Newby deep well calculations

[daustin]

First time poster here.

I'm trying to be able to have a backup battery system for (rare) grid failures. I'd like to run frig and freezer circuits minimum as well as be able to pump our deep well. Evidently, that's where it gets challenging. We have a Franklin 1 HP pump sitting about 400 feet deep. It is a 3 wire pump. On the control box it says 8 Amps. I took that at face value (OK, now I've learned different). I figured OK, even 10A at 240v = 2400 watts. I bought an EcoWorthy 100A 51v server rack battery and a Wzrelb 4000 watt split phase inverter. It runs my frig and freezer circuits fine, but refused to start the well pump. Looking around here a little, I realized I needed an inrush reading, ordered a meter from Amazon, and (ouch!) 37A on both of the hot legs. OK, that hits in at 37 x 120 x 2= 8800 watts. No wonder the inverter (with stated 2x surge capacity) didn't cut it.

I started looking at higher power inverters, and actually ordered one (from Amazon), until I got to thinking about battery power needed, and that's what I'd like someone to confirm for me and my calculations. In the EcoWorthy manual, it states that Maximum discharge current is 100A, so doesn't that mean that I can only get 100a x 51v = 5100 watts from the EcoWorthy, and thus I appear to be short on both inverter and battery power here?

Even if I order a 2nd EcoWorthy and a bigger inverter, don't I still need 8800 / 51 = 174A for startup surge (from the battery) for the pump? Also, in an actual power outage, once I ran the frig and freezer for a few hours, I'd no longer have 174A left, and thus could only run the pump very early in the outage?

Can someone confirm these conclusions? I've since canceled the bigger inverter order to look into this more.

Thanks, David

 

[BentleyJ]

Definitely 2 batteries and you should either be looking for a Low Frequency Inverter

Or perhaps installing a soft starter on the pump if that would be compatible. The difficulty with pumps is that the impeller is flooded even at rest so the motor is starting under load.

 

[HighDesertOffgrid]

I echo the above reply. Low frequency inverter 6KW-ish and a 2nd battery. Near to the wzrlb price point is sungold.
Also the Sungold and Aims inverters (perhaps others) have built in soft-start as a bonus.

 

[Brucey]

Can someone confirm these conclusions? I've since canceled the bigger inverter order to look into this more.

Consider a Schneider XW Pro on close out for around $1400. Still has 10 year warranty. 6.8kW but can surge to 12kW and beyond.

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[OzSolar]

Or look into new pump, a Grundfos SQ. It's a soft start pump so no surge. Dollar wise it might pencil out but likely only if you can pull the pump yourself. At 400' that's almost impossible. We put a new pump in our spare 200' deep well, static is 45' and it was a bear. Several chances for things to go wrong.

Or maybe if your current pump is 25 years old, like our house's well pump, it might be time to replace it anyway. Just some ideas.

Or perhaps installing a soft starter on the pump if that would be compatible. The difficulty with pumps is that the impeller is flooded even at rest so the motor is starting under load.

This comes up often. When we get to digging into it we find that there is no such thing as retrofit/add on soft starter for a well pump. If you can point to one that would be great.

 

[42OhmsPA]

My pump pulls about the same, a tad higher if I remember correctly.
I've had no issues starting it with a TP6048 (LVX6048 clone) or a single SRNE ASF / ASP, the latter has 0 issues whereas the former had a light flicker worse than the grid.
I also made sure it would run on a single 200A BMS, even though I have multiple packs in power parallel

2 100A in parallel should be just fine.
You can still run it without full capacity, as long as voltage sag doesn't cause a disconnect.

 

[daustin]

I really appreciate the several responses so quickly. Thanks for confirming what I thought the numbers were telling me, although it certainly is a budget buster. Firstly, I'll need to pick out a higher capacity inverter before the 2nd battery can come around, but then it should handle it when it does. I might need to make the old cistern suffice for emergency water in the mean time. Thanks again.

 

[jimf909]

I might need to make the old cistern suffice for emergency water in the mean time.

An old cistern or new 500 gallon water tank will provide a backup for grid outages, pump failures, etc. and possibly cost less than an additional battery and new inverter.

 

[Mattb4]

There is a work around that sometimes allows you to start and run a well pump or compressor. You must start it at zero discharge or tank pressure. Typically you have a pressure switch that starts at 20 or 30psi that adds considerably to start surge requirements.

 

[daustin]

I also made sure it would run on a single 200A BMS, even though I have multiple packs in power.

Could someone explain what is being said here? Thanks

 

[daustin]

There is a work around that sometimes allows you to start and run a well pump or compressor. You must start it at zero discharge or tank pressure. Typically you have a pressure switch that starts at 20 or 30psi that adds considerably to start surge requirements.

Very interesting. Mine seems to be set at 35-55 from watching the gauge on the tank

 

[42OhmsPA]

Could someone explain what is being said here? Thanks

My typo. Multiple packs in parallel not power. Going back to edit.

Edited.
I ran with a single 200A BMS to ensure I had water if multiple BMS failed. Currently I have 4 in parallel, soonish to be 6...
If things got really bad in a shtf I'd bypass the BMS completely

 

[NC_hydro]

You can add a VFD controller on your pump and eliminate the large surge. Probably your cheapest option.

 

[xjaw4]

Or look into new pump, a Grundfos SQ. It's a soft start pump so no surge. Dollar wise it might pencil out but likely only if you can pull the pump yourself. At 400' that's almost impossible. We put a new pump in our spare 200' deep well, static is 45' and it was a bear. Several chances for things to go wrong.

Or maybe if your current pump is 25 years old, like our house's well pump, it might be time to replace it anyway. Just some ideas.


This comes up often. When we get to digging into it we find that there is no such thing as retrofit/add on soft starter for a well pump. If you can point to one that would be great

I found there are variable frequency drives that have inputs for solar and AC for driving a traditional AC well pump off solar or AC with solar assist.

https://www.inverter.com/2-2kw-solar-pump-inverter

Just one example

 

[OzSolar]

I found there are variable frequency drives that have inputs for solar and AC for driving a traditional AC well pump off solar or AC with solar assist.

https://www.inverter.com/2-2kw-solar-pump-inverter

Just one example

Looks like an interesting product, but like the handful (a few dozen) of VFD's I've installed, it's limited to a 3 phase output. (below snip is from the link you sent).

In North America the most common well pump is single phase.

If there is an inexpensive AND proven retrofit option for running a legacy single phase well pump off a VFD I've not seen it. Certainly not saying is doesn't exist, only saying it's hard to find.

Can you provide an example of VFD retrofit for the single phase well pump that this thread is about?

 

[RzrProR]

As someone mentioned, concentrate on replacing the pump whether you think that you need it or not.
You'll be surprised once you start calculating your needs both present/future and start calculating a few simple system head curves *from major manufacturers that compete in regards to efficiency/the latest technological pump/motor advances*. Don't limit yourself on the discharge side if the piping can be changed for the better.
Once you've done that, concentrate on how much power that you'll need in the end...not the other way around.

 

[RzrProR]

Looks like an interesting product, but like the handful (a few dozen) of VFD's I've installed, it's limited to a 3 phase output. (below snip is from the link you sent).

In North America the most common well pump is single phase.

If there is an inexpensive AND proven retrofit option for running a legacy single phase well pump off a VFD I've not seen it. Certainly not saying is doesn't exist, only saying it's hard to find.

Can you provide an example of VFD retrofit for the single phase well pump that this thread is about?

View attachment 292955

Great points that reinforce the importance of (re)evaluating current/future system flow/head requirements. Unless you start out with an unsolvable power limitation involving single phase at a known value(?) the pump/system evaluations and any possible savings resulting from a redesign come first. Even then, the goal is to squeeze just as much energy in to that pump efficiently when you're dealing with the inefficiencies of renewable energy. Here is a quick explanation of how Grundfos approaches it and a rundown of (as Oz indicated) their 3Ph only vfd units: https://www.grundfos.com/us/learn/research-and-insights/demystifying-variable-frequency-drives