Replies

1. 
   17whippoorwill | Dec 10, 2024 03:59pm | #1

   On the chance folks will reply, here are my specific, calculated needs, for battery backup:
   I would like to power my well pump, grinder, and septic pump with battery vs. fossil fuel generator. I've done some calculations, but am not qualified enough to come to a conclusion or product recommendation. Prefer to buy an off the shelf product.
   The following calculations may be wrong, but I think this is the energy needed for one 30 second cycle of these three motors:
   using this Formula: Energy (kWh): (motor wattage)/1000 x Time in hours = kWh
   Well pump: Energy (kWh) = (1600 w)/1000 x .83 hours = 1.328 kWh (LRA 41.8)
   Grinder: Energy (kWh) = (1380 w)/1000 x .83 hours = 1.15 kWh (LRA 22.5)
   Septic pump: Energy (kWh) = (1210 w)/1000 x .83 hours = 1.00 kWh (LRA 19.6)

   If my calculations are correct even a 7kWh Delta Pro Ultra would barely get two 30 seconds round for each motor.

   Thanks

1. Expert Member
   BILL WICHERS | Dec 10, 2024 06:27pm | #3

   Youre calculations are off:

   Well pump is 1.6kw, running for 30 seconds gives 1.6kw * (30 seconds / 3,600 seconds/hour) = 0.0133 kwh for each increment of 30 seconds of run time. Chances are your pump cycles on for more around 5 minutes at a time though, which would be more around 0.133 kwh per cycle.

   Grinder would be 1.38kw * (1 minute / 60 minutes/hour) = 0.023 kwh per minute of operation.
   Septic pump would be 1.21kw * (1 minute / 60 minutes/hour) = 0.02 kwh per minute of operation.

   Let's assume the well will run 10 cycles per day, so it will use 1.33 kwh per day. Let's be conservative and double that to allow for motor starts and call it 2.6 kwh per day. Let's allow for the septic pump to run twice as much, for 4 kwh (using the same "double it to allow for starting").
   I have no idea on the grinder, but let's allow for it to run as much as the septic pump, and when using the same "double it for starting" that gives us 2.3 kwh.

   Total for a day here would be 8.9 kwh used per day. That 7kwh batter would get you a bit over 18 hours, and I'd guess maybe 10-12 hours in practice after allowing for inefficiencies and the reality that you'll probably have some other loads (lights, fridge, etc.) running besides just the three things you mentioned. That means that 7kwh battery is good for about a half a day of runtime for your home. This is pretty optimistic too, since the utility industry assumes about 1-1.5 kw per home, which means about 24-36 kwh per day per home. If we pick the middle of that range, that 7kwh battery is good for a little over 5 hours of runtime for a typical home. Not very much.

   If you want to stick with batteries, plan to only run a small number of small loads. Batteries aren't very practical to run a house for any extended power outages. You're much better off with a generator for that (and note that "battery generators" aren't really "generators" at all). I prefer Kohler's (Now "Rehlko") generators for residential applications. You're probably going to be around $10-15k to install one that runs on propane or natural gas. I recommend putting in a transfer switch that can run your entire home too, and not trying to save money sizing the generator to only run "critical" loads. It doesn't cost much more, if anything, to size the system to run the entire house, and it's much nicer to have everything working when the power goes out.

   Note that if you're in an area with very infrequent power outages, you can use a power "inlet" and interlock kit to use a portable generator instead of a permanently installed one, and you can save a lot of money this way. You cold even use one of the big battery "generators" to power a house through this type of system, but you'd be very limited on runtime as explained previously.

   Bill

1. 
   Malcolm_Taylor | Dec 10, 2024 08:07pm | #4

   Bill,

   I agree on having the ability to run anything you may want to use - but not a the same time. Sizing a generator to run all the loads in a house is what people around me have been doing recently, and the amount of fuel they go through in an extended outage is shocking.

2. 
   17whippoorwill | Dec 12, 2024 04:01pm | #5

   Bill -- thank you for your detailed and accurate calculations and advice.
   Stuart

2. 
   begreener | Dec 10, 2024 04:43pm | #2

   I just saw an ad on Youtube for this product that seemed reasonably priced for what you get ...

   https://batteryevo.com/batteryevo-deals/

   22 kWh + 12.5k Inverter for $5200