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Design a Battery OR-ing system

Abed Meguenni
Prodigy 60 points
Other Parts Discussed in Thread: LM74700-Q1, LM74700DDFEVM, UCC39002

Hi,

I want to realize a passive battery monitoring module (BMM). Two battery will be connected to this BMM and it will have one output. Both battery should discharge at same time (it means that if a battery have an higher voltage it should discharge first until it has the same voltage of the second one) it can be compared to a OR function. The BMM should be able to handle a voltage up to 48V and a current of discharge of 40A.  Moroever the system should be reversible, it means that we must be able to charge the battery with the same connector (the charge current is about 10A).

From what i have seen, an Or-ing controller (with smart diode) should work. But can i built them into head-to-tail to be able to charge and discharge ?

What do you think of using smart diode ? And can you provide me some component (with their evaluation board if possible) that could fit my requirement ?

Regards,

Abed

  • 0
    TI__Guru 57737 points

    Hi Abed,

    Thanks for reaching out to us.

    To achieve ORing functionality while the batteries power the load,  you can consider using LM74700-Q1 controller + FETs  in the configuration as shown below. The key aspect of ORing function is reverse current blocking. Therefore, the charging path of the batteries needs to be a different  from the discharge path. 

    Can you share the block diagramof the power path of battery monitoring module. This will help us in understanding the system better and pitch in the right parts to you. 

  • 0 in reply to Praveen GD
    Prodigy 60 points

    Hi Praveen,

    First thanks to respond this quick ! 

    Can you share the block diagramof the power path of battery monitoring module 

    As you can see it's a passive BMM that should be able to handle 2 battery for a load but it should also be able to charge the battery. (If possible with the same port)

    Can i make two OR-ing path ? One for the battery to load and the other in reverse to be able to charge again the battery ? (I just draw for Vin1 but it also applicable for Vin2)

    About the LM74100-Q1 i was considering it with the EVM LM74700DDFEVM. So i should take 2 EVM and change some component (like the FET) to fit my requirement. 

    Moreover could it be possible that i need to add a current sharing controller ? (like the UCC39002)

    Regards,

    Abed

  • 0 in reply to Abed Meguenni
    TI__Guru 57737 points

    Hi Abed,

    In the implementation that you have shown below, the reverse current blocking functionality of the ORing - LM74700-Q1 would be compromised. This is because the body diode of the FET driven by the anti-parallel LM74700-Q1 (to charge the battery) would allow current to flow through to it when the voltage at load is > battery voltage.

  • 0 in reply to Praveen GD
    Prodigy 60 points

    Hi Praveen,

    So it's seems "impossible" to do an ORing with same path for load and charge ? I should create 2 different ORing one for discharge only and the second for charge only ? About the charge path does it have the same parts as the "typical ORing application" or should i becarefull of something ?

    Regards,

    Abed

  • 0 in reply to Abed Meguenni
    TI__Guru 57737 points

    Hi Abed,

    May I know what batteries are you using ? The reason why I am asking this is to understand if you require any battery charging mechanism depending on the battery chemistry. 

  • 0 in reply to Praveen GD
    Prodigy 60 points

    Hi Praveen, 

    I'm going to use Li-ion battery.

    Regards,

    Abed

  • 0 in reply to Abed Meguenni
    TI__Guru 57737 points

    Hi Abed,

    I wanted to understand if you have a battery charger which can charge two batteries. If not, I can loop in our battery charging team to help you with choosing the right battery charger IC. 

    For the ORing circuit, as we discussed LM74700-Q1 in below configuration can be used to achieve ORing from 2 batteries to the load. 

  • 0 in reply to Praveen GD
    Prodigy 60 points

    Hi Praveen,

    About the charger, yes i have my own charger and it's capable to charge two batteries.

    About the ORing circuit i have a question : If the load reinject some current, for exemple if our load is a motor, it seems complicated to take back this current to charge our batterie but what should i do to avoid any damage on my OR-ing ?

    Regards,

    Abed

  • +1 in reply to Abed Meguenni
    TI__Guru 57737 points

    Hi Abed,

    When Motor load tries to inject some current back into the input (batteries) the LM74700-Q1 turns OFF the FETs and blocks reverse current. To allow reverse current flow to charge the batteries, you will have to disable the reverse current blocking feature. But, as you know this feature is key to achieve ORing functionality, we cannot disable this feature.