question

Disclaimer: While I am somewhat experienced in the area of off-grid electrical systems, I have yet to have any hands-on experience with Victron's products, so the following question comes from the perspective of someone who has only been able to read the datasheets and manuals.

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A friend of mine is tired of having to run the noisy fuel-guzzling generator every day to recharge the battery bank on his 49 ft sailboat. Instead of incrementally installing random PV panels until the problem goes away, he wants to first install equipment for recording his DC usage this cruising season so that he can determine his real-world requirements and design a system that balances the desire for extra capacity against seaworthiness concerns and aesthetic considerations.

The plan is to meter the loads downstream of any charging equipment, so as to not have the data obscured when the "service"/"house" battery bank is being charged, such as when motor-sailing or running the generator. For typical DC loads, this is fairly straightforward, and Victron's SmartShunt product in "DC energy meter" mode looks like a good option. If combined with one of Victron's "GX" products, I gather there is even the option of taking the sum of the values from multiple SmartShunts in "DC System" mode, which would be convenient if my friend later decides that he wants to get collect data on individual system branches while still seeing/recording his overall energy use.

The main complicating factor is his third party inverter/charger, which can either be a DC load or a DC source, depending on whether or not he's got the generator running (or is connected to shore power). Short of replacing the inverter/charger with discrete devices, I can think of a few approaches to this issue, some of which are better than others, but none of which seem ideal:

• We could install a single SmartShunt downstream of the inverter/charger, but then we'll fail to account for all of the DC that goes into supporting AC devices via the inverter.
  
  
• We could install parallel SmarShunts (one for the inverter/charger and one for everything else), but then I would imagine our "DC System" readings in the GX software will be thrown off whenever the inverter/charger is in charging mode.
  • A less-than-complete workaround here would be to suppress/zero-out the readings from the inverter/charger's SmartShunt whenever the inverter/charger is acting as a source. Is there a way to do this in the GX software? If not, has anyone achieved this by using a high-current relay/contactor to bypass the SmartShunt and short the inverter/charger's DC- connection directly to the upstream DC- bus? (I'm imagining an AC relay/contactor that is activated whenever generator/shorepower is live.)
    
    
  • I have characterized the workaround discussed in the previous sub-point as less-than-complete because it fails to allow us to take into account for what the DC inverter's consumption would have hypothetically been if generator had never been switched on. Does anyone have a solution here? Does Victron have a standalone GX-compatible AC current sensor that we could use to record the load on the third-party inverter/charger's AC output at times when it is in AC bypass mode due to generator/shorepower (and only at those times)? The idea would be to convert use the data for these periods into estimations of what our inverter/charger's DC use would have been had the generator/shorepower not been online, taking into account the inverter's conversion loss.

Thanks in advance for any solutions!