Author Topic: Li-Ion pack parallel charging with adjustable current and BMS  (Read 637 times)

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Offline No_ShortyTopic starter

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Hey, so I'm just thinking through if the following is possible, and what I would need to achieve it:

If I have 2 or more 14s9p Li-Ion packs capable of 15A charge and I have one charger capable of supplying charge voltage at 30A - is it possible to switch the charger to supply 30A and 'split' this between the packs? This is with both back having their own individual BMS.

The charger has adjustable CC and CV, so when charging one battery it would be set up to charge at the 15A, but I was hoping I would be able to achieve the same charge time when connecting an additional pack.

« Last Edit: June 20, 2020, 05:03:42 pm by No_Shorty »
 

Online Siwastaja

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Re: Li-Ion pack parallel charging with adjustable current and BMS
« Reply #1 on: June 20, 2020, 07:15:16 pm »
Charger by definition is active circuit that controls current. So while it's possible to do just that, it means designing and building two such circuits; i.e., two "chargers". Guesstimating from your question, you are likely after a simple solution, which does not exist; easiest is to either charge in parallel in a dumb way (see below), or buy two completely separate chargers.

Note that you can just parallel the packs and work with the single charger, but only after you have charged or discharged the packs separately to the same state-of-charge so that their voltages match closely. Be very careful here; a large voltage mismatch causes massive currents during the time of making the parallel connection, exceeding the current ratings (especially the max charge current rating of the pack which happened to be at lower voltage). Paralleling packs is hence impractical when you need to separate them again for discharge. Semi-permanent paralleling is manageable.

Even with permanent parallel connection of series packs, each should have their own cell-level BMS; paralleling every balance tap as well (measuring the voltages match beforehand, again!) gets rid of this requirement.
« Last Edit: June 20, 2020, 07:17:09 pm by Siwastaja »
 

Offline No_ShortyTopic starter

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Re: Li-Ion pack parallel charging with adjustable current and BMS
« Reply #2 on: June 21, 2020, 10:31:05 am »
 I thought that would be the basic answer.

The batteries would be drained individually, so the SoC would be different and not managed outsode of their internal BMS.

So essentially you need to either build two circuits after the charger each managing the CC, or as you say just buy two chargers.

The question really arose as it looked like I was going to have to buy a much more powerful CC PSU than I wanted for a single battery charge, but I have since realised one of lower spec would be suitable, and buying two the much easier option!
 


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