How to Power Up

 

 

 

Now I am still waiting for my PCB for the Battery Management System (BMS) so I still have plenty of other things to do. Like working on the problem of cold start the EV. All battery stacks will be self contained and disconnected from the main power rail. Each stack will have its own micro controller (uC) that will measure the total voltage of the stack and control its current flow. The uC will also control the contactor. While the BMS itself will be connected to the individual cells, they can only be put to deep sleep. All the uC however shall be turned off when not operated. They will get their supply from a dedicated power net.

So if everything is off, how can we turn it on?

My solution will be a master battery, that will be hard wired to a mechanical switch. That switch, once pressed, releases current to the contactor of the master battery. This will power up the rest of the controller network and connect the other battery stacks to the power net.

The diagram below might help to visualise the logic: initial on logic

So far for theory, on to the prototype.

Below are the schematics and the first layout on the breadboard.

I picked the IRF 9610 because it can operate on the full stack voltage of 72V and I hope I will be able to find a contactor that will not draw more current that the MOSFET can supply.

latchingSwitch

 

If anyone has a tip on a suitable low power contactor that can sustain 1200A, please leave me a message.

The next step is to draw the layout for the analog part and the digital logic and then to demonstrate its behaviour.

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