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Help needed: Sizing inverter for well pump

V

Vardaman

New Member
Joined
Sep 28, 2024
Messages
13
Location
65622, Buffalo, MO, USA
I was hoping someone could tell me why the inverter I have won't start my pump. Here are the specs:

The pump is 120 V on a 20A circuit. The inrush current is 35.7 amps.

Power should be about 4300 watts

The inverter is

Xantrex Technologies 8133000UL Xpower Inverter 3000w Gfc​



Specifications

  • AC Output Waveform: Modified sine wave
  • AC Output Type: Two GFCI outlets with 20A fuses
  • AC Output Frequency: 60Hz
  • Inverter Efficiency: 90%
  • DC Input Voltage Range: 10.5-15.5V DC
  • DC Input Current: Max. continuous output-260A; Five-minute rating—310A
  • No-Load Current Draw: <0.6A
  • Continuous Capacity: 2500W (21A)
  • Surge Capacity: 5000W
Anyone know why this inverter won't start the pump?
 
Vardaman said:
I was hoping someone could tell me why the inverter I have won't start my pump. Here are the specs:

The pump is 120 V on a 20A circuit. The inrush current is 35.7 amps.

Power should be about 4300 watts

The inverter is

Xantrex Technologies 8133000UL Xpower Inverter 3000w Gfc​



Specifications

  • AC Output Waveform: Modified sine wave
  • AC Output Type: Two GFCI outlets with 20A fuses
  • AC Output Frequency: 60Hz
  • Inverter Efficiency: 90%
  • DC Input Voltage Range: 10.5-15.5V DC
  • DC Input Current: Max. continuous output-260A; Five-minute rating—310A
  • No-Load Current Draw: <0.6A
  • Continuous Capacity: 2500W (21A)
  • Surge Capacity: 5000W
Anyone know why this inverter won't start the pump?
Click to expand...
Chances are the surge capacity of the inverter is insufficient to start the pump. I.e it can deliver 5000W but for half a second. Alternatively, the battery system is unable to deliver the current demanded by the inverter.
 
There's a lot going on.

Please elaborate on "won't start it". Is the inverter shutting down or throwing a code. What is that code?

12v inverters often struggle with starting bigger loads, even when they are within thier "ratings".

Watts don't equal VA and the VA of pumps could be 150% or more than the Watts. Inverters must be sized to deal with VA.

What is the actual surge rating of your inverter? 5000w for 1 second vs. 5000w for 5 seconds makes all the difference.

The shortest properly sized (preferably oversized) cables with good connectors between the inverter and the battery are crucial.

I'd put my meter on the inverter's DC terminals when the pump is trying to start as see what voltage is.
 
Brucey said:
Chances are the surge capacity of the inverter is insufficient to start the pump. I.e it can deliver 5000W but for half a second. Alternatively, the battery system is unable to deliver the current demanded by the inverter.
Click to expand...
Have to agree.
As Oz has already suggested, check the incoming dc voltage right at the inverter during start up.
Twelve volt systems are particularly difficult to design where there are very high inrush surges.
 
What is the wire gauge between the battery and inverter and how long are those wires? You probably need thick wires (1/0 or bigger) and a short run (3 feet or less).
 
Your going to need at least 5000 watts for 10 seconds or so to start this pump definitely worth going 24 volt for this application
 
These days it is better to go with PSW versus a MSW inverter. Depending on your other loads going up in inverter DC voltage (12 to 24 or 48v) will help with starting difficult loads. Your present setup likely has too much voltage slump.
 
Vardaman said:
I have 2 SLX246-12 GS batteries. My battery cables are 1/0 I believe but coming out of the charge controller they're pretty small.
Click to expand...
Can you try heavier cables? 1/0 seems awfully small for the current your pulling.

As Matt said above, upgrading to a higher voltage inverter would probably be the best bet.
 
As a general rule of thumb I have used for over 30 years with pumps with a 12 volt battery system is a max inverter of 2000 watts
24 volt system at 4000 watts.
I would move up to a PSW inverter and a minimum 24 volt battery.

Or replace the pump with a Grundfos inverter pump.
 
Vardaman said:
fyi, I just used them and got an open box Magnum that was supposed to be 'brand new' and they were loathe to accommodate me. If anyone needs one I still have it.
Click to expand...
Sorry to hear that, the problem with the warranty with victron if you buy from a small local dealer and they go out of business victron would have to find another place for you to send it that would be willing to work on it I have heard of rv people having issues with warranty work a lot of these dealers only work on what they have sold so finding the right dealer is very critical imo on the bright side you probably won’t have a problem it’s very good equipment
 
rodrick said:
Sorry to hear that, the problem with the warranty with victron if you buy from a small local dealer and they go out of business victron would have to find another place for you to send it that would be willing to work on it I have heard of rv people having issues with warranty work a lot of these dealers only work on what they have sold so finding the right dealer is very critical imo on the bright side you probably won’t have a problem it’s very good equipment
Click to expand...
Like I said though, that WAS NOT Inverters R Us, I was mistaken.
 
Vardaman said:
Would it be better idea to reconfigure this at 24 Volts?
Click to expand...
Generally speaking 48V is the preferred battery voltage, lot of options for gear, room for future expansion and the lowest amps on your system, but if all you're ever going to do it try to run this well pump then 24V is likely OK.

Can we circle back to your original post? 120v well pumps are pretty uncommon, forgive me for asking but are you sure it's a 120V well pump?
 
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