Enhansement Discussion ON How SOC is calculated on a BMV or smartshunt

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Paul B asked Mar 5, '21

Enhansement Discussion ON How SOC is calculated on a BMV or smartshunt

Yes I know that its basically a flow meter giving a sum of what goes in and out.

However I see on the forums and from the issues I have with customers, that most dont understand that this is based on the rated battery capacity thats placed in the units ie 200A/Hr

I would like to discuss the possibility of having a OPTION for 2 or more different ways or calculation methods if needed by a selection option.

1. as it is done now, Standard

2. ADVANCED - that a new option for SOC based on battery voltage and type of battery be considered and then how the SOC is calculated. Ie

a. battery voltage when at rest , or

b. averaged over the last hr (but not when charging or heavy discharge use option c

c. taking a at rest reading when stable for 2 hrs and reset to level then adjust via flow until the next stable period.

anyway there has to be a way to get a better SOC with less ongoing explanations and customer misunderstandings.

PLEASE ADD YOUR COMMENTS and thoughts as to ways to do this if you thinks its something that would help the overall customer experience.

Sample voltage based charts below

sample Lead Acid chart SOC based on Voltage at rest

Lithium Phosphate SOC based on voltage at rest

Customers see

SOC

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1614912381195.png (8.4 KiB)

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Answer 1 · 2021-03-05T07:47:31Z

harold answered · Mar 05, 2021 at 07:47 AM

Personally,

I would not argue the calculations, but its prresentation, as in your last example, but it could or should be possible to add a gauge or symbol to show

"empty" - full (for the end user)

(which is 50%-100% SOC) or other bottom level.

Harold

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Answer 2 · 2021-03-07T01:31:26Z

gro answered · Mar 07, 2021 at 01:31 AM

The SOC could be learnt parameter by having the user go through a couple of charge discharge cycles. However with large capacity batteries you might find that people may not be prepared to cycle their battery over many hours to give the instrumentation an opportunity to learn what the capacity of the battery is.

I think that having the user insert a couple of values that are consistent with their battery, is a good quick way to get started. If the topic is too difficult for the user to grasp then perhaps they should consult their dealer or other knowledgeable person able to do the job.

I am prepared to use voltage to determine the minimum and maximum charge a cell can take as is done when top or bottom balancing cells. However for the other points on the SOC curve I feel that there is an amount of variability which we should not have to put up with. If your system has a shunt with the smarts to Coulomb count then this would be my preferred method to establish SOC.

How the results are presented either as a text value or as a gauge is a secondary issue.

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