Philip avatar image
Philip asked

Do I need a shunt with Multiplus ?

I'm trying to understand the sense of having a shunt with the system as below:
- 1x Multiplus Compact 12/1600 with MK3 cable
- Cerbo GX on Raspberry Zero 2W
- MPPT 75/15 with cable to USB + PV 100W
- Victron AGM 90ah 12V
- Grafana on a external server
- no other DC Loads
- in a near future a AC-coupled SMA Inverter on AC Out with 1500 Wp

1. Is something wrong with the battery monitor built into Multiplus ? Is it precise for ESS ?
2. Will the system work better (and how in details) with a external Smart Shunt, will the SOC be more precise and does it matter ?

What I need is the ESS on Multiplus to work as good and efficient as possible.
I don't need to have the SOC shown anywhere, no need for battery % visualization, no displays required - only remote console is what I need.

So ... do I still need a shunt ?

ESSSmartShuntSOCmultiplus ve.bus
1 comment
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klim8skeptic avatar image klim8skeptic ♦ commented ·
Your battery bank is bit small?
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2 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

The current measurement within the Multi can only measure DC current in and out of the Multi. This is sufficient of there are no other DC loads OR charging sources. Since you have an MPPT, you need a battery monitor (SmartShunt) to properly accumulate current in/out of the battery. Without it any charging current from the MPPT will not be counted. The battery monitor should be connected to the Pi running Venus OS via VE.Direct to USB cable. You may need a powered USB hub to get the SmartShunt and MPPT connected at the same time.

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nickdb avatar image nickdb ♦♦ commented ·
Are you sure about this? The multi knows what is being produced and can do some arithmetic to Work out what goes where. Its really inaccurate but was always under the impression it does try to work out what the mppt provides.
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Kevin Windrem avatar image Kevin Windrem nickdb ♦♦ commented ·
The MPPT knows the solar production numbers, the Multi does not. So the Multi SOC calculation can not include solar production contribution.
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Philip avatar image
Philip answered ·

Kevin, thanks for you quick answer.

Since I can't add pictures to the posts than I can't clearly proof what follows:

I'm quite sure that on my graphs on sunny hours, when MPPT claims to produce current, SOC definitely rises though I don't have a shunt.
Both the Multi and Victron MPPT 75/15 are connected to Venus OS via USB hub with and MK3.

Could you please double confirm I'm wrong in what I think I see in the graphs ?

I hope the links below to pictures on Google Photo will work:
Remote Console
Grafana Graphs with SOC, Volts and Current
VRM Remote
Venus OS Settings
VE Configure

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shaneyake avatar image shaneyake commented ·
The SOC will rise as the voltage rises but you aren't using the Battery Monitor in the Multiplius as intended so the SOC number displayed will not be accurate.

This is probably less import with AGM batteries but if you switch to Lithium it will not work correctly.

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Kevin Windrem avatar image Kevin Windrem commented ·
You are probably seeing charging from the Multi's charger. I don't see a way for the MPPT's charge current to be included in the battery SOC calculations. The GX device could technically include the MPPT charge current if IT were calculating SOC but it's the Multi doing the calculations in your system and it has no visibility of the MPPT data.
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Philip avatar image Philip Kevin Windrem commented ·
OK, I get it, thanks !

I was just hoping Multi gets the data from MPPT through Venus OS, which indeed has that data.

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