Cheap and multifunctional Li-Ion battery protection idea

too bad - would be realy nice to have such a relais. car relais are just for 12V systems - not 48V systems (i dont like it to use stuff outside there tolerances)

but hey - plese finish your project and give us some feedback!

@Hummie

You probably donā€™t use something like this:

Even the cells in parallel can have slighly different capacity so they may not discharge/charge equally. But the truth is that they will - because they are all almost the same capacity.

@fuelre

In the datasheet for the car relay: Switched voltage max 75V DC Doesnā€™t that means itā€™s capable of switching 75V?

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nice - i didnt know that

Yeah, but itā€™s still made for 12V even it can handle 75V. The question is lifespan.

Off topic: itā€™s late there in central Europe ( 22:45 ). Iā€™m going to sleep, I have to wake up early, will reply tomorrow.

i have a charger just like that from meanwell. the little screwdriver slot is the same in the picture and it adjusts the voltage. i think parallel cells may not have the same capacity but a low capacity cell in parallel will hit the high voltage faster ā€¦the whole paralllel pack will have less capacity but no cell will individually go above or below the pack as a whole and itā€™s safe that wasy

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Please add this. I dont plan on using a vesc.

I definitely will :slight_smile:

I have improved the design ( thanks to everyone for your feedback ), noticable changes:

  • added 12V rail, used for switching the relay, but can also be used as a power supply for your LED strips or other lights / devices that require 12V to operate ( max. 3A ).
  • added MOSFET which will handle switching the relay ( 5V pin of the uC goes to the gate ).
  • added MOSFET which will switch the 12V rail ON or OFF ( only need 5V for uC when device is off )
  • added flyback diode ( thanks @fuelre ).

Will draw the new schematic for you once I have enough time to do so. Believe it or not, hand-drawing the schematic can take quite a long time if you want it to look nice.

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Hi, bad news. As I have changed my mind and I will go with LiPo for my project, this project is now discontinued. But for you, who were interested, I drew the last schematic:

Current design is capable of handling up to 50V ( 12S ). Actually, the regulators can handle up to 60V as well as relay can, but the voltage divider is 10:1, so that would result into 6V on the ADC pin of the ATTiny and thatā€™s not good. However, if you want, you can use different ratio on the voltage divider and increse the limit to 60V max.

Also, there is an 12V 2.5A output which is only active only when the output is switched on, you can use this for your lights or anything that requires 12V.

5V rail is always active as it powers the microcontroller which is in standby mode until it receives the signal from the power switch which will wake it up, it will switch on the display ( in SW ), enable 12V rail and switch on the relay.

There is also a small push button that can be used to switch between different modes ( voltage / percentage ). Small 3mm led ( D6 ) can be used as an indicator of something ( errors and so on ).

Firmware can be easily updated using the AVR ISP programming header.

There are probably quite a few things you can do better than I did, so feel free to make any changes to the current design, would be nice if you share it with us, but you donā€™t have to ( MIT license ).

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