# OffGrid - Automatic Jet Pump

Registered Users Posts: 32 ✭✭

I’m new in the forum, hi all.

I have a off-grid solar system, 6kW inverter 48V. I also have a jet pump 120VAC 3/4Hp 6.6A but every time the pump start the lights are flickering for maybe 1 second and then everything runs well.

Is there any product that could help me with this situation?

Does anyone knows a pump not to expensive with soft starter?

Any ideas...?

Tagged:

• Super Moderators, Administrators Posts: 32,027 admin

Welcome to the forum Fred.

What brand & model of inverter do you have?

How long is the cable and what awg wire?

What type and size of battery bank?

Bill

Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 32 ✭✭

Hi Bill

Sigineer Pure Sine Wave Inverter 6kW APC, The pump is connected very close to the main break less than 15ft and I believe maybe I’m wrong but the cable is 10AWG (3 wire) , I have 12 SAGM 205 @48V

• Super Moderators, Administrators Posts: 32,027 admin

Is this the model of AC Inverter?

Looks like you are not in the US, but overseas with a 230 VAC (50 Hz?) power system?

Regarding your DC bus cabling, is this 3x #10 AWG wires in parallel, or is it 1x 10 AWG positive, 1x Negative, and 1x Ground wire on the DC bus?

Looking at the manual, it calls for a 1/0 ("one aught") minimum cable size for a 48 volt battery bus... Just to give you an idea of what kind of current you are talking about for a fully loaded 6 kWatt inverter (that can surge over 12 kWatts):

• 6,000 Watts * 1/0.85 AC inverter eff * 1/42.0 volts battery bus voltage = 168 Amps

If you had 15 feet of 10 AWG cable, with 6 kWatt load, using a simple voltage drop calculator:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=42&phase=dc&noofconductor=1&distance=15&distanceunit=feet&amperes=168&x=47&y=31

## Result

Voltage drop: 5.03

Voltage drop percentage: 11.99%

Voltage at the end: 36.97

If you had 15 feet of 1/0 cable, that would give you about 0.5 volt drop (perfectly OK for a 48 volt battery bank and AC inverter):

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.3224&voltage=42&phase=dc&noofconductor=1&distance=15&distanceunit=feet&amperes=168&x=59&y=23

## Result

Voltage drop: 0.50

Voltage drop percentage: 1.18%

Voltage at the end: 41.5

Your 3/4 HP pump could surge to ~1,200+ Watts... If you have other loads on the Inverter, a true 10 AWG cable is way too small (good for possibly 30-60 amps at best).

For your battery bank, I guess it is 4x 12 volt @ 205 AH AGM batteries in series (for 48 volt bus), by 3x parallel strings for 48 volts @ 615 Amp*Hour capacity.... And properly wired, that bank can support a 6 kWatt (12+ kWatt surge).

Things to check/try;

1. Double check the DC Bus wiring, 10 AWG is probably wrong (too small). And 15 feet is a pretty long distance (voltage drop issues).
2. Check your battery bank voltage... Typically, fully charged and resting (about 3+ hours) is 52 volts, and well discharged (resting) i around 48 volts... If it is below 48 volts resting or below ~46 volts running, your battery bank is either undercharged and/or the batteries are starting to fail (sulfating).
3. A very simple method to reduce starting surge on a pump or compressor is to get a medium duty 50-100 foot extension cord and wire it between the AC inverter and the water pump... The resistance of the long cable reduces the starting surge, but still carries enough current to start+run the pump.

-Bill

Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 32 ✭✭

Thx, I will check it and let you know

• Solar Expert Posts: 1,386 ✭✭✭✭
edited April 2019 #6

You could wire a time delay relay to a solenoid valve on the pipe from the pump (ie, valve closed while it is starting). It should help with starting (very roughly 1/2 the power normally needed). Is there back pressure and a check valve on the pump output when it starts? If so, this might not have much effect (since flow will be zero until it reaches pressure).

Unfortunately, as far as I know, nobody makes an AC booster (although it is certainly possible to do so).

I am available for custom hardware/firmware development

• Registered Users Posts: 32 ✭✭
Update:
I installed a Grundfos Submersible Pump, it has low start up. Is working great and there is no lighting flickering.