I'm a hobbyist, so my electrical engineering skills are not top notch.
I'm service tech and I'm working on modifying portable coolers (thermoelectric and compressor based) where we add batteries to said coolers to make them work without being connected with cables.
Currently we are making our own battery packs, and our problem is charging the batteries safely. At the moment we are using these cheap - around 5$ per piece "XL4016 300W step-down CC/CV converters"
that are quite bad in terms of efficency (80%) and power usage when running on battery (the battery self discharges in a week when connected to the DC-DC converter by it's own - 133 Wh), so I'm willing to spend a lot more for high quality.
I'd like to design my own battery charger / step-down converter that is more efficent, and doesn't discharge the battery when unpluged.
Current system looks like this:
My biggest hurdle is searching for appropriate DC-DC controller or dedicated 3S battery charger IC that has all the features that I'd like to have. Most of DC-DC controllers and battery ICs don't have proper parameters on LCSC, so searching for one is complicated. Finding coils, caps, FETs shouldn't be an issue.
My design criteria are:
BOM price: around 20$ - 30$ from LCSC at ~20 pcs pricing (for assembly from JLCPCB)
Low power draw when disconnected from power supply.
Input voltage: 13 V - 36 V (up to 24 V for charging from battery in truck, so 33 V max nominal)
Output voltage for battery charging: 12.6 V (3S Li-Ion configuration)
Optional output voltage: 12 V (would like to add additional optional step-up converter to have stable 12V - 13V output, as some compressor coolers have integrated low voltage detection, so the batteries are not fully discharged, thus needing additional step-up converter to get the most juice from battery)
Output current: 0A - 6 A / 0A - 12 A, selectable either via potentiometer or jumpers (could incorporate 2 different versions, as we usually need 70 watts of power max, but for some coolers 100 watts is needed. Not sure how to design this kind of different versions; additional MOSFETs/diodes/etc?)
Reverse voltage protection
Super optional: coulomb counter / gas/fuel gauge with display; while looking for said chips they are super expensive. But customers are often confused when they plug in the charger and it's showing 100% SOC when in reality it's 80% (CV charging mode)
Is there a chance that my project could be made, any tips?
