One thing to note in this discussion about ACR's and Isolators is that the ACR is only a good choice for FLA batteries. It closes at 13.3v and opens at 12.8v. This means that it will open shortly after the charging current is removed.
It is a very bad choice for LFP batteries because they are almost flat dead when the voltage drops to 12.8v. I have pulled 400Ah out of my 560Ah pack and it was still significantly above 13v. It will in effect be permanently in parallel with my AGM start battery.
I am currently still using my diode-based isolator with voltage sense from the AGM start battery which works fine but will upgrade to a FET based isolator.
Both my AGM and my LFP are charged with an absorption voltage of 14.2v so connecting for charging is fine. The other advantage of the isolator is that it works as a one-way valve. When the isolator is closed, it will allow current to flow from the alternator to both of the batteries, but it does not allow current to flow FROM either battery to the others. This is important for LFP. Let's say that my LFP is near full at 13.2v and the start is near empty at 11.5v. With an ACR relay the current can flow both ways so once the charge current trips it at 13.3v it will dump huge current easily 200A+) from the LFP to the AGM which would be a very bad thing.
It is a very bad choice for LFP batteries because they are almost flat dead when the voltage drops to 12.8v. I have pulled 400Ah out of my 560Ah pack and it was still significantly above 13v. It will in effect be permanently in parallel with my AGM start battery.
I am currently still using my diode-based isolator with voltage sense from the AGM start battery which works fine but will upgrade to a FET based isolator.
Both my AGM and my LFP are charged with an absorption voltage of 14.2v so connecting for charging is fine. The other advantage of the isolator is that it works as a one-way valve. When the isolator is closed, it will allow current to flow from the alternator to both of the batteries, but it does not allow current to flow FROM either battery to the others. This is important for LFP. Let's say that my LFP is near full at 13.2v and the start is near empty at 11.5v. With an ACR relay the current can flow both ways so once the charge current trips it at 13.3v it will dump huge current easily 200A+) from the LFP to the AGM which would be a very bad thing.
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