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I have 2 pack x ~900 Wh (each consisting of 24s2p LG M50LT cells). I’m planning to buy 3rd pack - but dealer have only packs of Samsung 50E cells. Is it ok to connect them in parallel to increase total capacity? They are nearly the same capacity, but 50E cells have 500 cycles, M50LT have 1000 cycles. Also existing packs have nearly 30 cycles. Worth mention that each pack have its own BMS.

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  • \$\begingroup\$ What peak charge and discharge currents are we talking about? \$\endgroup\$
    – winny
    Mar 4, 2023 at 22:08
  • \$\begingroup\$ Well, they will power a 2kW nominal power motor, peak - idk, could be 6kW or more. Since batteries are 100V when charged, probably ~60-80A peak discharge. Peak charge could be something similar (a bit lower), as the motor uses battery as break. \$\endgroup\$
    – CappY
    Mar 5, 2023 at 6:37
  • \$\begingroup\$ LG M50LT has a max discharge of 1.5 C or 7.2 A so that’s not happening. \$\endgroup\$
    – winny
    Mar 5, 2023 at 8:43
  • \$\begingroup\$ What is not happening? \$\endgroup\$
    – CappY
    Mar 5, 2023 at 19:06
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    \$\begingroup\$ Section 2.9: cdn.shopify.com/s/files/1/0481/9678/0183/files/… \$\endgroup\$
    – winny
    Mar 6, 2023 at 8:05

2 Answers 2

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Not a good idea, any variation could create charging issues especially as a lifetime of the cells run down.

In addition to that the cells probably do not have the same internal resistance which could also create issues and hazards

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  • \$\begingroup\$ Even if each pack have its own BMS? \$\endgroup\$
    – CappY
    Mar 4, 2023 at 21:59
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NO.

The problem is that each battery has (doesn't it?) its own BMS. A BMS can turn off its battery to protect it, while the other one continues to operate. As soon as the first BMS turns back on, excessive current will flow from the higher voltage battery to the lower voltage battery, degrading it or even causing damage.

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  • \$\begingroup\$ Every pack have own BMS (currently have 2 packs = 2 BMS), but since they are nearly same capacity - it will not turn it off sooner? Only probably after 500 cycles (because Samsung 50E are rated at 500 cycles/80%, LGs are at 1000 cycles/80%) - but even if it turns it off - and then on - it will limit the charging at safe-levels, right (both ways, charging and discharging? That's what the BMS is for ? \$\endgroup\$
    – CappY
    Mar 6, 2023 at 18:25
  • \$\begingroup\$ "it will limit the charging at safe-levels". Yes. But a BMS cannot limit the current. When two batteries at different SoC levels are connected in parallel, excessive current will flow from the higher voltage battery to the lower voltage battery, degrading it or even causing damage. \$\endgroup\$ Mar 6, 2023 at 22:45

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