Is there any way to run the emontx v3 on a battery pack not the ideal power cord

Is there any way to run the emontx v3 on a battery pack not the ideal power cord. I was wondering if you can run the entire unit with a 9 aa battery pack I use to use on my arduino.


first, you can already run the emontx on 3 batteries, you need to open the housing and insert 3 AA batteries. Experts will confirm but I don’t think a 9V DC will work standard as it uses a 9V AC adapter ( to be able to get the AC line to calculate power)
You could use the emontx via the mini-b usb but that is 5 V DC, maybe via a little device lowering your 9V battery to 5 V DC ?

see page linked below with more details about the emontx

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All the multi-AA-cell battery packs I’ve ever seen have the cells connected in series. Unless the OP has a 9-cell pack that’s connected in an oddball series/parallel combination, he’s got a 13.5 Volt battery pack.

It will work without the AC-AC adapter, but will not be able to measure real power.
That is to say, it will measure apparent power.

if I power the device using the usb on the board, it will do the same thing as power it through the 9v ac?

Thought about using this for the 9v ac

Yes and no. The emonTx will work, and it will measure current, and only current. Therefore, as Bill says, you can only estimate apparent power provided you tell it your nominal voltage. If your actual voltage varies from that, or you have a load that is partly reactive, what you read will not correspond with your electricity meter.

The 9 V a.c. supply does two things: it provides power to operate the emonTx, it also measures the voltage and the relationship between the voltage wave and the current wave so that the emonTx can calculate real power. Real power is the measure by which you pay for your electricity.

I’d need to go away and check the ratings of the power supply components within the emonTx, but you might be able to connect that battery unit to the a.c input, but you can never measure the mains supply voltage.

Is there a way to change the log to feed number? So let say that the log to feed is 79 running on the battery but 45 running on the AC. Can you get the log to feed number and times it by .60 to display 47.4 as the new value?

thanks for all the help

I don’t understand the question. What is a “log to feed” number? Do you mean the present value of the data in the feed from your emonTx?

I think you’d better tell us the full story about what you’re trying to achieve, and what you have done so far, because there’s a danger that with only knowing dribs and drabs, we will be giving you bad advice.

Sorry about that. I had three of these hooked up to three lights. Each one was putting out 261w when hooked up using the AC adapter. Now that I’m using the battery it has gone up 461. I know that the lights are putting out 261 when I measured it. Is there any way to adjust the value that is coming in from the ct on each board?


Yes. If you read the calibration instructions in Resources > Building Blocks, you will find the full details. If you don’t want to calibrate your emonTx, you can adjust the numbers in “scales = …” in your emonhub.conf file.

The change you are probably seeing is due to two things: When you have the a.c. adapter, you were using the actual measured supply voltage. You were also calculating real power (watts). When running on battery, you cannot know the mains voltage, so the calculation uses a pre-programmed value that should be the nominal supply voltage, but clearly the actual voltage can and will vary. You are also now calculating the apparent power (VA) which is always equal or greater than real power. Again, you can read about that in Building Blocks.

But I have to warn you that 260 W is well outside the specified range over which the standard 100 A CT is accurate, and although we know you can get meaningful results in that sort of area, nothing can be guaranteed.

Thanks Robert for all the help man.