Generator--->AC Panel--->Inverter Questions

mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
I'm trying to wrap up the design of my small solar system for my offgrid cabin, and I have a few questions for the group here. Most of my power comes from a 5500W generator connected to an AC distribution panel in my detached garage. The AC panel then feeds into the cabin to provide AC power. I'm planning to install a small solar system to run a few DC lights in the garage, a DC pressure pump to feed water pressure from a holding tank into the cabin. I also want to be able to utilize an inverter to run a 3/4 HP deep well pump once a week to fill the holding tank. My plan is to use an E-Panel with an Outback VFX3524 inverter. I'll wire my battery bank in 24V, and then use a 24V-12V converter to run my DC lights and DC pressure pump. My generator uses a 4-wire connection to power the AC panel (neutral, ground, and 2 hots). I plan on then connecting the AC panel to the E-Panel/inverter (neutral, ground, and 1 hot). The purpose of this will be to charge the batteries whenever the generator is running, and allow me to run the deep well pump off the AC power (via the inverter) whenever the generator is running, rather than off the batteries. I'm also using a DC timer switch to manually turn the inverter on/off once a week to run the deep well pump for 30 mins (so the inverter is not running the remaining time). I wanted to see if anyone can note any flaws with my proposed wiring, especially the generator to AC panel (4 wires), and then AC panel to the E-Panel/inverter (3 wires). Attached is a PDF of my proposed wiring diagram. It's a bit light as to the specific wiring within the E-Panel, but I'm relying on a pre-assembled E-panel w/ the inverter, charger, breakers, mate, hub, etc. Any suggestions would be greatly appreciated.


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Generator--->AC Panel--->Inverter Questions

    Forget about running the water pump off the inverter: it's the biggest power hog imaginable. For one thing, a 3/4 HP pump will almost certainly be 240 VAC and the OB 3524 only puts out 120 without a transformer.

    If your main purpose is to supply 12 VDC for some lights, et cetera, you'd be better off to go with a 12 Volt system to begin with and use a small, less expensive inverter to supply basic AC loads. Then fire the generator "as needed" to recharge when the sun can do it and/or run the well pump. The trick with the latter is large capacity pressure tank(s) to store up water for use when the pump is not available. This is what I do, only my pump is much smaller and runs off the inverter when there's full charge in the batteries (midday).

    Furthermore, your generator is 240 VAC and the OB's input is 120. In short, it's too much generator for the inverter. Not that it couldn't work, but it would be fairly inefficient.

    Shall we go back to the beginning and look at your loads and use requirements, hopefully before you've spent all your money?
  • mjp24cohomjp24coho Solar Expert Posts: 104 ✭✭✭
    Re: Generator--->AC Panel--->Inverter Questions

    Thanks for the input. I misspoke on the deep well pump - it's actually a 1/2 HP, and listed as only 115 V. My primary need is to be able to have the ability to automatically run the well pump once a week (when I'm not there) to fill the 600 gal holding tank, to irrigate trees/plants between my monthly visits. My research indicated I would need the 3524 to be big enough to run the pump, which is why I thought to go with a 24V battery system. To be clear - I haven't purchased the inverter and E-Panel yet - just trying to put finalize the design. The deep well pump and tank are already in, and are functioning off the existing generator (without the ability to automatically refill the tank during the week). And I have a 205W panel and small battery bank in place to power the 12V pump for water pressure for the weekends that I'm there. My plan would be to add to the solar array and battery bank once I make the upgrade. I also realize the generator would be a bit overkill, but I'm trying to piece this together with components I had already purchased before deciding to do this upgrade.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Generator--->AC Panel--->Inverter Questions

    Even a half-horse pump is a big power user. But if this is what you already have and the need to automate it via solar is there, it can be done.

    You should start by getting a Kill-A-Watt (or similar) meter and run the pump through it. This will give you some real-world power usage which can be extrapolated into the time-frame you have in mind. Or to make it understandable, let you figure out how much power you need to supply from the inverter. Remember it's not just a matter of Watts, but Watts over time: Watt/hrs.

    The 3524 will definitely run it, with power to spare. It is exactly the inverter I have. But you need to figure out how much time you'll need to run that pump. 600 gallons is a lot. How often will that tank need to be refilled? I can't tell you the pump's rate without more data, but up to 10 gpm is certainly realistic. That means it would have to run for an hour to fill the tank completely.

    A rough idea of how that calc would go: pump running uses (guess work, not an absolute figure) 1500 Watts. Over one hour is 1.5 kW/hrs. To supply that you need approximately 63 Amp/hrs usable. That would be a minimum of 126 Amp/hrs of battery. More is better, as that would be relying on 50% DOD which is maximum. Take it up to the standard 225 Amp/hr 'golf cart' batteries. To charge that much battery you'll need around 675 usable Watts of panel.

    But none of that has any efficiency factors or accounting for when/how often you need to run the pump. Setting a timer so it fills during daylight would be good, or even a relay control off the charge controller's auxiliary so it only comes on when the batteries are 'floating' would be a good idea.

    Lots of stuff to deal with, eh? :p
  • mikeomikeo Solar Expert Posts: 386 ✭✭✭
    Re: Generator--->AC Panel--->Inverter Questions
    pump running uses (guess work, not an absolute figure) 1500 Watts

    This chart estimates 1000 watts running for 1/2 horse submersible pump with around 3000 watts surge

    10 gpm down to 100 feet is possible with a 1/2 hp pump
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