SimpBMS Tesla State of Charge

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freds

New member
Joined
Dec 3, 2019
Messages
10
I have a solar system using Tesla SimpBMS and the SOC numbers always seems to be off. I.E. After charging from shore power or solar, if I power cycle the BMS the SOC numbers always change.

The default configuration show a 100AH battery which is obviously not correct. How do you calculate based on the number of modules that you have what the configuration values should be?

Assuming I only want to charge to 90% is that the default or do I have adjust battery parameters?

I am using DVCC mode with my Victron control head and noticed really reduced charge rates at 24.25 volts so not sure what the charge goal is. Is the charging rate based on voltage or percent of charge?

For current sensing I am using the LEM can bus current sensor.

Thanks
 

Redpacket

Member
Joined
Feb 28, 2018
Messages
1,328
The expected SoC numbers should be factored from:
a) your understanding of the actual AmpHr capacity of your cells incl your best guess (at first) for cell life.
b) your range of operation, eg 10% to 90% of the above AmpHr capacity
c) testing a few full cycles & correcting if needed
You would set the SoC in the SimBMS to be your best assessment of b)
The DVCC mode is discussed here but not jumping out to me what that filters down to.
It seems like it uses the inverter charge voltage point to limit the charging voltage of the pack by CAN bus control.
I'm thinking you would set the CV point in the inverter to be = the 90% SoC point at nominal temperature, eg 20 or 25degC.
You'd have to watch out that cable resistance didn't skew the results with current flow.
 

bigbear

New member
Joined
Nov 22, 2021
Messages
1
I have a solar system using Tesla SimpBMS and the SOC numbers always seems to be off. I.E. After charging from shore power or solar, if I power cycle the BMS the SOC numbers always change.

The default configuration show a 100AH battery which is obviously not correct. How do you calculate based on the number of modules that you have what the configuration values should be?

Assuming I only want to charge to 90% is that the default or do I have adjust battery parameters?

I am using DVCC mode with my Victron control head and noticed really reduced charge rates at 24.25 volts so not sure what the charge goal is. Is the charging rate based on voltage or percent of charge?

For current sensing I am using the LEM can bus current sensor. Friday Night Funkin

Thanks
Coincidentally, I was in the same situation as you.
 

Redpacket

Member
Joined
Feb 28, 2018
Messages
1,328
Might have missed answering this:
How do you calculate based on the number of modules that you have what the configuration values should be?
Basically you add the amp hour capacities of the modules that are in parallel so eg, if each module is say 40 AHrs (total guess!) & you had 5, that'd be 200AHrs.
So using 80% of that (10% to 90%) would be 160AHrs operating range.
You could calibrate the BMS to either the full capacity or your operating range depending on what you'd like to see displayed I guess :)
 

freds

New member
Joined
Dec 3, 2019
Messages
10
Actually I emailed Tom:

Code:
Upon Power On the BMS calculates the SOC based on the SOC vs Cell Voltage parameters.

The “Normal” operation is done but counting the current utilizing the reported values from the CAB300. This of course uses the capacity setting. The only time the current would not be used is if you set the Voltage only SOC.

Kind Regards,
Tom de Bree

You can set SOC based on voltage by:

Main menu

C = Current Sensor calibration

Option 2 with a value of one
 

Redpacket

Member
Joined
Feb 28, 2018
Messages
1,328
Yes, setting SoC by voltage would be an initial starting point, then like Tom said, it's current counting ("coulomb counting").
+ other above settings needed too....

But seemed like you were asking how to figure out your battery bank's capacity & then getting that into your SimBMS's capacity settings.
Hope hints helped.
 
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