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I was planning to use two 18650 protected batteries (each comes with its own internal protection circuit against overcurrent, overcharge and undercharge) to power a load of 5 V, 4 A. Their maximum discharge current is 8 A. I know the battery duration won't be very long at that current, but that's fine for me.

Powering the load in itself wouldn't really be a problem; I just have to make sure the two batteries are charged equally and connect them to the load.

My issue is finding a good charging/powering solution that would be integrated in the device, allow me to charge batteries at 1 A each (so 2 A in total,) and still have 5 V, 4 A out.

Here is what I gathered so far:

  • The typical TP4056 (and other cheap charging circuit solutions) can only handle 1 A out, so it won't work for my solution.
  • BMS boards seem like a good way to protect the batteries, but since the batteries already have that kind of protection integrated, is that even useful for a parallel setup?
  • For efficiency purpose, I heard that it's easier to put the batteries in series with a BMS instead of parallel and use a buck converter to lower the voltage. Would that still work with the batteries integrated circuit?
  • Some people are saying that for protected batteries, or using a BMS, it would actually work connecting them directly to a 5 V PSU and the load. While it might work, it doesn't sound like a safe solution, does it?
  • There seems to be power delivery compatible circuits out there made for various devices that would work well for my case too, but I can't find any ready-to-use circuit nor guide or anything.
  • Repurposing a 18650-based power bank is another popular solution, but I couldn't find any that can supply 4 A.
  • Is there any readily available charging/regulator circuit that would match my needs?
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  • \$\begingroup\$ Welcome! I would prefer 2P configuration in order to not have to bother about balance charging. Regarding 4 A not available, most offerings have 2 A USB-A in mind but there is nothing stopping you from bucking or boosting to 5 V and 4 A. Do you plan to use USB-A outputs or something completely different? \$\endgroup\$
    – winny
    Commented Mar 21, 2023 at 9:35
  • \$\begingroup\$ Thanks for the answer. Yeah I plan to power 2 usb devices that each take a bit less than 2A. Afaik we can boost voltage but current is only relative to what the charger can provide, and since most charging circuits are limited to 1 or 2A, I can't find what I need sadly. \$\endgroup\$
    – Stremon
    Commented Mar 21, 2023 at 14:41
  • \$\begingroup\$ That’s because of the USB-A limitation. You need to provide a 2 A handshake for each output. 4 A isn’t allowed over USB-A. \$\endgroup\$
    – winny
    Commented Mar 21, 2023 at 14:43
  • \$\begingroup\$ I am not talking about PC USB here, there is no data, only power. USB chargers can go way over what standard USB-A do. Same with externally powered USB HUB. \$\endgroup\$
    – Stremon
    Commented Mar 21, 2023 at 14:54
  • \$\begingroup\$ Does not matter. You still need power negotiation per port. \$\endgroup\$
    – winny
    Commented Mar 21, 2023 at 15:18

1 Answer 1

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Would this solve your problem?

schematic

simulate this circuit – Schematic created using CircuitLab

TI Webench list 16 different devices which can all do 3-4.2 V to 5 V at 4 A. Here is one of them: enter image description here

Over at Analog.com, you have the LTM4661 all-in-one solution with inductor baked into the IC. On the non-integrated side of things, they list 66 parts which meets your criteria. How about the LTC3124?

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  • \$\begingroup\$ Thanks. I already tried that, but this method as a few issues; 1. doing the drop down then boost for the incoming usb power isn't great when wanting to get enough power to charge and use the device at the same time. (I solved it by doing a bypass of the converters, to directly power both when connected) \$\endgroup\$
    – Stremon
    Commented Mar 29, 2023 at 3:28
  • \$\begingroup\$ 2. I am using 5V 4A, and all of the boost circuits readily available (even the ones that say they can provide as much) just don't work or badly overheat, which is one of the points of my question. 3. using buck then boost (and a BMS obviously) doesn't give you any info on the battery level, this requires specific charging chipset, which, again, either don't support 4A or aren't really easy to source. \$\endgroup\$
    – Stremon
    Commented Mar 29, 2023 at 3:29
  • \$\begingroup\$ @Stremon 1. If your USB power negotiation does not give you 4+ A on the input, you won't have 5 V 4 A on the output without taking energy from the battery. 2. Plenty of circuits which can do 5 V 4 A out. I'll update my question with some. 3. Sure it does, just measure the battery voltage and calculate SOC. \$\endgroup\$
    – winny
    Commented Mar 29, 2023 at 6:42
  • \$\begingroup\$ 1. what you said has nothing to do with what I said. Again, a solution that doesn't power the device in parallel of the battery when plugged in, and has make all power go through the drop down THEN the boost, is pretty silly. 2. I said readily available circuits. your exemples are just IC which I have to make my own circuit with, and hoping I don't fuck it up and blow something. 3. There too, as I said, it needs an extra battery management circuit that measure it, and that might not work with my circuit. Thanks for trying to help, but no need to waste your time here if there is no solution. \$\endgroup\$
    – Stremon
    Commented Apr 2, 2023 at 9:28
  • \$\begingroup\$ Then you need to refine your question that you need an already purpose made module, which most probably does not exist on the market so the answer is no. Buck and boost ICs are readily available, which is what EEs use to design circuits. If you are looking for a product, that’s off topic here. \$\endgroup\$
    – winny
    Commented Apr 2, 2023 at 11:33

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