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emonTx V3 battery life?

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Has anyone got real world data on how long the emonTV3 lasts when powered from 3 x AA batteries? Where possible I always install using an AC-ACadapter to get more accurate real-power readings. However, I am aware that in some install locations battery power is the only option.

Just wondering if someone has got some real world data on battery life. We have estimated between 6-12 months depending on the number of CT’s being sampled.

Glyn, I’ve got to point out that shortening the transmitted message can also result in worthwhile savings.

The ‘standard’ message is 4 powers, the voltage, 6 temperatures and a pulse count. That’s 26 bytes of payload + 9 housekeeping bytes = 280 bits. At the standard data rate of 49 kb/s, this takes 5.71 ms to transmit drawing 45 mA in the process - just for the transmitter, forgetting the processor needs to be kept awake as well. If that transmitted packet is reduced to remove unused variables, that burst of power can be more than halved, in the extreme case.

Let’s say in the extreme case it is just measuring 2 currents, and only power is displayed in emonCMS, then the message could come down to 2 powers only: 4 bytes + 9 housekeeping = 104 bits taking 2.12 ms. Transmitting every 10 s, the saving amounts to about 0.4 mAh per day. Yes, I did pick the most extreme case, but it illustrates the point.

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Agreed, there could definitely be optimisations. I would be interested to hear how many users are actively running emonTx V3 on battery power. We have been discouraging it for accuracy reasons.

I just came across this post while searching for for how to monitor battery voltage. I’ve had a TxV3.4 running only a temperature sensor (DS18B20, no CT inputs) and its battery pack just expired. It was setup on Jan 22, and died on August 17, so 207 days. The batteries were Energizer 3000 mAh and the readings were every 10 seconds. Assuming everything is linear and battery capacity fade losses are zero this comes down to approx 1.7 microamp-h per reading. Assuming average battery voltage of 1.2 V this means about 7 mJ/reading. Does that sound right?

Yes, that sounds about right. Thanks for sharing.