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I want to use a connector to charge the 4S Battery of my underwater robot. The connector is the 6 Pin hybrid Cobalt Series connectors from BlueTrail Engineering (https://www.bluetrailengineering.com/product-page/cobalt-series-bulkhead-connector).

This connector will provide +Batt and -Batt of the battery as well as the balance connectors of the battery used in this project (https://bluerobotics.com/store/comm-control-power/powersupplies-batteries/battery-li-4s-15-6ah/).

I would like to avoid having the battery tension available on connector's pins during survey (to avoid corrosion on pins, even if I have a watertight lid), but I want to be able to charge the battery (i.e. to have the battery connected to the charging connector) when I want to charge the robot.

To do so, I would like to use if possible the switch used to connect the battery to the circuit when the switch is pushed (through a Mosfet), and which could "connect" the battery to the Cobalt Connector when the switch is released. Here is the switch / Mosfet schematic used to let the battery current flow in the circuit, when the switch put the Mosfet grid to the mass.

enter image description here

I have two questions :

  • Is it possible to connect / disconnect the battery from the Cobalt Connector through an electronic circuit ?
  • Is it possible to use the general ON/OFF switch such as when the system is not powered, the battery can be charged through the port ?

Many thanks for your help

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  • \$\begingroup\$ Do you have any free pins in the connector? \$\endgroup\$
    – vir
    Commented Mar 15 at 22:26

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First:

Don't do that. The protector BMS needs to be always physically with the cells, not elsewhere. Connect the BMS permanently to the cells. Do not rely on a BMS that at times is connected to the cells and other time it is not. When the BMS is not connected to the cells is when you'll blow up your battery.

Second:

Instead of needing to press a switch, simply place an "ideal rectifier" circuit between the charging port and the protector BMS (permanently connected to the cells). That circuit will let power flow into the battery and prevent power from flowing out of the battery into the charging port. For an example of an ideal rectifier, see this Stack Exchange question.

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  • \$\begingroup\$ don't? why not? many power tools and laptops do do that. \$\endgroup\$
    – Jasen Слава Україні
    Commented Mar 16 at 0:05
  • \$\begingroup\$ "many power tools and laptops do do that". Yes. But they know what they're doing. I wouldn't be sure that OP does. Those tools have two protector BMSs: one in the charger and one in the tool. \$\endgroup\$
    – Davide Andrea
    Commented Mar 16 at 2:00
  • \$\begingroup\$ Thanks for the explanations. I planned to use a balance LIPO battery charger such as this one bluerobotics.com/store/comm-control-power/… which is in charge of balanced charging the battery. Is this possible to "chain BMS" (one in the charger, one connected to the battery), or should I only find a way to provide power from the charger to the BMS near the battery ? \$\endgroup\$
    – Teusner
    Commented Mar 16 at 9:14
  • \$\begingroup\$ "Use a balance [Li-ion] battery charger". Doing so is hardly necessary in most applications. A regular "bulk" charger will be just as effective for an underwater robot. Balance Li-ion chargers are considered in UAV applications because they can reduce the weight of the UAV. Weight is not a concern in your project. I suggest you should avoid the added complexity of using a balance Li-ion charger. \$\endgroup\$
    – Davide Andrea
    Commented Mar 16 at 12:36

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