Electron without battery - capacitor requirement

I’m designing a pcb to use my electron in a vehicle. I have everything pretty much sorted out, except the power supply.

It’s a 12v system with a secondary battery isolated to run accessories, and I’m using a RECOM DC DC converter that outputs 5v at 2 amps. The power is fed to VIN on the Electron. digikey link
It gets too cold to use a lipo here. If I can supply 5v/2A is it neccessary to use a capacitor on vin? I don’t seem to have any trouble testing without it, but I’m not sure if a small one would be advisable.

It depends on the chemistry of your battery and how mobile the charges are when a sudden current demand occures.
In batteries you typically have ions carry the charge over a longer distance while caps store their charge in electrons with less “inertia” and virtually no travel distance - hence caps are typically way faster.
Also ion based charge mobility is typically decreased at cold temperatures (at least with fluid or gel electrolyte) while electron based transport gets better the colder it is.

However, some battery chemistries (like LiPo) do have very mobile charges and hence can be responsive enough (within their rated temp range) without the need for caps.

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Sorry, I wasn’t clear enough. I’m supplying power from a 12v SLA battery in the vehicle. I’m stepping it down from 12v to 5v to protect the electron from the voltage spikes vehicles are prone to. The limiting factor would be the 2 amps the Recom converter can supply.

The need for bulk capacitance isn’t clear in the docs. I had a 1000uF cap in parallel with vin and the electron really did not like to communicate.

I found the AN006 Vehicle Power page, where they state that one of the schematics that supplies 5v at 2 amps should be sufficient to power any particle device with or without a battery. I will continue to test without a capacitor, it seems to be working.

You fail to mention whether you’re using the 2G Electron or 3G Electron. I can power the 3G Electron with just USB cable without LiPo but I’m having hard time using the 2G version without a LiPo connected. I’m using the exact same Recom R78 converter and it just cannot handle the transient current spikes generated by the 2G modem. I’m currently investigating whether I can power the 2G Electron directly from a 12V battery. VIN can take up to 17V. However I’m not having luck there either.

Also, I think the PMIC has a resistor connected to the ILIM pin which will cap the input current from the external power source to 1.5A (at least that’s how I’ve understood it) which is not enough for the 2G modem which requires 1.8A. Finally you would need a perfectly tuned antenna for the 900-950Mhz range. Otherwise the current requirement can be even higher.

I’m having some success with a R78 2.0 coupled with a LT1085-3.6 (with 330uF low-ESR cap on the output) connected directly to the LI+. I can also run LT1085-3.6 alone but it gets a bit hot. I’m using a sketch which sends a MQTT message every second. There is a bit flickering in the blue led during transmit so there seems to some voltage fluctuation . However, seems to be running stable.