12v Leisure Battery made from 18650 cells? RV,

Hello

My leisure batteries on my RV are on their way out. Currently I have 250A/h of sealed lead acid.

If I were to consider making a 18650 or other lithium battery pack what should I be looking for? Is there an off the shelf solution already?

Looking for ideas and advice on sourcing a solution. Also would I need to have 250A/h if it were Lithium?

I have vehicle charging of course, a 12v "smart" charger for the Lead acid and I have 250w of solar .

TIA.

Kevin

Biggles said:

Hello

My leisure batteries on my RV are on their way out. Currently I have 250A/h of sealed lead acid.

If I were to consider making a 18650 or other lithium battery pack what should I be looking for? Is there an off the shelf solution already?

Click to expand...

Why would you do that? Would you make a pack out of AAA alkalines, or CR2032 coin cells? Make it easier on yourself, and use cells or modules that are in the right scale for your project.

Here's something that only needs BMS added. Three of those gets you all the capacity you have now, and you can use a lot more of it without scrapping your batteries.

If you want the house batteries to charge at the same voltage as your starting battery or other lead batteries, then you want to look for lithium iron phosphate cells and use them in 4S configuration.

These guys can have some cheap solutions maybe not today but they get stuff in and sell it out quick.
https://batteryhookup.com/products/bmw-oem-3s-12v-85ah-869wh-battery-module.
I like lifepo4 at 4s for 12v auto long life.
Plus I don't know what the stats are but 200ah is about 250ah of lead or more.
https://batteryhookup.com/products/200-a123-ahr32113-ultra-b-cells-40c-beast
I would wait for new cells. Or maybe tell them what you want. Family business.USA.
Or I'm battery

Balmorhea » Sep 16 2020 4:08pm

Biggles wrote: ↑Sep 16 2020 3:51pm
Hello

My leisure batteries on my RV are on their way out. Currently I have 250A/h of sealed lead acid.

If I were to consider making a 18650 or other lithium battery pack what should I be looking for? Is there an off the shelf solution already?

Click to expand...

Why would you do that? Would you make a pack out of AAA alkalines, or CR2032 coin cells? Make it easier on yourself, and use cells or modules that are in the right scale for your project.

Here's something that only needs BMS added. Three of those gets you all the capacity you have now, and you can use a lot more of it without scrapping your batteries.

If you want the house batteries to charge at the same voltage as your starting battery or other lead batteries, then you want to look for lithium iron phosphate cells and use them in 4S configuration.

Click to expand...

That is cheap, wonder how much shipping would impact the price. Think I need one.

ZeroEm said:

That is cheap, wonder how much shipping would impact the price. Think I need one.

Click to expand...

I got a bigger pack from them that weighed about 30 pounds, and paid about $30 for shipping.

Have been wanting a 12v shop battery for my solar panels to charge and supply me with a needed 12 source. This looks great.

the first lithium pack I built for my van was with 156x 18650 cells it was a 3s26p x2 total 94ah pack. So its possible to build one, but very labor intensive, you need to test every cell, you need to get a tab welder, have some soldering skills. My current house battery is a 4s40p lifepo4 220ah, also labor intensive. The 18650 pack I just solder every cell, the lifepo4 I used a tab welder and it sped up the process tremendously.

If you can find a simpler method with already built components that would make everything easier, the important thing is get a very good bms for the system, it has to be as failsafe as possible and reliable, you never want to overcharge any lithium. I been using the chargery bms8t, I recommend that for a house battery. And whatever system you use, having active balancers the qnbbm model, would be a good idea, I use them on my house battery. They help when you charge at high amps, lithium has a tendency to go out of balance the nearer it gets to full.

With lithium you only need half the amp hours as lead, 125ah of lithium will replace 250 of lead acid, you can drain the lithium all the way to zero percent. If building using 18650, you need to use a 3s system if you plan on charging with your alternator, 4s voltage will be too high to get a full charge, even from solar it might not charge to full unless you the controller can go above 16 volts.

94ah (3s26p x 2 packs connected in parallel) house battery (weighs about 25 pounds) this pack worked extremely well and stayed in perfect balance. Back then I use cells as low as 1200 mah, today I might use only cells above 1800mah. This 3s pack ran everything my lead acid it replaced ran. I never had to use any boost converters.


110ah 4s lifepo4 (weighs about 30 pounds), I got 2 of these 110ah packs connected in parallel (220ah) as my house battery for the past 2 years.

I would not reco the dangerously fire-risky cell chemistries commonly used for propulsion for this use case.

LFP or maybe LTO only.

Brand new cells, and learn to benchmark test capacity (also resistance) to gauge SoH / proactively predict EoL

Going from lead, can reduce Ah capacity by 35%, unless you think you might need more later.

Avg DoD% at 65% may triple lifespan vs 85%

john61ct said:

I would not reco the dangerously fire-risky cell chemistries commonly used for propulsion for this use case.

Click to expand...

Oh, do you mean the ones that get used in hundreds of thousands of cars and operated by technically ignorant people?

I agree with you if we're talking about quadcopter batteries or a bajillion 18650 cells. But large format automotive cells are safe enough for e-cars, which are safer than gas cars... which many people keep inside their homes all the time.

I use a 48p 6s pack with a Victron smart charge controller set to cut off at 24volts and a 260W panel.
I use a 24 to 12 volt dc/dc converter for all the house 12 volt needs and a 2000 watt 24 volt Inverter for my AC needs. Since the cells are only charged to 4 volts and seldom drawn down below 3.6volts the pack has remained perfectly balanced and should last quite a while.

These fire-risky batteries used in commercially produced propulsion systems

have very sophisticated BMS and thermal management systems that cost millions in engineer hours to design and implement to be "fool proof".

Pull the packs out of those protective systems and they are 5000x less safe.

We are talking about living inside a small space with the bank, not just driving around a few hours a week.

If a single adult is fully aware of the risk, go for it, but don't park near me, and I certainly would not recommend putting it in the same living space as my family members.

Sure DIY EV types need the very high energy density, so they take their chances.

This use case does not, there is no functional upside only higher risk.