question

davidv avatar image
davidv asked

In an ESS system why the "cut-off voltage for a discharge current" multiPlus the assistant must be able to edit down the SOC?

J'ai un système ESS en 3 phases, si je veux baisser le SOC je dois changer la valeur par défaut de la tension de coupure pour un courant de décharge dans l'assistant de multiplus ...

Pourquoi?

ESSAssistants
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3 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

I do not speak French, but google translate has your question as:

I have a ESS system in 3 phases, if I want to lower the SOC I have to change the default value of the cutoff voltage for a discharge current in the multiplus wizard. Why?

I am not sure exactly where you are limited, but one possible reason is that if you are using a battery (such as lithium) with a different voltage profile as a lead acid, the bottom part of the state of charge is not available unless you deeply discharge it.

In a lead acid battery you want to protect AGAINST a deep, low voltage discharge, but for a lithium this is desirable.

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davidv avatar image
davidv answered ·

I have big lead acid batteries, I am well aware that for protected should avoid deep discharges.

Most of the time the SOC stays at 80%.

From time to time energy consumption lowers the battery reserve to 80%, if there is sunshine the after day I drop the SOC to improve the efficiency of the installation. (just for 8 or 10Hrs)

If the parameters of the cutoff voltage for a discharge current in the multiplus wizard are those proposed the SOC remains 80% blocked ...

In order to use the SOC setting I must change the cut-off voltage parameters for a discharge current in the wizard.

Maybe this wizard's setting does not match the characteristics of my big batteries ...

What does C mean in calculating the cut-off voltage for a discharge current in the wizard? I can not find anything in the manual of use.

In France an installation ESS of this type is very expensive and the price of the energy of the rather weak network ...

I mount this system in my house because I love ESS and Victron, that's why I remain vigilant on the performance of my installation.

sorry for my very bad english

Thank you for your attention

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tilo avatar image
tilo answered ·

xC means the current in A compared to (divided by) the capacity of the battery in Ah. If you have a battery capacity of 100Ah, then the current of 2C means 200A of current, and 0,25C means 25A. Just multiply the C value with your battery capacity (given in Ah), and the resulting number is the current in A.

Do not confuse this with another usage of the "C" letter related with batteries. The capacity of lead-acid batteries in Ah is always related to a certain time of discharge in hours, expressed in the number AFTER the C. Example: a 100Ah C20 battery has 100Ah at a discharge time of 20 hours (discharge current of 5A). When you discharge the battery faster, the capacity is less. The same battery might have a C10 capacity of just 96Ah, or a C100 capacity of 115Ah (Peukert factor).

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