I just acquired a couple of Electrons and have installed them onto a pair of NCD relay boards. The latter have their own power supply which also powers the Electrons. If I connect the Particle-provided batteries to the Electrons, will there be any conflict between the two power sources? If not, and if there is an AC power interruption that causes the batteries to power the Electrons, will the power connected to the NCD boards recharge the batteries once power is restored?
The NCD relay boards power the Electron by the VIN pin. It’s normal to power by VIN (or USB) and use the LiPo battery.
If the power is lost, the Electron will continue to be powered by the LiPo battery, but note that the NCD relays will not be powered, so you won’t be able to energize a relay on battery power. But the battery will recharge when there is power again.
Very helpful! Many thanks. I understood that the battery would not operate the relays, but was hoping that the Electron would hold on to a cellular connection and it appears that indeed it will!
This is super useful. I’m brainstorming the same scenario and had already identified that my use case requires both the Relay AND the Particle to have power.
Because of this, I intended to use a mini-UPS to back up both the NCD relay board and the Boron.
Documentation states: Boron will intelligently source power from the USB most of the time and keep the battery charged. During peak current requirements, the additional power will be sourced from the battery ---- but would it even be aware that it was drawing on battery if the NCD board is kept alive?
Another question:
This is all backup mode, but during normal operation, a larger system would be communicating with the Particle > NCD board via USB.
In the event of a blackout, i want to make sure that no power can drain out via the usb. For longevity, I want battery backup limited to the NCD + Particle devices, allowing the rest of the system to fail.
I have a few of the NCD Relay boards operating straight from a 12V SLA battery. The SLA battery is maintained via a “wall-wart” trickle charger or Solar. That lets you select whatever size battery that you require for your emergency run-time, verses the mini-UPS.
It’s a little larger, but cheaper and more capacity.
Thanks can you diagram that a bit? Ive been assuming I’d power the NCD via the barrel jack. Are you describing: AC > trickle charger > 12V SLA > Barrel jack?
Does that have any negative impact on the battery’s lifespan? I’d been assuming that if i configure it that way, i’d need a smarter battery device - hence looking at the Mini-UPS unit.
I’m also interested in a battery that can report on its health via GPIO… Maybe that also would tilt me towards a UPS board?
The NCD boards also have screw terminals for power input (in addition to the barrel jack), that’s what I use, but they are the same.
The 12V SLA lands on the NCD screw terminals.
An automatic trickle charger is connected to the 12V SLA directly.
I use a 5:1 Voltage Divider (cheap Chinese module) to monitor the 12V SLA status via analog read.
Select a NCD Relay board with 2A power system, some are smaller.
I don’t use/need the Li-Po (for current spikes) with this setup for Electrons.
Nothing wrong with a UPS board… just sharing ideas with you 
OK - in your use case, are you doing anything to tell the particle that its on battery backup mode?
thats the key part of my question. For folks using the LiPo jack, Doesn’t particle automatically shifts into somewhat power saving condition when it loses power from Vin or USB?
but in the configuration you describe, the 12v backup > NCD > Particle ensures the particle never loses power on Vin…
No, the Particle Electron doesn't know that the 12V battery is discharging if you have lost primary "mains" power (except for measuring the 12V SLA voltage through the voltage divider).
Not that I know of, but you can add this feature to your Code. The electron will source it's Power from Vin until that Voltage drops too low, then it uses the Li-Po. But in this case, the NCD board will provide a stable source on Vin until the 12V SLA battery is discharged. Using a Li-Po with the NCD Relay board doesn't hurt anything. I personally have a few locations where the temperature gets too high inside the enclosure to be comfortable with a Li-Po, that's the only reason I wouldn't install the Li-Po. Completely your choice.
Correct, that's the plan anyway 
.