Victron inverter for well pump and septic pump

[Maple]

Hi DIY Solar Folks,

Thanks to your many helpful posts, I am considering adding solar power to my rural home near Madison, WI.

First I want to consider a minimal system to run a well pump and septic pump, one at a time, during a power outage. I think each requires no more than 10 kW to start and 3 kW to run.

If I use two Victron MultiPlus-II 120V inverters in split-phase:
- For 2x 48/3000/35-50, continuous power is 2x 2400 = 4800 W and peak is 2x 5500 = 11000 W.
- For 2x 48/5000/70-95, continuous power is 2x 4000 = 8000 W and peak is 2x 9000 = 18000 W.

I think I can use 2x 48/3000/35-50 to run my well pump and septic pump, one at a time. Is that true?

If it is false, would 2x 48/5000/70-95 do the job? Or which minimal Victron inverter(s) would do the job?

Thank you.

P.S. Here are details on the pumps.

The well pump is a STA-RITE 10P4E02H-03, 230V, 1 HP, on a 15 A breaker, locked rotor amps (LRA) = 41.8 (says manufacturer, which also said inrush is close to and a little less than LRA; and that starting current is about 4x running current). I think it requires 41.8 A * 230 V = 9614 W to start and about (1/4) * 9614 W = 2404 W to run.

The septic pump is a Gould WE1012H, 230 V, 1 HP, on a 20 A breaker, maximum current: 12.5 A, locked rotor current: 36.2 A. I think it requires 36.2 A * 230 V = 8326 W to start and no more than 12.5 A * 230 V = 2875 W to run. (A cheap clamp meter showed a max of 32.68 A, which more-or-less matches the specified locked rotor current.)

 

[ricardocello]

I did a similar exercise for my well and septic when I installed my Dual Victron Quattro 48/5000/70-100/100 120V in split phase.
I also put a clamp meter in the panel to actually measure peak inrush current (not all meters do this accurately).
The LRA number was a little higher than measured. For the well, the resistance of the 12AWG wire over 400 ft of wire reduced the peak current.
Running on inverter, my 3/4 HP well pump barely makes the lights blink (but it is visible).

You’ve done all of your detailed homework, and your math is correct.

The 5000VA victron MP-2s will start either pump without issue, depending on what other power is being used.
Personally, I would not consider the 3000VA MP-2s.

The worry would come if both pumps start at the exact same time (unlikely, but possible),
but think about showering with continuous water usage.
In principle, the surge performance of the 5000VA MP-2s should have you covered.

Someone here will likely tell you to try a soft start. This is only possible if you have a three-wire well pump and control box.
If you have a two-wire pump like me, it isn’t feasible (but see my post below).

Someone will also likely tell you about other pumps which are friendlier to inverters, but I assume you want to use what you have.

Also, do you care about UL listing and approvals?

 

[ricardocello]

Also, see this thread from me
Thread 'Schneider Soft Start on 2-Wire 240V Well Pump'
https://diysolarforum.com/threads/schneider-soft-start-on-2-wire-240v-well-pump.68882/

 

[Maple]

Thanks for that feedback.

A soft start interests me, but I'd be happy to have running pumps with dimming lights. Right, I hope not to replace my pumps.

> The worry would come if both pumps start at the exact same time ...

If I did not prevent this by turning one circuit off, and the inverter surge wasn't enough, what would go wrong? Inverters shut down? Inverters damaged? Pumps damaged?

> Also, do you care about UL listing and approvals?

I don't know yet. I will finish installing a generator transfer switch soon. When my helpful inspector reviews it, I will ask him about solar requirements. From reading here, I could imagine that for indoor equipment, I'll need UL. Or for equipment in a shed (possibly feeding my transfer switch's power inlet box), maybe he won't care (?).

 

[ricardocello]

Inverters shut down? Inverters damaged? Pumps damaged?

Inverter shutdown, most likely.
Damage to pumps very unlikely, though i’m sure someone out there will be paranoid about that.

Victron only has a limited number of UL listed multiplus-iis, check carefully if that is required.

 

[MichaelK]

What I have read is that soft-start electronics on a well-pump is a BAD idea. My understanding is that water lubricates the pump bearings, and slow-starters allow the pump to turn with inadequate water flow, damaging the bearings. That being said, I don't actually personally know anyone that has tried to put a SS on a pump, so I can't verify this from personal experience.

I have a 1hp Grunfos pump, and I've measured the inrush at 38A, just a bit below what you are documenting. Unless your meter has an "inrush" setting, I would question the value you are seeing. I also first attempted to find the startup power required with a regular clamp meter. I read 17A for one second, before it dropped down to 10 running amps. What I was seeing was just the tail-end of the inrush.

 

[Pyrofx]

Dont wory about cooling . It's only starting slow fow 20 seconds or so.