Calculate usage with Alternator and mppt after shunt?

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justinm asked May 19, '23

Calculate usage with Alternator and mppt after shunt?

I'm following victrons examples when wiring my RV and have batteries before the lynx shunt then everything after the shunt including the alternator, victron mppt, and inverter. So if I'm driving down the road with the alternator making 3000w, solar pulling 1400w and genny is on bringing in another 2000w through inverter. Solar and inverter are Victron and the alternator has a wakespeed controller canbus to victron cerboGX. Is it recording all this? I feel like the mppt and alternator should be on the lynx power in side of the shunt.

lynx shunt

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Answer 1 · 2023-05-19T23:07:03Z

Sarah answered · May 19, 2023 at 11:07 PM

Hi @justinm It all depends on what you are trying to measure. If you want to measure battery state of charge then everything in and out of the battery has to go through the shunt (which is sounds like you have but hard to tell without a diagram). If you want to measure 12 volt load then you would typically add a second shunt (configured as an energy meter) with the battery, mppt, alternator, and inverter on one side and the load (e.g. fridges, lights, etc) on the other.

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Answer 2 · 2023-05-19T23:20:48Z

justinm answered · May 19, 2023 at 11:20 PM

So it would go Lynx power in ---> Lynx Shunt --> Lynx distribution (alternator, inverter, mppt) --> Lynx 2nd shunt --> Lynx distribution (all loads)?? I didn't know we could have 2 shunts and it record both.

I need to know SOC but I just want to know consumption. I dont care as much where it comes from.

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Sarah commented · May 20, 2023 at 02:20 AM

Yes, this will give you SOC and load. On the Cerbo it looks a bit like the attached picture I have a third shunt for the alternator.

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img-8117.jpeg (141.6 KiB)

kevgermany ♦♦ commented · May 20, 2023 at 05:30 AM

Just one lynx shunt. Use a smart shunt in other places.

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hjohnson commented · May 20, 2023 at 10:01 AM

That's how I have my boat configured. Of course, I've gone a bit shunt crazy on my boat... I have a cheap shunt so that my wakespeed can monitor its own current (also makes it more stable), the shunt integrated into my BMS (I run a DIY LFP battery with a REC ABMS), and then I have a Smart Shunt monitoring my DC load. Lastly, I have a BMV-712 monitoring my starting battery, but that doesn't really factor into things.

But yes, my Alternator, Inverter/Charger, and MPPTs all connect to my high-side power bus, while my DC house loads have their own connection to the battery.

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Answer 3 · 2023-05-19T23:48:45Z

Kevin Windrem answered · May 19, 2023 at 11:48 PM

You can have many shunts configured as a DC meter. By default the "DC System" number is calculated from other "known" values and tends to change quite a bit since values from other devices don't change at the same time. Currently, the Victron code combines PV charger, AC charger, Fuel cell, Inverter/charger, inverter only, and battery.

I believe the Wakespeed provides alternator power to the DC bus so you don't need an extra shunt for that. This power is NOT removed from the DC System number.

The MPPT will also provide power numbers to the system so no shunt is needed here.

Configuring a shunt as a DC meter and subtype DC Load will stabilize the DC System number and will report anything on the load side of this shunt. The battery side of this shunt would be connected to the load side of the main battery monitor shunt. How you connect this is totally up to you but if you have lots of connections multiple Lynx distributors might be a clean way.

GuiMods provides a flow overview that shows more devices, alternator in your case.

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