LiFeP04 sump pump backup

[welnat]

Hello guys,

am looking to build a battery backup to run my sump pump in event of grid down while away.

The battery will be the sinopoly type recommended by will (because I want to try it)

It will be installed in a basement that does not freeze.

The pump is a 1/3 hp 120v pump that needs to be able to run 15 seconds every 15 minutes for 3 days.

I figure this is drawing 2.9 amps when it is running.

I'd like to do a 12 or a 24v system and I'd like to try the grundig better pure sine wave inverter will recommends.

What I'd like help with:

size of the 24v battery to only discharge from 90% to 30% over the three days.

Recommendations on a charger for the battery.

I would like to add solar over time and based on the experience scale this battery size up - to a whole home potentially of 7-10kw 48 v system.

The intermediate step would be to duplicate the system on a small camper next year.

Things I want to avoid - smart charger / bms/ low voltage disconnect / temp sensor - anything that has wifi/bluetooth, etc. We have enough rf in our lives already.

 

[svetz]

Welcome to the forums Welnat!

Facts battery backup to run my sump pump in event of grid down while away. (we have a couple of these, search for "sump" to see what they're doing) Sinopoly LiFePO4 Non-freezing location pump is a 1/3 hp 120v (2.9A) that needs to be able to run 15 seconds every 15 minutes for 3 days (1 min/hr). 12 or a 24v system Want to avoid - smart charger / bms/ low voltage disconnect / temp sensor - anything that has wifi/bluetooth Want to add solar some day Questions (if I missed any let us know) size of the 24v battery to only discharge from 90% to 30% over the three days. Recommendations on a charger for the battery.

I can't help with #2, but for #1 you probably want to look over How to figure out how much Solar and inverter wattage is needed to charge a battery

How many watt hours does the pump take per day?
watts = amps x volts = 120V x 2.9 amps = 348 watts
watt hours = watts x hours = 348 watts x 24 h/d x 1m / 60 m/hr = 140 watt hours per day

How many watt hours do you need for 3 days
3 days x 140 = 420, assume 90% inverter efficiency, 420 / .9 = 467 watt hours.

How many amp hours at 12 or 24V @ 60% capacity?
467 / .6 / 12 = 65 Ah
116 / .6 / 24 = 33 Ah

How big should the inverter be?
Since the pump is 2.9 amps at 120V, that's 350 Watts. But, an induction motor can take a lot more current to start up, I've heard as much as 5x the continuous draw. You'd probably be better off getting a DC pump, that way the in-rush current can be supplied by the battery and you can eliminate another component.

 

[welnat]

Thank you for the reply!

So I plan to buy 2 x 12v 40 Ah battery (sino poly will recommends) and power with the 2000w giandel 24v he also recommends)

UNLESS ( are there any 24 / 48 v switchable pure sine wave inverters?)

I plan to charge it with this (which I already have) :

Is charging the two 12v batteries with this charger a bad idea? It has the advantage of being already bought, and I like it.

I still need to select a BMS and a low battery protect. Any thing else I am missing?

I don't want to replace the pump with dc, due to wanting to trial this battery on a small scale, and maybe build a bigger one after this.

 

[welnat]

anybody?

 

[svetz]

Not familiar with it. The Tech Spec section says it can do LiFePO4 and to look for the blue light. Probably best to contact the vendor and ask or see if there's anything in the manual more specific about two 40 Ah LiFePO4s.

 

[Mars]

I would recommend measuring the pump energy usage to get a better idea of what it will take to run this. Get a P4400 Kill-A-Watt meter if you don't already have one. Measure the energy usage over a few days.

On start up, motors typically take about 6x the full load amps (FLA). A pump can take a significant amount of time to get the water flowing. While starting it is taking more power than 2.9 A x 120V.

My gut feeling is that a 65 AH x 12 V battery is undersized.

If it is only running for 15 seconds at a time, then that tells me the sump is undersized, and/or the pump is oversized.

 

[welnat]

On it, will measure for a week and report back. Clarification - I am looking to do a 24v system using 2 x 12v batteries

 

[welnat]

I abandoned this project and did a larger battery which I can patch to whole home if needed. I would still like to do this, but would likely buy a pre-built lip04 with a bms and stick a 12v charger on it plugged into wall.