question

timevans2000 avatar image
timevans2000 asked

Smart shunt location on a DIY battery build

Can I mount the smart shunt between the JK BMS and the battery cells or is it better after the JK BMS?

If i wire the smart shunt between BMS and cells, In the event of a BMS shut down the smart shunt will still be providing cell voltage info to the Victron MPPT charger. Will this raise the voltage on the bus to dangerous levels if the bus is disconnected from the cells by the BMS? Will. The MPPT be damaged?

SmartShunt
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5 Answers
matt1309 avatar image
matt1309 answered ·

I personally keep the smart shunt after the BMS. (As it would be on any other off the shelf battery) I imagine your proposed setup is niche and therefore may lead to unforeseen issues that not many people have ran into.

Out of curiosity what is the benefit of having Smart shunt before BMS? Is it just to stop the smart shunt going off when you turn BMS off?

I'd argue that if you're turning BMS off you should also have first turned off all the Victron kit/loads connected to the battery.

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timevans2000 avatar image
timevans2000 answered ·

I was thinking about the effects of a bms shutting down on fault.

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matt1309 avatar image matt1309 commented ·
Yeh i wouldnt chance it. If BMS shutsdown odds are somethings bad happening and you want everything disconnected and like you said having shunt after might fool victron system into thinking something still connected. (Can't imagine it does but i wouldnt risk it)
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klim8skeptic avatar image
klim8skeptic answered ·

I would think that uninterupted battery voltage, Soc and temp would be important.

Shunt between batt and BMS.

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matt1309 avatar image matt1309 commented ·

I think I disagree but for the same logic as you. I would say

Battery <-> BMS <-> Smart shunt.

If there is an abnormality in the battery the smart shunt can't disconnect the battery whereas the BMS can. I would say it's more crucial for BMS to have the uninterrupted data of Battery voltage, and temperature. And in the event of fault the smart shunt will just disconnect and be noted as such in Victron system.



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timevans2000 avatar image timevans2000 matt1309 commented ·
The smart shunt only controls the MPPT by virtue of the voltage via the VE network. The BMS controls the battery. If the BMS isolates the battery the smart shunt will still be sending the battery vo.tage info to the Mppt. Put the BMS next to the battery and the smart shunt gets isolated by the BMS. The pain is the smart shunt then resets to 100% SOC. So putting smart shunt next to cells, what happens to voltage on the bus in the event of a BMS shut down?
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nesswill avatar image nesswill timevans2000 commented ·

The pain is the smart shunt then resets to 100% SOC.

You can keep the SOCscreenshot-20230608-145908.jpg

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luphi avatar image
luphi answered ·

I have the shunt between BMS (Daly) and battery in my Camper van.

Advantage: Current values are more accurate (you also measures the current running through the BMS)

Disadvantage: During winter, when the BMS disables charging due to low temperature, the shunt is not measuring ANY current even not ongoing discharge current.


Cheers, luphi

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sarah1331 avatar image
sarah1331 answered ·

I have found an issue that doesn’t work for both before and after the bms

After BMS : if bms shuts battery down mppt charges nothing raising voltage to shunt and shunt resets to 100%

Before bms : shunt sends voltage data to mppt if the bms cuts the battery off the shunt tells the MPPT to up the voltage as it’s not getting to the battery and the mppt is reading low voltage thus over volting the entire system after the battery

We need a BMS setting for the aux input

Has anyone got a workaround

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