Can I power a well pump on marine batteries?

bearmtpicnic
bearmtpicnic Registered Users Posts: 3
Hi there,

Total newbie here. I purchased an off-grid property that came with a 1970's fifth wheel RV, two brand new marine batteries, a generator, and a 1/2HP 230V well pump.

So now I'm trying to add a solar panel to the system but still work with the existing puzzle pieces as much as possible, to save costs, for now. My usage needs are small: 2 DC circuits in the trailer; one for lights and one for an outlet (cell phone charger). I don't use any of the appliances in the trailer. For AC, I need to run power tools occasionally and the well pump maybe once a week to fill up the water tank. (The water system is totally external to the trailer and is gravity-fed and solar-heated.)

I am trying to buy things that will work as I upgrade the system, without being too expensive, but still work with each other and with the existing crappy batteries. I want to minimize generator use.

I bought this kit: http://www.solar-electric.com/rvkitwi140wa.html
and installed the 140W panel and controller/charger. I took the batteries out of the trailer and wired directly from the controller to the batteries, connected the batteries in parallel, and from the batteries to the trailer's circuit breaker. (The way they were positioned in the trailer was stupid-- the batteries were in separate compartments on either side of the rig, both underneath the fifth wheel overhang part, so very difficult to access not to mention on the other side of the trailer lengthwise from the circuit breaker.)

So that is working (whew!)-- the trailer DC power works, batteries stay charged, all is well.

Now I want to add an inverter and transformer to power the 110V tools and 230V well pump. Can I do this, say with an 800W inverter and a 1000W transformer? Or will it just trash these poor little batteries? They are rated 80AH each.

If I can do it, then I have several follow up questions. :)

Thanks in advance !

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can I power a well pump on marine batteries?

    Welcome to the forum.

    First the bad news, then we'll get to the bad news. :p

    Your panel is just on the edge of being able to recharge those two 80 Amp hour batteries. On a good day you'll make 5% charge current. But you're not going to have anything to spare while charging. It is working for now because you're keeping your loads to a minimum.

    Now the bad news: a 1/2 HP centrifugal pump is about as far from a minimal load as you can get before you run in to compressors. There's the start-up surge to begin with, which could be a whopping 8 Amps on 230 VAC. On 12 VDC it will be more like 160 Amps, and will completely "flatten" those two batteries in an instant. The draw could be so high that any 12 Volt inverter will simply fault out rather than start the pump. There are a lot of "could be's" here because pump draws vary a great deal depending on the exact unit and what it has to do to start (lift of water, psi at start, size of piping).

    An 800 Watt inverter would stand no chance against this load, btw. A MSW type one even worse. Don't throw your money away.

    Instead, re-evaluate your pumping requirements. Do you really need such a big pump? How deep is the well, how far must the water be pumped, and how slow can you stand to have it flow? With a good pressure tank system you can substitute time for brute force pumping and use something like one of the Shurflo pumps which consume far less power: http://www.solar-electric.com/shacdcwapu.html There are 12 VDC and 110 VAC versions which might fit the bill. It will probably be far less expensive to change the pump than to come up with the power to run that big one.
  • bearmtpicnic
    bearmtpicnic Registered Users Posts: 3
    Re: Can I power a well pump on marine batteries?

    Yeah, that's what I figured. I'll keep using the generator until I can afford to replace the pump.

    Can I run a small inverter for occasional 110 power tool use?

    If I want to increase the load eventually, can I use the same batteries with additional panel(s)?

    Thanks!
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Can I power a well pump on marine batteries?

    For a small 12 volt inverter, I would highly recommend the MorningStar 300 watt TSW inverter... There is nothing else out there that is even close.

    For larger tools (power saws, drills, etc.), I would just get a "cheap" MSW inverter.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can I power a well pump on marine batteries?

    A small inverter should be no problem, providing you define small as "under 400 Watts". Above that and the batteries are going to be straining to supply the load. This Morningstar is probably the best small pure sine inverter you can get: http://www.solar-electric.com/mosu300wasiw.html

    As long as the tools are under 300 Watts it will handle them fine, and that includes battery chargers (which sometimes have problems with MSW type inverters). It has an extremely low standby power draw too.

    However it and anything it runs is still an additional load. Right now your single 140 Watt panel could provide about 400-450 Watt hours DC at best. Since you don't have a battery monitor you don't know how much you're drawing those batteries down before recharging. Have you at least got a hydrometer? About $5-$10 at an auto supply store. You can take specific gravity readings of the cells (I'm assuming they're not sealed batteries) before and after charging and see how much you're using now before adding any more loads.

    Otherwise adding on more panels, to a point, can only be a good thing. I'd recommend one more 140 Watt, but the charge controller you have now isn't sufficient to handle additional power either (SunSaver 10 Amp, one KD140 is about 7 Amps; two would be 14-ish). You can parallel charge controllers, or change out for an even bigger one that would allow for future expansion. Right now your battery capacity doesn't need more than 16 Amps for charging, really. But down the road?

    A configuration that works well in a 12 Volt RV set-up is two golf cart 6 Volt batteries in series: 220 Amp hours @ 12 Volts.
    That would "like" about three of those 140 Watt panels in parallel on a 25 to 30 Amp charge controller. From it you could expect up to 1 kW hour AC per day with a small inverter.

    One caveat: if you're adding panels, changing controllers, putting in different batteries ... always check to be sure the wiring is up to handling the increased current. And don't forget the fuses/breakers.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Can I power a well pump on marine batteries?
    If I want to increase the load eventually, can I use the same batteries with additional panel(s)?
    As Cariboocoot mentioned, you should add more panels... you barely have enough panels to keep the batteries charged without a load.

    If you want to increase your load beyond a few lights and a cell phone charger, you don't just need more panels, you will also need more battery capacity. When you start using power tools you may over discharge your batteries and ruin them. Batteries are the weak link in off-grid technology, and they are expensive. You need to learn how to monitor and maintain your batteries. A battery monitor might be a good investment.

    You mention that you have a generator. Do you have a battery charger? If so, you can run the generator in the morning to get the charging started, and then let the panels take over for the finish charge. Try to plan your power tool use and water pumping for the morning generator run.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • bearmtpicnic
    bearmtpicnic Registered Users Posts: 3
    Re: Can I power a well pump on marine batteries?

    Ah, speaking of that...

    I just bought a Powermax 45A converter charger, but haven't used it yet because I'm not yet 100% clear on the best way to connect it to the existing system and don't want to fry anything, most especially myself. I think I just have to run extension cord from the generator to the charger; put the charger near the batteries but not in the same box; ground the charger; attach pos and neg to battery terminals using 8AWG (or larger) wire. Yes?
    Do I need to ground the batteries as well? Currently (I hesitate to admit) nothing is grounded except the circuit breaker panel.
    Or is it better to just attach it with clamps when I run the generator, and leave it disconnected the rest of the time?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Can I power a well pump on marine batteries?

    That is basically the way a converter/charge is wired: AC in one end, DC out the other. The nuances are the thing.
    Definitely you want 8 AWG or larger wire for 45 Amps, and keeping it close to the batteries will reduce the Voltage drop and resulting problems. You can "hardwire" it; make sure you have a fuse or breaker on the output that can handle the current (check the instructions to get this right).

    Now, grounding ... You want to start an argument? Ask two electrical engineers "How do I ground this?" :p

    Right now you probably haven't got anything grounded. Is there a big copper-clad rod driven 10' into the ground with some #6 wire connecting it to anything? If not then you don't have a real Earth safety ground. If things just have their ground connections wired to the RV chassis, that doesn't really do much for it. It is perhaps better to leave things "floating". You can get into a lot of trouble with improper ground (especially when inverters are added to the mix).
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Can I power a well pump on marine batteries?

    You should consider a generator to run the pump with. A 230V inverter will be really pricey, you will need at least 4KW output to start the motor reliably.

    I've got a 1/2 hp motor pumping 160' head, and it RUNS on 1,000 w as reported by the inverter. Starting power would be at LEAST 4x that. And no way it could run off a 12V battery.

    And you need a backup generator anyway!
    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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