Rookie question perhaps, but I currently use a SmartSolar 100/30 charger to connect my 520W Smart panels to my 24V lead-acid starter batteries, which also feeds an Orion 24V/12V dc-dc charger for my 12V domestic batteries. Both battery sets are also fed directly by conventional 24V and 12V alternators.
I’m changing the 12V batteries to Lithium - is it good idea to use an XS between the 12V alternator and lithium battery, while the Orion is still connected to it? Is there a problem with the two units fighting (eg not recognising engine shutdown)?
I don’t really want to have to manually switch between engine and solar charging.
Please take note that an Orion is a battery to battery chargers, not an alternator to battery chargers, you will still need to have a 12V lead acid buffer battery on the 12V alternator output. This serves 2 purposes, the first is the Orion control is erratic if there is not battery, the battery lamps the voltage response (buffers it). People who have tried without a buffer battery report wild voltage cycling. Secondly, if the lithium battery BMS stops charging while the alternator is running hard ( load dump), the alternator output voltage can spike badly damaging the alternator and other equipment. With a 12V lead acid buffer battery the voltage spikes is absorbed and kept to acceptable levels.
As long as you keep a 12V lead acid buffer battery then there is no issue charging the lithium batteries simultaneously with an Orion from the 24V battery and an Orion XS from the new 12V battery. Engine shutdown detection works on the input voltage so the two Orions will not fight as they have separate source batteries. As the lithium battery gets full, one of the Orions will tend to reduce charging first, but absorption time is short on lithium so this should not be an issue.
So - to clarify - 12V Lucas alternator to lead acid battery to XS B2B to LiFePO4 battery, with the 24V-12V Orion (fed from 520W solar panels via an MPPT controller) feeding the LiFePO4 in parallel with the XS? Any guidance on settings for both Victron units? On workdays the engine is running 6-8 hours a day - should I have different Summer/Winter or workday/weekend settings to allow for more/less solar/alternator contribution ?
You should use the default lithium setting to start from, but check that the settings are compatible with your batteries and if not edit the settings. You need to make sure that you only have a short absorption period and then go to float at 13.5V which will hold the batteries at just under 100%. Hopefully you have got Bluetooth enabled batteries do you can make sure the cells stay in balance and are getting enough absorption time for balancing. You must not allow them to sit at 14.0V or more for long periods. 10 or 20 minutes is enough if they are in balance, longer only if they need balancing from time to time.