Feed Li-Ion BMS from MPPT or PWM (or not at all :-)

Abogado

My questions concern a 7s-24V Li-Ion battery system for different off-grid purposes. The system comes with a BMS that can draw or deliver 60A.

Regular charging of the system would be done through a power supply (BMS takes between 15V-60V).

My question is whether an MPPT or PWM charger could deliver the required input for the BMS (no worries mike95490 - not yet bought one ;-)

My current thoughts:

-- the charger will need to have a setting that 'disables' charging algorithims in order to deliver stable output ('load always on')

-- the BMS will then receive from the charger whatever voltage it is set to

-- setting the charger to 24V for the 29.4V rated system, to be converted to charge 7 packs of each 6 cells up to max 4.2V each should be no issue

-- I understand that an MPPT needs power for its CPU from the battery it is charging. This could be an issue, considering the BMS as a 'one way street' for the power fed into it. There may be a way around, if the BMS out-port can feed back into the MPPT or the MPPT can be fed some other way

-- My main concern would be the 'variable' power output from the charger. The voltage will likely be kept constant, meaning that the BMS gets to deal with a fluctuating current. Would there be a way to prevent or minimise this - if the BMS is not engineered to handle variable current input (separate question: outstanding with supplier).

-- Some other factors may come into play in the interaction between BMS and charger, that I have not thought of.

Many thanks for your thoughts (as well as for other great answers re: Li-ion - glad to have found this forum)

Ben
Amsterdam NL

Estragon

I think a controller needs battery voltage to boot up, but once booted most (all?) should be happy running on solar input. A pwm controller may also need battery voltage to boot.