Smartshunt and DC system measurement

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buddhafragt asked Mar 15, '24

Smartshunt and DC system measurement

Hello,

I am dealing since days with this problem:

I have 2 MPPTs connected to a Rasp Venus 2.94 and DVCC switched on, a LiFepo4 with DIYBMS connected to CAN, it is a stand-alone system. DVCC on, ESS not present.

Now I connect a Smart Shunt (see the drawing) in the system, as consumers I have 3 Inverters (120V, 220V, 12V). DC system is switched on, Smartshunt is configured as DC System.

Problem: The reading of the Smartshunt is completely wrong. (see sample readings in the drawing). Instead 188W the Smartshunt show 84W.

Can someone help?

Venus OS SmartShunt

screenshot-20240315-1331432.png (179.5 KiB)

drawing.jpg (30.5 KiB)

system.png (81.2 KiB)

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kevgermany answered · Mar 15 at 08:24 PM

The smart shunt must be in series with the BMS shunt, at the moment it won't see the MPPT current. So connect the MPPT output to the consumer/load side of the shunt.

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buddhafragt commented · Mar 16 at 02:05 AM

If I do so, the Smartshunt measure exact the same as the BMS shunt, thats not the sense....

The Smartshunt should measure the consumption of all loads, and the current can come from the battery or from the MPPTs.

the BMS shunt measure what is going in and out from the battery.

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Modifications Space

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Answer 1 · 2024-03-16T02:57:37Z

kevgermany answered · Mar 16 at 02:57 AM

Sorry, misunderstood you.

Which Venus version is on the RPi?

Have you used a clamp meter to measure currents and confirm the values from MPPTs, BMS, smartshunt?

I'd guess that one or more loads bypasses the shunt. Or possibly timing differences between the three measurements, especially if the loads vary frequently.

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Answer 2 · 2024-03-16T06:24:35Z

buddhafragt answered · Mar 16 at 06:24 AM

Rasp Venus 2.94...

right now the MPPTs are off and the BMS shunt, which is very exact measure 240W, the Smartshunt 80W. I measure also with a Shelly, which are also exact.

After checking the values for a while, I see the Smartshunt measure almost exact 1/3 from the real consumption... strange!

There is no load bypassing, if a 120W load is switched on, the Smartshunt show 40W more!

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buddhafragt commented · Mar 16 at 03:50 PM

Now I have it... stupid error!

The Smartshunt lost the connection and Venus replace the real values with a calculation... hard to see, I notice when I was taken a look for the device.

Thanks for the answers! The circuit at the drawing is working.

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