Running sump pump 24/7 off LiFePo4 battery/inverter/charger

[monochromatic]

Hi, I have a 110v sump pump that I'd like to run off battery when the power goes out. Unfortunately I don't have room for a 12v backup pump in the sump pump pit.

After considering lots of options, I'm wondering if I can do the following:

• Victron Phoenix 12/1200 inverter connected to the sump pump
• Inverter connected to a 12v LiFePo4 100Ah battery
• Victron Smart Blue charger connected to the battery

Is there any reason this wouldn't work? Due to Kirchhoff's law, it seems like the inverter and sump pump would be powered from the battery charger (grid power) once the battery is fully charged, but then automatically be powered from the battery once the power goes out. Would this cause too much strain on the battery in this configuration, assuming voltages are properly configured?

Thanks!

 

[BentleyJ]

Without more information regarding the electrical specs of the sump pump its impossible to answer your question. Need to know the Run Load Amps and Locked Rotor Amps otherwise known as inrush.

 

[monochromatic]

Thank you Bentley! The sump pump is a Zoeller M53 model rated for 4.8-9.7 amps. My testing with a clamp meter is that it draws 9 amps for a split second, then operates at about 5 amps. Running time is 5 seconds to empty the pit. I can't seem to find the official specifications for the locked rotor amps (inrush). I've successfully run the sump pump off an Ecoflow River Pro (600W and 1,200W surge) for hours on end on about six different occasions, if it's any help.

Appreciate it!

 

[BentleyJ]

At 9 Amps starting current (assuming the clamp meter is fast enough to capture the max inrush, does it have a Max Hold feature?) at 120V that's approaching the limit of the 1200W inverter although Victron is good equipment so probably OK. However, a 100Ah LFP battery likely has a 100A or less limit programmed into the BMS. So at 12V it takes 10+ times as much battery current to produce 9A at 120V. So here again you may be at the limit of the battery discharge C rate. It all depends on how fast the BMS reacts and what it is set at.

 

[BentleyJ]

Since the Ecoflow River Pro did run the sump pump, I would have to believe the Victron with the 100Ah LFP battery should also. It seems like the run amps must be closer to the 4.8 value than the 9.7. Ultimately there is only one way to find out, try it.

 

[monochromatic]

Great points, thank you. I forgot about the max hold feature, and just got about 15 amps. It must happen for a few milliseconds, because the highest value I see without the max hold is ~9a. Then it runs at about 5-6 amps for 5 seconds. I googled some more and it sounds like these pumps can draw around 20+ amps inrush if there's debris in the water.

A couple questions if you're willing:

• The 100Ah LFP batteries I'm looking at (AmpereTime) have a 280 amp max for 5 seconds, so their BMS must be able to handle it?
• The Victron Phoenix inverter has a surge rating of 2200W, so maybe good to go?
• If the pump gets clogged and draws 20a for a long time, what's the worst case scenario? Will the BMS shut down the battery, or will the inverter blow up? Or what?
• Is there any concern about battery degradation in this configuration?

Thanks again!

 

[BentleyJ]

280A for 5 seconds is very generous, even a bit unusual, for a 100Ah battery, that should be plenty of "head room" to start the pump.
Victron is generally high quality and performs as per the datasheet specs, 2200W at 120V is 18.3A so should handle 15A for that fraction of a second.
If the Victron gets overloaded due to a clogged impeller the built in over current protection should kick in and shut down before anything bad happens.

 

[BentleyJ]

There was a post on the Forum the other day featuring a YT video of a home brew inrush current limiter using NTC thermistors housed in a single gang electrical box with a blank cover. Someone commented that it was bit "hacky" I agree but in your application it would certainly do the trick if starting the sump pump turns out to be borderline with the equipment you listed.

 

[time2roll]

I think 1200 watts rated might work fine for a 1/3rd hp M53. No guarantee. I have an M98 in service but use a portable 1/2 hp for emergency service that just barely starts with a 1000 watt inverter.. Clogged impeller should not be an issue with the vortex design.

 

[monochromatic]

Thanks for your replies! It looks like it has enough on paper. I'll check out the inrush current limiter idea, sounds interesting!

Does this look good to you guys?

 

[time2roll]

I think I would use a transfer switch instead of full time on inverter-battery.
Not sure the duty cycle or the charging power but could deplete the battery in difficult conditions even if utility power is available.
Depends on the damage risk of rising water. Or just swap the plug into the utility outlet if needed.

I also recommend a spare pump if damage risk is high. I have seen the shelves of HD cleared of all pumps and generators during times of need.

Otherwise diagram looks fine.

 

[monochromatic]

Thanks time2roll! What transfer switch would you recommend? Here are some numbers that brought me down this path:

• Duty cycle: ~200 on/off in the heaviest rain over 8 hours.
• Longest power outage ever is 8 hours.
• Pump runs for 5 seconds each cycle.
• Math is: 5s * 200 = 1,000 seconds (17 mins) run time at ~700W = 200Wh. Excludes inrush.
• Assuming a full day of power outage in heaviest rain = 200Wh * 3: ~600Wh needed
• I chose the Victron inverter because of its 10W standby and 91% efficiency. Costs more, but higher quality.
• The Victron charger will charge at 15a with 94% efficiency and .5W standby.

So theoretically even in a bad storm with lots of rain and a 24 hour power outage, the numbers seem to add up. But I'm a total novice with this stuff, so could be wrong.

Good call on the extra sump!

 

[time2roll]

Something basic like this 15a KISAE: https://www.donrowe.com/KISAE-TS15A-Automatic-Transfer-Switch-p/ts15a.htm
Or the Prowatt if wire leads are preferred: https://xantrex.com/products/accessories/prowatt-sw-inline-transfer-relay/

Yes my perspective is my M98 can run continuous for an hour+ in a heavy rain while the entire driveway becomes part of the pit. Five second cycle is way less.

 

[monochromatic]

Thanks, that gives me something to think about. I think the transfer switch makes sense.

Is there anything fundamentally wrong about having it always on? Will it damage the battery in some way? Or just make the inverter burn out faster?

 

[time2roll]

Nothing fundamentally wrong with running on battery-inverter full time. Nothing wrong with idling the inverter for years waiting for the power to go out.

My concern was running near continuous in a hard rain depleting the battery some and then the power goes out.

Either way the battery will be near 100% most of the time and may have a shorter life. A lower float voltage should help some. Still should last a solid 10+ years with minimal cycling.

 

[Rocketman]

My thought is if any of the critical items die, the charger, the bms in the battery or the inverter, you would not know until the pump doesn’t run.

You may want to look for a 120v alarm, that if the power to the pump goes off it sounds. Or a 120v led light that is always on - so you would notice it if it was off.

Just a thought

 

[monochromatic]

My concern was running near continuous in a hard rain depleting the battery some and then the power goes out.

Got it, yeah that concern makes a lot of sense. Thankfully I have spent thousands upgrading gutters and exterior drainage so the pump hopefully never does that!

Thanks for your help!

 

[monochromatic]

My thought is if any of the critical items die, the charger, the bms in the battery or the inverter, you would not know until the pump doesn’t run.

Good point; I plan on integrating the Victron capabilities with my smart home network and I have cameras in my garage. But a nice bright LED makes a lot of sense.

 

[MiSh]

Buy the Victron from Amazon. Test it by running a hose into your sump. If it doesn't work to your liking, send it back. I had a Victron 12/1200 and an issue of the inverter fan immediately going on when the pump went off even though technically the initial amp draw was well under their specs (small pump). Concerned me enough that I went with an AIMS 1500/3000 inverter. No issues now.

Also, as others have eluded to, you don't need to have your inverter and charger on 24/7. I keep mine off more than on if I'm home. And, depending on where you live and your climate, you're obviously not going to need your backup sump pump in the dead of winter.

 

[monochromatic]

I had a Victron 12/1200 and an issue of the inverter fan immediately going on when the pump went off even though technically the initial amp draw was well under their specs (small pump).

Thanks for the info!

And, depending on where you live and your climate, you're obviously not going to need your backup sump pump in the dead of winter.

Unfortunately I live in the PNW where most of our rain comes in the winter, and lots of it!

All of this makes me wonder if it's worth it to just get one of the combo units off Amazon, like the PumpSpy 2000W sump pump backup: https://www.amazon.com/PumpSpy-Primary-Emergency-Superior-Intelligent/dp/B0B3S4CXX7

It's basically an inverter, charger, and transfer switch all in one for $500. My thought going down the Victron route is that it's supposedly the highest quality and worth the extra money, but maybe I'm overcomplicating it...

 

[Rocketman]

If you go that route they recommend AGM’s not lithiums.

I always like separate components- easier to understand and troubleshoot

KISS - keep it simple and serviceable

 

[time2roll]

Yes I would be Victron any day over a random amazon inverter. LFP all the way... just a matter of what size.

 

[Bud Martin]

BTW, the Phoenix 1200 is 1200VA/1000W 2400W surge. I have 12V/1200 model without V.E. direct, it is able to start my fridge (25 cu.ft) that has over 30A of startup surge, it is built like a tank and heavy, the only thing I do not like is the little hum from the TOROIDAL transformer.

 

[monochromatic]

Thank you all for your replies! I think I'll go the Victron route and report back.

 

[vvadym]

I think I would use a transfer switch instead of full time on inverter-battery.
Not sure the duty cycle or the charging power but could deplete the battery in difficult conditions even if utility power is available.
Depends on the damage risk of rising water. Or just swap the plug into the utility outlet if needed.

I also recommend a spare pump if damage risk is high. I have seen the shelves of HD cleared of all pumps and generators during times of need.

Otherwise diagram looks fine.

Hi, just trying to understand the scheme and build my topology, pretty fresh of the boat))
In case if the switch is placed before the battery charger it means that the load (pump) must be manually toggled from switch to inverter, am I right?