Accurate monitoring of DC power consumption

I have a pretty small Victron system installed in my travel trailer:

Cerbo GX & Display
Victron Smart Batteries
Lynx input and distributor
Lynx Smart BMS
two Multiplus for the 50 amp service

I just added a SmatShunt to from the Lynx Distributor to the RV DC system:

What is up with the difference between the estimate and what the Shunt is showing? Is that what things like the Cerbo, three MPPT's, Multiplus (even though they are off), are consuming?

I do have GUI Mods installed, is there any way to get the system to show both on the main page?

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Alexandra ♦ commented · Jun 23 at 02:23 PM

Is your shunt configured as a DC meter? Looks like the mod isn't drawing its information from it.

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sam-carleton Alexandra ♦ commented · Jun 24 at 12:58 PM

I do have it configured as a DC meter, not a battery monitor. I assumed I would have to go into the Cerbo somewhere and tell it what type of DC Monitor it is, but I have yet to find that while poking around.

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pwfarnell sam-carleton commented · Jun 24 at 01:40 PM

You tell the SmartShunt what it is measuring using Victron connect, choose from things like DC system, wind power, fuel cell etc. etc. In your case it should be DC System if it is to the RV DC loads. The GX also needs the "Has DC System" enabled on the System Setup page.

/pg/SmartShunt/en/all-features-and-settings.html#UUID-4d8c0755-7f10-f76d-494a-26f9745051bf

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sam-carleton pwfarnell commented · Jun 25 at 02:26 AM

Thank you, I think I had the shunt set to Generic Load, not DC System. I made the change and all is good!

Now, how can I see how much overhead the two Multiplus actually use?

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pwfarnell sam-carleton commented · Jun 25 at 02:42 PM

Try some math depending on your system. The Lynx BMS will give total ex batteries, your new SmartShunt should capture all DC loads if set up right, you do not mention solar. With the inverters at idle without shore power connected they will be using the difference between the Lynx and the SmartShunt. The one issue I do not know is if the Lynx BMS measures the Cerbo current if connected to aux.

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pwfarnell pwfarnell commented · Jun 25 at 02:58 PM

Or the current taken by the contactor because if it includes the BMS overheads and Cerbo then it will not be possible to get an accurate answer unless you take the datasheet values for these.

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kevgermany ♦♦ sam-carleton commented · Jun 25 at 04:38 AM

It depends where the shunt is in the system. You might need a second shunt in the feed to the Multiplus.

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sam-carleton kevgermany ♦♦ commented · Jun 25 at 12:14 PM

Yea, the current shunt is between the Lync Distributor and the RV. Right now both Multiplus have two negatives, for a total of four. Because of this, I am thinking I am not going to put a shunt on them, but if I did, how would that be setup? Would I need to use the SmartShunt 2000A so each wire had its own connection?

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derrick thomas sam-carleton commented · Jun 25 at 02:17 PM

You would connect a shunt directly to the battery negative and then connect the load side to a busbar or a lynx DC in box and then connect all the negatives to it.

Edit: disregard this comment. I just realized you have a lynx bms already. Do some basic math as suggested by @pwfarnell

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kevgermany ♦♦ sam-carleton commented · Jun 25 at 05:28 PM

In essence for every measurement you need a shunt. If you can bring the two negs for a multi to a single point (battery side of the shunt from the distributor) and then connect the other side to the multi, you need two more. But it's expensive.

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