Sump Pump Battery

[bythebay]

I am looking for a battery, either to build or buy one, that will sit idle for 99.9% of the time but needs to run a 12v backup sump pump that draws 16 amps. I know I can use AGM but hear so many stories where they fail when needed after sitting for years unused or overcharged. Looking for a batter/charger setup that will keep the battery fresh and properly maintained for many years. I would love to build my own but am concerned that may be overkill for my application.

Thanks in advance!

Rob

 

[offgriddle]

I have been really happy with the performance of my lithium ion phosphate batteries; they blow the doors off of ancient, lead acid battery technology. The batteries I purchased have a built in BMS, (battery maintenance system), which is crucial to maintaining the life and performance of the battery. You should purchase the charger intended for lithium ion phosphate. Keep in mind that you cannot charge the batteries if the battery temp drops below 32 degrees farenheit BUT some batttery models have built in heaters to account for this. You can purchase LIPO batteries from many sources, here is just one >> https://energizedoutdoors.com/collections/lifepo4-battery

 

[b.james]

Yep I have a small recovered LFP in my shed that sits unattended and unused for months sometimes and its always good when I get back to using it for my radio . It requires a charge every 6 months or so but will sit happily for much longer . The blurb says they self discharge at about 3% per month. But the biggy is they recharge without any memory effect or loss of capacity . Do that to L/A and they are quickly stuffed. Worth the investment.

 

[offgriddle]

Yep I have a small recovered LFP in my shed that sits unattended and unused for months sometimes and its always good when I get back to using it for my radio . It requires a charge every 6 months or so but will sit happily for much longer . The blurb says they self discharge at about 3% per month. But the biggy is they recharge without any memory effect or loss of capacity . Do that to L/A and they are quickly stuffed. Worth the investment.

Happy modulating!

 

[svetz]

I am looking for a battery ... needs to run a 12v ... 16 amps.

What is the duration run time? With that you can determine amp hours. See the Battery FAQ for explanation on why a 100 Ah battery may not really have 100 Ah in it.

...will sit idle for 99.9% ...

Lithium is great as it has a lot of cycles and is light. But, if the battery is hardly ever going to be used (e.g., only when that emergency hits) you're not racking cycles up on it. I would think the less expensive AGMs would be a better fit in this use case.

...I know I can use AGM but hear so many stories where they fail when needed after sitting for years unused or overcharged...

AGMs are sealed batteries, other than self-discharge which can be handled by a tender, I thought they were no muss no fuss. Hopefully one of the guys with experience can tell you better about this. Definitely stay away from Flooded Lead Acid, they are a lot of fuss and muss.

But, it sounds like its important for the area not to flood - regardless of the system stuff can happen (e.g., debris in the float switch). Whatever you pick, you might think about a secondary sensor. If you're there an audible alarm like one of these might work. But if you're not something like a SmartThing that can send a text message to your cell phone might be good. Someone also might also know about battery monitor/sensor that can detect an issue with the battery and report via SMS.

 

[offgriddle]

The AGM is a lead acid battery. Lead acid batteries are good at putting out high current for short periods of time. As a rule of thumb a 100 amp hour lead acid can only be discharged about 30% before it requires recharging. Over discharge, over charging or storing lead acid batteries in a discharged state, severely diminishes their performance and shortens their already short cycle life. Have a nice diaz.

 

[bythebay]

What is the duration run time? With that you can determine amp hours. See the Battery FAQ for explanation on why a 100 Ah battery may not really have 100 Ah in it.

Yes I understand the rating is for optimal conditions with a light load. There is no way to tell how long a power outage could be so run time is a guess. I am thinking that if I run an AGM into the ground, I'm out a few hundred bucks. If I trash a Lithium battery, I'm out a grand or more...

 

[svetz]

There is no way to tell how long a power outage could be so run time is a guess.

Yep. It's all any of us can do and typically it's a struggle between pocket book and caution.

I am thinking that if I run an AGM into the ground, I'm out a few hundred bucks.

Probably not. As it's only for emergency use it's fine to run it to nothing. Folks like @offgriddle are telling you how to maximize the AGM's life and you don't really care about that. Sure, you'll only get a hundred cycles, but if the power goes out 4 times a year, that would be 25 years (although in practice it would still probably die in under a decade regardless).

If I trash a Lithium battery, I'm out a grand or more...

The BMS would prevent you from discharging to deeply, so no worries there. But, if it's really cold (power's out after all) then yep... that can hurt a lithium battery.

Flooding?
Would the batteries be in the basement with the pump? That is if the basement floods the batteries would be submerged? Anyone know what happens with lithium or lead in that case?

Update: TheHullTruth seems to think sealed AGMs would be okay submerged.
Update2: Battle Born says they can get wet, but you shouldn't submerge them.

 

[bythebay]

Batteries would be on a shelf - not on the floor. If my basement gets below zero I have much bigger issues than water infiltration...
I appreciate all the feedback and will do some more research before I decide which way to go. Leaning towards AGM due to cost and simplicity.

 

[offgriddle]

I recently upgraded from two hundred rapidly decaying amps of lead acid, (that's about sixty usable amps for new lead acid batteries), to forty amps of lithium ion phosphate batteries and baby, it's a whole, new, world of power. Lead acid freaks like Svetz, (?), keep pushing the circa1854 acid technology, but I say once you go Lithium, you'll never go back! PS: Forty actual amps of lifepo with built in BMS will run you about $275 bucks.

 

[svetz]

Batteries would be on a shelf

Lead's heavy, that'll have to be some shelf!

Leaning towards AGM due to cost and simplicity.

Lithium isn't more complex. You can get drop-in replacements that look like lead-acid batteries and chargers for them same as lead and dead simple to boot. Lithium only seems more complex because DIYers are making them from scratch and have to figure out all stuff out (like proper charging voltages).

Lead acid freaks like Svetz, (?)

Just so happens I have built a DIY lithium battery and will be installing a few kW of Lithium in the upcoming months.

But ByTheBay's purpose is different, there's no need to pay for 3000 cycles if they will only ever use 20. Just because something is new doesn't make it a panacea to be used in all cases. Both still have a place in the world and to know which is right you have to do the math, not use platitudes or put labels on people to downplay their opinions.

...keep pushing the circa1854 acid technology...

Old doesn't meant bad or useless. The wheel, for example, is far older than the battery and I think it still has a place in the world.

Forty actual amps of lifepo with built in BMS will run you about $275 bucks

Thats 40x12x.9=430W, which a 16 amp pump would drain in ~2.2 hrs. A 100 Ah battery at 16 amps rate is really only ~87 Ah (see the battery FAQ if you're not sure why), which if you're willing to suck it dry and accept the damage is ~5.4 hrs. If you want to stay above a 50% DoD, then think about lithium. With a lead acid you'll probably want to include a low-voltage cutoff that you can program to meet your needs (if not, when the voltage gets low enough the pump will stop but might not stop draining the batteries doing unnecessary damage). A drop in lithium battery with BMS should have a low voltage cutoff built in.

Amazon has a 40 Ah lithium drop in for $379 with a 10 yr warranty with everything needed except for low temperature. That's about the same price as the Sinopoly DIY Will likes on Amazon. Amazon also has a 100 Ah Renogy sealed gel for $216 and an AGM for $203. Not endorsing either product, don't know anything about them but wanted to give some ballpark pricing.

 

[offgriddle]

Lead's heavy, that'll have to be some shelf!


Lithium isn't more complex. You can get drop-in replacements that look like lead-acid batteries and chargers for them same as lead and dead simple to boot. Lithium only seems more complex because DIYers are making them from scratch and have to figure out all stuff out (like proper charging voltages).


Just so happens I have built a DIY lithium battery and will be installing a few kW of Lithium in the upcoming months.

But ByTheBay's purpose is different, there's no need to pay for 3000 cycles if they will only ever use 20. Just because something is new doesn't make it a panacea to be used in all cases. Both still have a place in the world and to know which is right you have to do the math, not use platitudes or put labels on people to downplay their opinions.


Old doesn't meant bad or useless. The wheel, for example, is far older than the battery and I think it still has a place in the world.


Thats 40x12x.9=430W, which a 16 amp pump would drain in ~2.2 hrs. A 100 Ah battery at 16 amps rate is really only ~87 Ah (see the battery FAQ if you're not sure why), which if you're willing to suck it dry and accept the damage is ~5.4 hrs. If you want to stay above a 50% DoD, then think about lithium. With a lead acid you'll probably want to include a low-voltage cutoff that you can program to meet your needs (if not, when the voltage gets low enough the pump will stop but might not stop draining the batteries doing unnecessary damage). A drop in lithium battery with BMS should have a low voltage cutoff built in.

Amazon has a 40 Ah lithium drop in for $379 with a 10 yr warranty with everything needed except for low temperature. That's about the same price as the Sinopoly DIY Will likes on Amazon. Amazon also has a 100 Ah Renogy sealed gel for $216 and an AGM for $203. Not endorsing either product, don't know anything about them but wanted to give some ballpark pricing.

"Old doesn't mean bad or useless", why that's the nicest thing anyone has said to me in a very long time, thank you Svetz!

 

[svetz]

Just realized, this is for when the power is out... so the sump pump is probably AC... so 16 amps at 120 or 240 volts is 2000 or 4000 watts? That's a hungry beast! Anyway, it also means the time calculations in the previous post are probably wrong. If you want to stay AC, you'll need an inverter and you'll also lose power to the inverter's inefficiency. But, you can find them with a built in ATS and charger (example) so they'll switch to battery power when the grid is out, automatically recharge the battery when the grid comes back, and they also typically have a low-voltage cutoff.

You could get a DC bilge pump and float switch, that would save you the cost of the inverter and give you a second pump option. Not sure if the ones linked would work for your application, probably depends on how high you have to pump the water. But they're typically less than 100W power, so that could significantly reduce your costs if they'll work (see this article, the higher the water exit is the lower the flow, but can at 100W you could use a few).

Update: Forgot to mention, as you add more lead batteries the more efficient they become. In the example above a single 100 Ah battery only had a realistic rating of about 87 Ah with a 16 amp load; but with two you draw half the current so they'd both be about 92 Ah. If you get enough the current draw per battery is so low it'll go over the 100 Ah rate.

"Old doesn't mean bad or useless", why that's the nicest thing anyone has said to me in a very long time, thank you Svetz!

More than welcome!