Power requirements of OEM components

Are the power requirements of OEM components documented anywhere? I’m thinking of fitting UPS to the power supplies (i.e. a power bank in the 5V line between the power supply wall wart and the emon-whatever device).

Apart from wondering whether this is a truly sensible idea? I also haven’t been able to find the power supply requirements (i.e. current draw) of the emonTx and emonBase. Are these posted anywhere (min, max, average)?

The emonTx probably doesn’t need one, because there’s going to be nothing for it to measure.
I would say it is sensible for the emonPi or emonBase, simply because of the danger to the SD card.

I don’t own a recent RPi, so I can’t measure one for you.

For the record, the emonPi will be principally the power required by the RPi, the ‘emon’ part is by my calculations about 70 mA absolute maximum - that’s when transmitting at full power (45 mA) with the optical pulse sensor (7.5 mA) and a couple of temperature sensors (2.2 mA each), the LED (1.45 mA) and the processor (8.2 mA).

The ‘normal’ (i.e. most of the time) running current will be the 8.2 mA for the processor plus about 3 mA max depending on the sleep mode for the idle current of the RFM module. The transmitter is only on for about 10 ms at the most, and the LED and optical pulse sensor only take current when working. That leaves the temperature sensors, and if they are connected via the screw terminals, the power for those is under software control and only needs to be on while readings are being made.

Unless it’s counting pulses from a mechanical device that continues to pulse during blackouts. I’ve been playing with a PoE based energy monitor recently, and because my ethernet switch is plugged into the UPS, I no longer have to re-sync the monitor to my Elster water meter’s reading after a blackout.


There just had to be an edge case I didn’t think about. :face_with_hand_over_mouth:

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Thanks for the data Robert. Yes that’s all swallowed up in the pi’s consumption :slight_smile:

Don’t start me about water meters! My water meter is even further north than my electricity meter, on the property boundary, so I don’t see any way to be able to log data from that. :frowning: I’d either have to run an armoured cable, and probably a data cable, out to the meter - another 10 m or so - or install another meter in the house and accept it wouldn’t record consumption in the garage. Which would mean it wouldn’t have noticed the flood we had in there a few years ago :frowning:

Am I right in thinking that the case of an emonTx losing power is ‘safe’ in the sense that as long as the emonBase keeps running it will recover correctly when the power comes back? There’s a theoretical worry about a timing issue if both the emonTx and the emonBase go off and come back together IIRC?