WS 500 + Dedicated Shunt + Cerbo = 2x DC Power Reported

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nate-costello asked Mar 10, '23

WS 500 + Dedicated Shunt + Cerbo = 2x DC Power Reported

I recently installed a dedicated shunt for my 24V Alternator/Wakespeed charging source (CAN connected to Cerbo and BMS). This is on a system with a REC BMS that provides its own battery current data (sensed by its own shunt) to the Cerbo via CAN.

Now when I'm charging with the alternator, the DC power displayed by the Cerbo and VRM is ≈2x what really is. I've looked around for settings on Cerbo, and read the documentation but I can't seem to find anything to correct the display.

Prior to installing the dedicated shunt and configuring the wakespeed to use it, DC Power was correct. My suspicion is the CERBO is adding the battery current to the wakespeed reported charging current, hence ≈2x.

I do have "has DC system" enabled because the majority of my system loads are DC. Any help would be appreciated.

cerbo gx VE.Can alternator

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pwfarnell commented · Mar 10, 2023 at 04:22 PM

Is this an alternator current shunt connected to the WS500, or a battery current shunt connected to the WS500 a Victron Smartshunt set up as a DC energy meter connected to the Cerbo. Just wanting absolute clarity.

The only immediate thought is if the shunt is connected to WS500 then have you got the right setting for the shunt location in the CST line of the WS500 configuration file. The other question is are you running GUImods as there have been some questions about potential differences in DC load handling.

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nate-costello pwfarnell commented · Mar 10, 2023 at 05:03 PM

This is a dedicated "dumb" shunt only serving the alternator, on the positive side. I have the correct CST line in the WS500 configuration and can see the WS correctly reporting charging amps over CAN (with custom CAN logging code).

There is a separate "dumb" shunt serving the REC BMS on the negative side of the battery.

Both the BMS and Wakespeed report their respective data over CAN to the Cerbo.

I'm not running any GUImods.

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pwfarnell nate-costello commented · Mar 10, 2023 at 07:48 PM

I am stumped then, I have a WS500 ready to install with a dumb shunt in the positive and Victron BMV in the battery supply so I may be in the same position as you. There have been comments that Victron have not yet fully sorted the DC system calcs with extra DC sources and loads.

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Answer 1 · 2023-03-10T20:40:03Z

hjohnson answered · Mar 10, 2023 at 08:40 PM

That’s odd. I’ve not noticed that on my boat. I have a similar setup, REC BMS, WS500, and Cerbo, albeit at 12V nominal rather than 24. Once I got all my shunts in place, connected the right way around (made that mistake more times than I’d like to admit) all my numbers match up. The only real difference is that I also have a smartshunt measuring my DC system.

The biggest issue I have is a disagreement between the current reported by my REC, and what’s coming in from the alternator and multiplus. In my case, though, it’s about a 10% difference, not a doubling like what you’re seeing.

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pwfarnell commented · Mar 10, 2023 at 09:26 PM

I have a SmartShunt to go on my DC system in my upcoming install so hope that I will also be OK then, good to hear positive comment on this.

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nate-costello commented · Mar 14, 2023 at 12:34 AM

@hjohnson does your wakespeed current flow through that smart shunt? In my case the Battery KW is correct, its just the DC System KW that is wrong (doubled).

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hjohnson nate-costello commented · Mar 14, 2023 at 12:38 AM

It flows through the BMS shunt and the Wakespeed Shunt, but not through the SmartShunt. The SmartShunt is between the battery negative bus, and the negative bus for my house DC Fuse panel.

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