Hi all,
I am installing an ARCO Zeus A225s smart alternator regulator on a sailing vessel. The battery bank is a 12V LiFePO4 pack (3P4S, 840Ah, EVE LF280K cells) managed by a REC Active BMS v2.94.
The Zeus has an ATC (Allow To Charge) input, which I have connected to the REC BMS charge optocoupler output (pin 14, OPTO CH C). The idea is that the BMS signals the Zeus to stop charging before the MAIN relay opens, protecting the alternator against load dump.
However, I cannot find documentation that confirms this actually works as intended, and I have a specific concern:
According to the REC ABMS 2.9.4 manual (page 32), errors are confirmed after 3 measurement cycles × 1.25s = 3.75s, after which the MAIN relay opens. What I cannot find is whether the charge optocoupler (pin 14) opens at the same moment as the MAIN relay, or whether it opens earlier — giving the Zeus time to ramp down before the battery is disconnected.
If they switch simultaneously, the Zeus has no advance warning and load dump protection is not guaranteed.
For comparison: the Victron Lynx Smart BMS explicitly supports this with a dedicated "Alternator ATC" relay mode (configurable in VictronConnect), which is documented to disconnect the ATC signal 2 seconds before the contactor opens. This gives the alternator regulator a guaranteed window to shut down safely.
My questions:
1. Does the REC Active BMS charge optocoupler (pin 14) open before the MAIN relay? If so, by how much?
2. If they open simultaneously, is the ATC connection actually sufficient for load dump protection, or is an additional measure needed?
3. Has anyone successfully used the REC Active BMS with the ARCO Zeus (or similar smart alternator regulator) and can confirm the load dump protection works in practice?
Thanks in advance!
