I have a 5HP well pump that's paired to a Franklin Electric SubDrive Connect VFD - the unit converts input 240VAC single-phase into three-phase power (30hz-60hz). I'd like to put a battery backup in the well shed powering only the well pump so power outages aren't as rough comfort-wise. I expect to exercise restraint during outages and only run one faucet at a time. According to my observations, the motor consumes about 2kW when starting up and then settles down to about 1kW.

I'm planning on getting 6kWH worth of batteries (12V) and using a 4kW pure sine inverter (12kW surge for 30sec). Would this be adequately sized/safe for the pump? I've read online about how there can be harmonic frequencies that can destroy the pump if the inverter can't keep up, but I'm not knowledgeable enough to understand what that is.

Alternatively there's a 6kW model for the inverter as well.

  • Is there any reason you want to run the bank at 12V instead of 48V? Also, what make/model of inverter are you proposing to use? Commented Dec 5, 2021 at 4:19
  • Any voltage is fine, the batteries i was looking at are 12V each. Connecting 4 in series works as 48V right?
    – atanamir
    Commented Dec 5, 2021 at 4:44
  • Was looking at sungoldpower.com/collections/… there's a 12, 24, and 48v version
    – atanamir
    Commented Dec 5, 2021 at 4:45
  • (I'm open to suggestions for other brands as well if you have one to recommend. This was just from a cursory search from amazon). Would prefer to have the ATS and charger all in one.
    – atanamir
    Commented Dec 5, 2021 at 5:20
  • 2
    Keep in mind that lead-acid batteries can't use their full nameplate amp-hour capacity. If you regularly even use 50% of it you will shorten the life of the batteries. Using 100% will result in very rapid failure. Smart people use only 30% on a daily basis. Yes, this makes lead-acid banks cost 3 times more and makes lithium more competitive. Commented Dec 6, 2021 at 6:20


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