0
\$\begingroup\$

I am installing a large LiFePO4 battery system in my RV. I have four server rack mount 48 V, 100 Ah batteries (EG4-LifePower4). I would like to have two on each side of the RV for weight distribution. Is it OK to make 2 banks of 2 with about 3 feet between the pairs (connected in parallel)?

\$\endgroup\$
1
  • \$\begingroup\$ Which pair would you wire the load circuits to? Or, maybe you have a different plan? \$\endgroup\$
    – Andy aka
    Dec 28, 2022 at 20:23

1 Answer 1

1
\$\begingroup\$

The distance is fine. The parallel connection is not. These batteries have a built-in BMS that can turn off the battery at any time it needs to do so to protect the cells. If one battery is off and a second one in parallel with it is still on, the state of charge of the second one will change under use. Later, when the first battery comes back on, there will be a damaging inrush of current from the most charged battery to the least charged one. That's bad for the cells and bad for the BMS. So, do not connect Li-ion batteries in parallel.

The only safe way to increase capacity of a Li-ion battery is to connect cells directly and permanently in parallel.

\$\endgroup\$
5
  • \$\begingroup\$ Why is the parallel connection not ok? \$\endgroup\$
    – floppydisk
    Dec 28, 2022 at 21:41
  • \$\begingroup\$ Makes no sense at all, they cell preconfigured racks of 3 and 6 parallel connected using a bus bar \$\endgroup\$
    – mark1234
    Dec 29, 2022 at 13:19
  • \$\begingroup\$ @mark1234 Just because the issue is not clear to you, or this is not the answer you want to hear, is not a good reason for you to down-vote an instructive answer. Rather, I suggest you may want to read-up on the subject. There is a difference between Li-ion cells directly in parallel (good) and protected Li-ion batteries in parallel (usually bad). Batteries controlled by a central master can be made safe. But your batteries are "dumb" (no offense) and can't protect themselves from this event. \$\endgroup\$ Dec 29, 2022 at 13:24
  • 1
    \$\begingroup\$ @DavideAndrea I didn’t downvote because it’s not what I want to hear. look at their web site, they sell them interconnected. So who’s right, you or the company that makes them? \$\endgroup\$
    – mark1234
    Dec 30, 2022 at 11:01
  • \$\begingroup\$ The cells are somewhat damaged each time a BMS turns back on if the SoC of the two batteries is different. There are two possibilities: 1) that manufacturers doesn't understand that or 2) that manufacturer does understand that but hopes that the user doesn't complain when the batteries do not perform as well after some time. There are techniques to avoid the damage, but they require expensive electronics, and such battery manufacturers do not implement them. \$\endgroup\$ Dec 30, 2022 at 14:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.