BMS blew, wondering why

[photonelectronconverter]

Hi,
I have just started to get into electronics (doing some online courses) and I am finding it slow going. As a side project I bought a small 3S BMS from eBay. I have put together some lithium 18650 batteries and I was looking to make a mini UPS for some network gear. Anyway, once I wired it up and plugged in a 2A 12V supply the board (and the power supply) blew. The power supply popped and fizzed a lot with some smoke. The board blew the part circled in the attached photo. The polarity is correct.

As I am still learning I am looking to see if anyone might let me know what the circled part is and what may have caused the outcome. As you might notice, this is the first thing I've ever soldered but I am pretty sure there is no short at that side. The solder actually looks worse in the photo as the flux shows up more brownish.

thanks!

 

[Nigel Goodwin]

You don't connect a power supply to it, you connect a suitable 3S charger - so you may have killed it using by a PSU.

 

[photonelectronconverter]

You don't connect a power supply to it, you connect a suitable 3S charger - so you may have killed it using by a PSU.

Thanks for the reply.
The docs said it was suitable for 12.0-13.8 input voltage. I thought that would make the 2A 12V PSU good, no?

 

[Nigel Goodwin]

Thanks for the reply.
The docs said it was suitable for 12.0-13.8 input voltage. I thought that would make the 2A 12V PSU good, no?

You don't charge Li-Ion just from a PSU, you need a proper charging circuit.

 

[photonelectronconverter]

OK. I don't really understand what you're saying.
The charging profile for Li-ion is pretty standard (**broken link removed**). The BMS has over voltage, under under votage, short protection etc. Can you explain what you mean, technically, about a proper charging unit? Surely if the BMS is managing and balancing the voltage/current the input type is irrelevant? That is, if the PSU can mange the correct power the BMS should regulate/balance and cutoff the charge to the cells as required?

 

[Nigel Goodwin]

OK. I don't really understand what you're saying.
The charging profile for Li-ion is pretty standard (**broken link removed**). The BMS has over voltage, under under votage, short protection etc. Can you explain what you mean, technically, about a proper charging unit? Surely if the BMS is managing and balancing the voltage/current the input type is irrelevant? That is, if the PSU can mange the correct power the BMS should regulate/balance and cutoff the charge to the cells as required?

A BMS isn't a charger - and it expects to be fed from one - the BMS is only there to protect the batteries, and mostly to prevent them catching fire.

 

[rjenkinsgb]

Surely if the BMS is managing and balancing the voltage/current the input type is irrelevant?

It "manages" only by hard switching certain connections on or off. They do not have voltage or current _regulation_
That part of the system is the responsibility of the charger.

The charger needs precise voltage regulation and current limiting, so it does not give excess current when the battery voltage is lower than the charger voltage.

If you connect a normal PSU set to the full charge voltage, to a flat high-current capable battery, the initial current will be whatever the PSU limits at.