My present project- like so many others uses a single lithium battery. I think that’s the common denominator to my post… you would think that lots of vendors would cater to this reality and offer a little micro-module that can output a useful voltage/current within the typical voltage range of that battery. I mean that’s thing #1, but following that same thought- its pretty typical to also want to charge that battery via standard 5v usb, right? Also, nothing out of the ordinary here. So we’ll want a BMS module. Why are these almost always two things and for the former, why is there literally a single compact module on amazon that can offer a regulated 3.3v output from a lithium battery? So that’s today’s “am I taking crazy pills?” state of mind. Maybe the answer is that some microcontrollers (like Xiao) have integrated BMS already so who cares? Maybe it’s some embarassingly obvious thing that I’m somehow missing, but today I just can’t. Its come up today because my present project doesn’t need a microcontroller, just LED’s (despite my posting on an arduino forum haha..)
Well yes one would think so. Combining a LiPo charger like a TP4056 combined with either a step-up to 5v or a step down to 3.3v would make the most sense. One would also like to add a circuit that allows for load sharing i would say. Maybe there is a market for such items, particularly for low current applications these things would not be hard to design or produce.
There are more things that somehow don't exist, though i would say there should be a market for them, like a rechargeable clip-on guitar tuner. But hey how can we decide what the Chinese produce.
Wanting, and being able to get are two different things.
Because Amazon sell crap at inflated prices.
One good supply of DC/DC converters is Pololu, but I have just checked them and the prices have gone through the roof, I don't know why. I would expect to pay about £18. for one. Not sure if they have shut down due to Trump Tariffs.
Any way check out respectable distributors like RS and Farnell you get a good specification and devices that actually work.
Stay away from a lot of eBay crap unless your current requirements are very modest and you are not trying to have a too high multiplier. Also look at Pimoroni and Adafruit for these.
I actually just found this ONE example of what I’m talking about. Viktor Sobetskiy gets it! Unfortunately it seems like its still essentially DIY (or get PCBway to make it for you). Also, its a bit bigger than I was hoping for my particular application, but lets have a round of applause for Viktor. Awfully generous to also post it all publicly to github.
It’s not just the boost-buck converters, it’s the integrated BMS that seems like a terribly obvious compliment to the circuit. Searching that at adafruit yields no results.
Maybe you're using the wrong search terms.
Adafruit has the "PowerBoost 1000"
Boost converters draw more current than they deliver, so generally speaking not what you want when on battery power. Most newer sensors also come in a 3.3volt-only version.
5volt power seems to be slowly disappearing.
Leo..
will that output 3.3v though? (or 3, even?). Seems like its boost only to 5vdc. It occurred to me just now that maybe I ought to divert to the flashlight community as I’ve discovered some modules like this that defintely include bms- its not quite clear to me if they are boost-buck operation but I don’t know how else they might manage to supply a steady voltage through regular battery discharge to an led if not, and they certainly have compact size and usb plug as high priorities.
A 5 to 3.3volt buck converter is rarely used. Most 5 to 3.3 regulators are linear.
Voltage difference between 5volt and 3.3volt is too small for most switching converters to work properly. And the efficiency gain is too low to justify a more complex circuit.
The flashlight board you linked to is all linear (I see no inductors).
Most likely a TP4056 chip (the most commonly used Chinese charging chip).
BMS is usually a term used with multiple cells in a pack. Not so much for single cells.
A BMS system has a ballancing circuit, to help with equalising voltage across multiple cells in a multi-cell string. A single-cell charging system doesn't have or need that.
Single cell chargers sometimes also have over/under voltage and over-current protection.
The big 8-pin chip is the actual charging chip ()TP4056). The small 6-pin chip is ove/under voltage detection and the medium-sized 8-pin is the mosfet switch that disconnects the battery when needed. Not all boards have the two smaller protection chips.
Some (protected) LiPo cells have the two protection chips included.
Thanks, that was a very useful response! You’re right of course for the term “BMS” but I didn’t know what other term to use to describe a single cell charging system.
Then either your definition of a BS is diferent, or you didn't look in the right place. Instead of giving us solutions, tell us what problem you are trying to solve.
That is JUST a charger, if he is going to remove the battery from the load then that is adequate but if he wants full power management then a BQ.... board is the modern solution, when the TP4056 is used for that there are two additional boards plus a Mosfet and maybe more, but that is now somewhat dated.
The market is full of combined boost/charge circuits designed to connect to USB for charging, and provide USB voltage (5V) to charge phones/etc. This is a consumer item, sold by the millions, and available in vending machines and as part of disposable electronics.
Fortunately for us, you can also buy the bare modules from the likes of aliexpress (and the amazon and eBay vendors that seem to exist by reselling stuff from them.)
A similar module providing 3.3V is considerably less interesting, from a sales PoV. It's essentially of interest only for internal use of electronics. That would be OEMs that can put the circuit directly in their product for less $, and a small set of electronics hobbyists. Little opportunity to sell millions of modules.
Also: realistically, a Li-ion battery at 3.3V has so little capacity remaining that you might as well use a LDO buck regulator.
This Pololu buck regulator (one of the better/documented ones) needs at least 4volt to make 3.3volt. Rather useless with a LiPo battery. A low-power linear regulator can still work down to 3.4volt input, utilising much more of the battery capacity.
Leo..
Well, I can't think of a single battery powered project where I would need one. I can see the need for a buck or a boost but when would you ever need a buck/boost.
My battery projects have a single LiPo cell with the micro and every sensor running from 3.3volt. I design from the ground up, trying to avoid power-wasting voltage conversions.
Please share your whole project. There could be solutions you haven't thought off.
Leo..
Like not changing the voltage of the battery at all. An AVR will run on a fair range of input voltage and the same goes for a lot of sensors. A charging system which includes load-sharing can be really useful and safe.
