LiFePO4  Batteries - With or Without Balancing - Page 1
Forum section: electronics / general

author: NY2KW
author_rank: Regular Contributor
timestamp: April 23, 2023, 06:09:53 pm
content: I have been looking for a 10Ah 12vdc battery as a long term (6-8week) rechargeable solution to powering a remote RF controlled antenna switch. It seems most of the LiFe batteries that look like direct replacements for sealed lead acid types in lawnmowers or motorcycles only have + and - lead for both charging and discharging while other LiFe batteries like those for the RC crowd all have an additional balance cable (# of pins dependent on number of series cells). Are the performance characteristics of LiFe batteries with and without balance feature very different, e.g. number of charge cycles, how deep a discharge can go before voltage dropout, etc, etc?TIA Jerry

author: langwadt
author_rank: Super Contributor
timestamp: April 23, 2023, 07:10:05 pm
content: sure the balancing and protection isn't just buildin on the two terminal batteries?

author: NY2KW
author_rank: Regular Contributor
timestamp: April 23, 2023, 07:22:28 pm
content: i thought that might be the case but the same 10Ah battery without the external balance cable sells for much less than the RC style equivalent. I would have thought if they had the internal balancing circuitry they would cost more?

author: PlainName
author_rank: Super Contributor
timestamp: April 23, 2023, 09:58:51 pm
content: QuoteDifferent markets. Maybe the RC crowd are a bit like audiophools

author: CobaltBlue
author_rank: Newbie
timestamp: April 25, 2023, 03:40:24 am
content: NY2KWWhat your looking for in your situation is a LiFePO4 (LFP) battery with a BMS (Battery Monitoring System), a basic BMS at least will provide cell balancing as well as protecting the battery/cells from Overcharge & Over-discharge. When fully charged and cells balanced the BMS will draw next to no current, a battery just sitting with a BMS connected will basically have the same standby life as a battery without a BMS connected.There are times (less common today as cheap BMSs are about the same cost) where LFP batteries are fitted with just a cell balancer in place of a BMS, there is a bit of a gamble here in that cell balancer can keep up and maintain balance, which in some cases it wouldn't be able to and the battery being killed early due to overcharge or over-discharge on one or more cells. They are also relying 100% on the charge being terminated at the correct voltage without any overshoot and the user not drawing the battery down into unhealthy levels.The RC batteries you looked at with the extra leads are to be connected to an external BMS or cell balancer as you have noted. Any LFP pack with just a +ve and -ve output and not having a BMS or cell balancer would be junk, its lifespan would be rather shorter than expected as there is no way to see/check/stop cell drift, once one or more of the cells are out of balance they will be overcharge or over-discharged while the battery is charged or used in its normal charge range.So LFP with BMS would have about the same capacity and lifespan as a LFP with a cell balancer that had vigilant monitoring by an organic BMS (a person) to ensure no overcharge or over-discharge. It would have less capacity but longer lifespan than a LFP with a cell balancer that had allowed to overcharge or over-discharge regularly. And not worth comparing to no BMS or cell-balancer.Most if not all of the LFP batteries in the SLA battery cases will have at least a basic BMS in them, which sounds good for what you want to do. If you need to go for the heat shrink wrapped packs check the details for any mention of a BMS.In regards to the other conversation about how packs without cell wires can be cheaper than packs with, make a comparison between figures like maximum discharge rate. Very likely high discharge cells went into the RC packs and lower rate (less expensive cells) went into the others, also from memory it now costs around US$2 or less to have a basic low power BMS fitted during battery manufacture in China, economies of scale have brought the prices right down for BMSs.

author: NY2KW
author_rank: Regular Contributor
timestamp: April 25, 2023, 01:29:35 pm
content: Outstanding information and many thanks !Jerry