mysik avatar image
mysik asked

Charge limit voltage (CVL) precision

I have a question about Charge Voltage Limit (CVL) when using BMS connected via CAN bus. In my system (VenusGX and Multiplus II) I'm using BMS connected via VE.Can (Batrium BMS). I would like to set Charge Voltage Limit (CVL) to 56.75V, but it looks like precision is fix to just one decimal place, so I need to set it to 56.7V or 56.8V. Is there a way to have 2 decimal places (e.g. 56.75V). All settings in VE Configuration tool have precision to 2 decimal places, why CVL (and CCL as well) is different???

Kind Regards

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1 Answer
nebulight avatar image
nebulight answered ·

I'm not a batrium user, but have looked into it previously. I believe this limitation is on Batrium as their GUI sets the limits, correct? Maybe talk to them to see if they can increase it? However .5 volts over 16 cell groups is such a small amount that I'm not sure it would really make a difference (56.75 is 3.546875v per cell where 56.7 is 3.54375‬ and 56.8 is 3.55).

Since you can set your balance start voltage, I don't really see why you would need to higher than 56v.

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mysik avatar image mysik commented ·

That is not Batrium limitation. In Batrium config you can change scaling to 100 and that will give you the 2 decimal places ( you can even change it to 1000 and have 3 decimal places if you wish). So this functionality is already built in. The problem is that if you set the limit 56.75V in Batrium, VenusGX will read it as 567.5V. Venux only reading one decimal place.

And BTW my system is 14 cells not 16, and the difference is 0.1V not 0.05V. It is especially important when you setting your bypass voltage. With charge voltage you need to set it up high enough to balance cells, but not too much to make sure you are not just burning energy and reducing you cell monitor life span.

Also you have different cells chemistries and 0.1V for cobalt type liion cells might not be a problem but for LiFePO4 where discharge curve is very flat it can make a huuuge difference.

At the end of a day, in VE config I can set my voltage limits with 2 decimal places, why I can't do the same through CAN Bus?

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ mysik commented ·

Hi @Mysik

0,1V in a 14S battery is 0,00625 V per cell.

Please keep in mind that both the measurement of the inverter and of the BMS will be less accurate than that.

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Related Resources

DVCC chapter in GX manual  

Additional resources still need to be added for this topic

Victron VE.Bus BMS product page

Victron 3rd party BMS compatibility page