Powering EmonTX via battery and AC adpter at the same time ?

Submitted by Eric_AMANN on Mon, 15/06/2015 - 13:35

Hi,

When powering the unit via 5V USB/battery it is advisable to remove the JP2 jumper if an AC-AC adapter is present

Found in the Emontx page of the main site:

When powering the unit via 5V USB/battery jumper connection JP2 should be removed.

What does it means exactly ?

I'm wondering that because I'm going to use the same emontx in several different places. In some cases, I will be able to power the emontx via the AC adapter. In some others cases, it will not be possible.

I would be convenient to let the batteries inside the emontx all the time and then be able to measure the real power when using the AC adapter or the apparent power when not using the AC adapter.

Is it possible ?

Eric

Re: Powering EmonTX via battery and AC adpter at the same time ?

Submitted by Robert Wall on Mon, 15/06/2015 - 15:15.

It means that there is a reverse feed from the 3.3 V regulated supply via the MCP1702 regulator (from the battery or the programmer/USB) into the output of the MCP1754 regulator, which is part of the supply chain from the ac adapter.

You can still measure real power using the AC adapter with the link removed while using the batteries to provide the operating power.

You will need to restart/reset the emonTx when changing to/from the ac adapter so that the sketch uses the correct branch (if (ACAC) ... ).

Re: Powering EmonTX via battery and AC adpter at the same time ?

Submitted by Eric_AMANN on Mon, 15/06/2015 - 19:49.

Hi Robert,

Thank's for replying.

It means that there is a reverse feed from the 3.3 V regulated supply via the MCP1702 regulator (from the battery or the programmer/USB) into the output of the MCP1754 regulator, which is part of the supply chain from the ac adapter.

OK but what are the possible consequences of that ? It can be dangerous ? or it can affect the calculations ?

You can still measure real power using the AC adapter with the link removed while using the batteries to provide the operating power.

You will need to restart/reset the emonTx when changing to/from the ac adapter so that the sketch uses the correct branch (if (ACAC) ... ).

ok, that's a good point. Do you have a rough idea of the autonomy if I send a message every 10 second ?

Re: Powering EmonTX via battery and AC adpter at the same time ?

Submitted by Robert Wall on Mon, 15/06/2015 - 21:53.

"what are the possible consequences of that ? It can be dangerous ? or it can affect the calculations ?"

Without knowing the internal arrangement of the regulator in detail, I cannot say.

"Do you have a rough idea of the autonomy if I send a message every 10 second ?"

I think you have the wrong word there in "autonomy" - in English that means self government, freedom to make your own decisions.

If you mean battery life, it will of course depend on the capacity and quality of the batteries, and at what power you operate the radio module. I can't recall any posts that confirm or refute the Wiki's claim of 1 year on a set of alkaline cells.

Re: Powering EmonTX via battery and AC adpter at the same time ?

Submitted by Eric_AMANN on Tue, 16/06/2015 - 08:22.

Well, I was talking about the battery life !

Re: Powering EmonTX via battery and AC adpter at the same time ?

Submitted by glyn.hudson on Wed, 24/06/2015 - 11:52.

I would recommend removing black jumper JP1, this would allow emonTx to by powered by batteries and AC adapter will be used for AC reference.

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