Below is the one I have on hand, but if there are others that have built in BMS then I can switch. See note below too that says this battery does not have it. If there are individual 18650 cells that have built in protection that would be great! Can you point me to an Amazon (or orher) listing? All the listings I see for cells do not mention anything about built in protections. Thanks!
The product safety warnings specifically state "NEVER Over-charge or Over-discharge lipo battery" and emphasize that you must monitor cell voltage manually (keeping it between 3.2V-4.2V per cell). This indicates the battery relies on external protection from your RC model's ESC (Electronic Speed Controller) or a low-voltage cutoff alarm.
Traditional RC LiPo batteries like this one require you to monitor usage and stop when voltage drops too low to prevent damage.
Don't worry, I didn't look for protected ones.
Protected ones are 3mm longer than standard ones and don't fit in holders designed for standard ones. And availability is very limited from japanese brands.
You can find them quite easily, usually button top instead of flat. But they are usually designed for single cell use..
Then , you just need to monitor the battery voltage with your Arduino. However the 50C rating is quite questionable. You should find the maximum continuous discharge rate and make sure it's greater than the maximum that you will need.
I think we've come full circle. I was hoping to not depend on using the Arduino for monitoring and use a separate module - perhaps like the ones I showed above. I may want to power something in the future that doesn't use an Arduino so trying to get a more generic understanding on how to safely use these higher power batteries. It looks like I have several options: buy a 35 (or more) LiFePo4s that has built in protection, use individual cells that have built in protection (inserted into a holder Jim-p showed above), or add external protection using the modules like the ones above. Goals is to get cutoff voltage near as possible to 6v min and 5A+ continuous current draw capability
Thanks kmin. Well, I mainly want to be sure the output to my Arduino does not fall below 5v. Since i will using a buck to get my 5v, I need some headroom. Make sense?
Hi Jim-p, can you elaborate on that please? I’m not sure I follow. I’m assuming (perhaps incorrectly) that when the battery voltage drops below the cutoff that the BMS will shut down the output (0V), is that not correct? What I’m trying to avoid is having the output voltage from the battery through the buck drop below 5v for any time. Even with a buck/boost if the input voltage stays too low then the output will go unstable.
I was attempting to answer jim-p’s question about why I was concerned about going below 5v if at the cutoff the voltage will go to zero. I want the voltage to go to zero. If it didn’t and instead very slowly ramped down to zero then that would be bad for the Arduino and associated circuitry. Even with a sepic the voltage output will be unstable at some point if the input gets to low.
Bottom line is that this is not an issue - the voltage will go directly to zero from cutoff at a level well above 6v - so I’m good!
Well, I didn’t make it very far before hitting a snag. Now that I know a bit more (thank you) I’m doing better at finding related videos and tutorials. One thing I learned is that apparently many of the 3s modules require “you have to wake up the BMS by plugging in a charger or power supply for 16.8V.” I looked through the comments for the Amazon board I noted above and sure enough this is the case. Soooo, how is this supposed to be done in an embedded project? I don’t want to have to “jump start” my battery every time I power up! I must be missing something. Is this the case with LiFePO4 packs too?
That will all depend on the Arduino, the buck you are using and your particular set-up. It will never just go from 5V to zero and having an unpowered Arduino connected to powered devices will be a problem.
If you want a safe set-up then do as I suggested back in post #15. Building your own battery pack using unprotected cells and a balance board with protection may not turn out the way you expect.
Thanks Jim-p. You are right that most of the listings for 18650 cells do seem to have protection built in. So just using a 3 cell holder and a buck converter (perhaps one for my 5v output and another for 6) should be the simplest solution.
But since I’m trying to learn and may be of use in the future can you elaborate on what you mean by only having to “jump start” the protection modules once? Do you mean once per power up, once per battery recharge, once per module (so never have to do again after for that module), or something else? If I only have to do once for the module that’s fine, but if I have to do it every time I recharge or power up then that would be a pain.
From what I've seen before it's only once after you receive it and then never again. I know of at least one protection IC that acts that way.
Make sure you buy the battery holder for the 18650 battery and not one for AAs because they are a little longer.