problem in trying to size an inverter to run an electric chain saw (1.8 kw running). You say "it's the starting amps that kills inverters" and that is the same worry I have. My tests show starting amps could be as high as 12 kw - not something your typical 2 kw inverter can handle with a 3 or 4 kw surge rating. Which may mean going to modifed sine wave and 24 or 48 volts, to get something even remotely affordable (cheaper inverter and smaller DC wiring).

    Anyway, to relate this to the souler's post maybe he will need MSW for his pump, and something much larger than 2 kw.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • solar_davesolar_dave Solar Expert Posts: 2,346 ✭✭✭✭
    Re: Minimum Backup Sizing For AC Pump

    Perhaps a better solution would be to have enough water storage to carry you a couple days during a power outage and not have to pump except from a local tank or use gravity flow.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Minimum Backup Sizing For AC Pump

    Pumping water is one of the most difficult things you can do with solar/battery power. Water is heavy, and it takes a lot of power to move it. From the OP's info, we get 5 Amps * 230 Volts = 1150 Watts - and as Mike pointed out that doesn't include the start-up surge. In all likelihood that particular pump would need something like an XW6048 to run it, and that's a lot of inverter for just one pump.

    Batteries? How long does it have to run for? That's the tricky question there.

    As for recharging those batteries, doing it "slowly over time" is a recipe for sulphated batteries needing to be replaced long before you should have to. Who wants to throw out expensive batteries after just a couple of years?

    Best bet for that pump situation is to get a cheap, big generator to run the pump on those occasions when the power goes out. Since this is a commercial operation, there probably is no need to run it at night so the noise shouldn't be troublesome.

    As for using cheap, MSW inverters for AC motors - not a good idea. They are the #1 thing that won't run on MSW, and even if they do they will consume more power and you will gain no advantage.

    Investing in solar power for occasional use is a waste of $. Buy a generator.
  • soulersouler Registered Users Posts: 12
    Re: Minimum Backup Sizing For AC Pump

    Thanks, At least one of you has a similar deep well pump running on inverter. OK, apparently the term 'artesian' is wrong here. My well trickles over the top in prolonged wet seasons and never ran dry in droughts. Possibly mine's over sized but no regrets there. In a better world, better fits for everything would be likely.

    I do have 150 gallon water tanks in attic. One for solar hot water collection, the other for 'cold' (Both on gravity flow distribution). .... Filling them to go into weeks of downed grid is one concern. It's always more complex especially with CME looming dead ahead: I too have 2 gas generators. I even have contemplated a steam turbine powered by my winter-time-wood-heat, (micro co-gen)...... I wouldn't stay too confident about fuel generators alone. Google CME + sun for the list of scenarios. In case the grid never gets the much needed surge suppressors installed in time. Fuel pumps and deliveries will really get backlogged while transportation generally suffers. Big transformer stations could potentially be killed everywhere, unless suppressors are installed, (as a national emergency). Besides, war mongers keep grabbing all the money in the world. I heard it can ordinarily take years to order and install just one big transformer. Delivery of fuels could become very upset for multiple reasons. (Like gas pump power outages along delivery routes). We lost power for 15 days once in unprecedented ice formations.

    In any case, an inverter has other huge-convenience advantages. The water pumping requirement is holding up my choice of which inverter size. Also, the use of batteries in maybe 10 differing scenarios are much less than the water pump would be. Use of gas generator is clearly expected as re-charge for emergencies, but once again, it makes much more sense to match the fuel-generator size to filling the battery bank at optimal efficiency. My 1000w Honda generator barely runs half my minimum 'surge' needs but... Does it fill a decent battery bank at good efficiency without sulphation? Combined with solar float charging, at other cruising-times... To just top off batteries and avoid grid use during unstressed periods of time?

    I had a 1000w inverter (1973 variety) which ran power tools for a while but died unexpectedly. I also want to build confidence that current inverters can handle all fridges, freezers small power tools, for years ahead. Generators get old too. I hate having more individual engines to maintain than needed.
  • techntrektechntrek Solar Expert Posts: 1,372 ✭✭✭
    Re: Minimum Backup Sizing For AC Pump

    I'm completely in agreement on the potential for disaster with CME's. I can't find it right now, but newscientist.com had a great cover story a year or so ago on the problem. Add on the lack of other major grid upgrades needed (and not happening any time soon) and I believe within the next 10 years we'll start to see semi-regular "incidents". Grid instability + potential CME are the #2 and #3 reasons for my want of a decent sized solar installation.

    Also agree on the "having more individual engines" problem. Three cars, generator, pressure washer, tractor... I finally decided to go all-electric and my next purchase was an electric log splitter. If the CME comes and my PV survives I'll still be able to split my wood! Won't be able to go anywhere, or wash my deck, or mow my lawn...
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Minimum Backup Sizing For AC Pump
    souler wrote: »
    This emergency use may happen only rarely, but is our primary concern.

    That's from your original post. Now you are talking about supplying power for a highly-unlikely-to-occur "doomsday scenario". :roll:

    "I'm sorry, my responses are limited; you have to ask the right questions." - Dr. Lansing's holographic recording, 'I, Robot' (Isaac Asimov).

    If you want to waste thousands of dollars on a solar electric system you'll never need, that's your business. My answer was the correct one for the original question.
  • soulersouler Registered Users Posts: 12
    Re: Minimum Backup Sizing For AC Pump
    ......................
    If you want to waste thousands of dollars on a solar electric system you'll never need, that's your business. ...............

    Not hardly. I'm just analyzing skeleton-system options. The well pump extras would demand/provide for more general battery capacity. Making batteries/inverter more useful to practice at grid-use-reduction. Providing a skeleton backup system in case a repeat, 15-day outage happens again. Also as micro business people work towards off-grid business schemes. (This takes time.) Skeleton re-charging options need more clarity. Half-budgeted folk might in fact expand the solar market-- If there were 'skeleton' approaches to grid-reduction. This intermittent approach to off-grid should provide some business electricity like lights or small tool uses, (besides having reserve-ability to fill water tanks). To help micro business experiment with grid reduction schemes.

    So concerning a minimal skeleton system with AC pumping possible (for emergency only)....

    1) Is there a FAQ or chart on small pv-panel-set, to be used as float-charger and emergency slow charger?
    2) How often would grid charging be needed to blow off sulphation?
    3) Can a 1000w generator occasionally power a grid-battery-charger for 4 typical Trojans? (In case of prolonged emergency outage).
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Minimum Backup Sizing For AC Pump
    souler wrote: »

    So concerning a minimal skeleton system with AC pumping possible (for emergency only)....

    There's your first problem: a "skeletal system" isn't going to run the existing pump you have. It needs a lot of power available to it. I know, because if it weren't for the pumps in my system I would not need a 3.5 kW inverter, and that's a 1/3 HP water pump and a 1 HP "soft start" digester pump.
    1) Is there a FAQ or chart on small pv-panel-set, to be used as float-charger and emergency slow charger?

    There's a lot of FAQ's here, but design details aren't included (so far) because of the number of site-specific variables. Lots of good battery info here: http://www.windsun.com/Batteries/Battery_FAQ.htm That explains most of the charging info you'll need to know.
    2) How often would grid charging be needed to blow off sulphation?

    You can't. Although proponents of desulphators might say otherwise. This might be an application where running a desulphator would help. Usually you can only avoid sulphation, not reverse it. It's tricky to do on a system that isn't cycled regularly, as deep cycle batteries also "like" to be discharged as well as charged. If you kept them at float daily, and then discharged/recharged at the 10% current rate once a month you could probably keep them healthy for many years.
    3) Can a 1000w generator occasionally power a grid-battery-charger for 4 typical Trojans? (In case of prolonged emergency outage).

    Yes it can. If the 4 are configured for a 24V system: 22.5 Amps (charge rate) * 28.4 Volts (charge Voltage) = 639 Watts (same Watts for a 12V system, just different current/Voltage). Don't expect the generator to provide much supplementary power at the same time.

    Your four Trojans could provide at most 2.7 kW hours of power, which is significant. A good choice for small, off-grid set-up. For solar recharging you'd probably want around 800 Watts of panel.

    Now, will it run that 2HP pump? Probably not. In fact you might want to look into resizing that pump as your first conservation measure. Pumps are frequently over-sized, because it guarantees it will be enough. Often it's 2-3X enough.

    As for minimizing grid use or dependence, conservation is always step #1. Grid-tie solar is the best way to get a return on your investment. Off-grid (battery-based) systems are down the list because they are more expensive and less efficient with higher maintenance. But it's better to find these things out before you spend your hard-earned $!

    Forgot to mention the float-charge aspect!
    Staying ahead of self-discharge is one thing. It doesn't take much power, but it takes more power the older the batteries get. You could probably keep the 4 Trojans happy with a 100 Watt panel and small charge controller. You're looking at 1-5 Amps of current.
    Keeping them floating while there's a load being drawn is trickier, as you have to be able to counter-act the load.
  • BB.BB. Super Moderators, Administrators Posts: 29,744 admin
    Re: Minimum Backup Sizing For AC Pump
    souler wrote: »
    1) Is there a FAQ or chart on small pv-panel-set, to be used as float-charger and emergency slow charger?
    Roughly, a 1% rate of charge will keep most batteries floated well. Especially for fork lift / flooded cell batteries--your end of bank life will be when the self discharge is more than the 1% panels can recharge.
    2) How often would grid charging be needed to blow off sulphation?
    Sulfates form when a battery sits for days/weeks/months below ~75% state of charge. If you keep them above 75% SOC (at ~13.7 volts), they will not sulfate (at least, they will should have a long service life).

    Normally, people will need 5% rate of charge every ~1-6 months for "equalization". Note, only equalize when cell specific gravity vary between cells (0.030 or more according to one battery vendor). Equalization is hard on batteries too--only equalize when needed.

    Another issue is that Flooded Cell batteries may actually last longer when cycled occasionally rather than just being kept on "Float" charging.

    And (especially for "tall" flooded cell batteries) you can get electrolyte stratification... The dense (high specific gravity) electrolyte drifts to bottom of cell, and the lighter (less dense) s.g. floats to the top... So you end up with an overcharge battery at the bottom and an under charged battery at the top... You need 5%-13% (one mfg. recommends 10%) charging current once in a while to stir the battery (generate enough gasses to circulate the electrolyte).
    3) Can a 1000w generator occasionally power a grid-battery-charger for 4 typical Trojans? (In case of prolonged emergency outage).
    Say you have 4x 225 AH * 6 volt batteries... The recommend charging power would be:
    • 4x 225 AH * 6 volts * 0.01 = 54 watts maintenance/float
    • 4x 225 AH * 6 volts * 0.05 = 270 watts minimum "functional" charge
    • 4x 225 AH * 6 volts * 0.13 = 702 watts maximum recommended charge
    For a 12 volt battery bank, a 5% rate of charge would be:
    • 270 watts / 14.5 volts charging = 18.6 amps
    A Honda eu1000i (900 watt continuous rating) can run a 20 amp typical battery charger very nicely... A 40 amp charger may be too big (there are other charger design issues regarding power factor and efficiency that could allow a larger battery charger on a small genset).

    Depending on your needs, you may want to look at a Honda eu2000i instead. Somewhat larger, but more power (1,600 watt continuous) and still pretty fuel efficient. Can power both your battery charger and other AC loads directly (more efficient to power your larger AC loads directly from the genset when it is running vs through the battery bank--I.e., charge the battery bank in the morning and power your irrigation pumps from the genset. Run the battery/inverter at night for lights/radio/etc.).

    Both are very quiet generators.

    You can first run the charger from AC Grid power (and generator backup), then later add solar panels as your budget allows. Remember that for the above "wattage" into the battery bank, you should derate solar panels by 0.77 for real life panel+charger output. I.e.:
    • 54 watts maintenance/float * 1/0.77 = 70 watts of solar panel
    • 270 watts minimum "functional" charge * 1/0.77 = 351 watts of PV
    • 702 watts maximum recommended charge * 1/0.77 = 912 watts of PV
    Note that the above numbers--if you are within ~20% of them--that is no big deal (I carried out the number accuracy so you can check my math).

    The rules of thumb are just starting points. You can go outside them for good (or not so good ;)) reasons. I like to use them because they give conservative results and will usually give you a system that, at least, meets your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • soulersouler Registered Users Posts: 12
    Re: Minimum Backup Sizing For AC Pump

    These are some great , concise notes, people, thanks so much. Just the comparison level of caveats, sought for in my case. Trouble being, we are stuck with awkward starting positions, (odd assortment of givens)... The point is the solar market should have variable entry points. I don't feel it is the least bit shameful to explore skeleton system packages where the global markets are stratified beyond comprehension. Some of us realize that the boom and bubble years are not coming back for the good ole USA. Skeleton systems will be in great demand. The sooner a vendor provides access to workable minimiums, however unideal, i'll bet first-time buyers will start buying. With the well understood expectation that they are simply protecting their lives during turbulent times (and not expecting bubbly phantasies).
  • mike95490mike95490 Solar Expert Posts: 8,471 ✭✭✭✭✭
    Re: Minimum Backup Sizing For AC Pump
    2) How often would grid charging be needed to blow off sulphation?

    Not possible to just "blow off sulfation". you have to prevent it.

    For your nightmare avoidance system, maybe try looking at Iron-Nickel batteries, or some of the new lithium batteries.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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