Minimum useful battery capacity for Electron?

I’m using the electron for a project with an extremely limited size budget. The power supply wasn’t built to handle the sorts of current spikes that cellular communication will cause, so it seems I will need a LiPo battery hooked up to the electron to handle this. I would normally get an arbitrarily large capacity, but the space constraints make that implausible. I was curious if anyone has tried using a battery with very little capacity (150mAh and less) and what the results were. Has there been any official testing done on this? My specific application will use data relatively sparingly, but I’m curious about experiences with small LiPo batteries in all use cases.

If you only require the LiPo to back bursts of current draw but not for keeping the device powered off grid, then you could also consider a big enough cap (possibly a supercap).

Didn’t consider that! A supercap seems like a good option, sounds like it has a faster response to current spikes than a battery would, giving the power supply an easier time.

I’ll experiment with different values and report back with my findings. Before I start, is there any sort of profiling that’s been done on how long increased power demand states last, like how long the 2A peaks last (and how frequent they are)? Milliseconds, tens of milliseconds, hundreds? Just to have an starting point for choosing capacitor size.

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I’d have to forward that one to the hardware guys - I think @mohit might know (or know who knows).

@treykeown, neither a 150ma/hr nor a supercap will be able to handle sustained/multiple connection attempt conditions. The 3G Electron can draw up to 850ma or so attempting to connect. This depends on tower distance, signal strength, etc. A supercap may handle a single retry event but it wont’t be able to handle multiple. Also, keeping the supercap charged will require a different circuit than the LiPo charger on the Electron. In the least I would go with a LiPo sized to bridge what your supply can provide and the 850ma needed for spikes.

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Yeah - supercaps are not made for this, I would not recommend them.

They are designed to supply tiny to moderate amounts of current over a period ranging from a few seconds to many months. They are not designed to supply somewhere north of an amp for a few milliseconds, their equivalent series resistance is just too high for that.

A common workaround is to use several standard capacitors in parallel - this has the effect of increasing the capacity, and decreasing the apparent ESR.

However, I don’t think you can/should replace the battery with these capacitors, you should just ensure that they have a very low impedance path between Vin and Gnd.

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