Hi Forum, I’ve built 100’s of Arduino projects but have never needed to use battery power. I’m looking to power my next project with either a 2S or 3S lipo battery. I’ve seen many posts about using a single cell with a step up buck to drive 5v, but I also have a couple 6v motors that draw about 1A each and a 5v DFplayer. So my thought was to use a 3S or 2S LiPo going through “a thing” that would feed both a 5v-out buck for the Arduino Nano and DFplayer and a second 6v-out buck for the motors. I understand that I need some sort of battery management system (BMS) to make sure the lipo charge does not drop too low and perhaps also adresses other important lipo safety concerns (??). My hope is that such “a thing” exists!
I see many BMS modules available, but these all seem to be addressing charging the LiPo. I am more concerned about safely using it to power my project. Yes it would be great if I can also hook up a simple USB line to recharge the cell, but it’s also fine with me to remove the cell for charging using a stand-alone charger.
I have seen postings where people connect LiPo cells directly to their Arduinos and also employ a resistive voltage divider to drive an Arduino analog input to monitor for low voltage, but I also keep seeing that protecting the LiPo from over-discharge is part of what a BMS does. If I use the Arduino to detect undervoltage then I have to add a relay or similar to cut the power. Plus, I’ve also seen postings that say connecting the LiPo directly to an Arduino is not safe regardless. Again, was hoping there was an off-the-shelf “thing” that protects both the LiPo and the rest of my project.
I have seen postings that suggest the simple solution is to buy a LiPo battery pack that has built in BMS, but then I’ll see postings that say things like, “be sure to add a BMS when using a battery pack.” And when I try and search on LiPo battery packs I can’t find good info to explain if they have built in BMS or exactly what it does.
So, bottom line iis I’m struggling to find the best way to connect a 2S or 3S LiPo to safely power a project that will require 5v at about 1A and two motors at about 2A. Or should I give up on LiPos and use a NiMH battery to feed my two buck converters?
I have to disagree, even some <$1 BMS from AE offer over discharge voltage and discharge current protection.
And yes, you need BMS if you want to safely use lithium batteries.
Also, get datasheets of your motors to find the voltage range and current draw (nominal/stall) before you decide what approach to take (buck/boost/direct/mix).
For example 2s LiFePo4 might fit without conversion to power the motors, so you only need step down for low current devices.
kmin: yeah, I guess I’m just still not getting it. I do see that some of the modules on AE discuss overdischarge - which does seem to imply that they are intended to go between the LiPo 3S and my project. But all the wiring information seems to only address how to wire up the module to use for charging the LiPo. Can you help me understand (or point me to some tutorial) how to wire up an example module between a 3S LiPo and the input to my project? Thanks!
Railroader: I will do some research on powerbanks - I’ve not used one but this sure looks like it might be exactly what I need - looks to take care of risk of driving the battery too low and also other safety risks.
Hi kmin, the DC motors I’m using run at 6v and draw about 1A each at load. I’m also driving two servos that I want to run at 6V and can draw about 1.5A each at load. Regardless, I’d really like to learn how to safely use LiPos for this and potentially future projects. So, I’d really appreciate any help getting me smarter on this topic. If you can point me to one of the AE modules and help me understand how to wire it up, I’d really appreciate it!
UPDATE: ok I think I’m starting to understand. The modules support both charging and discharging (powering). I was thrown off because they all seem to use the word “charger” and I was not really looking for a charging solution. Also I guess the wiring confused me because the module output and input connect to the same place on the module. It looks like most of the low-cost boards are 1S which then can be fed into a boost converter to get 5.0-5.2v at a fairly low current. But I’d really like to get a higher voltage at a higher current. I found this “3S 12V 10A Lithium Ion Battery Charger BMS Module” on Amazon that looks promising. It looks like it has separate connections that tie to the ends of each cell in the 3S stack - which makes sense for balanced charging. But do I need to connect those if I just want to use the board to provide power out to my project? I can remove the battery to put it on a dedicated charger rather than charge in place. Seems like this might be a good and safe solution.
I still call for the datasheets/specs of all your motors/servos.
Motors don't just have one fixed voltage, but range. Also, nominal current matters, but if you are willing to use voltage converters, you have to know/estimate the stall current.
Ideally you choose a battery setup that doesn't need converters to power motors. For example 2S LiFePo4 voltage range would be 6-7V and might be compatible with your motors.
I’m using small DC motors and hobby servos so getting detailed specs is unlikely. But the amperage I stated before was measured stall current - add Arduino Nano and DFplayer with some headroom - should be around 5A max worst case for the project Please let’s just assume that and move forward I promise that if the draw ends up more than that that I will revisit the solution.
Jim-p - Everything I have read says that all LiPo batteries do require at a minimum some sort of system to keep them from overdischarging. I’ve seen many posts where people use an resistive voltage divider to feed an analog input to monitor the voltage level, but if I can just use an inexpensive module that will provide this and other safety measures, then I’d rather do that.
I did just find a reference that explains that it is important to connect the individual cells to the BMS even if not using it for charging because each individual cell is monitored for low discharge. Sooo, it looks like this Amazon board should work for me if I connect up both the LiPo output lines and the charging plug. It would be great if someone can confirm if this should work for me. Perhaps I need to post to an electronics forum??
It looks like all of these boards were made to be side clipped into some custom enclosure since there are no mounting holes on any of the variants I can find - such a pain! I really hate just shrink wrapping it and leaving it hang - any suggestions on cleaner mounting would also be appreciated.
As I already said if you are using a 2S, 3S pack there is no need for a BMS. However you may want to use a protection circuit if it is not already built in.
Thanks, yep - I want to add protection to a “raw” 3S LiPo pack. As per kmin’s suggestion - looks like a LiFePo4 would work (and be cleaner) since it already has the BMS integrated But I think I would need to use a 3S since the cutoff for a 2S would drop below 5v. So with a 2S I’d have to add additional circuitry which kinda defeats the benefit of the nice all-in-one solution. I’m seeing plenty of 2S and 4S LiFePo4s but not any 3S (just started looking tho) The 4S ones are physically pretty large!
By raw I meant just the 3 batteries in series with no circuitry. But I’m really confused now. If you can just put them in a holder and directly power your project with no BMS wont that risk over depleting the batteries? I’m still learning about how to safely use LiPos (why I’m here) but I’ve seen multiple times that it’s not a good idea to use them without a BMS - if for no other reason than to avoid over discharge because that can ruin the LiPos. Is that not accurate??
At 6V LFP4 would have only 10% charge left
Your motors likely don't mind for <6V and for arduino/DF you can use up/down converter designed for this use case. Pololu has good ones.
If you find LFP4 with built in protection, that's ideal choice. But they are rare.
No.
Unless they say otherwise, all cylindrical and prismatic (flat ones) Li-ion batteries you can buy today have protection circuits built in for overcharge, overdischarge and over current.
