First Lifepo install. Serial worries.

I am pretty sure I want to go 24v in my Truck Camper. Battery space is limited so I wonder if I should focus on fitting 24v batteries instead of 12v in serial. I have read a few posts that indicate serial is potentially more problematic. Got any advice to offer?

Editied for my earlier silly mistake

SolarSoon said:

I am pretty sure I want to go 24v in my Truck Camper. Battery space is limited so I wonder if I should focus on fitting 24v batteries instead of 12v in parallel.

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Don't you mean "...should focus on 24v batteries instead of 12v in Series"?

Well I was super sleepy when I posted that. I meant to say series instead of parallel. I have found some 12v 200ah batteries that will fit in one of my smaller bays near the original battery. I just want to understand any pitfalls.

t depends on the battery. I assume you are talking about one of the LiFePO4 drop-ins. Most of them can handle two in series.... but check to see what the limit is before you buy. The other thing is to make sure they are both fully charged before you put them in series.

Other than that, you should be fine.

FilterGuy said:

The other thing is to make sure they are both fully charged before you put them in series.

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I would add that two batteries being put in series should be at the same SOC before going in series. Charge them together in parallel to ensure the same voltage/SOC then you can put them in series.

I have two drop-ins in series. At first I charged each one separately and then I put them in series. I had some strange issues when charging during float. Took them out, put them in parallel, and charged them together. Once fully charged and at the same SOC I put them back in series and the strange issues were gone.

Check to make sure series connecting is possible, some are, some aren't.
Title says Lipo, hopefully it is LiFePo4 you intend to use, they are much safer.

If the base vehicle is a 12v systen consider a complete 12v system unless you intend to use an inverter at 2000 watts or over.

Mike

Yes, LiFePo4 (edited title) pre built and likely from the better names (Victron, Battleborn etc.) I do plan on a big 2-3k inverter. Main goal is to be able to run AC, and or Microwave for 2 hrs or so. Generator makes too much noise for some places we stop. Also switching to a DC refrigerator and want it running all the time.
Will series batteries need to be tended more than a pure 24v system? I understand the need to have them both at the same state of charge when first putting in series.

Without knowing the battery details it's impossible for anyone to provide anything other than speculation, details are important, the more the better.

Ok lets try this. With the option of using 4 Battleborn 24v 50ah in parallel vs 4 12v 100ah in series/parallel. Same cost for the batteries.

4 batteries in 4P require 6 wires to connect between the batteries. These batteries are fairly easy to keep balanced.

4 batteries in 2S2P require 4 wires to connect between the batteries. The series pairs must be balanced correctly. This is a little extra work upfront and maybe a couple of times per year to rebalance if needed.

Both setups are assumed to use the "diagonal" method for the parallel connections. Both need more if you setup battery busbars for the parallel connections.

It's my understanding that BB will ensure your batteries are properly matched if you tell them they will be wired in series when you order them.

One other benefit of going with the 24V 50Ah option is that if one battery fails you simply remove it and the other three keep going. If you have 12V 100Ah batteries in 2S2P and one battery goes bad, you effectively lose two batteries and are now down to half instead of 3/4.

Good info, thank you! I think I am now feeling better with the choices ahead of me.

There are considerations for both parallel and series configurations.
Neither is perfect and both can be made to work well.

Series Batteries:
With series, the primary concerns are all around keeping the multiple batteries balanced. If one starts out with a lower state of charge, that will define what is possible for storage for all the batteries in the string.
My guess is that if you start with Balanced LiFePO4 cells, you will be fine for a long time to come.

Note: There are battery balancers that are designed to balance batteries in a string but I have no experience with them.

Parallel Batteries:
The primary concern with parallel batteries is uneven ware due to slight voltage differences due to different resistance values of the path to the batteries.

The leads between cells will have small voltage drops as shown in the (not recommended) diagram below.


In the above bad example, battery 4 will provide more of the current than the other 3, battery 3 will provide more than 1 & 2 and so on.
Over time, this means battery 4 is worked harder and presumably will wear out quicker. This problem is very real with lead acid.... I have seen debates about how real it is for LifePO4, but I just assume it is a problem.

The good news is that there are ways to wire parallel batteries to avoid this.

It turns out that if you wire two batteries like this, they remain balanced as long as the interconnecting leads are the same size.


For 4 batteries, this is a way to wire them that keeps them balanced:

Putting 3 heavy wires on one battery terminal can be problematic, so this is an alternative:

Finally, you can always just wire each battery separately:


The other approach is to use very heavy duty bus bars that have such low resistance that the voltage drop is negligible. Some Battel Born batteries have a unique post layout that allows Busbars between the batteries. I try to show this in the image below: