please recommend the course of action - Li-Ion 4.2v cells build

[mrbizzy]

Hello. Even it does not look difficult at the first look, i get confused with some choices in my first attempt to build a battery myself.
I need to make a storage for 12V system in my home on wheels to go on a prolonged journey through Europe starting soon..

I have 33 Yuasa (can get more) LEV46 SD Li-Ion cells with maximal voltage of 4.2Volts and rated at 46Ah each which tests to 99% capacity.

It will be charged by Victron Smart Slar controller with 50A (700W at 12v or 1400W at 24v)rating.

And i have the old (originally installed) AC-DC block that was designed to charge the 12V lead leisure battery and which is integrated in feeding of the 220v to system as well when connected. it seems to do its job well so far So i do not want to rebuild that part and keep it as is as it is already wired to all the switches in the panel.

And i would probably need a AC/DC charger separate for the battery, which i am willing to invest in as well.


I see 3 options:

1. make it 3S which means max voltage is 12.15V and it is about 80-85% and most appliances will cut off when the battery reaches it 25% level at ca 10.6V

2. make it 4S IF there is a solution to have the battery charged at 16.2V but feed to the system max 13.8V - this would make a higher voltage that the appliances are more stable with than sub 12V. and the second benefit in my view is that i would not have to think about separating the current AC/DC charger as well as the alternator as i can let them charge the battery up to 14.2 volts without a worry.

3. make it 6S and use a 24/12v DC/DC connected to a 12v deep discharge led battery - this again would let me not to worry about the integration of battery into current 12v system as it is a led battery that all appliances are connected to and which in turn is fed by the 24v storage constantly (While it has juice off course) . also no need for a high current DC/DC as if the demand spike over the dc/dc rating lead battery acts as a buffer.
Also this way would let me install one more solar panel as for the 24v system i can have up to 1400W
Also a benefit with this scenario is possibility to use a 24v AC inverter.


now, my mind is not wired electrically but rather i am looking for the most practical solution to use the maximum that my batteries can offer (up to 85% charge to 25% discharge) for the longest period of time.

If you have the experience or knowledge and some spare minute please share with me which way would you do this and why as i am also interested to understand why i will be doing what i will.

 

[Short_Shot]

This is a rather annoying issue that keeps me away from these cells for 12v applications.


Here's one thread on it where they talk about both.

3s or 4s for 12v battery

Do you prefer to build 12v lithium batteries with 3 or 4 cell groups and why?

endless-sphere.com

 

[Short_Shot]

Also I think some folks use 7s for 24v as on possible option. Full charge is 29.4v?

Which is within range of most chargers with adjustable outputs.

Again I'm not the expert here.

 

[mrbizzy]

This is a rather annoying issue that keeps me away from these cells for 12v applications.


Here's one thread on it where they talk about both.

3s or 4s for 12v battery

Do you prefer to build 12v lithium batteries with 3 or 4 cell groups and why?

endless-sphere.com

thanks. will check that out.

 

[mrbizzy]

Also I think some folks use 7s for 24v as on possible option. Full charge is 29.4v?

Which is within range of most chargers with adjustable outputs.

Again I'm not the expert here.

29.4V seems too high for my application. 6S would work out as a 24V which would fit one of my imagined solutions.

Any other insights people?

 

[NVS]

You want to build a 7s lithium ion battery pack 29.4v. It is closer to lifepo4 voltage range. 28.8v you will get more usable capacity out of this voltage range. It will work better with inverters voltage range of operations. Which is usually 21v to 30v. I'm building a portable solar generator out of (840) 18650 cells. So it will be a 7s120p battery pack. This inverter has manual charge parameters so you can set it to charge your battery.

2400w 24v 110v Hybrid MPP Solar inverter 80A MPPT charger 60A AC charger | eBay

Find many great new & used options and get the best deals for 2400w 24v 110v Hybrid MPP Solar inverter 80A MPPT charger 60A AC charger at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[mrbizzy]

You want to build a 7s lithium ion battery pack 29.4v. It is closer to lifepo4 voltage range. 28.8v you will get more usable capacity out of this voltage range. It will work better with inverters voltage range of operations. Which is usually 21v to 30v. I'm building a portable solar generator out of (840) 18650 cells. So it will be a 7s120p battery pack. This inverter has manual charge parameters so you can set it to charge your battery.

2400w 24v 110v Hybrid MPP Solar inverter 80A MPPT charger 60A AC charger | eBay

Find many great new & used options and get the best deals for 2400w 24v 110v Hybrid MPP Solar inverter 80A MPPT charger 60A AC charger at the best online prices at eBay! Free shipping for many products!

www.ebay.com

thanks. indeed!
i already have bought the solar charge controller which is Victron MPPT 100 / 50 which i can also adjust to my needs and it has the lifepo4 preset as well so i can go that route and by using that voltage also increase the solar panel power.

Now if that part of the system is made to work at 28v-29v range i need to find out the less troublesome method to connect it into my 12v system.

I understand the general idea is to use a dc/dc. that will transform the 28-29v to my needed 12-14v.
Looking at Victron i see this option: https://www.victronenergy.com/uploa...DC-converters-high-power,-non-isolated-EN.pdf
I guess the 70A would be enough for a medium motor-home.

But is there another approach to this situation?

And just to be double safe - if i wire in this kind of DC/DC converter, i just connect it to existing 12v system, where the 220v charger is integrated as well and when connected to the grid those 14.4v will not harm the dc/dc converter?

Any other things that i could not be aware of in this scenario?

 

[Short_Shot]

29.4V seems too high for my application. 6S would work out as a 24V which would fit one of my imagined solutions.

Any other insights people?

As stated, 6s is actually too low.


If you need 12v nominal you should be using a 12v pack though. By doing the 4s pack and just charging it to the lower 14.x volts your life will be easier and your pack will be safer/less likely to overcharge.

 

[BlueFox]

You want to do the higher cell count (4s or 7s for 12v and 24v) for 2 reasons.

1) Voltage sag under load will stay in the 'normal' range that would be expected from a lead acid or lifepo4 battery. IE; draw high current from a 3s li-ion pack and it'll drop to under 10V pretty quickly, leading to inverter shut down or low voltage alarm. Whereas 4s should stay above 13V.

2) Charging to a lower voltage is significantly better for cycle life, for example with 4s you'd charge to 15.6V or something like that which is a ~70% charge, and should increase cycle life at least 3x or more. You need extra batteries to make up the lost capacity, but lifespan should be extremely good.

The downsides are inverter low voltage shutdown won't function, as a 4s pack will never drain that low. And you need chargers that support a custom voltage high enough to set it at 15V+