I've been struggling with designing a battery charging / protection into my application. I don't want to start from scratch, so I'm going with pre-made BMS boards.

Initially I wanted to power this from USB (5V), but none of the USB-powered charger-boards with on-board boosters had any kind of discharge protection. So I settled on using a regular BMS board that needs about 8.4V DC input, at about 2 amps.

Finding a plain AC adapter that puts out 8.4 Volts seems impossible, they all seem to have charger circuits built in, which is likely going to interfere with the BMS I'm adding to the pack.

My current train of thought is to use a 9V DC adapter and put a silicon diode and a schottky diode in series with the DC coming from the adapter, this should get me between 8 to 8.2 V DC.

Does that seem legit, or am I missing something?

 

You are definitely missing something.
What is your application?

 

You are definitely missing something.
What is your application?

Can't go into much detail, but basically it's a battery powered circuit that draws between 15mA in idle state, up to 2.5 A peak, at 5V DC.

I have the choice of:
- powering this by a single 3.7V cell (18650) with a boost converter to get 5V

or

- 2 x 3.7 in series for 7.4V, then use a linear regulator to get 5V

I have been unable to find a battery management system (in the $4 or less) price range that will do ALL of the following:

(a) Work of a single 5V supply for charging
(b) Provide charge-protection (overcurrent, overvoltage)
(c) Provide discharge-protection (overcurrent, short, undervoltage)

I did find some modules that claim to do all of the above, with a 5V output, but they don't provide 2.5A and they also briefly cut the output when the 5V charge supply is turned on.

I really want to be able to charge this from an external 5V supply (like any old USB power brick), so the current thinking is to combine a BMS that satisfies (b) and (c), and supply it with the required 8.4V by using a 5V boost converter that is internal to the appliance but not part of the BMS. It just boggles my mind that there isn't a ready-made solution for this.