5S3P Series parallel reverse polarity protection ?

[Bka]

Hello guys.

We are working on a project and looking for someone who can draw/make us a circuit for this particular scenario.

I like to know if it's even possible, if so send me a quote please. If it is not, i like to hear your solution.

Can you build a circuit with reverse polarity protection on each cel in Series parallel connection using 18650 cells (5S3P ) ?

Thank you in advance.

 

[HarryA1]

Do you need reverse polarity protection only when in use?  As I take the batteries out of my camera to charge them.

Only when you are charging the batteries?

Or both?

 

[Bka]

Hi Harry.

The batteries use the same circuit for charging and discharging. Thinking about something between the main pcb and the batteries that prevents short circuit in case of swapped polarity  and cuts out the main feed to the pcb. This way both would be protected.

I need this connection because of balance charging.

Thank you 

 

[HarryA1]

See "PCB Protection Board For 18650 Li-ion Lithium Battery Cell "

https://www.ebay.com/itm/2S-3S-4S-6S-BMS-PCB-Protection-Board-For-18650-Li-ion-Lithium-Battery-Cell-US/283479999258?ssPageName=STRK%3AMEBIDX%3AIT&var=584554774361&_trksid=p2057872.m2749.l2649

Also see "Build a 2S Li-ion Battery Pack with Protection"

https://www.youtube.com/watch?v=VwIYAiDlMz4

 

[Bka]

Hi Harry

Thank you for your suggestion.

I spent 48 hours on google learn about these components, and i came up with this please see below.

Do you think it is a viable setup? I know it is full of errors, however if the principal works it can be refined.

Circuit to prevent damage if batteries polarity swapped.

Any of  the fuses blown turns on the transistor then the LED and the same line switches the SSR that turns off MOSFET so that break the whole circuit. 

The diode placed above the MOSFET is for charging.

Load: 

• 21v
  
•  Average 5A-15A, Peak 20A
  

BOM

• Fuse SMT PTC - VDC 6V max, Hold 7A, Trip 14A, Max to trip 35A
  
• MOSFET Max 30V 50A
  
• Battery 3.7V 3A
  

Thanks for reading.

 

[HarryA1]

Are the leads from R13, R14, & R15 shorted by the interconnections between B10, B11, & B12 ? As the fuses interconnect them. I do not understand why, in say laptop batteries, the cells are interconnected that way. Perhaps for balance charging?

It is common practice to put a diode around each cell in reverse connection for protection.

 

[Bka]

I updated the circuit in the meantime. Changed the resistors to the right ones I hope. The batteries connected to each other the same way as  on my first post. That’s because of balance charging your right.

Diode would be an easy solution. I guess voltage loss would be significant as 0.6v loss per diode. 

Here, if you swap one shorted to it’s pair above or below. After the fuse blown there is only one way to go which is the transistor.

Correct me if I’m wrong. I rather go with the easy solution.

Here, the ssr relay (U2) is always on according to the datasheet. When it gets + to the pin 6, connects SB to drain.

 

[HarryA1]

Diode would be an easy solution. I guess voltage loss would be significant as 0.6v loss per diode. 

Yes, you would want the diode across the cell not in series thus they would only conduct on reversed voltage.

Your cells are connected in parallel due to the interconnectors thus I see no way to monitor the voltage of individual cells.