I have a system with SmartSolar MPPT 100/50, Multiplus 12V/800W/35A-16A and a 100a LiFePO4 battery with built in BMS. The battery voltage meter on the battery BMS and SmartSolar have the same value witch is also true to a multimeter. The Multiplus on the other hand is way of and the result of that is that its not charging full and have a wrong float value.
Multiplus is set to the recommended float and absorption, tried battery monitor on and of.
Any thoughts?
Have you checked the Multiplus voltage with your multimeter to confirm if the Multiplus is reading correctly or not.
Without the cross check noted above, the most likely cause is a high resistance connection on the Multiplus positive or negative cables or any components on there such as fuses or isolators. Check each cable connection is crimped onto the cable really tight and that each terminal is bolted up tight. Use you multimeter to try and determine which connection is to blame by measuring the voltage at each connection or each side of fuses or isolators.
The types of isolators/ breakers shown below ate often responsible for large voltage drops.
