Hi, I understand that my solar controller should be connected to the battery before the solar panels
I’m concerned that my battery will run low during the night and the BMS will shut it down while the solar controller is still connected to the panels. In the morning the solar panels will start to generate but the controller will be disconnected from the battery.
Is there a way that I can safely leave the controller connected to the panels when the battery is shut down?
There is no need. They are designed to black start the battery.
So they power on from solar and wake up the battery (as many batteries to switch them back on from a low battery cut off the operation is to conect a charger)
As an addition though, you should have at least a dc breaker on the panel side for maintenance/repair reasons so you can safely disconnect live things while working there.
The reason for the connect to battery first sequence on initial install is so that the battery voltage can autodetect correctly and it will be immediately obvious and recoverable if you reverse polarity connect the battery. Once the system programmed up and running it will not be a concern
Thanks for your reply. The solar charger is on a boat, mainly dedicated to keeping the LiFePo4 house battery charged. There may be a case where the SLA start battery needs emergency charging so I have a procedure for connecting the solar controller output to this battery and changing the battery in the settings in the controller. I assume that the charger will program itself again whenever I change the battery type setting. Please confirm.
TIA
Ian
I actually overheard a “technician” at my local distributor tell a retail customer that if you hooked up the solar without battery first the MPPT would start on fire. Now that guy needs some more training or shouldn’t be at the front desk.
The charger will not “program itself”. That is not what “auto detect” means. You will need to change the charging parameters each time for different battery chemistry.
It only auto detects voltage the first time.
And yes change the battery profile if you are switching battery types and chemistry. That is why you can either choose from a preset or create your own custom ones.
Well. I do know of one person who started a fire connecting an mppt solar only first… (Disclaimer-It was not a victron mppt.) There are people who have made a fire on connect a reality connecting live is bad idea.
Not everyone is in the same place in their learning and experience. We all started nowhere and are going somewhere… I too have had bad intel and learning and shared it along the way. Mine for example was learning that the battery and pv negative are not isolated after telling someone who was stuck in the middle of nowhere they couldn’t put the pv negative in with the battery negative as a stop gap unitl they got back into town. 
i kicked my own behind hard and apologised to the client.
I do know about the black start as i have seen it work use it i offgrid designs and set ups. And also the power supply as an option.
… presumably the first time after each battery type change in the controller settings
I am curious about this.
So you are saying that once a Victron MPPT is configured with the battery, even if the battery dies, the MPPT will potentially recharge it even without battery voltage to power the MPPT?
No just the very first time it is ever connected. After that it is a second and thrid time.. there can onky ver be one first time.
The mppt can power on from the PV side first.
So the MPPT logic will power up if PV voltage is sufficient regardless of the battery voltage? I do understand that the PV voltage needs to be 5V over the battery voltage to start charging.
With the battery bms off what is the battery voltage? There is also the programmed voltage as reference.
Usually a person will have panelled sufficiently for it to be above the battery voltage when it is present.
Charging yes as tou need potential to raise the voltage.
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