Smallest viable battery for E-Series (LTE M1 or 3G)


#1

Hi—I’m wondering if the new E-Series for LTE M1 will allow us to get away with smaller batteries. In my application, putting sensors on surfboard/paddleboard/kayak fins for coastal ocean data exploration (https://blog.particle.io/2018/06/19/smartfin/), battery size is a limiting factor in what we can put our sensors into.

A 500 mAh battery (with extra capacitors, I suppose?) would fit in many more things than a 2,000 or even 1,000 mAh battery, simply due to our admittedly somewhat insane dimensional restrictions. Users can recharge the device after every use so that isn’t as much of a concern.

In searching the forum, I found a few threads, most notably this one (Powering Electron with Li-SOCl2 Batteries (and no LiPo cell)) where I saw @ScruffR’s note:

So I’m a little discouraged from trying a smaller battery with (super)capacitor, knowing that the E-Series 3G needs ~ 2 A peak, but curious if anyone has a suggested workaround or knowledge of lower power requirements for the E-Series LTE M1 or even with the 3G.

Thanks!


#2

The upcoming Boron will be featuring a less power hungry main controler and also the cell modules are expected to draw less.

BTW, it’s actually the 2G versions that draw up to 2A, 3G should be short of 1A (IIRC).


#3

Ah, interesting, thanks. I’ve been keeping a close eye on Boron development and when I see the mass production form factor that’s promised in the enterprise mesh FAQ, I may very well make that transition.

I’m trying to develop for global applications, too, so I think the E-Series 3G has everything I need for now. I guess I’ll do some other tests with the 3G modems to see how small I can get the batteries to work for me.


#4

I’ve certainly not seen the 3G go over 1A in any testing. At least not at my sampling rates.


#5

You can get smaller capacity batteries that can still handle the 1A or more current that a 3G Electron needs to connect successfully without needing a supercapacitor.

Are you 3D printing the fins? I imagine if you were you could design a cavity in there to hold a 1000, 1500, or 2000mAh pouch cell.


#6

Yes, I am 3D printing fins with cavities. Even the 1,000 mAh cells are ~ 6 mm thick (or if they’re thinner, their other two dimensions are much larger). If you are familiar with different fin designs, this works for longboard fins, which are larger in every dimension, but not shortboard fins. The 500 mAh batts are almost the exact (maximum) shape/size that the shortboard fins can accommodate. So I should be looking for a 500 mAh batt with 2C discharge capabilities?


#7

Where all have you looked for batteries?

Here is a selection of Li-Ion cells with discharge rates of more than 2C.

They have one on there that is a 1500mAh cell that is only 3.5mm thick.


#8

That looks like a great resource, thanks! I was spending some time on https://www.all-battery.com/li-polymer_single_19to1000.aspx as well as Adafruit.com and, of course, google, but I wasn’t using great search terms. The 1500 mAh one is probably too big in the other two dimensions (I know, annoying constraints!) but the 1050 might just squeeze in. I’ll scour this website when I’m back at my desk and more carefully search for high discharge rate options—thanks again!


#9

Hi again,

I purchased some of the batteries from BatterySpace recommended by @RWB (thanks!) but they come without internal protection circuitry. This has me nervous. I’ve read up on various threads on the forum, including: (1) PMIC (only sometimes) not charging when battery voltage is below 3.5V, (2) Bug Bounty: Electron not booting after battery discharges completely, and some of the threads linked in both, all of which has me pretty convinced that the E-Series’ on-board PMIC is insufficient for undervoltage protection.

Is anyone (@RWB and @BDub, you were both really helpful in the above threads!) able to offer any words of wisdom for dealing with lithium battery protection or if it’s even needed beyond the already included PMIC? I have been unable to find batteries that meet my size specifications (~ 3.5 mm thick) and the ~ 1 A peak discharge that come with built-in protection so I’m trying to make sure I know how to deal with that. Can I tweak anything on the PMIC (or do I even need to) to ensure I have proper battery protection?

Thank you!


#11

I would advise against not using a protected lipo, aka always use a protected lipo. If you must buy something smaller that doesn’t seem to come with a protection circuit, most battery manufacturers can add a protection circuit for you. I would make sure the max discharge currents of the protection circuit are similar to the batteries we use with the Electron & E Series products. You could possibly get away with a slightly lower limit for 3G and LTE though. I believe our batteries currently can handle a continuous 2.7A discharge current before the protection circuit kicks in and opens up the connection and have a discharge voltage cutoff of 3.0V.

In general the PMIC settings should not need to be changed, and the protection circuit on the battery itself is going to offer the most reliable safety mechanism. Depending on the temperature requirements, you might be able to make the charging cycle safer by reducing the cutoff voltage even further than it’s currently set by default at 4.112V.


#12

I would contact Batteryspace and just tell them you need a super small PCM for the battery your using. They have access to tons of different protection circuits and should be able to get you exactly what you’re needing even if it would require a new PCB design for your specific use case.

For the size battery, your using the PCM can be very small like the one on the battery that comes with the Electron.

You could actually just reuse the PCM board that’s attached to the standard 2000mAh LiPo that is attached to the standard Electron battery.


#13

Thanks very much, @RWB and @BDub, and sorry for the slow reply (I was actually busy working with Particle’s marketing team in SF the past two days and just catching up on engineering…).

Okay, I’ll definitely go with protection circuitry separate from the PMIC. BatterySpace.com has this board which appears to have similar specs (lower voltage cutoff, though, so I may need to find something higher).

I appreciate the help!


#14

That board from Batteryspace should work just fine for your setup.