Attaching PV to SMBS40 Inbox

[Mike M]

Hello fellow Electrodacians. 

I have built a portable battery box based around the SMBS40 battery management system, which I acquired a number of years ago but only now am starting to use now that batteries are becoming inexpensive.  I posted a few pics of the unit, it's a 100AH 12V 1P4S LifePo4 config. You can see there are two binding posts that I use to attach 12V peripherals, the small ones are from the LOAD output on SMBS40, and the big ones are directly connected to the battery  +V through a 500uohms shunt.  My main application for this box is to power my 12V fridge for my car, I am doing that through the load output and it seems to be fine with it. I am currently using a bench supply with current limiting to charge the batteries through the PV input with the DFET turned off.    I would like to add solar panels on the car, the sbms manual has the panels direct-connected to PV but my research indicates that  a charge controller might be necessary if the PV is not perfectly matched to the 12V battery, is this true or am I mistaken? What panels should i use for this setup if I want say 200W of capacity?  Also, is it OK to run a battery charger through PV or the shunt with DFET turned on, or will this be confusing to the charger? I have  a LTC4015 based charger which as MPPT charge control but I think it will not like it if the load was present in parallel with the battery.

Thank you!
Mike

[Dacian Todea (electrodacus)]

Mike,

You can use the Load and charge at the same time with no problems. You can charge trough PV input or trough the external shunt but if you charge trough external shunt you will not be able to see the load current just the battery current. The SBMS40 has two internal current shunts one for PV input and one for BATT and with those two it can calculate the Load+ output current also and then is the external current trough witch the SBMS40 can measure current in both directions.

You can connect PV modules directly to PV+ on SBMS40 assuming PV modules  will be 30 to 36 cell. It will be easy to find 32, 33 or 36 cell modules rated around 200W or 2x 100W connected in parallel.

You can use an MPPT if you prefer but there will be no advantage when used with a matched PV modules.

The important thing is

1) never remove or insert the 10pin cell monitoring cable while anything is connected to PV+ input or Load+ on the SBMS40

2) do not install anything between the battery+ terminal and current shunt  (so no fuse or circuit breaker and those should be after the shunt).

I can't see the photos so I can not comment on that.